; LTESS ;--------------------------------------------------------------- ;! makes mosaic images by linear combination ;# Task Imaging ;----------------------------------------------------------------------- ;; Copyright (C) 1995-1996, 2002-2003, 2005, 2011, 2016 ;; 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 ;----------------------------------------------------------------------- LTESS LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC LTESS : Task do make linear combination mosaics 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 Image noise, units are * (Jy/BEAM) BLC 0.0 4096 Bottom left corner of LTESS TRC 0.0 4096 Top right corner of LTESS PBSIZE PB FWHM in arcseconds: < 0 - no PB correction = 0 - use PBPARM > 0 - use Gaussian PBPARM Beam parameters: (1) Cutoff 0 -> 0.07 (2) > 0 -> Use (3)-(7) (3)-(7) Beam shape BADDISK Disks to avoid for scratch. ---------------------------------------------------------------- LTESS Type: Task Use: LTESS is used to make a linear combination mosaic by correcting for the individual primary beam patterns and optimizing signal to noise. The individual images must all be already placed on the desired output projective geometry including image size and reference pixel. NOTE: FLATN can also do this tesselation among other things and it takes care of the image geometry for you. Adverbs: INNAME......The input image name. Standard defaults. INCLASS.....The input image class. Standard defaults. INSEQ.......The input image seq. #. 0 => highest. If NMAPS > 1 then images having sequence numbers INSEQ,INSEQ+1,...,INSEQ+NMAPS-1 are operated on. INDISK......The input image disk drive #. 0 => any. OUTNAME.....The LTESS image name. Standard defaults. OUTCLASS....The LTESS image class. Standard behavior with default = 'xLTESS' if INCLASS = 'xMAP', where x is any character 'LTESS' if INCLASS = anything else OUTSEQ......The LTESS image seq. #. 0 => highest unique. If >0; image will be created if new, overwritten if image name exists. OUTDISK.....The LTESS disk drive no. 0 => highest with space NMAPS.......Number of maps to be combined. Must be in sequence starting at INSEQ. NOISE.......The estimated R.M.S. error for each image is NOISE (Jy/beam). NOISE(64) is used for fields > 64. BLC.........Bottom left corner of LTESS image, BLC(3) gives the channel number to combine. 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. 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. ---------------------------------------------------------------- LTESS : Task which makes linear combination mosaics DOCUMENTOR: R.Braun NRAO/VLA DATE OF DOCUMENTATION: 17 Dec. 1987 RELATED PROGRAMS: VTESS, STESS VERSION: 15JAN88 PURPOSE LTESS is used to make linear combinations of up to 4087 input images which must already reside on the same grid with the same projection. This can be arranged with HGEOM for example, remembering to LTESS was intended primarily to work on images produced by MEM-based tasks VTESS and UTESS. The references below apply to those tasks. 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). -------------------------------- Primary beam correction FACES corrects an image for the primary beam attenuation of the antennas. The function used to model the primary beam for normal VLA frequencies F(x) = 1.0 + parm(3) * 10E-3 * x + parm(4) * 10E-7 * x*x + parm(5) * 10E-10 * x*x*x + parm(6) * 10E-13 * x*x*x*x + parm(7) * 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 PBPARM(3) through PBPARM(7). The flag, PBPARM(2) must be set to a positive number to invoke this option and PBPARM(3) 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 PBPARM(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). Default values of PBPARM for the VLA are 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 For the Karl G Jansky VLA ("EVLA"), the defaults are frequency dependent. If the observing frequency is between two tabulated frequencies, then the beam is computed for each of the tabulated frequencies and then interpolated to the observing frequency. The values used are far too numerous to give here, see EVLA Memo 195, "Jansky Very Large Array Primary Beam Characteristics" by Rick Perley, revision dated June 2016. Obtain it from http://library.nrao.edu/evla.shtml RICK PERLEY'S (OLD) 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.