; PCAL ;--------------------------------------------------------------- ;! Determines instrumental polarization for UV data ;# TASK UV CALIBRATION POLARIZATION ;----------------------------------------------------------------------- ;; Copyright (C) 1995-1997, 1999-2004, 2006-2007, 2009-2011 ;; 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 ;----------------------------------------------------------------------- PCAL LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC PCAL Task to compute polarization corrections 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 # Data selection (multisource): CALSOUR Sources to calibrate with 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. BIF 0.0 100.0 Lowest IF number 0=>all EIF 0.0 100.0 Highest IF number 0=>all ANTENNAS Antennas to solve for. UVRANGE 0.0 UV range in kilolamdba SUBARRAY 0.0 1000.0 Subarray, 0=>all Cal. info for input: DOCALIB -1.0 101.0 > 0 calibrate data & weights > 99 do NOT calibrate weights GAINUSE CAL table to apply. CLEAN map (optional) BLVER BL table to apply. FLAGVER Flag table version DOBAND -1.0 10.0 If >0 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. ICHANSEL Array of start and stop chan numbers, plus a channel increment and IF to be used to select channels to sum to find the polarization. 0 => all channels IN2NAME Cleaned map name (name) IN2CLASS Cleaned map name (class) IN2SEQ 0.0 9999.0 Cleaned map name (seq. #) IN2DISK 0.0 9.0 Cleaned map disk unit # INVERS -1.0 46655.0 CC file version #. NCOMP # comps to use for model. 1 value per field FLUX Lowest CC component used. NMAPS 0.0 4096.0 No. Clean map files CMETHOD Modeling method: 'DFT','GRID',' ' CMODEL Model type: 'COMP','IMAG' 'SUBI' (see HELP re images) DOMODEL -1.0 2.0 > 0 => use model, do not fit source Q and U = 2 use CP table model PMODEL Source poln. model SPECPARM Spectral index: I Q U V for each CALSOUR SOLINT Soln. interval (min) 0=>5. SOLTYPE Solution type: 'ORI-', 'APPR', 'RAPR' SPECTRAL -1.0 1.0 > 0 do spectral PCAL <= 0 do continuum PCAL INTPARM Smoothing parameters for spectral mode PRTLEV 0.0 10.0 Print statistics 0=>none 1 = some, 2 = lots. Use 1. REFANT 0.0 90.0 Reference antenna, 0->pick BPARM Task enrichment parameters for SOLTYPE 'ORI-' only: (1) if > 0 use default initial feed parameters. (2) > 0 -> no error calc. (3) if > 0 then fit for R-L phase difference (4) initial R-L phase (5) >0 solve for Vpol. (6) >0 fix ref. ori. 1 (7) >0 fix ref. ori. 2 (8) >0 fix all orientations (9) >0 fix all ellipticities (10) >0 fix source poln. CPARM Task enrichment parameters (1) >0 => average in IF and find common solution. (2) >0 => update source table with pol. solution (3) >0 => do NOT interpolate over flagged channels (4) CP table version if DOMODEL = 2 (8) >0 => max. no. iter (9) >0 => conv. tolerance (10) >0 => conv. tol. BADDISK 0.0 9.0 Disk no. not to use for scratch files. --------------------------------------------------------------- PCAL Task: This task reads a UV file, calibrates, subtracts a model and determines the effective feed parameters for each antenna and IF. These parameters are then placed in the antenna (AN) table. Polarization corrections can then be applied by setting DOPOL=1 in LISTR or SPLIT. If a polarized model is given then only the feed parameters are determined. If no model is given then a point source is assumed for SOLTYPE='APPR'. For SOLTYPEs 'ORI-' and 'RAPR' the source may be resolved but the polarized flux is assumed to have the same distribution as the total intensity and the polarization angle is assumed to be constant. Model images made with both values of IMAGR's DO3DIMAG option are handled correctly, as are multi-scale images. Set NMAPS = NFIELD * NGAUSS. The frequencies within each IF are averaged by PCAL before doing the solutions. So the phase has to be flat within each IF. Therefore the data have to be phase calibrated by FRING or by PCCOR before PCAL. In 31DEC10, PCAL has two modes. In the old, familiar one, PCAL averages spectral channels and determines antenna D terms and optionally source Q and U on a per IF basis. The results are written to the antenna (AN) and optionally the source (SU) tables. In the new mode, PCAL determines the D terms and optionally the source Q and U on a per spectral channel basis. Such results are written to the PD and CP tables, respectively. 