A Progress Report on the Data Quality Observations ================================================== Bob Sault, Robin Wark 15 September 1995 Observation Problems (specifically for 27/6/95 and 22/8/95) =========================================================== * The XY phases on one IF on the second set of frequencies was far from zero. Possibly CACAL is not getting run on the second set of frequencies (??) but then we might expect bad delays (which we are not experiencing). The resultant step in XY phase (~40 degrees) was interpreted as a system glitch by the "SYSCAL" flagging algorithm in atlod. 25% of the data for the first IF was consequently flagged. We are going to check this at the first opportunity (after VLBI finishes). * There was an error in the sched file, where the blank field declination was misentered by 20 degrees (!) for the 20/13 cm observation. * Probably the observations should use no on-line time averaging (these observations used 30 sec averaging), and a 13 cm frequency of 2368 MHz (2382 was used). * Overall data quality was far from as good as the ATCA can produce. Reduction Status ================ * MHW has implemented automatic flagging of the data. Reduction now takes ~1 hour of elapsed time for 12 hours observing (3 fields x 4 pol'n x 4 freq). * The automated flagging still leaves some bad data. We probably need to do better here (new flagging tasks needed). * The reduction produces a superabundance of plots and numbers (100s pages). Some effort has gone into condensing this, so that problems will get noticed in the mass of data. Still we can do better here. Some results ============ * The 1934 field clearly shows confusing sources at 20 cm at the 10's mJy level (agrees with NEBK's previous images). * The blank field is not very blank. There are two ~14 mJy sources at 6 cm, with one of the sources still ~6 mJy at 3 cm. * The thermal noise limit has been reached in some of the polarisation images (6 and 3 cm). Residual sources limited the "blank field" I images. * For XX and YY, theoretical closure phase is reached at 4800 for both the on- and off-axis 1934 fields. 1344 and 2382 are not bad, but undoubtedly limited by confusion. 8640 is about 1.5 times theoretical, possibly as a result of decorrelation within the 30 sec effective integration time. * Off-axis polarimetric response is quite apparent. The 13 and 3 cm responses are grossly similar, and differ from 20 and 6 cm. Questions ========= * What are we trying to achieve? Possibilities include - Detect gross errors (e.g. is the array working?) - Understand more subtle effects (off-axis polarimetry?) - Produce a deep image of particular fields (science?) Are we willing to put the manpower into it? * Do we really want to do the analysis with no flagging. * Do we need a better blank field? ======================================================================== Summary of Data Quality Observations of 22/08/95 ------------------------------------------------ Array: 6D Fields: Calibrator 1934-638 Offset Calibrator 1934_a Blank Field 1934_b Frequencies: 1344 2382 4800 8640 MHz