[asac] report.tex
Neal J. Evans II
nje at strw.strw.leidenuniv.nl
Tue Mar 28 05:17:10 EST 2000
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\begin{document}
\title {\bf Report of the ALMA Scientific Advisory Committee:
March 2000 Meeting}
\affil{ALMA Scientific Advisory Committee}
\author {Arnold Benz (Switzerland), Geoff Blake (USA), Roy Booth (Sweden),
Pierre Cox (France), Dick Crutcher (USA), Neal Evans (USA, Chairman),
Mark Gurwell (USA), Rafael Bachiller (Spain), Karl Menten (Germany,
Vice-Chairman), John Richer (UK), Nick Scoville (USA),
Ewine van Dishoeck (Netherlands), Malcolm Walmsley (Italy),
Jack Welch (USA), Christine Wilson (Canada), Min Yun (USA)}
\affil{Active Observers }
\author{Leo Bronfman (Chile), Yasuo Fukui (Japan), Tetsuo Hasegawa (Japan),
Masahiko Hayashi (Japan), Ryohei Kawabe (Japan), and Naomasa Nakai (Japan)}
\section{Introduction} \label{intro}
The ALMA Scientific Advisory Committee (hereafter ASAC) was formed in
late 1999, as requested by the ALMA Coordinating Committee (hereafter
ACC). The role of the ASAC is to provide scientific advice to the ACC,
the ALMA Executive Committee (hereafter AEC) and the project, via the
project scientists. As requested, the ASAC developed its own charter,
which we supply as Appendix \ref{charter}. The ASAC decided to hold
monthly telecons and regular meetings. For the near future, we will meet
before each meeting of the ACC, in order
to deliver a report in time for the ACC meeting. The telecons will supply
rapid responses to queries from the project management and project
scientists, and the minutes will be posted on the web.
The meetings will allow exploration in more depth of particular issues
and will result in a written report, such as this one.
To ensure good communications,
the ASAC will designate members to act as liaison to each of the
working groups in the project; these are listed in Appendix \ref{liaison}.
The ASAC members also committed themselves to helping to educate
the larger community about ALMA.
This document reports on the first meeting of the ASAC, held in Leiden,
The Netherlands, on March 10-11, 2000. The topics covered at the meeting
emerged from our telecons or from queries from the working groups.
Some issues require further study and some topics were deferred to
future meetings. These are listed in section \ref{future}.
We summarize the overall recommendations in section \ref{summary}.
\section{ALMA Liaison Group Issues} \label{alg}
The possibility of a contribution of Japan in the ALMA
project has received strong and positive support from
the ASAC. Such a contribution will
make ALMA the largest international collaboration in
astronomy and enhance the project in a number of important ways.
It will increase
the sensitivity of the array and add new technical capabilities.
If this collaboration is achieved, Japan
will have an equal partnership in the ALMA project with America and
Europe and share the infrastructure and running costs.
The basic contribution of Japan to the ALMA project will be to
add 12-meter antennas to the agreed 64 x 12-meter antennas.
This greater collecting area will result in a better sensitivity
(or observing speed), close to the original goal of a
$\rm 10,000 \, m^2$ array. This improved sensitivity will
compensate the need to share the observing time with a greater
number of users.
Further contributions of Japan to an enhanced ALMA project
are related to specific technical developments, including
the participation in the future correlator, construction
of the highest frequency receivers, or the photonic LO system.
It is too early for the ASAC to prioritize the importance of
these; further discussion is needed.
It is clear that the contribution of Japan in the ALMA
project could also open new perspectives for the project. In
particular, the possibility to add to the project
a compact array of smaller, high accuracy dishes
would be a most interesting addition. It would
improve the image quality for extended sources
and the performance at the highest frequencies.
This possibility should therefore be rediscussed
when the Japanese participation is confirmed.
\section{Receivers} \label{receivers}
Along with the telescopes, the receiver packages largely determine
the capabilities of ALMA. The Joint Receiver Development Group (JRDG)
has raised a number of questions and requested clarification from the
ASAC. These may be broken down into questions concerning the
frequency bands and their priority, the total power stability,
the Water Vapor Radiometer (WVR) specs
(dealt with in a separate section), polarization requirements,
calibration accuracy, and receiver configurations (principally
single sideband versus double sideband operation). Recommendations
for each of these areas are outlined below.
