From kmenten at mpifr-bonn.mpg.de Tue Jun 6 13:44:09 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Tue, 6 Jun 2000 19:44:09 +0200 (MEST) Subject: [asac] letter to ASAC (fwd) Message-ID: Dear ASAC members, On behalf of the ALMA Science Software Requirements Committee, Robert Lucas has produced the attached document with questions of the SSR regarding a number of important issues. Please send me your opinions on these issues so that I can collect them and we can start discussing them at the upcoming ASAC telecon. Cheers, Karl ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 -------------- next part -------------- to ALMA Project Scientists and Alma Science Advisory Committee Members: ----------------------------------------------------------------------- Object: Project-wide issues of specific interest to Science Software Requirements During our past six months of work in the Science Software Requirements Committee we have encountered several issues on which we agree that further input on your side will be needed before our work can be completed. Our preliminary report (ALMA memo 293) has been recently officially reviewed and we take this opportunity to raise the following questions. These are mainly issues related to the way ALMA is operated as a whole. For each issue we would like to have either a definite answer or a baseline/fall-back alternative. The questions are given in order of decreasing importance. 1) Array Scheduling We have been assuming that ALMA will be dynamically scheduled so that each project is observed during weather conditions (seeing, opacity, wind) that allow its objectives to be achieved. This implies dynamic scheduling in near real time (Dynamic Scheduling) as stressed in mma memo 164, and in ALMA Project Book, Chapter 2(III.4). This has implications on the feedback from the PI, on the basis of calibration data and images produced by the pipeline: this feedback can only be offered at the end of one transit (observing session), assuming the project observations are divided into several transits either due to schedule optimization (as high elevations are preferred) or intentionally by the insertion of breakpoints. This limitation on `interactivity' has to be realized. We believe it is a small price to pay for the increase in productivity expected from dynamic scheduling. An alternate scheduling method is the traditional interactive observing, which should be available since it can be useful for test purposes and for special -- timely and unforeseen -- observations. Our question: Is dynamic scheduling to be the default mode of scheduling, accepting the restricted interactivity implied by this mode ? 2) Purpose of the pipeline The data flow ALMA Project Book, Chapter 2(III.5) will include a pipeline that may be used to fulfill several purposes: a) check that the data obtained can be calibrated, with feed back to the observing process to use the optimal phase calibration cycle. b) give feed back to the dynamic scheduler by monitoring the observed phase noise. c) produce calibrated uv data and maps of test quasars to check in real-time the quality of observations, with feed back to the dynamic scheduler. d) produce calibrated uv data and maps of the project source(s) to enable the PI to evaluate her/his data at the end of the observing session and to proceed with scientific interpretation when the project is finished (after improved reduction if needed), while incrementing the ALMA data archives. e) use calibrated uv data and maps of the project source(s) in order to derive simple quality parameters (noise level, signal to noise ratio) that may be used to define when the project goals are attained. f) use calibrated uv data and maps of the project source(s) in order to derive similar or more sophisticated parameters (source size, number of sources ... see examples in memo 293) to be fed back into the project's observing process, which may then take automatic decisions. While we believe that a, b, c and d should be implemented as baseline features, there is some concern that f) and maybe e) might be too ambitious goals (software has a cost too) or even may increase the distance between the astronomers and the instrument to an unwanted level. Our question: Which degree of sophistication should be set as a goal for the ALMA data pipeline ? 3) Operational aspects For the specification of GUI (graphical User Interfaces) a clear description of the relative duties of the operators and local staff astronomers will be needed, in view of the following tasks - Allocation of antennas to simultaneous projects (e.g. a sub-array for calibration, a sub-array used for astronomy, some antennas in maintenance) ? - Control on the dynamic scheduling process - Communication with the PIs if needed Our question: Can the relative duties of the staff in charge of controlling the array be already outlined ? 4) Policy on data propriety: We are assuming, as is the usual practice in most observatories, that only the proposing team has access to the data during a limited proprietary period and that the data ultimately become public. The actual length of the propriety period can be probably be set later, but some policy questions may affect the software requirements, such as: 4.1 is only the scientific data covered, or all header information including monitoring data, or some header information only (like coordinates and frequencies) ? 4.2 if public data is reprocessed in the pipeline by others, to search for unforeseen scientific results, does this start a new proprietary period ? Our question: Can the proprietary data policy of ALMA be already outlined ? 5) Special modes Some specific observations (Sun, Pulsars, ...) may need very short integration times, fast frequency changes, ... for which the exact scientific software (and hardware ?) requirements need to be investigated in detail. For these issues we would like having specialized astronomers as correspondents, so that we may include their contributions in our requirements, in a coherent manner. 6) Other details - is an audio channel from the antenna cabins to the operator planned ? (see comment 95) - We assume, as DSB mode is clearly an option for some frequency bands, that side band separation has to be handled by software for interferometric work in those bands. Robert Lucas, on behalf of the Science Software Requirements Committee From kmenten at mpifr-bonn.mpg.de Thu Jun 8 03:25:35 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Thu, 8 Jun 2000 09:25:35 +0200 (MEST) Subject: [asac] ALMA SAC Telecon on June 12 Message-ID: Dear ASAC members, The next ASAC telecon will be on Monday, June 12 at 21:00 UT (i.e. 23:00 Central European Summer Time, 17:00 Eastern Daylight Savings Time). Please send topics for discussion to me. So far, the following topics have been suggested: (1) Date of next face to face meeting in Berkeley. How about September 12-13? (2) ALG Meeting (3) Science Software Requirements (email by R. Lucas) (4) Priority list for features to add in case additional partners join the project, e.g.: more RX bands, small antenna array, more 12m antennas, ... Al Wootten will email you instructions for phone access to the telecon. Hoping to hear from you soon, Karl From awootten at NRAO.EDU Fri Jun 9 16:28:42 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Fri, 9 Jun 2000 16:28:42 -0400 (EDT) Subject: [asac] Meeting Monday 12 June at 2100 UT Message-ID: <200006092028.QAA25948@polaris.cv.nrao.edu> Folks: I have posted an agenda at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/juneagenda.html When I have the phone numbers, they will appear at that location; additionally I will email them (probably Monday morning). Clear skies, Al +--------------------------------------------------------+ | Alwyn Wootten (http://www.cv.nrao.edu/~awootten/) | | Project Scientist, Atacama Large Millimeter Array/US | | Astronomer, National Radio Astronomy Observatory | | 520 Edgemont Road, Charlottesville, VA 22903-2475, USA | | (804)-296-0329 voice Help us build The ALMA| | (804)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From nakai at msv1u.nro.nao.ac.jp Mon Jun 12 10:46:01 2000 From: nakai at msv1u.nro.nao.ac.jp (Naomasa NAKAI) Date: Mon, 12 Jun 2000 23:46:01 +0900 (JST) Subject: [asac] ASAC document Message-ID: <200006121446.XAA01512@m202u.nro.nao.ac.jp> Dear Karl, Regarding item 4 of the ASAC, I am sending separately (via Dr. Nakai) a draft of planning for an enhanced ALMA and the Japanese contribution for it. I hope it is not too late to be included in the 12th telecon. Regards, Yasuo ========================================================================== ??????? Plan for an Enhanced ALMA ??????????? 12 June 2000 ?Japanese members of ASAC Japan will participate in an enhanced ALMA project as an equal partner as the US and European sides by bearing 1/3rd of the project. To realize the project, we will ask the budgets of its design for FY2001 (which starts from 2001 April) to the government in 2000 June and of its construction for FY2002 to FY2008 in 2001 June. Our plan is that construction of the Japanese portion finishs in FY2008, adjustments with the US and European portions are made in FY2009 and FY2010, and full operation for astronomical observations starts in FY2010. However the detailed schedule will be decided under nagotiation with the US and Europe and we keep in step with the other partners. Dr R.L.Brown asked ASAC prioritizing the plan of an enhanced ALMA on May 12 to send a report to AEC until June 23. According to this seeking, we have made the following plan for the enhanced ALMA on the basis of science return and construction cost and present it here to ASAC for discussion. Boundary conditions considered for the plan is .that the total cost or "value" of the enhanced ALMA is $552M/2 x 3 = $828M, .that the costs (values) of the parts follow the estimation and equations in "PLANNING FOR JAPANESE PARTICIPATION IN ALMA" (R.L.Brown, 12 May 2000) for simplicity, except the second generation correlator whose cost has been estimated by ourselves. Since the cost of antennas is the biggest, its unit price influences the total plan of the project largely. When the cost of an antenna is fixed, we would have to re-consider the plan. Plan for an Enhanced ALMA 1) Antennas A number of 12-m antennas is 78. Each antenna should have enough capability for submillimeter observations. Science merits: Sensitivity of the array is increased by increasing the number from 64. A compact array of seven 6 - 8m antennas is added. The value of a small antenna should be equal to that of a 12-m antenna. Science merits: Since the minimum anntena spacing becomes shorter to be 8 - 11m, capability of the array for extended sources is improved, especially for shorter wavelengths. Total cost of all antennas = $20M + $3.0M x (78 + 7) ? ?????? ?= $275M Japan will bear 1/3rd of the total number 85 of the antennas. 