The offset calibrator field was offset in RA,DEC from 1934-638 by 0,-60 arcsec at 1344 MHz 0,-60 arcsec at 2382 MHz 0,-60 arcsec at 4800 MHz 0,-60 arcsec at 8640 MHz See the end of this document for an explanation of terms and the filenaming convention. ------------------------------------------------------------------------ Flagging statistics after ATLOD ------------------------------- File XX% YY% XY% YX% ---- --- --- --- --- 1934-638.1344 25.0% 25.0% 25.0% 25.0% 1934-638.2382 7.1% 7.5% 7.3% 7.3% 1934-638.4800 29.2% 29.2% 29.2% 29.2% 1934-638.8640 0.0% 0.0% 0.0% 0.0% 1934_a.1344 0.0% 0.0% 0.0% 0.0% 1934_a.2382 7.1% 7.1% 7.1% 7.1% 1934_a.4800 0.0% 0.0% 0.0% 0.0% 1934_a.8640 0.0% 0.0% 0.0% 0.0% 1934_b.1344 0.0% 0.0% 0.0% 0.0% 1934_b.2382 7.1% 7.1% 7.1% 7.1% 1934_b.4800 0.0% 0.0% 0.0% 0.0% 1934_b.8640 0.0% 0.0% 0.0% 0.0% ---------------------------------------------- Closure phase statistics for the point sources File Th.Phase Sigmas ---- -------- ------ 1934-638.1344 0.014 14.00 1934-638.2382 0.018 4.00 1934-638.4800 0.039 1.08 1934-638.8640 0.069 1.75 1934_a.1344 0.011 17.09 1934_a.2382 0.016 4.50 1934_a.4800 0.027 1.26 1934_a.8640 0.059 1.86 --------------------------------------- Post-reduction flagging statistics ---------------------------------- File XX% YY% XY% YX% ---- --- --- --- --- 1934-638.1344-cal 39.1% 39.1% 39.1% 39.1% 1934-638.2382-cal 17.6% 17.6% 17.6% 17.6% 1934-638.4800-cal 34.7% 34.7% 34.7% 34.7% 1934-638.8640-cal 5.0% 5.0% 5.0% 5.0% 1934_a.1344-cal 15.6% 15.6% 15.6% 15.6% 1934_a.2382-cal 11.5% 11.5% 11.5% 11.5% 1934_a.4800-cal 8.8% 8.8% 8.8% 8.8% 1934_a.8640-cal 3.7% 3.7% 3.7% 3.7% 1934_b.1344-cal 1.7% 1.7% 1.7% 1.7% 1934_b.2382-cal 10.3% 10.3% 10.3% 10.3% 1934_b.4800-cal 2.7% 2.7% 2.7% 2.7% 1934_b.8640-cal 1.8% 1.8% 1.8% 1.8% ======================================================================== File Th. RMS Sigmas D.R. Pk Val ---- ------- ------ ---- ------ 1934-638.1344-low.icln-x 2.39E-04 10.50 5967 15.002 1934-638.1344-low.qmap 2.39E-04 8.34 5 0.009 1934-638.1344-low.umap 2.39E-04 7.27 5 0.009 1934-638.1344-low.vmap 2.39E-04 8.06 5 0.010 1934-638.2382-low.icln-x 2.94E-04 10.76 3649 11.551 1934-638.2382-low.qmap 2.94E-04 4.73 5 0.007 1934-638.2382-low.umap 2.94E-04 4.51 4 0.005 1934-638.2382-low.vmap 2.94E-04 7.17 4 0.009 1934-638.4800-low.icln-x 3.29E-04 4.04 4383 5.826 1934-638.4800-low.qmap 3.29E-04 1.82 5 0.003 1934-638.4800-low.umap 3.29E-04 1.49 4 0.002 1934-638.4800-low.vmap 3.29E-04 1.46 4 0.002 1934-638.8640-low.icln-x 3.26E-04 1.45 6030 2.847 1934-638.8640-low.qmap 3.26E-04 1.13 4 0.002 1934-638.8640-low.umap 3.26E-04 0.96 4 0.001 1934-638.8640-low.vmap 3.26E-04 1.23 4 0.002 1934-638.1344-full.icln-x 1.04E-04 12.75 11356 15.000 1934-638.1344-full.qmap 1.04E-04 8.87 5 0.004 1934-638.1344-full.umap 1.04E-04 7.77 5 0.004 1934-638.1344-full.vmap 1.04E-04 8.07 6 0.005 1934-638.2382-full.icln-x 1.03E-04 14.00 8040 11.541 1934-638.2382-full.qmap 1.03E-04 6.02 5 0.003 1934-638.2382-full.umap 1.03E-04 5.47 6 0.003 1934-638.2382-full.vmap 1.03E-04 8.60 5 0.005 1934-638.4800-full.icln-x 1.15E-04 5.78 8729 5.825 1934-638.4800-full.qmap 