{\bf Frequency Bands}. The ASAC concurs that the four bands to be
initially installed on the array should be (in order of increasing
frequency) Band 3 (86-116 GHz), Band 6 (211-275 GHz), Band 7
(275-370 GHz), and Band 9 (602-720 GHz). The ASAC reiterates that the
frequency coverage should be as complete as possible, but we respond
to the request for prioritization of the bands as follows.
\begin{itemize}
\item First Priority: Bands 3, 6, 7, and 9
\item Second Priority: Bands 1, 4, and 2 (see below)
\item Third Priority: Bands 5, 8, and 10
\end{itemize}
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.
The frequency intervals of the other bands are reasonable.
Band 10 is scientifically quite interesting.
It is in the third priority because the technology of
THz SIS heterodyne receivers is in an early state, and it will be
difficult to make ALMA work at its highest operating frequency.
Some delay in the installation of this band
will enable the most sensitive receivers to be installed and the
telescope performance to be optimized.
Note that Band 1 is in the second priority list, and it must
be considered in receiver layout. If it will not be in the main
Dewar, then designs for optics that allow a second Dewar, possibly
also containing the WVR, should be developed. It is not necessary
for the WVR and Band 1 receivers to operate simultaneously.
{\bf Total Power Stability}. For On-The-Fly (OTF) mapping
capabilities, the requisite total power stability is of order 10$^{-4}$
in one second. The ASAC recommends that this level be a goal, rather than
a hard specification, pending further study. The over-riding
concern is the receiver sensitivity, and better performance should not
be sacrificed for stability at this stringent level. However, this level
of stability may allow considerable simplication (avoiding nutating
subreflectors), and we encourage the JRDG to study the issue and report
back to the ASAC on the prospects for achieving this level of stability
and on possible tradeoffs in doing so.
{\bf WVR Specs}. These are discussed at length elsewhere
(Section \ref{wvr}). The main point here is that this system
must be incorporated into the overall design and receiver specs.
{\bf Polarization}. Polarization work will be an important part of
ALMA research. Strong efforts should be made to have the polarized
single-dish beams as stable as possible; consequently, the ASAC recommends
that careful consideration be given to placing the 345 GHz receiver
on-axis. For linear polarization work the basis state of feeds would
ideally be circular polarization. If circular feeds
impose important limitations on tuning range or increase
significantly the noise temperature, a system for rapid, accurate
calibration of linear feeds should be implemented. Obtaining zero and
short spacing polarization data is essential.
A nutating subreflector has a limited angular throw and introduces
varying angles with respect to the optical axis of the primary
mirror. The OTF technique proposed for total power
observations would be ideal for polarization if the requisite gain
stability can be achieved.
Finally, the different polarization properties of the two
prototype antennas and other polarization properties of the test
interferometer and single-dish techniques should be carefully measured
as they may be a consideration in procurement decisions (see Section
\ref{antennas}).
{\bf Calibration Accuracy}. The ALMA calibration spec of 1\%~is
adequate scientifically, perhaps even a bit agressive.
A cold calibration load in the primary Dewar is probably unnecessary.
{\bf Receiver Modes}. The superb quality of the Chajnantor
site and the non-ideal nature of any optical system means that the
theoretical improvement in single sideband (SSB) versus double sideband
(DSB) receivers may be difficult to realize in practice. DSB receivers
are far easier and cheaper to fabricate, especially at submillimeter
frequencies, and the ASAC recommends that a careful design study be
undertaken that assesses the likely performance loss for DSB operation.
If the loss is sufficiently small, considerable cost savings and ease of
operation can be realized. The ASAC would like to revisit this question
once the SSB versus DSB study is completed. It is very likely that
ALMA will become operational with both SSB and DSB receivers. This
change in operational characteristics has important implications for
the ALMA correlator, and the ASAC also recommends that the initial
and subsequent ALMA correlators be designed with both modes of operation
in mind. The operating system and software environment may also be affected.
{\bf Summary}. The ASAC confirms that Bands 3, 6, 7, and 9 have the
top priority and should be installed first. While complete frequency
coverage is important, we have divided the other bands into second and
third priorities. We recommend study of extending the lower end of Band 3
to include 86 GHz. In addition, the JRDG should consider placing the Band 7
receiver on-axis. Designs that accomodate the Band 1 receiver are essential.