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. The following are used for multisource data files only: CALSOUR....List of sources for which calibration constants are to be determined. '*' = all; a "-" before a source name means all except ANY source named. Note: solutions for multiple sources can only be made if the sources are point sources at their assumed phase center and with the flux densities given in the source (SU) table. All ' ' =>all. No more than 50 calibrators may be selected using this and the following two adverbs. QUAL.......Only sources with a source qualifier number in the SU table matching QUAL will be used if QUAL is not -1. CALCODE....Calibrators may be selected on the basis of the calibrator code: ' ' => any calibrator code selected '* ' => any non blank code (cal. only) '-CAL' => blank codes only (no calibrators) anything else = calibrator code to select. NB: The CALCODE test is applied in addition to the other tests, i.e. CALSOUR and QUAL, in the selection of sources for which to determine solutions. The following may be used for all data files (except as noted): TIMERANG...Time range of the data to be used. 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. BIF........First IF to process. Old values for feed parameters and calibrator polarizations for unprocessed IFs are unchanged. 0=>all. EIF........Highest IF to process. 0=>all higher than BIF ANTENNAS...A list of the antennas to have solutions determined. If any number is negative then all antennas listed are NOT to be used to determine solutions and all others are. All 0 => use all. UVRANGE....Range of projected spacings to be included in 1000's of wavelengths. 0 => 1, 1.E10 SUBARRAY...Subarray number to use. 0=>all. 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). GAINUSE....version number of the CL or SN table to apply to the data. 0 => highest. BLVER......Version number of the baseline based calibration (BL) table to appply. <0 => apply no BL table, 0 => highest. 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. BPVER......Specifies the version of the BP table to be applied. <0 => no bandpass correction done. 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). ICHANSEL.. Array of start, stop, and increment channel numbers plus an IF used for channel selection in the averaging to compute the average values used for solving for polarization. Up to 20 sets if channels/IF may be entered. The first having ICHANSEL(2,i) <= 0 terminates the list. ICHANSEL(4,i) is the IF number, with <= 0 meaning all IFs. If an IF has no ICHANSEL set for it, then all channels are used. IN2NAME....Cleaned map name (name). Standard defaults. Read DOMODEL (below) first. Note: a CLEAN image for only a single source may be given although it may be in a multi-source file. An Ipol, Qpol, Upol, and Vpol image of the same name are expected. If the first one of the polarization is missing, that polarization is taken to have a value of 0.0. If the source table contains a flux, then that flux will be used to scale the components model to obtain the stated total flux. This is needed since initial Cleans may not obtain the full flux even though they represent all the essentials of the source structure. NOTE: if a model image is given, then the task will not fit for source polarization if models for at least I, Q, and U are given. IN2NAME and IN2CLASS cause PMODEL to be ignored. IN2CLASS...Cleaned map name (class). The value given should be for the Ipol image, the Q, U, and V pol images will be assumed to be the same except for an initial Q, U, or V in the class. IN2SEQ.....Cleaned map name (seq. #). These should be the same for I, Q, U, and V images. IN2DISK....Disk drive # of cleaned map. 0 => any. INVERS.....CC file version #. 