1.15E-04 1.71 5 0.001 1934-638.4800-full.umap 1.15E-04 1.61 5 0.001 1934-638.4800-full.vmap 1.15E-04 1.79 5 0.001 1934-638.8640-full.icln-x 1.01E-04 4.46 6304 2.837 1934-638.8640-full.qmap 1.01E-04 1.21 4 0.001 1934-638.8640-full.umap 1.01E-04 1.08 5 0.001 1934-638.8640-full.vmap 1.01E-04 1.54 5 0.001 1934_a.1344-full.icln-x 8.97E-05 14.54 11471 14.954 1934_a.1344-full.qmap 8.97E-05 11.58 5 0.005 1934_a.1344-full.umap 8.97E-05 10.66 5 0.005 1934_a.1344-full.vmap 8.97E-05 5.71 7 0.004 1934_a.2382-full.icln-x 9.58E-05 15.36 7818 11.504 1934_a.2382-full.qmap 9.58E-05 13.49 6 0.008 1934_a.2382-full.umap 9.58E-05 14.98 6 0.009 1934_a.2382-full.vmap 9.58E-05 10.16 12 0.012 1934_a.4800-full.icln-x 8.47E-05 7.48 8995 5.694 1934_a.4800-full.qmap 8.47E-05 2.88 9 0.002 1934_a.4800-full.umap 8.47E-05 2.85 5 0.001 1934_a.4800-full.vmap 8.47E-05 1.94 5 0.001 1934_a.8640-full.icln-x 8.55E-05 3.36 9316 2.680 1934_a.8640-full.qmap 8.55E-05 7.16 18 0.011 1934_a.8640-full.umap 8.55E-05 5.92 7 0.004 1934_a.8640-full.vmap 8.55E-05 9.59 8 0.007 1934_b.1344-full.imap 1.10E-04 36.58 4 0.015 1934_b.1344-full.qmap 1.10E-04 3.51 4 0.001 1934_b.1344-full.umap 1.10E-04 5.17 3 0.002 1934_b.1344-full.vmap 1.10E-04 1.02 4 0.000 1934_b.2382-full.imap 1.23E-04 9.72 5 0.006 1934_b.2382-full.qmap 1.23E-04 1.28 5 0.001 1934_b.2382-full.umap 1.23E-04 1.55 4 0.001 1934_b.2382-full.vmap 1.23E-04 1.04 5 0.001 1934_b.4800-full.imap 8.95E-05 6.42 5 0.003 1934_b.4800-full.qmap 8.95E-05 1.01 5 0.000 1934_b.4800-full.umap 8.95E-05 1.03 5 0.000 1934_b.4800-full.vmap 8.95E-05 0.97 5 0.000 1934_b.8640-full.imap 9.23E-05 1.93 5 0.001 1934_b.8640-full.qmap 9.23E-05 1.01 5 0.001 1934_b.8640-full.umap 9.23E-05 1.00 5 0.000 1934_b.8640-full.vmap 9.23E-05 0.95 4 0.000 ======================================================================== Explanation of Terms: --------------------- XX%,YY%,XY%,YY% Percentage of XX, XY, YX and YY correlations flagged (excluding on-line flagging and shadowing). Th.Phase The theoretical closure phase (in degrees) based on thermal noise arguments (for the 5-minute time averaging used). Th. RMS The theoretical RMS in an image based on thermal noise arguments. Sigmas The factor by which the relevant meausre exceeds either of the above two theoretical levels. Ideally this should be 1. D.R. Dynamic range of an image, defined as the ratio of the peak absolute value divided by the RMS. For the CLEANed Stokes-I images of the calibrators, the RMS is evaluated outside the inner quarter of the image. Otherwise the RMS is evaluated over the entire image. Pk Val Peak value in an image in Jy. Explanation of File names: -------------------------- File names are of the form FIELD.FREQ Raw visibility data, giving the field name and observing frequency. FIELD.FREQ-cal Calibrated/flagged visibility data. FIELD.FREQ-low.TYPE Low resolution image, imaging the entire primary beam. TYPE gives the Stokes parameter and whether the image is CLEANed ("cln") or a dirty image ("map"). FIELD.FREQ-full.TYPE Full resolution image, but imaging only a subportion of the primary beam. TYPE is as above.