The ``relaxed'' WVR constraints may allow the Band 1 and WVR receivers to
share a Dewar, and the JRDG should consider such designs.
Finally, the ASAC requests a presentation at our next meeting of
a detailed plan for the mass production, integration and testing
of the ALMA Phase II receivers.
\section{System} \label{system}
The ALMA system deals with many aspects of ALMA. We expect to revisit
many of these areas in the future. We summarize below our recommendations
on the issues addressed at this meeting.
\begin{enumerate}
\item
The main array should consist of a number of 4 to 6 sub-arrays,
but the number of frequencies operating simultaneously will not exceed 3 or 4.
At present we could envision 4+1 subarrays. Namely:
\begin{enumerate}
\item
The main interferometric subarray
\item
Antennas for reconfiguration and baseline determination
\item
Two subarrays to simultaneously carry out two of the following
functions:
\begin{itemize}
\item
Secondary subarray at second frequency band
\item
Transient event monitoring
\item
mm-wave VLBI
\item
Testing, repair, receiver warm-up or cool-down, etc.
\end{itemize}
\item
The single-dish subarray or an ultra-compact array
(if included in the final project).
\end{enumerate}
\item
The prototype antennas should be equipped with nutators and stable
receivers. The number of ALMA antennas equipped for total power measurements
(nutators) should be 4, but this number will be reconsidered after the tests
with the prototype antennas. If feasible,
the rest of the array antennas should be equipped
with receivers of good gain stability ($\Delta G/G = 10^{-4}$
in 1 second).
(See also section \ref{receivers} and \ref{antennas}).
\item
Due to its scientific interest, the option of the 30-47 GHz receivers has
to be kept. The costs of including this band needs a more
detailed evaluation
(See also section \ref{receivers}).
\item
A detailed calibration plan, including polarization issues and phase
calibration, needs to be elaborated.
\item
Doppler tracking will be needed to provide accurate frequency calibrated
data.
\item
Polarization observations in total power mode with ALMA will impose
requirements on the system that deserve a detailed study.
\end{enumerate}
\section{Configurations} \label{config}
Within the Configurations Working Group most of the
discussion focusses on two major alternatives for the
basic array layout: the spiral zoom array concept described by Conway
(ALMA Memos \#216, 260, 283, and 291); and the ``doughnut'' array
developed by Kogan guided by the goal of achieving minimal sidelobes
(ALMA Memos \#171, 212, 226, and 247). For both concepts realistic array
layouts considering topographic constraints have now been studied
(ALMA Memos \#292 and 296). Both layouts appear to achieve comparable
sidelobe levels, which are of order 6--8\% (for snapshots!);
consequently, a decision to adopt one or the other design has to be based
on a number of other factors, such as logistics and scientific requirements.
For example, guided by experience with the VLA, one might expect that the
observers'
demand will be highest for the most extended configuration (for maximum
resolution) and the most compact one (maximizing surface brightness
sensitivity). Such considerations should be included in the choice
of array concepts.
A need for model images has arisen and a total of five images will be
chosen for use with all simulations.
More imaging simulations are necessary for arrays
involving baselines up to 20 km,
where terrain considerations are the major issue. Given ALMA's excellent
brightness sensitivity, imaging of thermal emission from gas and dust
with such long baselines will open new vistas.
Resolutions better than 10 milliarcseconds will be achieved, which
are essential for studies of some of ALMA's key science goals, such as
the formation of planets.
As decisions on antenna pad locations have to be made by late 2000,
we recommend that the Configurations Working Group report on progress
to the ASAC at our next meeting, after which we can make a final
recommendation.
Since the large size of the working
group might be conducive to excessive discussions, intervention by the
project scientists might be necessary to warrant a timely decision process.
\section{Antennas and Total Power} \label{antennas}
The prototype antenna contractors have been selected. We therefore
concentrated on recommendations for testing procedures and antenna issues
that impact other areas.
We considered the priorities when testing the prototype antennas.
For the prototype tests, we stress the following points.
\begin{itemize}
\item It is extremely important to test whether
and under what conditions
the pointing specifications (0\farcs6) are met. Developing observational
strategies aimed at optimizing the pointing is an extremely important
goal. In particular, one should examine the possibility of
installing optical telescopes on all antennas, together with a servo
system allowing real time pointing corrections. It seems likely
that such systems are only effective if they are planned as part of the
system and the committee recommends therefore that a system of this
type is considered soon.
