[daip] [!13970]: AIPS - Why is SAD reporting sources with lower than specified SNR?

[Robert Gray]

Robert Gray updated #13970
--------------------------

Why is SAD reporting sources with lower than specified SNR?
-----------------------------------------------------------

           Ticket ID: 13970
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/13970
                Name: Robert Gray
       Email address: roberthansengray at gmail.com
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 23 May 2019 10:24 PM
             Updated: 23 May 2019 10:24 PM
           Reply due: 27 May 2019 10:24 PM (4d 0h 0m)
      Resolution due: 16 February 2022 12:00 AM (999d 1h 36m)

Hi!I’m using AIPS SAD to find features in radio images, and it is writing out features below the SNR threshold I’ve specified, taking more storage space than necessary (adding up to many GB over many channels and cubes over years of processing, so it’s an issue). An example is below, where SAD reports “Errors determined by theory from RMS  1.20649” for an image, and reports “Sources found down to  6.032432 in JY/BEAM” which is consistent with the SNR=5 threshold I’ve specified.  But, all of the features reported are below that SNR=5 threshold, can you give me any lead as to why that might be happening?For example, SNR for feature #1 using Peak/RMS is 6.006/1.20649=4.98, a bit below the threshold of 5, and the other features have smaller SNR values. Thanks for your help!Bob Graylocalhos SAD (31DEC16) 1111 21-MAY-2019 21:26:49 Page 1130911WOW-X-.035815. 1 Disk 1 Plane 768 User 1111  Window BLC 10 10 768 1 1 1 1 TRC 1014 1014 768 1 1 1 1Sources found down to 6.032432 in JY/BEAMRetry level 0.100000 (JY/BEAM ) plus gain 0.100Reject components peak < 0.00000 in JY/BEAMReject components flux < 0.00000Reject components outside window > 0.0 cellsReject components outside image > 0.0 cellsReject residual flux > 0.00000 with gain 0.100Fluxes expressed in units of JY/BEAMNOTE: Fluxes marked by * have been divided by 1000.Errors determined by theory from RMS 1.20649Reference Center: 19 26 56.5108 -26 56 59.983All source widths, width errors, and both coordinate errors are in arc secondsNO corrections for bandwidth smearing have been madeSource peaks and fluxes NOT corrected for primary beam  # Peak Dpeak Flux Dflux RA---SIN DEC--SIN Dx Dy Maj Min PA Dmaj Dmin Dpa 1 6.006( 1.199) 6.297( 2.144) 19 35 55.7604 -27 33 14.217( 16.746 45.041) 549.154 140.651 163.8(109.620 28.069 4) 2 4.824( 1.206) 3.533( 1.707) 19 31 44.0255 -26 36 47.014( 22.072 32.385) 331.145 162.839 152.8( 82.820 40.719 13) 3 4.366( 1.206) 3.896( 1.939) 19 36 00.9551 -27 31 39.145( 17.428 67.627) 584.410 112.513 169.2(161.489 31.078 4) 4 3.691( 1.206) 1.766( 1.314) 19 31 37.6192 -26 34 05.015( 17.999 40.306) 294.707 119.517 168.7( 96.329 39.059 13) Component widths & PA: fit, deconvolved at fit and 1.30 sigma low and high from fit # MAJ-fit MIN-fit PA-fit MAJ-dec MIN-dec PA-dec R MAJ-low MIN-low PA-low MAJ-hi MIN-hi PA-hi Xpix Ypix MAXresid  1 549.15 140.65 163.8 286.84 0.00 176.6 U --- --- --- 516.10 110.26 36.0 113.7 388.7 2.12138 2 331.15 162.84 152.8 94.41 0.00 163.1 U --- --- --- 204.51 268.60 17.2 297.8 579.4 3.03404 3 584.41 112.51 169.2 364.65 0.00 3.6 U --- --- --- 655.45 44.03 47.9 109.8 393.9 2.13673 4 294.71 119.52 168.7 --- --- --- U --- --- --- 251.47 0.00 178.5 302.5 588.4 2.03979

------------------------------------------------------
Staff CP:  https://help.nrao.edu/staff
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listmgr.nrao.edu/pipermail/daip/attachments/20190523/7fdec5eb/attachment.html>