; UVMTH ;--------------------------------------------------------------- ;! Averages one data set and applied it to another. ;# Task UV ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 2007, 2010 ;; 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 ;----------------------------------------------------------------------- UVMTH LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC UVMTH Corrects one uv dataset with the average of another. INNAME File name to the averaged. INCLASS File class to be averaged INSEQ 0.0 9999.0 File seq. # to be averaged INDISK 0.0 9.0 File disk number SOURCES Source name QUAL -10.0 Calibrator qualifier -1=>all CALCODE Calibrator code ' '=>all TIMERANG Time range to use SELBAND Bandwidth to select (kHz) SELFREQ Frequency to select (MHz) FREQID Freq. ID to select. SUBARRAY 0.0 1000.0 Sub-array, 0=>all DOCALIB -1.0 101.0 > 0 calibrate data & weights > 99 do NOT calibrate weights GAINUSE CL (or SN) table to apply DOPOL -1.0 10.0 If >0.5 correct polarization. PDVER PD table to apply (DOPOL>0) BLVER BL table to apply. FLAGVER Flag table version DOBAND -1.0 10.0 If >0.5 apply bandpass cal. Method used depends on value of DOBAND (see HELP file). BPVER Bandpass table version SMOOTH Smoothing function. See HELP SMOOTH for details. DOACOR Include autocorrelations? IN2NAME Input UV file name (name) IN2CLASS Input UV file name (class) IN2SEQ 0.0 9999.0 Input UV file name (seq. #) IN2DISK 0.0 9.0 Input UV file disk unit # 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 #. OPCODE Operation 'ADD','SUB','MULT', 'DIV' (default SUB) ---------------------------------------------------------------- UVMTH Task: This task determines the time averaged visibilities for each baseline in a uv data set and applies them to another data set. The first input data set is averaged over all times after application of data selection, flagging, and calibration as desired. Each baseline and correlator (Stokes, spectral channel, IF) is kept separately. Only one subarray and one frequency ID are allowed, but multiple sources may be averaged together. These averaged data are then combined with the data of the second data set by addition, subtraction, multiplication, or division depending on OPCODE. The data of the second data set are not flagged, calibrated, or averaged in any way. If the second data set has more than one subarray or frequency ID, then only the subarray and frequency ID used from the first data set will be copied. The two data sets must have the same number of correlators in the same order (after the calibration is applied). The axis order is Complex, Stokes, Frequency, IF. If the second data set is not in this order, it may be converted by SPLAT. Adverbs: INNAME.....Input UV file name (name). Standard defaults. INCLASS....Input UV file name (class). Standard defaults. INSEQ......Input UV file name (seq. #). 0 => highest. INDISK.....Disk number of input UV file. 0 => any. ================================================================= The following adverbs are applied to INNAME during the averaging process. SOURCES....Source to be baselined. ' '=> all; if any starts with a '-' then all except ANY source named. QUAL.......Qualifier of source to be baselined. -1 => all. CALCODE....Calibrator code of sources to baseline. ' '=> all. TIMERANG...Time range of the data to be copied. In order: Start day, hour, min. sec, end day, hour, min. sec. Days relative to ref. date. SELBAND....Bandwidth of data to be selected. If more than one IF is present SELBAND is the width of the first IF required. Units = kHz. For data which contain multiple bandwidths/frequencies the task will insist that some form of selection be made by frequency or bandwidth. SELFREQ....Frequency of data to be selected. If more than one IF is present SELFREQ is the frequency of the first IF required. Units = MHz. FREQID.....Frequency identifier to select (you may determine which is applicable from the OPTYPE='SCAN' listing produced by LISTR). If either SELBAND or SELFREQ are set, their values override that of FREQID. However, setting SELBAND and SELFREQ may result in an ambiguity. In that case, the task will request that you use FREQID. SUBARRAY...Sub-array number to copy. 0=>1. DOCALIB....If true (>0), calibrate the data using information in the specified Cal (CL) table for multi-source or SN table for single-source data. Also calibrate the weights unless DOCALIB > 99 (use this for old non-physical weights). If the data are not in time order, then DOCALIB must be false. GAINUSE....version number of the CL table to apply to multi-source files or the SN table for single source files. 0 => highest. DOPOL......If > 0 then correct data for instrumental polarization as represented in the AN or PD table. This correction is only useful if PCAL has been run or feed polarization parameters have been otherwise obtained. See HELP DOPOL for available correction modes: 1 is normal, 2 and 3 are for VLBI. 1-3 use a PD table if available; 6, 7, 8 are the same but use the AN (continuum solution) even if a PD table is present. PDVER......PD table to apply if PCAL was run with SPECTRAL true and 0 < DOPOL < 6. <= 0 => highest. BLVER......Version number of the baseline based calibration (BL) table to apply. <0 => apply no BL table, 0 => highest. If the data are not in time order, then BL tables may not be applied and BLVER should be set to -1 if any are present. FLAGVER....specifies the version of the flagging table to be applied. 