2) Receivers and LO Bands 3, 6, 7, 9 which have been given first priority in ASAC in March are important. In addition to these bands, bands 8 and 10 are also important and should be given high priority. Science merits: (see attached appendix) .Band 8 includes important lines of CO(J=4-3;460GHz), CI(J-1-0;492GHz), CS(J=10-9; 489GHz) et al. and thus is useful for study of interstellar matter and to see the cores of star forming clouds and inner 10 AU of protoplanetary disks. .Band 10 includes extremely high excited lines such as CO(J=7-6;807GHz), HCO+(J=9-8;802GHz,J=10-9;892GHz), HCN(J=9-8;797GHz,J=10-9;885GHz) which are good tracers of high temperature and high density gas, and CI(J=2-1;809GHz). The band could detect redshifted strong CII from galaxies at z = 1.1 - 1.4. In addition, the band is useful to observe strong thermal emission from heated dusts which is quite important and useful to observe galactic regions of star and planet formation and external galaxies. .By increasing the number of receiver bands to be six, many excited lines of same molecules are observable, contributing accurate determination of physical and chemical states of galactic and extragalactic molecular clouds. Total cost of receivers = [$700k + $200k x 6] x (78 + 7) ???? ? = $161.5M Total cost of LO system = [$200k + $100k x 6] x (78 + 7) ????? = $68.0M Japan will bear two of the six bands. Since band 10 needs technical development of THz SIS heterodyne reveivers, Japan may take charge of the band. 3) Correlator NRAO will construct the first correlator which can correlate signals from 32 antennas. In addition to the correlator, Japan and Europe, collaborating each other, will develope and construct the second generation correlator which can correlate 125 kch/IF of signals from all the antennas 85. Science merits: .The second generation correlator can treat all the antennas. .The correlator can improve the sensitivity by corresponding to multi- bits of the A/D converters. .Its high capability for spectroscopy can observe many spectral lines in the broad frequency band simultaneously. .Such high spectral capability may make serendipitous discoveries which open new world in astronomy. Cost of the first correlator (filter+XF,32 anntennas,2GHzx8IF,4kch/IF) ??? = $7M (from correlator PDR) Cost of the second generation correlator (FX,85 antennas,4GHzx4IF,125kch/IF) ??? = $44M (Cost of A/D converters will be included in the following Backend Subsystem) 4) Others According to the suggestion in "PLANNING FOR JAPANESE PARTICIPATION IN ALMA" (R.L.Brown, 12 May 2000), we bring to the enhanced ALMA .additional $30M for site development, .additional money for backend subsystem, corresponding to the increased number of antennas, .increasing contributions for management, system engineering & integration, and science support by Japan by 50%, .additional contribution of $10M for computing subsystem by Japan, as follows, ALMA E-ALMA ??Management $24.6M + 12.3 = $ 36.9M Site Development 77.9 + 30 = 107.9 Backend Subsystem(IF,A/D) 32.9 + 32.9*(85-64)/64 = 43.7 Computing Subsystem 30.7 + 10 = 40.7 System Engin & Integration 21.3 + 10.7 = 32.0 Science Support 7.0 + 3.5 = 10.5 total 271.7 ? Total cost (value) of the enhanced ALMA Antennas $ 275 M Receivers 161.5 LO subsystem 68.0 Correlator 7 (first generation; NRAO) 44 (second generation; Japan & Europe) Others 271.7 Total 827.2M ======================================================================= From guillote at iram.fr Mon Jun 12 11:39:45 2000 From: guillote at iram.fr (Stephane Guilloteau) Date: Mon, 12 Jun 2000 17:39:45 +0200 Subject: [asac] ASAC Meeting Message-ID: <000701bfd484$6f7d08a0$cafc30c1@pctcp72.iram.fr> Following Dr.Nakai E-Mail, I would like to raise the following points - Number of antennas: 78 is 64xsqrt(3/2), which means that by sharing with 3 equal partners, each partner get the same sensitivity than sharing 64 antennas with 2 partners only. Each scientist thus sees no reduction, but we do more science - Number of small antennas; It is yet unclear that 7 antennas would be sufficient. I have been (slowly) working on that and consider that they make an appropriate match IF AND ONLY IF 1) the large antennas make mosaicing 25 % of the time 2) the small antennas observe in a compact array mode all the time 3) calibration is not considered as a limitation The two statements are somewhat contradictory since 3) would require a tied array mode for calibration while because of 1) and 2) the large and small antennas would be mostly doing different things (75 % of the time). Imaging issues are unclear also (is 7 antennas sufficient ?) If not, a number like 15 antennas preserve a better imaging capability, perhaps enough calibration accuracy even in stand-alone mode (no hybrid baselines). This is a "Safe Fall Back" Question: Does ASAC recommand to "sacrifice" a few large antennas (8) in order to be able to have more smaller ones. Final numbers could be Large antennas 70, Small antennas 15. - Receivers and LO I consider both for scientific and calibration reasons the 2-mm band to be essential (high redshift objects, see my contribution to the Washington meeting). Any comment from ASAC ? - Backend Does the correlator cost includes the cost of the required computing system to process the 125 kChannels per baseline ? If not, what would you estimate this cost to be ? Stephane From guillote at iram.fr Mon Jun 12 11:59:17 2000 From: guillote at iram.fr (Stephane Guilloteau) Date: Mon, 12 Jun 2000 17:59:17 +0200 Subject: [asac] Receiver specifications Message-ID: <001301bfd487$2a0e0aa0$cafc30c1@pctcp72.iram.fr> A) We have been asked by the Receiver group leader to refine the performance specifications of the receiver. Given the goal of getting the best possible receivers, yet producing them in due time and quantity, I propose to specify the noise performance in two steps 1) Receiver noise temperature should not exceed (NUMBERS GIVEN FOR Freq. below 370 GHz) for Single Side Band receivers, 6 h.nu/k averaged over the best 80 % of its nominal bandwidth, and 10 h.nu/k at any place in the nominal bandwidth for Double Side Band receivers, these numbers should be halfed 2) The receiver temperatures should be measured in a reference plane outside the dewar. - there is a technical issue here. The ideal would be a measurement at the secondary focus, including all receiver related optics, i.e. with the full final cryostat and optics. However, since receiver cartridges will be developped and tested separately, this cannot be performed on the development site. We should propose that the receiver group instruments the test cryostats foreseen for the cartridge testing in such a way as to provide a comparable receiver temperature reference plane. 3) Numbers have to be debated. I am unhappy with the current 10 h.nu/k in the proposal at all frequencies, and suggest 6 h.nu/k in (1). What about sub-mm frequencies. Would 10 h.nu/k be acceptable, conservative or too difficult ? 4) The proposed receiver specification do not define coupling efficiency with the telescope. Yet this is a major parameter in performance. A measurement scheme should be proposed by the receiver WG. 5) The sideband rejection of 10 dB is probably more than we need for sensitivity purpose only. Do you have any other requirement on that number (e.g. single-dish observing mode, calibration) ? B) The ASAC has also asked the project scientists to work out recommended sensitivities, since many different documents have been using very different numbers. I propose a two step approach, always using the mean receiver temperature as quoted above (6 h.nu/k at mm, 10 or more h.nu/k at submm) 1) Give a "rule of thumb" number for Tsys under normal conditions i.e. 75 % quartile of water vapor content for mm wavelengths 25 % quartile of water vapor content for submm wavelengths Frequency far from an atmospheric line This "rule of thumb" could take the form Tsys(nu) = 35 + 0.45 (nu/100 GHz) for nu < 400 GHz Tsys(nu) = 1000 K for nu > 400 GHz in the atmospheric windows (numbers to be derived according to receiver specifications) 2) For frequencies near an atmospheric line, the full atmospheric model should be used. I propose to use the same opacity reference as before. A simple atmospheric model may be sufficient ? I all cases, I suggest the forward efficiency used to be 0.95 at the lowest frequencies, falling down to 0.90 at 900 GHz (in a parabolic way). This is to account for telescope/optics performance degradation which is usually found on all mm telescopes. Note that these numbers are already better than any telescope currently in operation. Stephane ---------------------------------------------------------------------------- --------------------------------------- Dr. Stephane GUILLOTEAU ALMA European Project Scientist Phone: (33) 476 82 49 43 (IRAM) IRAM FAX: (33) 476 51 59 38 (IRAM) 300 Rue de la Piscine Phone: (49) 893 200 6589 (ESO) F-38406 Saint Martin d'Heres France E-Mail: guillote at iram.fr (IRAM) sguillot at eso.org (ESO) From awootten at NRAO.EDU Mon Jun 12 13:59:37 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Mon, 12 Jun 2000 13:59:37 -0400 (EDT) Subject: [asac] Meeting phone number and agenda Message-ID: <200006121759.NAA14437@polaris.cv.nrao.edu> Agenda is at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/juneagenda.html ALMA Science Advisory Committee Draft Agenda for ASAC Telecon June 12, 2000 2100 UT Conference Date: June-12-2000 (Monday) Conference Time: 2300 CET; 2100 UT; 1700 EDT; 1500 MDT ; 1400 PDT; 1700 Chile; 0600 (Japan 13 June ) Conference Duration: 1 hr Service Level: STANDARD Call Type: MEET ME Passcode is: ALMA Conference Leader is Wootten >From the US please dial: 888-831-2981 >From International locations please dial: +1-712-271-3821 News. (1) Date of next face to face meeting in Berkeley. How about September 12-13? (2) ALG Meeting (3) Science Software Requirements (email by R. Lucas) (4) Priority list for features to add in case additional partners join the project, e.g.: more RX bands, small antenna array, more 12m antennas, ... (5) Upcoming Reviews: Test Interferometer plans, Antenna PDR (June 20-23). (6)Change of hours for ASAC telecons: How about 14:00 UT (= 16:00 CEST = 10:00 EDT = 7:00 PDT = 23:00 JAPAN) for the next few ASAC telecons? From wilson at physics.mcmaster.ca Tue Jun 13 17:10:20 2000 From: wilson at physics.mcmaster.ca (Christine Wilson) Date: Tue, 13 Jun 2000 17:10:20 -0400 (EDT) Subject: [asac] Re: ALMA rx specs (draft version) (fwd) Message-ID: Hi, everyone, I was wondering if we should plan to discuss the receiver specifications and the questions raised by Stephane Guilloteau at our next telecon? I sent a couple of comments in today, which I've copied to you all below. Chris ---------- Forwarded message ---------- Date: Tue, 13 Jun 2000 16:58:53 -0400 (EDT) From: Christine Wilson To: Wolfgang Wild , jpayne at nrao.edu Cc: Christine Wilson Subject: Re: ALMA rx specs (draft version) Dear Wolfgang and John, I'm sorry to be sending you this comment late, but I thought the ASAC might discuss your memo in our telecon yesterday. One thing I was a little concerned about in your draft specs was the 4 GHz IF bandwidth as a fallback position for the initial bands. Is the intention to have this a temporary situation i.e. would the receivers be upgradeable to 8 GHz bandwidth, or if we did have to go to this fallback position, would the initial receivers be permanently at the lower bandwidth? Reducing the bandwidth has a significant impact on the continuum sensitivity of the array and on the ability of the array to do redshift searches, among other things. The other