0=> highest numbered version NCOMP......Number of Clean components to use for the model, one value per field. If all values are zero, then all components in all fields are used. If any value is not zero, then abs(NCOMP(i)) (or fewer depending on FLUX and negativity) components are used for field i, even if NCOMP(i) is zero. If any of the NCOMP is less than 0, then components are only used in each field i up to abs(NCOMP(i)), FLUX, or the first negative whichever comes first. If abs(NCOMP(i)) is greater than the number of components in field i, the actual number is used. For example NCOMP = -1,0 says to use one component from field one unless it is negative or < FLUX and no components from any other field. This would usually not be desirable. NCOMP = -1000000 says to use all components from each field up to the first negative in that field. NCOMP = -200 100 23 0 300 5 says to use no more than 200 components from field 1, 100 from field 2, 23 from field 3, 300 from field 5, 5 from field 6 and none from any other field. Fewer are used if a negative is encountered or the components go below FLUX. FLUX.......Only components > FLUX in absolute value are used in the model. NMAPS......Number of image files to use for model. For multi-scale models, set NMAPS = NFIELD * NGAUSS to include the Clean components of the extended resolutions. If more than one file is to be used, the NAME, CLASS, DISK and SEQ of the subsequent image files will be the same as the first file except that the LAST 3 or 4 characters of the CLASS will be an increasing sequence above that in IN2CLASS. Thus, if INCLASS='ICL005', classes 'ICL005' through 'ICLnnn' or 'ICnnnn', where nnn = 5 + NMAPS - 1 will be used. Old names (in which the 4'th character is not a number) are also supported: the last two characters are '01' through 'E7' for fields 2 through 512. In old names, the highest field number allowed is 512; in new names it is 4096. CMETHOD....This determines the method used to compute the model visibility values. 'DFT' uses the direct Fourier transform, this method is the most accurate. 'GRID' does a gridded-FFT interpolation model computation. ' ' allows the program to use the fastest method. NOTE: when using a model derived from data with different uv sampling it is best to use 'DFT' CMODEL.....This indicates the type of input model; 'COMP' means that the input model consists of Clean components, 'IMAG' indicates that the input model consists of images. 'SUBI' means that the model consists of a sub-image of the original IMAGR output. If CMODEL is ' ' Clean components will be used if present and the image if not. SUBI should work for sub-images made with DO3DIM true and sib-images of the central facet made with DO3DIM false, but probably will not work well for shifted facets with DO3DIM false. Use BLANK rather than SUBIM in such cases. CALIB will set a scaling factor to correct image units from JY/BEAM to JY/PIXEL for image models. If the source table contains a flux, then that flux will be used to scale the components model to obtain the stated total flux. This is needed since initial Cleans may not obtain the full flux even though they represent all the essentials of the source structure. DOMODEL....<= 0 => fit for the calibration source(s) Q and U. This still requires knowledge of the source(s) I flux. If there is only one source, this is given by PMODEL(1) if it is greater than 0 (required for single-source files) with a default of the fluxes in the source table for multi-source files. An image model is also possible for a single source. If there is more than one calibration source, then PMODEL and IN2NAME et al. are ignored and the I fluxes come from the source table. > 0 => use a model for the calibration source(s) I, Q, and U (and maybe even V) flux and do NOT fit for the source(s) Q and U. For a single calibration source, image models may be used and/or PMODEL if PMODEL(1) > 0. One of these must be done for single-source files. For multi-source files, the source table may be used to provide the full model instead and is the only place to get models for more than one calibration source. = 2 => use the I, Q, U, V model contained in an attached CP table (version given by CPARM(4)). PMODEL.....See first DOMODEL above. A single component model to be used instead of a CLEAN components model; if PMODEL(1) > 0 amd DOMODEL > 0, then use of this model is requested when a single source is being used PMODEL(1) = I flux density (Jy) PMODEL(2) = Q flux density (Jy) PMODEL(3) = U flux density (Jy) PMODEL(4) = V