0 => highest numbered table. <0 => no flagging to be applied. DOBAND.....If true (>0) then correct the data for the shape of the antenna bandpasses using the BP table specified by BPVER. The correction has five modes: (a) if DOBAND=1 all entries for an antenna in the table are averaged together before correcting the data. (b) if DOBAND=2 the entry nearest in time (including solution weights) is used to correct the data. (c) if DOBAND=3 the table entries are interpolated in time (using solution weights) and the data are then corrected. (d) if DOBAND=4 the entry nearest in time (ignoring solution weights) is used to correct the data. (e) if DOBAND=5 the table entries are interpolated in time (ignoring solution weights) and the data are then corrected. If the data are not in time order, then only DOBAND=1 may be used. BPVER......Specifies the version of the BP table to be applied 0 => highest numbered table. <0 => no bandpass correction to be applied. SMOOTH.....Specifies the type of spectral smoothing to be applied to a uv database . The default is not to apply any smoothing. The elements of SMOOTH are as follows: SMOOTH(1) = type of smoothing to apply: 0 => no smoothing To smooth before applying bandpass calibration 1 => Hanning, 2 => Gaussian, 3 => Boxcar, 4 => Sinc To smooth after applying bandpass calibration 5 => Hanning, 6 => Gaussian, 7 => Boxcar, 8 => Sinc SMOOTH(2) = the "diameter" of the function, i.e. width between first nulls of Hanning triangle and sinc function, FWHM of Gaussian, width of Boxcar. Defaults (if < 0.1) are 4, 2, 2 and 3 channels for SMOOTH(1) = 1 - 4 and 5 - 8, resp. SMOOTH(3) = the diameter over which the convolving function has value - in channels. Defaults: 1,3,1,4 times SMOOTH(2) used when input SMOOTH(3) < net SMOOTH(2). DOACOR.....> 0 => include autocorrelations as well as cross correlation data. ================================================================= IN2NAME....Input UV file name (name). Standard defaults. IN2CLASS...Input UV file name (class). Standard defaults. IN2SEQ.....Input UV file name (seq. #). 0 => highest. IN2DISK....Disk number of input UV file. 0 => any. OUTNAME....Output UV file name (name). Standard defaults. OUTCLASS...Output UV file name (class). Standard defaults. OUTSEQ.....Output UV file name (seq. #). 0 => highest unique OUTDISK....Disk number of output UV file. 0 => highest with space for the file. OPCODE.....The operation desired: 'ADD' adds the time averaged values of the second input data set to the first. 'SUB' subtracts the time averaged values of the second input data set from the first - default. 'MULT' multiplies the time averaged values of the second input data set by the first. 'DIV' divides the time averaged values of the second input data set into the first. ---------------------------------------------------------------- A use of this task is to remove correlator offsets. Ed Fomalont writes: We don't know what is producing the correlator offsets for the 25 MHz VLA bandwidths, but these errors produce artifacts near the center of an image of about 0.4 mJy (correlator mode 4A, 1.4 GHz) with extended sidelobes. The artifacts dominate the noise contribution near the center of the image after less than 30-minutes of integration. These correlator offsets vary with baseline, IF, polarization, and channel in unpredicatable ways. However, these offsets appear to be constant over a period of five hours or longer in any the above data streams. For weak fields where there is little significant emission near the phase center, a vector average of the data for each baseline/IF/pol/Channel over an period longer than one hour will be dominated by the correlator offsets over the noise/source contribution. The offsets can then be removed from the visibility data. This software already exists because of GMRT data at 610 MHz that Frazer Owen obtained about a year ago with the same defect---correlator offsets for each data stream. The data reduction processing needed is as follows. 1. Calibrate and edit the data in the AIPS multi-source files in the usual manner. You will usually have one BP table, one SN table which contains the temporal amplitude and phase corrections derived from the primary calibrator, and a final CL table. Also, FG tables for the necessary flagging of all sources. 2. Make an image of the target source, and the defects near the image center should be obvious. Revised from Ed's description for the new version of UVMTH: The input data set must have only one subarray and one frequency ID. 3. Use the AIPS task UVMTH with the data set as both INNAME and IN2NAME. Set SOURCES to select the target data which may be from one or more "sources". Note: do not select any "source" having significant emission at the center. Apply no calibrations or bandpass. (DOBAND=-1; DOCAL -1): The target data must be uncalibrated since the correlator errors are inserted (in some unknown way on-line) and any further calibration will change the correlator offset phases with time. Apply all of the FG tables. 4. UVMTH will subtract (OPCODE='SUB') the averaged target data from all data in the file. It will apply no data selection, flagging, or calibration during this step. This will produce an output data set equal to the input data minus the correlator offsets. 5. UVMTH will copy all tables from the input data set (IN2NAME) to the output data set, so one may continue with calibration, editing, etc. on the offset-corrected data. The resulting image should be much better than that from the original multi-source file.