\item
It is also very important to have some method of recovering
zero spacing flux using all or part of the array operated in single
dish mode (see Appendix \ref{powerapp}).
The committee recommends that a detailed comparison be
made of the relative merits of using nutators switching rapidly
(10 Hz) and On-The-Fly (OTF) mapping. A decision on the best strategy
for ALMA should be made subsequent to these tests. In particular,
one should test whether rapid OTF mapping (e.g 30\arcmin\
scans in 1 sec with 1 second turn-around) is feasible and
whether gain stability ($\Delta G/G$) of order
$10^{-4}$ per second can
be attained. Tests should also be made with the water vapor radiometer
(WVR) in order to assess the ability of the WVR to monitor
atmospheric emission fluctuations. Analogous studies are needed to test
how effectively chopping with a simple nutator eliminates atmospheric
fluctuations.
Equipping each prototype antenna with a nutator will facilitate these
studies.
With this information in hand, it should be possible to decide whether
nutators are or are not necessary for the array antennas. The
general opinion of the ASAC was that if one could reach the scientific
goals without using nutators, this was preferable. Thus one should
aim at a system that could do an OTF map with all 64 antennas
simultaneously.
\item
Polarization measurements are also sensitive to missing zero spacing
flux (see Appendix \ref{polapp}),
and thus it should be possible to do polarization OTF at at least
2 ALMA frequencies. The decision discussed above (OTF versus nutators)
may be different if one is measuring polarized flux and thus a test
of polarization OTF is desirable.
\item
Stabilizing the gain
of the front end to $10^{-4}$ can be accomplished by selecting components with
low temperature coefficients and by regulating their temperature to
$\Delta T \leq 10^{-2}$K.
Regulating the rest of the electronics in the laboratory to that level will be
difficult, and it might be best to use a (temperature regulated)
total power detector on the front end for
the continuum total power measurements, rather than trying to use the correlator
as the continuum detector. Because these are engineering issues, we
welcome iteration between the ASAC and the JRDG.
\end{itemize}
\section{Water-Vapor Radiometry} \label{wvr}
Accurate phase calibration is a critical requirement for ALMA, and the
baseline design of ALMA uses a 183 GHz receiver (mounted slightly
off-axis from the astronomical beam) to measure a strong atmospheric
water line. Under various assumptions about the atmospheric pressure
and temperature, and the location of the turbulence, the electrical
path above each antenna can be derived. Richard Hills and John Richer
contributed a report outlining the status of the 183 GHz
systems currently in place (Appendix \ref{wvrapp}),
and a series of suggestions for the requirements of a second
generation system. Christine Wilson presented a report by
David Naylor (Appendix \ref{irwvrapp})
on an alternative strategy that uses a 20$\mu$m
photometer to measure water vapor fluctuations in the infrared.
These reports were discussed in detail. The specific recommendations
of the ASAC are:
\begin{enumerate}
\item The water vapor radiometers are central to the scientific
success of ALMA, and the project should ensure that their development is
adequately resourced and integrated with all aspects of the ALMA
system.
\item The project should design and test preferably two (identical)
prototype/pre-production 183 GHz radiometers as part of the Phase~1
project. These should be tested on reasonable
astronomical sites when completed. The possibility of putting them on
the 12-m prototype antennas at the VLA site during the test
interferometer work is highly attractive, and the feasibility of this
option should be investigated.
\item The project should adopt a specification for the WVR system as
follows: it should correct the atmospheric path above each antenna to
an accuracy of 10(1+$w_v$)$\,\mu$m on a timescale of 1 second, over a
period of 5 minutes and allowing for a change in zenith angle of 1
degree; $w_v$ is the precipitable water vapor in mm.
\item Although it is not possible to put very firm design constraints on
the optics, the project should adopt as the specification that the
maximum permissible offset between radiometer and astronomical beams
be 10\arcmin, and (if possible) smaller for the higher frequency
channels.
\item The project should check that the above specifications are
sensible and adequate. In particular, the short timescale behavior
of the atmosphere should be quantified to ensure that correction of
phase on 1 second timescales is rapid enough.
\item There are scientific and productivity gains
to be made by correcting the wavefront tilt across each antenna (the
so-called ``anomalous'' refraction). This effect most strongly
compromises mosaic observations, and those at high
frequencies. However, given that there are large periods of time when
this effect will not be a major problem, the ASAC does not recommend
adopting such a system as the baseline design at present. Further
study of the loss of observing time this effect produces should be
made, and this recommendation should be reassessed at future meetings.
