AIPS HELP file for UVSIM in 31DEC24
As of Fri Apr 19 4:46:47 2024
UVSIM: Task to generate specimen u-v coverage.
INPUTS
INFILE Input data file name (name)
OUTNAME Output UV file name (name)
OUTCLASS Output UV file name (class)
OUTSEQ -1.0 9999.0 Output UV file name (seq. #)
OUTDISK 0.0 9.0 Output UV file disk unit #.
APARM (1) observing freq. (Hz)
(2) observing wavlength (m)
(3)-(4) array Bx (m)
(5)-(6) array By (m)
(7)-(8) array Bz (m)
HELP SECTION
UVSIM
Task:
Adverbs:
INFILE.....Name of the user-supplied file defining the array
configuration (number of antennas, their locations,
etc.)
OUTNAME....Output UV file name (name). Standard behavior
with default 'UV DATA FILE'.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #). 0 => highest unique.
OUTDISK....Disk drive # of output UV file. 0 => highest disk
with space for the file.
APARM......User specified array.
APARM(1): Nominal observing frequency (Hz).
APARM(2): Nominal observing wavelength (meters).
(A wavelength of 1 mm is assumed if neither
APARM(1) nor APARM(2) is positive.)
APARM(3)+(4) array Bx, meters
APARM(5)+(6) array By, meters
APARM(7)+(8) array Bz, meters
Here X is in the direction of the intersection of the
meridian of the reference location (long=0 for earth
centered) and the equator; Y is 90 deg. EAST along the
equator from X; Z is in the direction of the N. pole.
Note that:
BX = APARM(3) + APARM(4)
BY = APARM(5) + APARM(6)
BZ = APARM(7) + APARM(8)
The addition of two parameters allows the coordinates
to be specified with more precision than a single adverb
allows; on a 32-bit machines adverb values are only
accurate to 7 significant digits.
NOTE: Setting Bx, By and Bz is required for accurate IAT
times in the resultant UV dataset. This may or may not be
important, depending on what the data is used for. E.g.
UVFIX WILL NOT WORK correctly on this data unless Bx, By
and Bz are set.
NOTE2: If Bx, By, Bz are set then the site latituted is
calculated (normally input using the INFILE) using
these numbers, since it is assumed that this will be
more accurate.
EXPLAIN SECTION
UVSIM:
DOCUMENTOR: W. D. Cotton and F. R. Schwab, A. J. Mioduszewski, NRAO
RELATED PROGRAMS: Most AIPS tasks
PURPOSE
This task is used to generate specimen u-v coverage for
an interferometric array, given an array configuration
specified by the user. This task runs interactively, prompting
the user for such information as the source declination,
hour-angle coverage, integration time, minimum allowable
elevation angle, etc. The output is a standard AIPS u-v data
file, with all visibilities set equal to unity.
The "data" produced by UVSIM corresponds to a 1 Jy point
source at the phase center, observed on 1 Jan. 2000 and in 2000
coordinates. To simulate observations of an extended source, the
output of this task may be used as the input to the AIPS task
UVMOD or UVSUB. FOR THE TIME STAMPS TO BE CORRECT THE SITE
Bx, By and Bx MUST BE SET. IF THIS IS NOT DONE THEN PROGRAMS
THAT RECALCULATE THE U, V, W WILL NOT WORK CORRECTLY (e.g
UVFIX).
SPECIFYING THE ARRAY CONFIGURATION
The information defining the array configuration is read by
UVSIM from an auxiliary input file, supplied by the user. This
is a free-format text file. One must list, in the following
order:
1) The number of antennas,
2) The site latitude, in degrees (so that elevation angles
may be computed), if Bx, By, and Bz are set then this
number is recalulated.
3) A multiplicative conversion factor specifying how the
antenna coordinates, listed next by the user, can be
converted into units of meters; and a second
multiplicative conversion factor specifying how the listed
antenna diameters can be converted into units of meters,
4) The x-, y-, and z-coordinates of the first antenna (in a
right-handed system) and the diameter of the first
antenna, followed by the same information for the other
antennas of the array. The origin of the coordinate system
is at the center of the array. The z-axis points to the
North Celestial Pole, the y-axis runs east-west, and the
x-axis runs perpendicular to both pointing at the celestial
equator.
Here is a sample file for a six-element array (the antenna
coordinates of this array are the coordinates, in units of
nanoseconds light-travel-time, of the innermost elements of two
arms of the VLA, in D-configuration). The antenna diameters are
given here in units of meters, so the second conversion factor
is set to unity. Antenna diameters are required by UVSIM in
order to permit computation of geometric blockage of array
elements (i.e., shadowing).
6
34.07874917
.2997924562 1
2.350 0 1.590 25
-100.220 -15.980 152.410 25
-174.850 -27.630 262.290 25
151.290 23.190 -218.530 25
49.330 -124.060 -67.540 25
96.580 -248.700 -137.120 25
This numeric information can instead be given in E-format (e.g.,
2.997925E-1, etc.) or in mixed E- and F-format.
One must supply the name of the input file via the AIPS
adverb INFILE. Examples:
INFILE='disk$res:[fschwab.sim]test.ant' (VMS)
INFILE='myarea:test.ant' (Unix)
where MYAREA is an environment variable set before
starting AIPS:
percentsetenv MYAREA /mnt/fschwab/sim
ADVERBS REQUIRED
UVSIM records, in its output file, the (u,v,w) coordinates
corresponding to some nominal frequency, or wavelength, of
observation. The default choice of the program (for example,
when APARM(1)=APARM(2)=0) is to set the nominal observing
wavelength to 1 mm. Otherwise, if APARM(1) is positive, it uses
a frequency of APARM(1) Hz. If APARM(2) is positive, but
APARM(1) is not, then the program uses a nominal wavelength of
APARM(2) meters. (More simply stated: if you don't like the
default choice of 1 mm, then specify either your choice of
frequency or your choice of wavelength in APARM(1) or APARM(2),
respectively.)
No other AIPS adverbs are used by UVSIM, apart from those
that specify the input and output files.
RUNNING THE PROGRAM
To run the program one just types appropriate responses to
the questions that the program prints on the terminal screen.
The user is prompted for the following information:
1) The source declination,
2) The hour-angle coverage,
3) Minimum allowable elevation angle,
4) Integration time,
5) Maximum allowable fractional blockage of one antenna by
another.
The responses can be typed in free format, either E- or F-, and
with or without decimal points. The numbers, when more than one
is required, should be separated by blanks.
(E.g., 6 6.0 -12 12.0 3e5 3.0E5).
LIMITATIONS
At present, the program is mainly applicable only to compact
array configurations - as opposed, say, to VLBI arrays. It
assumes, for example, that the elevation angles of all array
elements are identical. However, it is expected that minor
embellishments will be added to UVSIM, removing such
restrictions as the need arises.