point I noted was that selecting and tuning a new band should indeed be as fast as possible. Since many observations with ALMA might be of quite short duration, 15 minutes tuning time could produce a lot of overhead and/or more demands on the dynamic scheduler to schedule "like" projects in sequence. Thanks, Chris Wilson From jsr at mrao.cam.ac.uk Wed Jun 14 05:11:28 2000 From: jsr at mrao.cam.ac.uk (John Richer) Date: Wed, 14 Jun 2000 10:11:28 +0100 (BST) Subject: [asac] receiver specs Message-ID: <200006140911.KAA06587@katje.ra.phy.cam.ac.uk> Hi all, To echo Christine's comments, I think we do need to provide some formal input from the SAC to Wolfgang and John fairly quickly - I spoke to them yesterday and it's clear that they are happy for feedback on the specifications document, but if they don't get any they will simply adopt the proposed specs for the system. They emphasised that it was important to fix the specs early on, and avoid changing them throughout the design process. I wonder if our next face-to-face meeting is early enough to send proper feedback, or if we should do it sooner. Specific issues of calibration and polarisation specifications were uppermost in their minds, plus the issues of coupling to the telescope and Rx temp spec. Of course Stephane's notes made some suggestions in these latter two areas. John -- John Richer Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE Tel: +44-1223-337246 Fax: +44-1223-354599 http://www.mrao.cam.ac.uk/~jsr/ From guillote at iram.fr Wed Jun 14 10:20:44 2000 From: guillote at iram.fr (Stephane Guilloteau) Date: Wed, 14 Jun 2000 16:20:44 +0200 Subject: [asac] receiver specs Message-ID: <002401bfd60b$ba39d5c0$cafc30c1@pctcp72.iram.fr> Dear ASAC members, As pointed out in John's message, getting the receiver specs is important. As usual, the sooner the better... The parameters have different influence on the receiver design. The polarisation purity requirement mostly influences the optics and horn/orthomode transducer. I would assume that the 1 % goal in calibration requires a cross-polarisation better than 20 dB, and that all antennas should be also co-aligned in polarisation to the same level. What do the polarisation experts (==> Dick Crutcher) think about that ? Note that it may be difficult to reach this level with an orthomode transducer... Can we accept lower specs ? The noise performance influence the mixer design and optics design. If we fail to set agressive enough specifications, engineers may be free to select a simpler but more noisy design... Yet we must be reasonable to avoid throwing out all receivers... This may require a faster input than the next face to face meeting. I can try to draft a recommendation on the lab measuring device to evaluate "cartridge" performance with B.Lazareff. Stephane From awootten at NRAO.EDU Fri Jun 16 17:53:56 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Fri, 16 Jun 2000 17:53:56 -0400 (EDT) Subject: [asac] receiver specifications Message-ID: <200006162153.RAA26184@polaris.cv.nrao.edu> Comments on Wild/Payne proposed receiver specifications: http://www.cv.nrao.edu/~awootten/mmaimcal/receiverspecs.html -------------------------------------------------------------------- 1.3 Definitions * 4 GHz IF bandwidth as a fall back position for the initial bands This is too vague. Does it apply to 900 GHz, not an intial band? I believe that any specific proposal for a design with less than 8 GHz bandwidth should be approved by others in the project whom it might affect. See below. *band 3 starts tentatively at 86 GHz (before 89 GHz) See below. The ASAC actually wrote (http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node3.html): 'We strongly urge that the JRDG study the possibility of extending the lower frequency range of Band 3 to include the SiO maser transition near 86 GHz. If this is possible, Band 2 would drop to third priority. ' See comments below. * a water vapor monitoring radiometer operating simultaneously with all frequency bands except band 1 I don't think this is worded correctly. The ASAC said: The ASAC does note that the simultaneous operation at 183 GHz and Band 1 receivers is not a scientific requirement, so it is straightforward to locate these systems in the same Dewar if that makes sense. In the best of all possible worlds, the WVR would work with band 1 as well as the other bands--this will be necessary under a wide range of conditions at Chajnantor for which ALMA may be operable at band 1 with WVR but ALMA would be shut down otherwise. However, if the cost of operating both simultaneously is very high one possible sacrifice might be simultaneous operation of WVR and band 1. This is very different from designing a receiver system which will not accommodate simultaneous operation of both from the outset, in my opinion. -------------------------------------------------------------------- Table 1 Band 3 should conform to the original recommendation, with a footnote as written. The ASAC actually said: (http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node3.html) 'We recommend study of extending the lower end of Band 3 to include 86 GHz.' Actually, since the VLBA receivers at 3mm will go down to 84 GHz, perhaps some attention should be paid to the actual number of the lower limit. I would suggest 84 GHz. -------------------------------------------------------------------- Reference Documents I would include the CDR, PDR reports at http://www.alma.nrao.edu/administration/index.html -------------------------------------------------------------------- 3.1 I'm not sure what available atmospheric frequency windows means. Change this to The ALMA receiver subsystem will cover frequencies between 30 GHz and 950 GHz as given in Table 1. -------------------------------------------------------------------- 3.2 Polarization The ASAC report at http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node12.html needs to be made more specific. Larry D'Addario and Steve Myers have put work into this, and his draft recommendations are located at: http://www.aoc.nrao.edu/~smyers/alma/polspecs-imcal.txt We invite comments on this document. -------------------------------------------------------------------- 3.4 Receiver noise performance. I think that this should be more specific. Stephane proposed: '1) Receiver noise temperature should not exceed (NUMBERS GIVEN FOR Freq. below 370 GHz) for Single Side Band receivers, 6 h.nu/k averaged over the best 80 % of its nominal bandwidth, and 10 h.nu/k at any place in the nominal bandwidth for Double Side Band receivers, these numbers should be halved ... What about sub-mm frequencies. Would 10 h.nu/k be acceptable, conservative or too difficult ?' I agree. In our memo on sensitivity goals, Bryan and I used an equation: TrxSSB= A * (hnu/k) + 4 K And for current technology, based on the review at the URSI 99 meeting: with A = 3 below 500 GHz DSB A = 6 for band 9 (602-720 GHz) A = 12 for band 10 (787-950 GHz) We suggested goals for these future receivers of: A = 3 below 500 GHz A = 4 for band 9 (602-720 GHz) A = 8 for band 10 (787-950 GHz) I believe that there should be specifications and goals, with achieved receiver performance to fall between the two. I like Steve Myers' suggestion: SSB hv/k inner / max Band 1-6 (below 275 GHz) Spec: A = 6 / 10 Goal: A = 3 / 5 Band 7-8 (275-500 GHz) Spec: A = 8 / 12 Goal: A = 4 / 8 Band 9 (602-720 GHz) Spec: A = 10 / 15 Goal: A = 6 / 9 Band 10 (787-950 GHz) Spec: A = 10 / 15 Goal: A = 8 / 12 -------------------------------------------------------------------- Sidebands, IF bandwidths and Simultaneous operation of bands This seems too unspecific to me. The goal is: SSB 2 x SB 2 x Pol = 4 x 8 GHz ( sideband separating ) The Munich PDR (http://www.cv.nrao.edu/~awootten/mmaimcal/ALMA-DesRevRec4.html) said: In addition to the baseline IF bands of 8 GHz Upper and Lower Sideband, receiver designers are free to select any of the following alternatives: 8 GHz Single-Side-Band, Upper or Lower, 8 GHz Double-Side-Band or 4 GHz Upper and Lower Sideband. In all cases, dual polarization for a total of 16 GHz IF band width. Sideband separation in DSB-mode will be possible for integration times in multiples of 1 sec. Depending on the choice, and maintaining the currently proposed LO coverage, this might lead to some loss of frequency coverage. The impact of this should be evaluated by the Science Group. Of course, I guess this is only a recommendation, but it might be a starting point. Larry made more specific recommendations toward a decision. -------------------------------------------------------------------- 3.7 This states that band 1 can operate without the WVR. As above, I think the system should only be designed this way if no alternative seems possible. -------------------------------------------------------------------- 3.8 Stability The ASAC report suggested 1e-4 over 1 sec. A memo from Wright http://www.alma.nrao.edu/memos/html-memos/abstracts/abs289.html suggested 1e-4 over 0.1s, which begins to define the spectrum of stability. -------------------------------------------------------------------- 4.3 Selection of a new observing band 'Selecting and tuning a new band shall require no more than 15 min.' I'm not sure where this came from, but it should be better defined. This time should be measured in seconds, along with the others. It shouldn't be several orders of magnitude different, as it is in this draft. The System PDR (ref above) said: ' Changing the band should be limited to intervals of the order of 15 minutes. ' but I never heard this discussed in Munich (neither did anyone I have discussed this with) so I remain unclear what it means. -------------------------------------------------------------------- Stephane also noted that: 'The receiver temperatures should be measured in a reference plane outside the dewar.' I agree with what he proposed for this. Further, he noted that coupling to the telescope remained poorly defined and should be made more definite. I agree. From kmenten at mpifr-bonn.mpg.de Mon Jun 19 04:30:45 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Mon, 19 Jun 2000 10:30:45 +0200 (MEST) Subject: [asac] ALMA Receiver Requirements and Specifications Message-ID: Dear ALMA SAC members, All of you should have received the "ALMA Receiver Subsystem Top Level Requirements and Specifications" document by W. Wild and John Payne, which was emailed on May 19 and is retrievable from http://www.cv.nrao.edu/~awootten/mmaimcal/receiverspecs.html Stephane Guilloteau and Al Wootten mailed you their comments on that document on June 8 and June 16, respectively. I would like to compose an ASAC reponse and would therefore like to know whether any of you has other comments on the document. If yes, please send me an email by Wednesday, June 21. Cheers, Karl ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 From kmenten at mpifr-bonn.mpg.de Mon Jun 19 12:05:22 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Mon, 19 Jun 2000 18:05:22 +0200 (MEST) Subject: [asac] Questions by ALMA Science Software Requirements Committee Message-ID: Dear ASAC members, Here's a first try at answering the questions of the ALMA Science Software Requirements Committee communicated to us by Robert Lucas. Please send me further comments