; FXALIAS ;--------------------------------------------------------------- ;! least squares fit aliasing function and remove ;# PROCEDURE UV SPECTRAL VLA ;----------------------------------------------------------------------- ;; Copyright (C) 2008 ;; 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 ;----------------------------------------------------------------------- FXALIAS LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC FXALIAS process data set to remove EVLA-EVLA aliasing issue INNAME Input UV file name (name) INCLASS Input UV file name (class) INSEQ 0.0 9999.0 Input UV file name (seq. #) INDISK 0.0 9.0 Input UV file disk unit # SOURCES Source names for line sources NO '-' usage CALSOUR Continuum source names NCOUNT 1.0 30.0 Use 1st NCOUNT CALSOUR for BP TIMERANG Time range to use FLAGVER -1.0 Flag table version BDROP 1.0 512.0 start chan in cal for cont EDROP 1.0 512.0 end chan in cal for cont 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 #. BCHAN Lowest channel for cals ECHAN Highest channel for cals ICHANSEL Select channels to fit: NOTE this is start,end,increment and IF for each region DPARM -1.0 1.0 <=0 => average polarizations, IFs, times, antennas (5) > 0 keep imaginary (6) > Hanning smooth ---------------------------------------------------------------- FXALIAS Procedure: EXPERIMENTAL PROCEDURE This procedure does a special spectral fit designed to correct for aliasing of the continuum into the observing band found only for EVLA-EVLA baselines when observed in the VLA-EVLA transition with the old correlator. The process which one must undertake to correct data affected by this problem is: 1. Flag EVLA-EVLA baselines in the FG table 2. Run BPASS on the VLA-VLA and VLA-EVLA baselines writing out amplitude-only bandpass functions 3. Undo the EVLA-EVLA baseline flagging in the FG table 4. Run SPLAT to apply the BP table 5. Run UVCOP on one or more calibrator scans to make a data set for the alias "cal" 6. Run FIXAL applying the cals of step 5. It reads in the data averaging each baseline.pol/IF separately. Sums up the cal channels BDROP through EDROP and divides the cal by this complex average. Then it fits the normalized cal to the channels of the input data to get the continuum flux and subtracts the channel-dependent part of that from the data. This procedure has been written to help implement this process. Note that it does these operations in the simplest way. If you want BPASS (step 2) run in special ways, SPLAT run with, for example, DOBAND > 1, etc. you may have to run the steps yourself. The DPARM parameter allows you to experiment with different aliasing functions. By default all baselines, polarizations, IFs, and times are averaged together and the imaginary part of the aliasing function is zeroed. You can remove some or all of this averaging and can select Hanning smoothing of the aliasing function for improved S/N. If you have a data set consisting of only EVLA-EVLA baselines from a frequency unavailable to VKA antennas, things are more difficult. You will need a data set at a nearby frequency that includes the VLA antennas. Run FXALIAS on this data set. Take the FXALIAS.UVCOP data set and run FIXAL on the bandpass cals of your main data. Specify only channels which are not affected too badly by the bandpass and by the alias. Then run BPASS on these cals. Apply the bandpass to the main data with SPLAT. Then run FIXAL on the SPLAT output with the FXALIAS.UVCOP file as the second input. NOTE, THIS IS NOT GUARANTEED TO WORK. 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 drive # of input UV file. 0 => any. SOURCES....Sources to be baselined using the specified ICHANSEL. ' '=> all except those in CALSOUR. The '-name' usage is not allowed here. CALSOUR....Sources to be baselined using BCHAN-ECHAN rather than ICHANSEL. ' ' => none. CALSOUR(1) is the primary bandpass and aliasing calibrator. TIMERANG...Time range of the primary aliasing calibrator to be used. In order: Start day, hour, min. sec, end day, hour, min. sec. Days relative to ref. date. FLAGVER....Version of flag table to be used. BDROP......Begin channel for alias calibrator unaffected by aliasing NO DEFAULT EDROP......End channel for alias calibrator unaffected by aliasing NO DEFAULT 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 drive # of output UV file. 0 => highest with space for the file. BCHAN......Lowest channel number in the input file to fit CALSOUR sources. 0=> Nchan/8 ECHAN......Highest channel number in the input file to fit CALSOUR sources. 0=> Nchan - Nchan/8 ICHANSEL...For sources named in SOURCES, selects up to 20 groups of channels/IF(s) to fit as sets of (Start,end,inc,IF), i.e., ICHANSEL = 6,37,1,0, 92,123,1,0 for two regions applying to all IFs. The first group for which ICHANSEL(2,i) <= 0 ends the list. Defaults: Any IF having no group assigned to it, gets a group including all channels. ICHANSEL(1,j) defaults to 1, 0 < ICHANSEL(2,j) < ICHANSEL(1,j) defaults to Nchan. ICHANSEL(3,j) < 1 or > ICHANSEL(2,j)-ICHANSEL(1,j)+1 defaults to 1. ICHANSEL(4) <= 0 => this group applies to all IFs. DPARM......(1) > 0 => do NOT average polarizations in fitting the aliasing function (2) > 0 => do NOT average IFs in fitting the aliasing function (3) > 0 => do NOT average times in fitting the aliasing function (4) > 0 => do NOT average antennas in fitting the aliasing function (5) > 0 => do full complex aliasing function < 0 => zero the imaginary part of aliasing function (6) > 0 => Hanning smooth the aliasing function ----------------------------------------------------------------