flux density (Jy) PMODEL(5) = X offset in sky (arcsec) PMODEL(6) = Y offset in sky (arcsec) PMODEL(1) must be > 0 to give an I flux for single-source data sets independent of the value of DOMODEL. The rest of PMODEL must be set intentionally when DOMODEL > 0 and IN2NAME is blank. PMODEL is ignored if IN2NAME or IN2CLASS is not blank. SPECPARM...The spectral index in I, Q, U, and V for each source to be used mostly when DOMODEL > 0. In the continuum case, it is applied only when PMODEL is used. In the line case, it is also applied in I, Q, U, and V when PMODEL is used. When DOMODEL <= 0, the I flux is still needed to solve for Q and U, so the I portion is still used. Thus meaningful values for SPECPARM(1,i) are helpful. Note that i is a sequential number assigned to all CALSOUR in the order of the source numbers in the source table (not their order in the adverb CALSOUR). SOLINT.....Time interval to average data before determining correction in minutes. 0 => 5 min. If there is a single calibrator scan, the task will reset SOLINT to 0.333 times the length of that scan. SOLINT is an interesting parameter to explore if having difficulties with solutions. SOLTYPE....Solution type: 'APPR' => linear approximation, 'RAPR' => linear approximation but allowing resolved sources. 'ORI-' => orientation- ellipticity allowing resolved sources other values = 'APPR' Note: 'RAPR' and 'ORI-' require nonstandard calibration procedures, see EXPLAIN PCAL for details. SPECTRAL...> 0 => do the solution as a function of spectral channel within each IF. Answers go into a PD table and source models, if they are part of the solution, go into the CP table. <= 0 => do the solution only as a function of IF. Antenna polarizations are placed into ther antenna table and source models (if DOMODEL<=0 and CPARM(2)>0) go in the SU table. INTPARM....After the data are calibrated with all parameters including SMOOTH, they may be smoothed in frequency further using the INTPARM selected function while taking into account ICHANSEL. This is to provide better S/N than one would have with unsmoothed single channels. INTPARM(1) = type of smoothing to apply: 0 => no smoothing 1 => Hanning 2 => Gaussian 3 => Boxcar 4 => Sinc (i.e. sin(x)/x) INTPARM(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 INTPARM(1) = 1 - 4. INTPARM(3) = the diameter over which the convolving function has value - in channels. Defaults: 1, 3, 1, 4 times INTPARM(2) used when input INTPARM(3) < INTPARM(2) (after application of defaults). PRTLEV.....If this value is larger than 0.0 then the intermediate diagnostics and solutions will be given on the monitor terminal and the message file. REFANT.....Reference antenna to use. If none is specified, the task will pick the lowest numbered one with the most samples. Previous methods that allowed "none" gave suspect results and could not measure uncertainties. BPARM......Task enrichment parameters (SOLTYPE='ORI-' only): (1) If BPARM(1) is greater than 0 then the initial values for the feed ellipticity and orientation will be that for perfect RCP and LCP feeds. Otherwise the values from the AN table, if any, will be used. (2) > 0 => suppress error calculation - which can be meaningless and can even get into an infinite loop. (3) If BPARM(3) is greater than 0 then fit for the R-L phase difference using BPARM(4) as the initial value. This option is only useful if at least one source has a fixed polarization model. (5) If BPARM(5) is greater than 0 then solve for Vpol. (6) If BPARM(6) is greater than 0 then fix the value of the orientation of the first polarization of the reference antenna to 0. (REFANT > 0) (7) If BPARM(7) is greater than 0 then fix the value of the orientation of the second polarization of the reference antenna to 0. (REFANT > 0) (8) If BPARM(8) is greater than 0 then fix the orientations at the values in the AN table. (9) If BPARM(9) is greater than 0 then fix the ellipticities at the values in the AN table. (10) if (BPARM(10) is greater than 0 then fix the source polarization parameters to the values given in the SU table. CPARM......Task enrichment parameters: (1) If CPARM(1) is greater than 0 then data in the selected IFs will be averaged before doing the