on these issues by Thursday, June 22, so that I can collect them for an "official" answer. Cheers, Karl ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 ------------------------------------------------------------------------ > > to ALMA Project Scientists and Alma Science Advisory Committee Members: > ----------------------------------------------------------------------- > > Object: Project-wide issues of specific interest to Science Software > Requirements > > During our past six months of work in the Science Software > Requirements Committee we have encountered several issues on which > we agree that further input on your side will be needed before our > work can be completed. Our preliminary report (ALMA memo 293) has > been recently officially reviewed and we take this opportunity to > raise the following questions. These are mainly issues related to the > way ALMA is operated as a whole. For each issue we would like to > have either a definite answer or a baseline/fall-back > alternative. The questions are given in order of decreasing importance. > > 1) Array Scheduling > > We have been assuming that ALMA will be dynamically scheduled so > that each project is observed during weather conditions (seeing, > opacity, wind) that allow its objectives to be achieved. This > implies dynamic scheduling in near real time (Dynamic Scheduling) as > stressed in mma memo 164, and in ALMA Project Book, Chapter > 2(III.4). This has implications on the feedback from the PI, on the > basis of calibration data and images produced by the pipeline: this > feedback can only be offered at the end of one transit (observing > session), assuming the project observations are divided into several > transits either due to schedule optimization (as high elevations are > preferred) or intentionally by the insertion of breakpoints. This > limitation on `interactivity' has to be realized. We believe it is a > small price to pay for the increase in productivity expected from > dynamic scheduling. > > An alternate scheduling method is the traditional interactive > observing, which should be available since it can be useful for test > purposes and for special -- timely and unforeseen -- observations. > > Our question: Is dynamic scheduling to be the default mode of > scheduling, accepting the restricted interactivity implied by this > mode ? > YES, unambiguously and strongly. > > 2) Purpose of the pipeline > > The data flow ALMA Project Book, Chapter 2(III.5) will include a > pipeline that may be used to fulfill several purposes: > > a) check that the data obtained can be calibrated, with feed back to > the observing process to use the optimal phase calibration cycle. > > b) give feed back to the dynamic scheduler by monitoring the observed > phase noise. > > c) produce calibrated uv data and maps of test quasars to check in > real-time the quality of observations, with feed back to the > dynamic scheduler. > > d) produce calibrated uv data and maps of the project source(s) to > enable the PI to evaluate her/his data at the end of the observing > session and to proceed with scientific interpretation when the > project is finished (after improved reduction if needed), while > incrementing the ALMA data archives. > > e) use calibrated uv data and maps of the project source(s) in order > to derive simple quality parameters (noise level, signal to noise > ratio) that may be used to define when the project goals are > attained. > > f) use calibrated uv data and maps of the project source(s) in order > to derive similar or more sophisticated parameters (source size, > number of sources ... see examples in memo 293) to be fed back > into the project's observing process, which may then take > automatic decisions. > > While we believe that a, b, c and d should be implemented as > baseline features, there is some concern that f) and maybe e) might > be too ambitious goals (software has a cost too) or even may > increase the distance between the astronomers and the instrument to > an unwanted level. > > Our question: Which degree of sophistication should be set as a goal > for the ALMA data pipeline ? > a)-d): yes! [d) means calibrated images as final data products! - This would result in a much lower useage threshold for non-radioastronomers]. e) would be useful in certain cases, but without a source model in general pretty difficult. Would it be that much better than the feedback described to justify the additional development work. f) I think should be left to the astronomer. To allow this and at the same time not to slow down project completion too much, a project could have predefined breakpoints, at which the astronomer evaluates the data taken so far, and the subsequent course of the project depends on the astronomer's decision. > > 3) Operational aspects > > For the specification of GUI (graphical User Interfaces) a clear > description of the relative duties of the operators and local staff > astronomers will be needed, in view of the following tasks > > - Allocation of antennas to simultaneous projects (e.g. a sub-array > for calibration, a sub-array used for astronomy, some antennas in > maintenance) ? > Operator, after consultation with astronomer. > > - Control on the dynamic scheduling process > Operator, but only in case of emergency. > > - Communication with the PIs if needed > Astronomer. > > Our question: Can the relative duties of the staff in charge of > controlling the array be already outlined ? > See above > > > 4) Policy on data propriety: > > We are assuming, as is the usual practice in most observatories, > that only the proposing team has access to the data during a limited > proprietary period and that the data ultimately become public. The > actual length of the propriety period can be probably be set later, > but some policy questions may affect the software requirements, such > as: > > 4.1 is only the scientific data covered, or all header information > including monitoring data, or some header information only > (like coordinates and frequencies) ? > I think all the header information should be available - even if that means that everybody can find out the coordinates of your secret quasar to observe with the VLT. > > 4.2 if public data is reprocessed in the pipeline by others, to search > for unforeseen scientific results, does this start a new proprietary > period ? > I don't think that would be useful - it would be easy to block data forever by periodically reprocessing them. > > Our question: Can the proprietary data policy of ALMA be already > outlined ? > > 5) Special modes > > Some specific observations (Sun, Pulsars, ...) may need very short > integration times, fast frequency changes, ... for which the exact > scientific software (and hardware ?) requirements need to be > investigated in detail. For these issues we would like having > specialized astronomers as correspondents, so that we may include > their contributions in our requirements, in a coherent manner. > > 6) Other details > > - is an audio channel from the antenna cabins to the operator > planned ? (see comment 95) > Would be useful, but is trivial. > > - We assume, as DSB mode is clearly an option for some frequency > bands, that side band separation has to be handled by software for > interferometric work in those bands. > > Robert Lucas, > > on behalf of the Science Software Requirements Committee From awootten at NRAO.EDU Tue Jun 20 22:42:58 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Tue, 20 Jun 2000 22:42:58 -0400 (EDT) Subject: [asac] ALG Issues Message-ID: <200006210242.WAA26389@polaris.cv.nrao.edu> Comments on 'Plan for an Enhanced ALMA' presented 12 June 2000 by Japanese members of the ASAC. I have incorporated comments from presentations by S. Guilloteau and Koh-Ichiro Morita at the ALMA Technical Workshop, 17 Feb 2000 in Tokyo, the ASAC meeting in Leiden, and other venues. I. Antennas: A. Additional 12m antennas As Stephane noted, increasing the number of 12m antennas from 64 to 78 results in an ALMA in which sensitivity per partner is conserved, and overall sensitivity is increased. This seems like a reasonable goal. B. The Terahertz Array A compact array of seven 6-8m antennas is added, with each antenna bringing an equal value to that of one 12m antenna. The exact number and size are poorly determined. An alternative which poses sizable problems for pointing and surface accuracy might be to build one submillimeter telescope of 24m diameter. Scientific Merits of a Compact Array: I believe that the compact array brings a very good enhancement to ALMA as it promises production of science otherwise not addressed by ALMA, at the highest frequency windows. The compact array could operate at supraTerahertz frequencies for the 15% of the time at which transparencies in the supraTerahertz windows exceeds 30%, for instance. As Guilloteau noted, this Terahertz Array could operate independently of, or in addition to the main array, with the antennas on the latter underilluminated to improve efficiency, field of view, and effective pointing performance. At 1 THz, the resolution could be 3-4" over a 10" field of view (FOV) for an 8m telescope, somewhat larger for 6m telescopes (but see below), operating as a stand-alone array. Issues affecting number and diameter of antennas includes a. As antennas become smaller, i.e. 6m, it may be difficult to accommodate a standard suite of receivers, and standard cabin, compromising the economy of scale. As the array becomes more specialized, it becomes more difficult to operate and maintain. b. As number of antennas increases, it becomes more difficult to pack them together to obtain the smallest baselines. The array need not be concentric with the large array, but should perhaps be located nearby for operation on medium baselines with underilluminated 12m antennas. The number of antennas is limited to perhaps 16. 