\item The baseline design for the water vapor radiometer remains a
183\,GHz system.
The alternative Canadian solution using 20$\,\mu$m radiometers
should be examined further, probably by the Canadians themselves, and
further reports on progress should be brought to the ASAC.
In particular, the correlation of
the 20$\,\mu$m and 183\,GHz systems should be examined on the JCMT.
The main theoretical problems of the 20$\,\mu$m technique that need to
be investigated are its ability to sample the correct patch of
atmosphere; its performance in differing cloud conditions; and the
accuracy of the path estimation as a function of pressure, temperature,
and water vapor distribution.
\item The baseline design should use a cooled 183 GHz radiometer.
Whether to cool or not is, strictly speaking, an engineering problem;
there was
some feeling that although not absolutely required to achieve the
required sensitivity, the benefits of cooling in terms of stability
and noise probably outweigh the costs.
\item The project should examine the role of the system water vapor
radiometers in the following:
a) the amplitude calibration system, through their
estimates of the atmospheric opacity above each antenna; and b) in
single-dish mode observing, where they could be used to estimate the
atmospheric emission. The scientific benefits of these techniques,
and the extra requirements they place on the system, should be
investigated.
\item The project should accelerate its work on understanding the
different atmospheric models used by the WVR systems to predict path
errors from water line measurements.
\item The location of the WVR is an engineering problem, and the
solution likely
depends on the degree of cooling required, and the final optical
design adopted. There appear to be no show-stopping problems with
locating it either in the same Dewar as the astronomical receivers, or
in its own cryostat. The optimum engineering solution should be
investigated. The ASAC does note that the simultaneous operation at
183 GHz and 30-45GHz (``Band 1'') is not a scientific requirement, so
it is straightforward to locate these systems in the same Dewar if
that makes sense.
\end{enumerate}
\section{Future Issues} \label{future}
There are many issues that require ASAC attention in future meetings.
We list here those issues that we expect to focus on in future telecons
and our next meeting.
\begin{itemize}
\item Planning for Phase II. We would like to see a presentation on
the plans for managing Phase II, including the procedures and criteria
to be used to select between parallel developments. A plan for construction
of the receivers (see Section \ref{receivers}) should be presented.
\item Configurations. This issue received considerable discussion, summarized
in section \ref{config} above, but we plan to revisit the topic after the
Configuration Working Group finishes the simulations recommended
above.
\item Ultra-Compact Array. One very interesting enhancement that Japanese
participation might add is an ultra-compact array of smaller, more accurate
antennas. The scientific potential of this array will need further
elaboration and study.
\item Local Oscillator Systems. Developments on photonic systems are still
ongoing, and we should evaluate the status of these. In addition, the
implications of some of our recommendations in this report for LO systems
should be evaluated.
\item Software. The planning for software systems is less advanced than
in other areas. We would like to hear a presentation on these plans
at our next meeting.
\item Spectrum Management. Since commercial broadcasting has interest
in bands in the ALMA region, we would like to hear a report on the status
of efforts to protect these bands.
\item Site. We would like a report on the status of site arrangements.
\item Outreach. Since the ALMA project still needs to be explained
to the larger community, we would like a presentation on the plans for
outreach.
\end{itemize}
\section{Summary} \label{summary}
We summarize our major recommendations. These are in the order discussed
in the text and not in any priority order.
More detailed recommendations can
be found in the section referenced by the major recommendations.
\begin{itemize}
\item We strongly support continued discussions aimed at including Japan
in the ALMA project (Section \ref{alg}).
\item We confirm that the first four bands to be implemented should be
Bands 3, 6, 7, and 9. We establish priorities for the remaining bands, but
emphasize that full frequency coverage is still desired
(Section \ref{receivers}).
\item Polarization studies will be a very important part of ALMA science.
We recommend attention to polarization in all aspects, but most importantly
in the receiver area (Sections \ref{receivers}, \ref{antennas}).
\item The advantages of SSB operation over DSB operation of the receivers
are not so clear. We recommend further study of the tradeoffs and
reconsideration of the issue at a future ASAC meeting
(Section \ref{receivers}).
