; STESS ;--------------------------------------------------------------- ;! Task which finds sensitivity in mosaicing ;# TASK IMAGING ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 2002-2003, 2005, 2007 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- STESS LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC STESS : Task which finds sensitivity in mosaicing Input image INNAME Image name (name) INCLASS Image name (class) INSEQ 0.0 9999.0 Image name (seq. #) INDISK Image disk drive # Output image OUTNAME Image name (name) OUTCLASS Image name (class) OUTSEQ -1.0 9999.0 Image name (seq. #) OUTDISK Image disk drive # NMAPS 1.0 4087.0 Number of maps to analyse NOISE * 0.0 Required residual, units are * (Jy/BEAM) BLC 0.0 4096 Bottom left corner of STESS TRC 0.0 4096 Top right corner of STESS PBSIZE PB FWHM in arcseconds CHANGED PBPARM Beam parameters: (1) Cutoff 0 -> 0.07 (2) > 0 -> Use (3)-(7) (3)-(7) Beam shape BADDISK Disks to avoid for scratch. ---------------------------------------------------------------- STESS Type: Task Use: STESS is an adjunct to LTESS which finds the sensitivity function of a mosaic. FLATN can now do this function also and it creates the output geometry as needed on the fly. STESS, like LTESS, VTESS, and UTESS requires the user to put all pointings into large images of the desired output geometry and image size (with modest regions having actual value) before running the task. EXPLAIN VTESS says: Sky-curvature effects will be important in some circumstances and will hinder the use of VTESS. For 20cm and shorter in the C and D configurations, you can usually get away with mapping each primary beam separately. The procedure is: 1. Observe at the requisite number of pointing centers, spaced every HWHM (e.g. 15 arcmin at 20cm). 2. Calibrate, edit each field separately. 3. Run UVMAP on each field separately WITHOUT any phase shifts. The size of each field must be double the full primary beam size (e.g. 512**2 with 15" cellsize is fine for 20cm D-array). 4. Choose one centrally-located field as the center of the coordinate system to be used. Pad the map and beam for this field up to twice the maximum field of view. The task PADIM does this nicely. This resulting image is the reference field image. 5. Put all the other images onto the same grid. OHGEO or HGEOM are very convenient for this: put the reference field image in slot two, and the image to be converted into slot one. 6. Pad the beams out to the required size. Really you should do step 5 on each beam but the shift will come out incorrectly then. 7. Set up the parameters for VTESS, and then run STESS to check the sensitivity function. Adverbs: INNAME......The dirty image name. Standard defaults. INCLASS.....The dirty image class. Standard defaults. INSEQ.......The dirty image seq. #. 0 => highest. If NMAPS > 1 then images having sequence numbers INSEQ,INSEQ+1,...,INSEQ+NMAPS-1 are operated on. INDISK......The dirty image disk drive #. 0 => any. OUTNAME.....The STESS image name. Standard defaults. OUTCLASS....The STESS image class. Standard behavior with default = 'xSTESS' if INCLASS = 'xMAP' where x is any character 'STESS' if INCLASS = anything else OUTSEQ......The STESS image seq. #. 0 => highest unique. If >0; image will be created if new, overwritten if image name exists. OUTDISK.....The STESS disk drive no. 0 => highest with space NMAPS.......Number of maps to be deconvolved. Must be in sequence starting at INSEQ. Can use up to 4087! NOISE.......The target R.M.S. residuals for each image are ERROR (Jy/beam). Note this controls the quality of the final STESS image. STESS tries to get fit to be less than 1.05 SIGMA. Can be changed by TELL. NOISE(64) is used for fields > 64. BLC.........Bottom left corner of STESS image, BLC(3) gives the channel number to deconvolve. TRC.........Top right corner of image; both BLC and TRC default do that the inner quarter is chosen. PBSIZE......Size of primary beam in arcsec, FWHM of Gaussian model. One number per field. If = 0, use PBPARM beam with defaults suitable to the VLA. If < 0, do no primary beam correction, e.g. for fields that are not interferometer data. If > 0, use a Gaussian of FWHM of