16 x 6m antennas has the same collecting area as one 24m antenna. c. As antennas become larger, it is easier to accommodate the standard suite of receivers. As the compact array may be operated as a standalone Terahertz Array, and may require additional receivers to operate at supraTHz frequencies, it seems unwise to restrict the receiver cabin. Some space may be recovered if the THz Array need not operate at the longest wavelengths. This suggests perhaps 8m antennas. However, existing implementations of inhomogeneous arrays have employed antennas with diameters varying by a factor of two. Nine 8m telescopes have the same collecting area as one 24m antenna. Seven 8m antennas provides adequate sensitivity for matching with an ALMA mosaicking 25% of its observing time. A. Imaging quality should be very much improved, through provision of a. short baseline information (6-10m) for imaging with the larger array. Although simulations are just beginning, ALMA is expected to proved excellent imaging at millimeter wavelengths, with some degree of quality loss at submillimeter frequencies. Especially at high frequencies, direct measurement of 8m spacings provides much better accuracy than recovery of this information through combination of interferometric plus on-the-fly mapping data. b. improved cross calibration between interferometer and single antenna performance c. improved performance for the combined array, particularly in bands 9 and 10. d. For a main array performing wide field imaging 25% of available time, the Terahertz Array spends essentially all its time collecting short spacing information for the wide field imaging experiments. This will pose some potential logistical problems--different atmospheric conditions, calibrator fluxes, scheduling conflicts but this difficulty is probably only at the annoyance level. e. The compact array may be constructed in a fixed array, with long baselines provided through baselines with underilluminated 12m antennas. Comments on 'Plan for an Enhanced ALMA' presented 12 June 2000 by Japanese members of the ASAC. I have incorporated comments from presentations by S. Guilloteau and Koh-Ichiro Morita at the ALMA Technical Workshop, 17 Feb 2000 in Tokyo, the ASAC meeting in Leiden, and other venues. I. Antennas: A. Additional 12m antennas As Stephane noted, increasing the number of 12m antennas from 64 to 78 results in an ALMA in which sensitivity per partner is conserved, and overall sensitivity is increased. This seems like a reasonable goal. B. The Terahertz Array A compact array of seven 6-8m antennas is added, with each antenna bringing an equal value to that of one 12m antenna. The exact number and size are poorly determined. An alternative which poses sizable problems for pointing and surface accuracy might be to build one submillimeter telescope of 24m diameter. Scientific Merits of a Compact Array: I believe that the compact array brings a very good enhancement to ALMA as it promises production of science otherwise not addressed by ALMA, at the highest frequency windows. The compact array could operate at supraTerahertz frequencies for the 15% of the time at which transparencies in the supraTerahertz windows exceeds 30%, for instance. As Guilloteau noted, this Terahertz Array could operate independently of, or in addition to the main array, with the antennas on the latter underilluminated to improve efficiency, field of view, and effective pointing performance. At 1 THz, the resolution could be 3-4" over a 10" field of view (FOV) for an 8m telescope, somewhat larger for 6m telescopes (but see below), operating as a stand-alone array. Issues affecting number and diameter of antennas includes a. As antennas become smaller, i.e. 6m, it may be difficult to accommodate a standard suite of receivers, and standard cabin, compromising the economy of scale. As the array becomes more specialized, it becomes more difficult to operate and maintain. b. As number of antennas increases, it becomes more difficult to pack them together to obtain the smallest baselines. The array need not be concentric with the large array, but should perhaps be located nearby for operation on medium baselines with underilluminated 12m antennas. The number of antennas is limited to perhaps 16. 16 x 6m antennas has the same collecting area as one 24m antenna. c. As antennas become larger, it is easier to accommodate the standard suite of receivers. As the compact array may be operated as a standalone Terahertz Array, and may require additional receivers to operate at supraTHz frequencies, it seems unwise to restrict the receiver cabin. Some space may be recovered if the THz Array need not operate at the longest wavelengths. This suggests perhaps 8m antennas. However, existing implementations of inhomogeneous arrays have employed antennas with diameters varying by a factor of two. Nine 8m telescopes have the same collecting area as one 24m antenna. Seven 8m antennas provides adequate sensitivity for matching with an ALMA mosaicking 25% of its observing time. A. Imaging quality should be very much improved, through provision of a. short baseline information (6-10m) for imaging with the larger array. Although simulations are just beginning, ALMA is expected to proved excellent imaging at millimeter wavelengths, with some degree of quality loss at submillimeter frequencies. Especially at high frequencies, direct measurement of 8m spacings provides much better accuracy than recovery of this information through combination of interferometric plus on-the-fly mapping data. b. improved cross calibration between interferometer and single antenna performance c. improved performance for the combined array, particularly in bands 9 and 10. d. For a main array performing wide field imaging 25% of available time, the Terahertz Array spends essentially all its time collecting short spacing information for the wide field imaging experiments. This will pose some potential logistical problems--different atmospheric conditions, calibrator fluxes, scheduling conflicts but this difficulty is probably only at the annoyance level. e. The compact array may be constructed in a fixed array, with long baselines provided through baselines with underilluminated 12m antennas. f. Radford notes: Should nearby mountain tops be condsidered for the location of a teraherz/super-terahertz array? Radiosonde profiles show the bulk of the water vapor is trapped below an inversion layer fairly close to the ground at least some of the time (e. g., flight 85, 1999 November 7 UT 4). Putting a high frequency array 400-700 m higher, i. e., on Cordon Honar (5400 m), Cerro Chascon (5650 m), or Cerro Sairecabur (5750 m), would lift it above the inversion layer and dramatically improve the observing conditions. This is not a novel idea -- it was suggested at the Cornell workshop last week, among other venues. At the very least, we should determine from the existing radiosonde data the expected improvement in observing time. And more radiosonde launches certainly would help. I note that, on the other hand, baselines to the ALMA array would not be particularly useful in most cases if the THz Array were sited far from it; cross calibration might suffer if the atmosphere at the THz Array site were very different from that at the main ALMA site. B. Science with the Terahertz Array To some extent, the compact array would bring the most identifiable new capability to ALMA. However, it is not clear that the technology is yet ready for construction of a Terahertz Array. However, that technology is being developed for the FIRST mission (2007), and may be available during ALMA construction. a. Frequency. The frequency extent addressed by ALMA would be extended to include the three supraTHz windows accessible from the Earth's surface with reasonable transparency. 1. 1-1.06 THz window. Recently, the HHT detected CO 9-8 in this window, which also contains the CS 21-20 line. Transmission is about 20% when transmission in the 450 micron window is about 70%. This will be referred to as the 1.03 THz window. 2. 1.25 - 1.37 THz window. This window is somewhat diced by atmospheric lines, rather like the Band 8 window, but contains the CO 11-10 line and reaches a transparency nearly that of the 1.03 THz window mentioned above. Of the three supraTHz windows, this is probably of least interest. 3. 1.5 THz window. This window contains the lower frequency of the two [N II] lines, the CO 13-12 transition, and the HCN 17-16 line. Owing to the uniqueness of the [N II] line as a probe of the ISM, and its strength in the Milky Way (measured by COBE) and other galaxies (estimated from ISO measurements of the higher frequency line in other galaxies using simple CLOUDY models), this is the primary interest of the three supraTHz windows. Transmission reaches 20% but the window is somewhat broader than the 1.03 THz window. 4. Dust continuum emission increases from most objects through these windows, and would provide an interesting target. Spectral baseline, for determination of spectral energy distributions, for example, suggests that the 1.5 THz window is of most interest. 5. [C II] emission at 2.2 THz enters the 1.5 THz window at z=0.47, providing a window on this line in galaxies at a time between the present epoch and that of peak star formation. 6. However, receivers to cover these bands would come at some future time when technology improves. In the interim, receivers using this future technology might be tested on the THz array antennas. Enhanced frequency coverage would not be part of ALMA construction. b. Sensitivity - 1. Sensitivity can be calculated for the proposed 7 x 8m array. These antennas should achieve better surface accuracy than the 12m antennas; an assumption of 10 microns might be reasonable, better might be achievable. This accuracy should provide an efficiency near 60%. With more baselines, and a diameter better targeted to filling the gap in spacings available to ALMA, a 16 x 6m array sensitivity is also calculated. 2. Goals of a THz Array, and a compact array operating to provide short spacings for ALMA at high frequencies, conflict somewhat in that both goals can only be achieved in the best weather. 3. Estimates - Proposed 7 x 8m array. For operation in the 1.5THz band, a receiver achieving 25 h nu/k is assumed (SSB). 20% zenith transmission through the atmosphere received by an 8m antenna with 55% efficiency and a main beam size of 7" are also assumed for a source at 1.3 AM. In one minute, the array could achieve 0.3 Jy sensitivity, of .01K in brightness temperature. In a single channel 1 km/s wide, this is 12 Jy km/s, or 0.5K with shortest baseline 1.5D=12m. 4. Estimates - Proposed 16 x 6m array. For operation in the 1.5THz band, a receiver achieving 25 h nu/k is assumed (SSB). 20% zenith transmission through the atmosphere received by an 6m antenna with 55% efficiency and a main beam size of 9" are also assumed for a source at 1.3 AM. In one minute, the array could achieve 0.23 Jy sensitivity, of .006K in brightness temperature. In a single channel 1 km/s wide, this is 9 Jy km/s, or 0.2K on baselines of 1.5D=9m. c. Implementation 1. Japan has proposed providing these antennas over the period FY2002-2008. 2. Some correlator redesign would be needed for an ALMA with an increased number of antennas. Escoffier has offered the opinion that the basic design could accommodate 88 antennas, sufficient for 78 12m antennas plus 10 smaller ones. However, since the THz Array antennas may not often be operated with the 12m antennas, some additional capacity may be available. II. Receivers and LO A. Receiver Bands The ASAC voiced interest in Band 4 (2mm) since CO at redshifts of 0.45 to 0.8 for the 2-1 line will fall in this range. Band 3 covers redshifts of 0. to 0.35 or so, depending upon its lower frequency, for the 1-0 line. Thus these two lines give good sensitivity to redshifted CO for the lowest excitation lines over the redshift range in which most evolution in the star formation rate has occurred, if one is to believe published estimates. For higher redshifts, the compaction of the spectrum provides readier access to a range of redshifts. I believe that this should be a priority also. It would be useful to lower the lower edge of band 3, in my opinion, from 86 GHz to 84 GHz (which allows complete overlap with the band covered by the 3mm VLBA receivers). This would have to reach 80 GHz for complete coverage of the two lowest CO lines for redshifts between 0.35 and 0.45. The weather at Chajnantor is not always submillimeter; I believe that Band 4 should be a priority, in place of Band 10, which I believe would benefit by waiting for the technology to mature. B. LO This was not really developed in the memo of 12 June. Does this include expansion of the photonic LO system to frequencies below 300 GHz? III. Correlator (from 12 June note plus Okamura presentation 17 Feb 2000) A. The proposal is that NRAO provide the first quarter of the correlator now planned, to be replaced by a second generation correlator producing 125 kch/IF from 85 antennas. Architecture to be determined by EU/Japan. Advantages cited, especially by Okamura in February for FX design, include: a. Increased number of baselines addressed b. Increased sensitivity by increasing the number of bits (not specified); easier with FX c. Increased bandwidths: advantages 1. Simultaneous wide bandwidths and high spectral resolution Advantages: multi line imaging not restricted by having only n IFs 2. Imaging line surveys possible with resolution matched to source 3. Wide velocity coverage with high resolution may be important where a range of conditions are encountered, such as protostellar disks with warm kinematically active centers and cold exteriors with, e.g. slow infall. 