; UVSIM ;--------------------------------------------------------------- ;! Generate sample UV coverage given a user defined array layout ;# TASK ANALYSIS UV ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 1996, 2003 ;; 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 ;----------------------------------------------------------------------- ;--------------------------------------------------------------- UVSIM LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC UVSIM Task to generate specimen u-v coverage. 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) ---------------------------------------------------------------- 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. ---------------------------------------------------------------- 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: %setenv 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.