\item If an ultra-compact array of smaller, more precise antennas
can result from participation of Japan,
it would add important capabilities. We recommend further study of this
possibility (Sections \ref{alg}, \ref{system}).
\item The capability for 6 subarrays should be kept, but with no more
than 4 simultaneous frequencies (Section \ref{system}).
\item The Configuration Working Group should complete simulations of
different array configurations and testing against a library of
test images in time for an in-depth presentation at the next ASAC
meeting (Section \ref{config}).
\item Recovering total power is a major issue for continuum observations
of extended sources. This may be best done
with OTF mapping if receivers can be built with gain stability of
$\Delta G/G = 10^{-4}$ (Sections \ref{receivers}, \ref{system}, \ref{antennas}).
\item Tests of total power techniques, comparing OTF with gain-stable
receivers to nutating secondaries should be made on the prototype
antennas. Decisions on equipping the array with nutating secondaries
should be based on the outcome of these tests (Section \ref{antennas}).
\item The water vapor radiometers are essential and must be integrated
into all aspects of the ALMA system (Section \ref{wvr}).
\end{itemize}
\newpage
\appendix
\section{THE ASAC CHARTER} \label{charter}
\begin{enumerate}
\item The ALMA Scientific Advisory Committee (ASAC) was formed by the
ALMA Coordinating Committee (ACC) to provide scientific advice to the
ACC, to the ALMA Executive Committee (AEC), and to the Project Scientists.
The ASAC will also provide communications to the wider community.
\item To fulfill these goals, the ASAC will take the following steps:
\begin{enumerate}
\item
Hold monthly telecons.
\item
Meet face-to-face as needed. In the current phase, we plan to meet before
each meeting of the ACC. The frequency of meetings may decrease
as ALMA becomes more fully defined, but we will probably meet at least
once per year.
\item
Produce a report to the ACC, with a copy to the AEC, before each meeting of
the ACC.
\item
Reply to questions from ALMA project staff and raise issues for their
consideration via minutes or ``white papers".
\item
Designate a member of the ASAC to act as liaison to each of the working
groups in the project.
\item
Establish a web site where the community can learn what issues we are
addressing and provide input. We will post minutes of telecons and
meetings there, as well as reports to the ACC, subject to approval
of the ACC.
\item
Announce our existence and membership in astronomical newsletters,
expressing our interest in receiving questions and advice and in
giving colloquia about ALMA.
\end{enumerate}
\item
We have agreed to the following procedures.
\begin{enumerate}
\item
We will have a Chairperson and a Vice-Chairperson at all times.
At the end of each face-to-face meeting, the Vice-Chairperson will
become Chairperson and we will elect a new Vice-Chairperson.
We expect the role of Chairperson to rotate between North America
and Europe.
\item
Decisions will be made by simple majority. A minority report
may be included in the report to the ACC.
\item
Normally, we will communicate through the Project Scientists,
both in receiving questions from the project technical staff and in
providing answers. However, direct communication with project staff
will be used for clarifications, information, etc. The liaison members
are an example of this direct communication.
\end{enumerate}
\end{enumerate}
\newpage
\section{ASAC Liaison to Working Groups} \label{liaison}
The liaisons to the Working Groups and other organizations are as follows.
To implement this system, the Chairpersons of the working groups should
incorporate these representatives of the ASAC into their email distribution
lists and telecons.
When possible and relevant, the ASAC representatives should attend
meetings of the working groups. To facilitate this, we have usually
listed a representative from each hemisphere.
\begin{itemize}
\item Management: Al Wootten, Stephane Guilloteau
\item ALMA Liaison Group: Pierre Cox, Neal Evans
\item Antennas: Jack Welch, Malcolm Walmsley
\item Receivers: Ewine van Dishoeck, Geoff Blake
\item Configurations: Min Yun, Roy Booth
\item Backend: Rafael Bachiller, Nick Scoville
\item Software: Mark Gurwell, Arnold Benz
\item Calibration, including Water Vapor: John Richer, Christine Wilson
\item System Integration: Dick Crutcher, Karl Menten
\item Site: Leo Bronfman
\end{itemize}
\section{Polarization} \label{polapp}
\section{Total Power} \label{powerapp}
\section{Water Vapor Radiometry} \label{wvrapp}
\section{Infrared Water Vapor Radiometry} \label{irwvrapp}
\section{Rationale for Band 1} \label{band1app}
\end{document}
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