4. At 1.5 THz, 2 GHz corresponds to 400 km/s, suggesting the existing design might place some restrictions on the THz Array. 5. Wideband high resolution imaging is useful for studies of radio loud quasars such as 3C84. High accuracy continuum subtraction needed 6. Recombination line studies suggest broad coverage at good resolution 7. Absorption line studies of distant galaxies 8. Serendipity, such as water masers in NGC4258. d. Disadvantages of increased bandwidths 1. Huge throughput may mean additional computing costs. These should be assessed. 2. FX design can result in higher development costs 3. More cabling needed for FX design. Clarity and light, Al From awootten at NRAO.EDU Sat Jun 24 21:29:29 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Sat, 24 Jun 2000 21:29:29 -0400 (EDT) Subject: [asac] Message from Neal Message-ID: <200006250129.VAA14526@polaris.cv.nrao.edu> Neal sent the following message from his Leiden account, where he is not a member of the asac list (only his Texan identity is a member)...Al ------- start of forwarded message (RFC 934 encapsulation) ------- From: "Neal J. Evans II" Message-Id: <200006211442.QAA10522 at strw.LeidenUniv.nl> To: asac at nrao.edu Subject: ALMA Receivers Dear colleagues, I hesitate to make a mass mailing, but I offer these thoughts on the receiver specs for consideration, particularly the idea of a figure of merit that weights the importance of T_rx and bandwidth. If you like the idea, send your votes on X and Y to Karl... Cheers, Neal Reactions to the Receiver Specs Document I agree with the points made by Stephane and Al. Where they differ, I agree with Al's formulation. In particular, the receiver specs should change with frequency, as noted by Al. The current spec is too easy at the low frequencies, and perhaps too hard at the high end. For clarity, I understand Al's A values to apply to SSB T_rx. I don't like the idea of relaxing the bandwidth spec so easily, but I recognize that there are tradeoffs. It would be better to formulate a figure of merit that balances T_rx with BW. If one sacrifices too much on T_rx to meet a spec on BW, one may quickly lose more than one gains. If we adopt Al's formulation, with R_rx = A hnu/k + 4 K and IF bandwidth symbolized with BW, the figure of merit for line observations is (I leave out the constant 4 K for clarity, but it could be worked in) F_line = T_rx/A For continuum, it is F_cont = (T_rx/sqrt(BW))/(A/sqrt(8GHz)) Note that this formulation relates to what you can achieve in a fixed integration time, which is a more realistic approach in my view than asking what integration time is required for a given sensitivity level, which would lead to squaring these figures. The overall figure of merit depends on your evaluation of the overall importance of line and continuum observations. Call the overall figure of merit F_total. Then F_total = X F_line + Y F_cont ; X + Y = 1 The ASAC could vote on the values of X and Y. My vote would be X= 0.6, Y = 0.4. The reason for this choice is not that I think line observations are more important than continuum, but because they are harder-- the continuum sensitivity of ALMA will be very good, but for some line problems, the sensitivity will be more marginal. One could make X and Y a function of band, but I think there won't be large differences. The idea is that one would relax the BW spec, replacing it with the spec that F_total be less than or equal to unity. On other items, I agree that selecting and tuning to a new band should take less than 15 min, unless I misunderstand what this means. Presumably, there will be look up tables and fast iterative procedures to optmize at a particular frequency. Cheers, Neal ------- end ------- From myun at aoc.nrao.edu Tue Jun 27 13:01:25 2000 From: myun at aoc.nrao.edu (Min Yun) Date: Tue, 27 Jun 2000 11:01:25 -0600 (MDT) Subject: [asac] Message from Neal Message-ID: <200006271701.LAA12158@zia.aoc.NRAO.EDU> Hi Karl, The following comment by Neal has been brought up several times previously, and we still don't seem to have an explanation as what this 15 minute spec for changing bands is and how it is derived. As I state below, the ability to scan thru continuum bands quickly will allow us to determine the redshifts of high-z dusty galaxies and to understand their evolution. We should ask the receiver group to clarify the situation and investigate ways to cut down on the switching time. > > On other items, I agree that selecting and tuning to a new band should > take less than 15 min, unless I misunderstand what this means. Presumably, > there will be look up tables and fast iterative procedures to optmize > at a particular frequency. > The latest number from the Large Millimeter Survey conference at U Mass last week is that 65% of all SCUBA sources are too faint to be identified at optical or NIR. The mm/submm SED modeling plus detections of CO transitions may be the only way to obtain redshifts and understand their evolution. Since even ALMA will have to search a wide range of frequencies to find the CO lines, quickly mapping out the dust SED would be a useful first step in the redshift determination (my presentation at the conference). While the 15 minute switching time for receiver bands is not completely limiting of this sorts of work, it is easy to see that this switching time dominates the total observing time by an order of magnitude. In fact, this would be true for any observation trying to characterize the mm/submm continuum spectrum (e.g. stellar photospheres, circumstellar disks). It would be good to avoid this situation if possible at all. -- Min From myun at aoc.nrao.edu Tue Jun 27 15:09:22 2000 From: myun at aoc.nrao.edu (Min Yun) Date: Tue, 27 Jun 2000 13:09:22 -0600 (MDT) Subject: [asac] Message from Neal Message-ID: <200006271909.NAA21150@zia.aoc.NRAO.EDU> Thanks for clearing that up, Geoff. This is consistent with what I have learned from Al Wootten today, but I felt we needed an official explanation from the receiver group. As I said in my e-mail, the particular example of measuring dust SED is not severely impacted by this limitation, but it does bother me that a project that needs only a few minutes of on-source integration would require an hour or more of obsering time simply because of this limitation. One cannot always assume that this type of study will be done for a cluster of sources. Study of a GRB, for example. Since there are some foreseeable scientific implications tied to this number, it would be good to scrutinize it a bit and urge the receiver group to find ways to minimize the impact on observations. -- Min > > Hi All, > > I believe Ewine's earlier mail summarized the 15 minute issue with the > receivers and it is the following. Three receivers (the WVR plus two > astronomy receivers) can be on at any one time. The 15 minutesis the time > needed to get a receiver up and going from a COLD start. It takes a bit > for the amplifiers to warm up and stabilize, etc. I suspect things like LO > switching and so forth are very much faster. So, the question is, if you > have two receivers that are on, and you need to switch to a third, how > much will that limit the available science. If this is a serious issue, > we should let the receiver group know very soon that we are concerned with > this length of time. > I would note to Min that if there are a few sources that are close > enough that the switching (i.e. moving and pointing) time is short, you > can do a few sources with the active receiver while the new tuning warms > up, so I find it hard to believe this will be a very serious limitation. > > Geoff > From awootten at NRAO.EDU Tue Jun 27 19:04:26 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Tue, 27 Jun 2000 19:04:26 -0400 (EDT) Subject: [asac] forwarded message from owner-asac@kochab.cv.nrao.edu Message-ID: <200006272304.TAA20362@polaris.cv.nrao.edu> For some reason, the mailer bounced Geoff's email, which I forward: Hi All, I believe Ewine's earlier mail summarized the 15 minute issue with the receivers and it is the following. Three receivers (the WVR plus two astronomy receivers) can be on at any one time. The 15 minutesis the time needed to get a receiver up and going from a COLD start. It takes a bit for the amplifiers to warm up and stabilize, etc. I suspect things like LO switching and so forth are very much faster. So, the question is, if you have two receivers that are on, and you need to switch to a third, how much will that limit the available science. If this is a serious issue, we should let the receiver group know very soon that we are concerned with this length of time. I would note to Min that if there are a few sources that are close enough that the switching (i.e. moving and pointing) time is short, you can do a few sources with the active receiver while the new tuning warms up, so I find it hard to believe this will be a very serious limitation. Geoff __________________________________________________________________________ Geoffrey A. Blake; Professor of Cosmochemistry & Planetary Science, Professor of Chemistry, and Deputy Director, Owens Valley Radio Observatory gab at gps.caltech.edu From kmenten at mpifr-bonn.mpg.de Wed Jun 28 10:16:46 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Wed, 28 Jun 2000 16:16:46 +0200 (MEST) Subject: No subject Message-ID: Dear ASAC members, I have finished a draft of the ASAC response to the ALMA Receiver Subsystem Top-level Requirements and Specifications document, which you find attached to this message. Please email me final comments by Thursday, June 29. Cheers, Karl P.S. The document can also be found on: http://www.mpifr-bonn.mpg.de/staff/kmenten/jrdg-response.txt ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 -------------- next part -------------- DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT*DRAFT* MEMORANDUM Date: 28-June-2000 To: Wolfgang Wild & John Payne, ALMA JRDG From: ALMA Scientific Advisory Committee (ASAC) Topic: Comments on ALMA Receiver Subsystem Top-level Requirements and Specifications (specifically Draft Version 1.3, 19-May-2000, http://www.cv.nrao.edu/~awootten/mmaimcal/receiverspecs.html) ------------------------------------------------------------------------ This document summarizes the ASAC's commnents on the ALMA Receiver Subsystem Top-level Requirements and Specifications document. ------ * Section 2.2 REFERENCE DOCUMENTS ASAC: Add CDR and PDR reports to be found at http://www.alma.nrao.edu/administration/index.html --- * Section 3.1 FREQUENCY COVERAGE (in particular Table 1): Issue: First sentence ("The ALMA receiver subsystem will cover all the available atmospheric frequency windows between 30 GHz and 950 GHz.") ASAC: Since the definition of "atmospheric frequency windows" is, e.g. opacity dependent, we recommend to change this to "The ALMA receiver subsystem will cover frequencies between 30 GHz and 950 GHz as given in Table 1." Issue: lower frequency range of Band 3 (now 86 GHz) ASAC: The ASAC actually wrote (http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node3.html): "We strongly urge that the JRDG study the possibility of extending the lower frequency range of Band 3 to include the SiO maser transition near 86 GHz. If this is possible, Band 2 would drop to third priority." Since the VLBA 3 mm receivers will go down to 84 GHz, perhaps some attention should be paid to the actual number of the lower limit. We recommend that 84 GHz is adopted. --- * Section 3.2 POLARIZATION ASAC: The ASAC report at http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node12.html needs to be made more specific. Larry D'Addario and Steve Myers have put work into this, and their draft recommendations are located at: http://www.aoc.nrao.edu/~smyers/alma/polspecs-imcal.txt We invite comments on this document. The polarisation purity requirement mostly influences the optics and horn/orthomode transducer. One would assume that the 1% goal in calibration requires a cross-polarisation better than 20 dB, and that all antennas should also be co-aligned in polarisation to the same level. Polarisation experts should comment on this! Note that it may be difficult to reach this level with an orthomode transducer. * Section 3.3 OPTICAL COUPLING TO THE TELESCOPE ASAC: The ASAC urges that coupling efficieny specs are defined and that a measurement scheme for various efficiencies are discussed. --- * Section 3.4 RECEIVER NOISE PERFORMANCE Issue: Receiver noise requirements ASAC: These should be stated in a more specific way. Our recommendation: The noise temperature measured at the dewar input window to the cartridge shall not exceed a value of TrxSSB for SSB response and 0.5*TrxSSB for DSB response. TrxSSB will in general be a function of the frequency nu and is given by the following formula TrxSSB= A * (h*nu/k) + 4 K where h and k are the usual physical constants. The frequency dependent quantity A has the following specification and goal values: Bands 1-6 (below 275 GHz) Spec: A = 6 / 10 Goal: A = 3 / 5 Bands 7-8 (275-500 GHz) Spec: A = 8 / 12 Goal: A = 4 / 8 Band 9 (602-720 GHz) Spec: A = 10 / 15 Goal: A = 6 / 9 Band 10 (787-950 GHz) Spec: A = 10 / 15 Goal: A = 8 / 12 For both, the specification and the goal values, two numbers are given. The first one of these refers to the value that A must not exceed over the 80% range of the nominal bandwidth that has the best performance, whereas the second value may not be exceeded at any frequency within the nominal bandwidth. Furthermore, the receiver temperatures should be measured in a reference plane outside the dewar, which involves the following technical issue. Ideally, one would like to measure at the secondary focus, including all receiver related optics, i.e. with the full final cryostat and optics. However, since receiver cartridges will be developed and tested separately, this cannot be performed on the development site. We propose that the receiver group equips the test cryostats for the cartridge testing in such a way as to provide a comparable receiver temperature reference plane. --- * Sections 3.5 SIDEBANDS, 3.6 IF BANDWIDTHS, and 3.7 SIMULTANEOUS OPERATION OF BANDS ASAC: Specs made here are rather vague. The goal is: SSB 2 x SB 2 x Pol = 4 x 8 GHz (sideband separating) The Munich PDR (http://www.cv.nrao.edu/~awootten/mmaimcal/ALMA-DesRevRec4.html) said: "In addition to the baseline IF bands of 8 GHz Upper and Lower Sideband, receiver designers are free to select any of the following alternatives: 8 GHz Single-Side-Band, Upper or Lower, 8 GHz Double-Side-Band or 4 GHz Upper and Lower Sideband. In all cases, dual polarization for a total of 16 GHz IF band width. Sideband separation in DSB-mode will be possible for integration times in multiples of 1 sec. Depending on the choice, and maintaining the currently proposed LO coverage, this might lead to some loss of frequency coverage. The impact of this should be evaluated by the Science Group." This is only a recommendation, but it might be a starting point for more stringent specs. --- * Section 3.6 IF BANDWIDTH Issue: 4 GHz IF bandwidth as a fall back position ASAC: The 8 GHz IF bandwidth is a very strong science requirement and every effort should be made to keep the IF bandwidth at 8 GHz at the lower frequencies, where continuum sensitivity and broad bandwidth for high-z CO line searches are most crucial. At higher frequencies, this could perhaps be somewhat relaxed, but only as a last resort. Officially declaring 4 GHz IF bandwidth as a fall back position even for only the initial bands is a significant deviation from the original specs. Any specific proposal for a design with less than 8 GHz needs more discussion. What would be the cost of upgrading receivers with 4 GHz IF bandwidth to 8 GHz bandwidth? As a basis for discussions of the tradeoffs between bandwidth and receiver temperature, Neal Evans has made the following proposal, which will be discussed by the ASAC. We include it here to indicate in which direction these discussions may lead. "I don't like the idea of relaxing the bandwidth spec so easily, but I recognize that there are tradeoffs. It would be better to formulate a figure of merit that balances T_rx with BW. If one sacrifices too much on T_rx to meet a spec on BW, one may quickly lose more than one gains. If we adopt Al's formulation, with T_rx = A hnu/k + 4 K and IF bandwidth symbolized with BW, the figure of merit for line observations is (I leave out the constant 4 K for clarity, but it could be worked in) F_line = T_rx/A For continuum, it is F_cont = (T_rx/sqrt(BW))/(A/sqrt(8GHz)) Note that this formulation relates to what you can achieve in a fixed integration time, which is a more realistic approach in my view than asking what integration time is required for a given sensitivity level, which would lead to squaring these figures. The overall figure of merit depends on your evaluation of the overall importance of line and continuum observations. Call the overall figure of merit F_total. Then F_total = X F_line + Y F_cont ; X + Y = 1 The ASAC could vote on the values of X and Y. My vote would be X= 0.6, Y = 0.4. The reason for this choice is not that I think line observations are more important than continuum, but because they are harder-- the continuum sensitivity of ALMA will be very good, but for some line problems, the sensitivity will be more marginal. One could make X and Y a function of band, but I think there won't be large differences. The idea is that one would relax the BW spec, replacing it with the spec that F_total be less than or equal to unity." --- * Section 3.7 SIMULTANEOUS OPERATION OF BANDS Issue: It is stated tha "The water-vapor monitoring radiometer shall operate simultaneously with bands 2 to 10, but not with band 1 which can operate without the water-vapor monitoring radiometer. ASAC: The ASAC actually said: "The ASAC does note that the simultaneous operation at 183 GHz and Band 1 receivers is not a scientific requirement, so it is straightforward to locate these systems in the same Dewar if that makes sense." In the best of all possible worlds, the WVR would work with band 1 as well as the other bands--this will be necessary under a wide range of conditions at Chajnantor for which ALMA may be operable at band 1 with WVR but ALMA would be shut down otherwise. However, if the cost of operating both simultaneously is very high, one possible sacrifice might be simultaneous operation of WVR and band 1. This is very different from designing a receiver system which will not accommodate simultaneous operation of both from the outset. --- * Section 3.8 RECEIVER STABILITY Issue: It is stated that "A preliminary suggestion for a gain fluctuation limit is: 1e-4 rms over a 1 sec interval." ASAC: This was indeed suggested in the ASAC report. A memo from Wright (http://www.alma.nrao.edu/memos/html-memos/abstracts/abs289.html) suggests 1e-4 over 0.1s, which begins to define the spectrum of stability. --- * 4.3 SELECTION OF A NEW OBSERVING BAND Issue: The statement "Selecting and tuning a new band shall require no more than 15 min." caused quite some confusion. ASAC: This issue was clarified by Wolfgang Wild, who states that "What we meant with the 15 min is not the tuning time, it means that you need to switch on a particular band 15 min before using it. This is to reach thermal equilibrium. In practice, this time could probably be shorter, but nobody has measured it so far. Switching from on band to another would be done in 1.5 sec (if the band is switched on). Since we cannot have all bands switched on at all times due to cryogenic limitations we introduced this spec to minimize the impact on scheduling." We recommend that this explanation should be incorporated into the document. From kmenten at mpifr-bonn.mpg.de Thu Jun 29 12:57:31 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Thu, 29 Jun 2000 18:57:31 +0200 (MEST) Subject: [asac] Reply to ALMA Sciene Software Requirements Committee Message-ID: Dear ASAC members, Attached you find a draft of the ASAC response to the ALMA Sciene Software Requirements Committee questions. Please email me final comments by Friday, June 30. Cheers, Karl P.S. The document can also be found on: http://www.mpifr-bonn.mpg.de/staff/kmenten/ssrc-response.txt ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 -------------- next part -------------- MEMORANDUM Date: 29-June-2000 To: Robert Lucas, ALMA Science Software Requirements Committee From: ALMA Scientific Advisory Committee (ASAC) Topic: Comments on issues raised by ALMA Science Software Requirements Committee (Email message by Robert Lucas, 18-May-2000) ------------------------------------------------------------------------ > > to ALMA Project Scientists and Alma Science Advisory Committee Members: > ----------------------------------------------------------------------- > > Object: Project-wide issues of specific interest to Science Software > Requirements > > During our past six months of work in the Science Software > Requirements Committee we have encountered several issues on which > we agree that further input on your side will be needed before our > work can be completed. Our preliminary report (ALMA memo 293) has > been recently officially reviewed and we take this opportunity to > raise the following questions. These are mainly issues related to the > way ALMA is operated as a whole. For each issue we would like to > have either a definite answer or a baseline/fall-back > alternative. The