solutions. NOTE: the IFs must be phase coherent for this to be useful. This is usually NOT the case for VLA data. (2) > 0 => update the source table with the fit source parameters. Note, because of the RL phase difference, the Q and U fit may not be correct. (3) In SPECTRAL > 0 mode, channels flagged either by the usual flags or by ICHANSEL and not recovered by smoothing with INTPARM will end up with solutions which are 0.0. The task will replace these incorrect ones with interpolated or extrapolated ones unless CPARM(3) > 0. (4) If DOMODEL = 2, the CP table version number to be used. 0 => the highest. (5)-(7) Not currently used. (8) If CPARM(8) is greater than 0 then it will be used as the maximum number of iterations for the SOLTYPE='ORI-' solution. (9) If CPARM(9) is greater than 0 then it will be used as a convergence criterion for the SOLTYPE='ORI-' solution. A value of 0 causes a default criterion to be used. (10) If CPARM(10) is greater than 0 then it will be used as a convergence criterion for the SOLTYPE='ORI-' solution. A value of 0 causes a default criterion to be used. BADDISK....Disk numbers on which scratch files are not to be placed. --------------------------------------------------------------- PCAL: Task to determine effective feed polarization parameters. Documentor: W. D. Cotton (preliminary version). Related Programs: CALIB, LISTR, SPLIT, CLCOR, LPCAL, SPCAL Use of PCAL is also described in EXPLAIN CALIBRAT. Polarization calibration of synthesis array visibility data consists of two distinct parts: 1) the determination of the effective response of the feed to the incident radiation and the correction of the observations to the values which would have been obtained with perfect feeds and 2) the determination and removal of systematic phase delay differences between the right and left hand polarization systems. PCAL determines the effective response of the feeds, the polarization of unknown calibrator(s) and stores this information in the AN and SU tables. Routines which can apply calibration tables can then be instructed to apply the polarization corrections by setting the adverb DOPOL=1. If the systematic phase delay differences between the right and left hand systems is time variable (e.g. variable ionispheric Faraday rotation) then these effects need to be removed before running PCAL (see CLCOR). If the systematic phase offsets are essentially constant then they may be removed after running PCAL by using RLDIF or LISTR with STOKES='POLC'; DOPOL=1 and appropriate calibration on a source with known polarization angle to determine the phase offsets and then applying them using CLCOR and OPCODE='POLR'. Note: this later method will modify the AN table as well as the CL table. SINGLE SOURCE FILES: In principle, PCAL can work on a single-source file followed by SPLIT to apply the correction. However, in practice, it is preferable to convert all of the files involved to multi-source files using task MULTI followed by DBCON with DOARRAY=TRUE to glue the files together. DBCON should be followed by INDXR to create an index table. The flux densities of the calibrator source(s) to be used by PCAL should be entered in the Source (SU) table using SETJY. Also, see the section on parallactic angles. After PCAL has been successfully run and any phase offsets have been removed, then single source, polarization corrected files can be obtained using SPLIT with DOPOL=1; DOCAL=TRUE and GAINUSE=(relevant CL table). PARALLACTIC ANGLE: When used with SOLTYPE='APPR', PCAL expects that the input data has NOT had the parallactic angle removed from the phase of the cross hand visibility data. The AIPS software makes this correction when the instrumental corrections are applied, i.e., when DOPOL=1. If this correction has been made (e.g. any data which has been through the VLA Dec-10) then PCAL will give invalid results. (VLA data read by the AIPS program FILLM has not had this correction made and can be fed to PCAL as is.) If SOLTYPE='RAPR' or 'ORI-' then the parallactic angle correction SHOULD have been made before phase calibration. Also for SOLTYPE='ORI-' the phase reference antenna used in the calibration process should be the same as REFANT given to