AIPS HELP file for STESS in 31DEC24
As of Sat Apr 20 2:16:33 2024
STESS: Task which finds sensitivity in mosaicing
INPUTS
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.
HELP SECTION
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.
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.
EXPLAIN SECTION
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).
--------------------------------
PRIMARY BEAM FUNCTION:
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 percent 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 percent. 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 percent 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.