questions are given in order of decreasing importance. > > 1) Array Scheduling > > We have been assuming that ALMA will be dynamically scheduled so > that each project is observed during weather conditions (seeing, > opacity, wind) that allow its objectives to be achieved. This > implies dynamic scheduling in near real time (Dynamic Scheduling) as > stressed in mma memo 164, and in ALMA Project Book, Chapter > 2(III.4). This has implications on the feedback from the PI, on the > basis of calibration data and images produced by the pipeline: this > feedback can only be offered at the end of one transit (observing > session), assuming the project observations are divided into several > transits either due to schedule optimization (as high elevations are > preferred) or intentionally by the insertion of breakpoints. This > limitation on `interactivity' has to be realized. We believe it is a > small price to pay for the increase in productivity expected from > dynamic scheduling. > > An alternate scheduling method is the traditional interactive > observing, which should be available since it can be useful for test > purposes and for special -- timely and unforeseen -- observations. > > Our question: Is dynamic scheduling to be the default mode of > scheduling, accepting the restricted interactivity implied by this > mode ? > The ASAC very strongly recommends that dynamic scheduling should be the default mode. > > 2) Purpose of the pipeline > > The data flow ALMA Project Book, Chapter 2(III.5) will include a > pipeline that may be used to fulfill several purposes: > > a) check that the data obtained can be calibrated, with feed back to > the observing process to use the optimal phase calibration cycle. > > b) give feed back to the dynamic scheduler by monitoring the observed > phase noise. > > c) produce calibrated uv data and maps of test quasars to check in > real-time the quality of observations, with feed back to the > dynamic scheduler. > > d) produce calibrated uv data and maps of the project source(s) to > enable the PI to evaluate her/his data at the end of the observing > session and to proceed with scientific interpretation when the > project is finished (after improved reduction if needed), while > incrementing the ALMA data archives. > > e) use calibrated uv data and maps of the project source(s) in order > to derive simple quality parameters (noise level, signal to noise > ratio) that may be used to define when the project goals are > attained. > > f) use calibrated uv data and maps of the project source(s) in order > to derive similar or more sophisticated parameters (source size, > number of sources ... see examples in memo 293) to be fed back > into the project's observing process, which may then take > automatic decisions. > > While we believe that a, b, c and d should be implemented as > baseline features, there is some concern that f) and maybe e) might > be too ambitious goals (software has a cost too) or even may > increase the distance between the astronomers and the instrument to > an unwanted level. > > Our question: Which degree of sophistication should be set as a goal > for the ALMA data pipeline ? > a)-d): yes! In particular, d) means that calibrated images are the final data products! - This would result in a much lower useage threshold for non-radioastronomers. e) would be useful in certain cases, but without a source model in general pretty difficult. f) This should be left to the astronomer. To allow this and at the same time not to slow down project completion too much, a project could have predefined breakpoints, at which the astronomer evaluates the data taken so far, and the subsequent course of the project depends on the astronomer's decision. > > 3) Operational aspects > > For the specification of GUI (graphical User Interfaces) a clear > description of the relative duties of the operators and local staff > astronomers will be needed, in view of the following tasks > > - Allocation of antennas to simultaneous projects (e.g. a sub-array > for calibration, a sub-array used for astronomy, some antennas in > maintenance) ? > Operator, after consultation with local staff astronomer. > > - Control on the dynamic scheduling process > Operator, but only in case of emergency. > > - Communication with the PIs if needed > Local staff astronomer. > > Our question: Can the relative duties of the staff in charge of > controlling the array be already outlined ? > See above > > > 4) Policy on data propriety: > > We are assuming, as is the usual practice in most observatories, > that only the proposing team has access to the data during a limited > proprietary period and that the data ultimately become public. The > actual length of the propriety period can be probably be set later, > but some policy questions may affect the software requirements, such > as: > > 4.1 is only the scientific data covered, or all header information > including monitoring data, or some header information only > (like coordinates and frequencies) ? > All the header information should be public immediately to avoid duplication. For the data, a proprietary period of 1 year seems reasonable. This applies to the target source data. Phase and flux calibrator data should be public immediately. In certain cases, in particular for PhD projects, the proprietary period might be extended. For complex projects, such as surveys or projects requiring many configurations, it mmight be appropriate to let the proprietary period start after all of the data have been collected. > > 4.2 if public data is reprocessed in the pipeline by others, to search > for unforeseen scientific results, does this start a new proprietary > period ? > We don't think that this would be appropriate - it would be easy to block data forever by periodically reprocessing them. > > Our question: Can the proprietary data policy of ALMA be already > outlined ? > > 5) Special modes > > Some specific observations (Sun, Pulsars, ...) may need very short > integration times, fast frequency changes, ... for which the exact > scientific software (and hardware ?) requirements need to be > investigated in detail. For these issues we would like having > specialized astronomers as correspondents, so that we may include > their contributions in our requirements, in a coherent manner. > Arnold Benz will organize a discussion at the IAU General Assembly in Manchester (August 2000) on solar, stellar and possibly pulsar science requirements for ALMA. He will in addition also contact some other specialists in the field that will not be in Manchester. > 6) Other details > > - is an audio channel from the antenna cabins to the operator > planned ? (see comment 95) > Would be useful, but is trivial. > > - We assume, as DSB mode is clearly an option for some frequency > bands, that side band separation has to be handled by software for > interferometric work in those bands. > > Robert Lucas, > > on behalf of the Science Software Requirements Committee From awootten at NRAO.EDU Mon Jun 19 22:27:25 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Mon, 19 Jun 2000 22:27:25 -0400 Subject: [asac] SSR comments Message-ID: <394ED68D.174813A6@nrao.edu> Our question: Is dynamic scheduling to be the default mode of scheduling, accepting the restricted interactivity implied by this mode ? My recollection is that this is stated in Chapter 2 of the Project Book. 2) Purpose of the pipeline The data flow ALMA Project Book, Chapter 2(III.5) will include a pipeline that may be used to fulfill several purposes: a) check that the data obtained can be calibrated, with feed back to the observing process to use the optimal phase calibration cycle. b) give feed back to the dynamic scheduler by monitoring the observed phase noise. c) produce calibrated uv data and maps of test quasars to check in real-time the quality of observations, with feed back to the dynamic scheduler. d) produce calibrated uv data and maps of the project source(s) to enable the PI to evaluate her/his data at the end of the observing session and to proceed with scientific interpretation when the project is finished (after improved reduction if needed), while incrementing the ALMA data archives. e) use calibrated uv data and maps of the project source(s) in order to derive simple quality parameters (noise level, signal to noise ratio) that may be used to define when the project goals are attained. f) use calibrated uv data and maps of the project source(s) in order to derive similar or more sophisticated parameters (source size, number of sources ... see examples in memo 293) to be fed back into the project's observing process, which may then take automatic decisions. While we believe that a, b, c and d should be implemented as baseline features, there is some concern that f) and maybe e) might be too ambitious goals (software has a cost too) or even may increase the distance between the astronomers and the instrument to an unwanted level. Our question: Which degree of sophistication should be set as a goal for the ALMA data pipeline ? Through d) is necessary for widebased support of astronomers and should be a goal of the pipeline. e) should be a goal, perhaps to be explored on existing arrays. I think f) is probably too distant a goal for initial implementation. Data through d) should come back to the astronomer remotely in realtime for interaction. e) can then be done semi-locally (i.e. data may exist on his machine or on the remote machine) at a breakpoint. f) could be implemented locally, by the astronomer on his home workstation after receiving the dataproduct; probably the full dataproduct will not be deliverable over the net from Chajnantor. The project could then proceed after consideration, possibly at several days delay. 3) Operational aspects For the specification of GUI (graphical User Interfaces) a clear description of the relative duties of the operators and local staff astronomers will be needed, in view of the following tasks - Allocation of antennas to simultaneous projects (e.g. a sub-array for calibration, a sub-array used for astronomy, some antennas in maintenance) ? The operator controls dynamic scheduling and assignment of antenna resources, such as might occur at the VLA now upon advice of the astronomer runnung the program, or, in his absence, the local staff astronomer. 4) Policy on data propriety: We are assuming, as is the usual practice in most observatories, that only the proposing team has access to the data during a limited proprietary period and that the data ultimately become public. The actual length of the propriety period can be probably be set later, but some policy questions may affect the software requirements, such as: 4.1 is only the scientific data covered, or all header information including monitoring data, or some header information only (like coordinates and frequencies) ? All data, particularly calibration data, should be available. All header information should be available so that a previous observer for example could reconstruct the state of the array when his project commenced. Reprocessing of data should not commence a new propiertary period. An audio channel would be useful. The remote observer should have audio contact with the operator or with the antenna channel also.