PBSIZE(I). PBSIZE(64) is used for fields > 64. PBPARM......Primary beam parameters: (1) Lowest beam value to believe: 0 -> 0.07 Sources outside this range are ignored. (2) > 0 => Use beam parameters from PBPARM(3)-PBPARM(7) Otherwise use default parameters for the VLA (or ATCA where appropriate) (3-7)..For all wavelengths, the beam is described by the function: 1.0 + X*PBPARM(3)/(10**3) + X*X*PBPARM(4)/(10**7) + X*X*X*PBPARM(5)/(10**10) + X*X*X*X*PBPARM(6)/(10**13) X*X*X*X*X*PBPARM(7)/(10**16) where X is (distance from the pointing position in arc minutes times the frequency in GHz)**2. For the VLA, these parms are, by default, given by Perley's fits: 0.0738 GHz -0.897 2.71 -0.242 0.3275 -0.935 3.23 -0.378 1.465 -1.343 6.579 -1.186 4.885 -1.372 6.940 -1.309 8.435 -1.306 6.253 -1.100 14.965 -1.305 6.155 -1.030 22.485 -1.417 7.332 -1.352 43.315 -1.321 6.185 -0.983 For the ATCA, these are by default: 1.5 GHz -1.049 4.238 -0.8473 0.09073 -5.004E-3 2.35 -0.9942 3.932 -0.7772 0.08239 -4.429E-3 5.5 -1.075 4.651 -1.035 0.12274 -6.125E-3 8.6 -0.9778 3.875 -0.8068 0.09414 -5.841E-3 20.5 -0.9579 3.228 -0.3807 0.0 0.0 See explain for details BADDISK.....This array contains the numbers of disks on which it is desired that scratch files not be located. BADDISK has no effect on input and output maps. ---------------------------------------------------------------- STESS : Task which finds the sensitivity function for mosaics DOCUMENTOR: T.J.Cornwell NRAO/VLA DATE OF DOCUMENTATION: 18 May 1987 RELATED PROGRAMS: STESS VERSION: 15OCT87 PURPOSE REFERENCES Cornwell T.J., and Evans K.F., "A simple Maximum Entropy deconvolution algorithm", Astronomy and Astrophysics, (1985) Burch,S.F, Gull,S.F., and Skilling,J., "Image restoration by a powerful Maximum Entropy method", Computer Vision, Graphics and Image processing, 23, 113-128 (1983). -------------------------------- The function used to model the primary beam for normal VLA frequencies F(x) = 1.0 + parm(1) * 10E-3 * x + parm(2) * 10E-7 * x*x + parm(3) * 10E-10 * x*x*x + parm(4) * 10E-13 * x*x*x*x + parm(5) * 10E-16 * x*x*x*x*x where x is proportional to the square of the distance from the pointing position in units of [arcmin * freq (GHz)]**2, and F(x) is the multiplicative factor to divide into the image intensity at the distance parameter x. For other antennas, the user may read in appropraite constants in DPARM(5) through DPARM(9). The flag, DPARM(4) must be set to a positive number to invoke this option and DPARM(5) must not be zero. This correction scales with frequency and has a cutoff beyond which the map values are set to an undefined pixel value GIVEN IN DPARM(1). At the VLA frequencies the default cutoff is 1.485 GHz 29.8 arcmin 4.885 GHz 9.13 arcmin 15 GHz 2.95 arcmin 22.5 GHz 1.97 arcmin and occurs at a primary beam sensitivity of 2.3% of the value at the beam center. Corrections factors < 1 are forced to be 1. The estimated error of the algorithm is about 0.02 in (1/F(x)) and thus leads to very large errors for x>1500, or at areas outside of the primary response of 20%. The cutoff level may be specified with DPARM(1). RICK PERLEY'S REPORT Polynomial Coefficients from LSq Fit to VLA Primary Beam raster scans. Functional form fitted: 1 + G1.X^2 + G2.X^4 + G3.X^6 where X = r.F, and r = radius in arcminutes F = frequency in GHz. Fits were made to 3% cutoff in power for 24 antennas. Poor fits, and discrepant fits were discarded, and the most consistent subset of antennas had their fitted coefficients averaged to produce the following 'best' coefficients. Freq. G1 G2 G3 ---------------------------------------------------------- 1.285 -1.329E-3 6.445E-7 -1.146E-10 * 1.465 -1.343 6.579 -1.186 " 4.885 -1.372 6.940 -1.309 8.435 -1.306 6.253 -1.100 14.965 -1.305 6.155 -1.030 22.485 (old) -1.350 6.526 -1.090 * 22.485 (new) -1.417 7.332 -1.352 43.315 -1.321 6.185 -0.983 ----------------------------------------------------------- The estimated errors (from the scatter in the fitted coefficients) are generally very small: G1: .003 at all bands except Q (.014) G2: .03 to .07 at all bands except Q (.15) G3: .01 to .02 at all bands except Q (.04) R. Perley 21/Nov/00 * The 1.285 and 22.485 old feed values are not used.