PCAL. If you are unsure about this correction then run LISTR with OPTYPE='MATX'; STOKES='POLC'; DPARM(1)=1; SOURCES='(your calibrator source)'; DOPOL=-1; DOCAL=TRUE; GAINUSE=appropriate CL (or SN for single source files) table. The parallactic angle may be determined from LISTR using OPTYPE='GAIN'; DPARM(1)=9. If the parallactic angle correction has NOT been applied then the phase of the RL correlations will vary approximately as the negative of the parallactic angle. If the range of phase of the RL correlator is much less than the range of the parallactic angle then the parallactic angle correction has been made and needs to be removed. REMOVAL OF THE PARALLACTIC ANGLE CORRECTION: Before removing the parallactic angle correction by modifying the CL table it is best to copy the current working CL table to the next available sequence number with TACOP and modify the copy. If something goes wrong you can start over using the previous version (also CLCOR refuses to modify CL table version 1). Remember to set the OUTNAME etc. in TACOP. If you have determined that the parallactic angle correction has already been made to your data then it can be removed using CLCOR with SOURCES=''; STOKES=''; BIF=1; EIF=0 TIMERANG=0; ANTENNAS=0; CLCORP=0; SUBARRAY=subarray number; GAINVER=CL table no. to modify; OPCODE='PANG'; BPARM=0. CLCOR will remove the parallactic angle correction by rotating the phases of the complex gains to be applied the the data. If there is more than one subarray present then CLCOR must be run for each subarray; the number of subarrays can be determined from the number of AN tables present in the file as shown by IMHEAD. After this correction is made, then PCAL should be run with DOCAL=TRUE and GAINUSE=(the CL table modified by CLCOR). To add the parallactic angle correction for SOLTYPEs RAPR and ORI-, use PANG in CLCOR with CLCORP(1)=1. CALIBRATION DATA MEASURED WITH LINEARLY POLARIZED FEEDS Data obtained with systems using linearly polarized feeds (especially the Australia Telescope) may determine the instrumental polarization using a linear approximation. This type of solution is indicated in the AN table as POLTYPE='X-Y LIN '. The standard calibration routines will apply these corrections if adverb DOPOL=1. NOTE: X-Y linear data (STOKES = -5) MUST be polarization before attempting to use Q, U or V polarization. SOLTYPE: SOLTYPE='APPR' does a fits a linear approximation to the feed parameters and source polarizations using one or more unresolved calibrator sources. SOLTYPE='RAPR' also fits a linear approximation to the feed parameters but allows the sources to be resolved. The method explicitly assumes that the polarization structure has constant position angle and is the same as the total intensity structure with a scaling factor. This assumption will seriously break down if the source is significantly resolved (larger that 1 - 2 synthesized beam widths). SOLTYPE='ORI' fits for feed ellipticity and orientation. Since this procedure can be quite expensive in compute time it should only be used in cases where the linear approximation breaks down (more than a few percent instrumental polarization). This method can optionally solve for the R-L phase offset if a polarization model is given. USING RESOLVED CALIBRATORS Although SOLTYPEs 'RAPR' and 'ORI-' allow resolved calibrators the assumptions inherent in their use break down in cases of significant resolution. In this case it may be useful to make a few iterations of PCAL, image, and deconvolve to develop a accurate model to give to PCAL (IN2NAME etc.). For calibrators that are very resolved, and/or have polarization structure, PCAL will not work well. LPCAL was designed for this case. LPCAL and SPCAL LPCAL allows you to put in multiple models for multiple source components. These are allowed to have different polarizations. If you have VLBI data it is likely you will have a resolved calibrator with varying polarization structure. If you have spectral line data or if you suspect that the D-terms vary across the frequency band try using SPCAL. However SPCAL does not allow the polarization to vary across the calibrator (like LPCAL). Both LPCAL and SPCAL will work for unpolarized calibrators.