; COHER ;--------------------------------------------------------------- ;! Baseline Phase coherence measurement ;# TASK UV IMAGING ;----------------------------------------------------------------------- ;; Copyright (C) 1998-1999, 2004, 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 ;----------------------------------------------------------------------- COHER LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC COHER: Finds coherence time for selected "BT" or "TB" order uv data INNAME Input UV data (name) INCLASS Input UV data (class) INSEQ 0.0 9999.0 Input UV data (seq. #) INDISK 0.0 10.0 Input UV data disk # APARM (1) Max. averaging time (min) 0 => 10*APARM(8) 0 is not recommended (2) SNR cutoff in coherence time estimation 0 => 5 (3) Min Vector/Scalar ratio; 0 => 0.8 (4) Prtlev; 0=>reasonable (5) Step in time in minutes; 0 => infinite (6) 0 => average frequencies with delay search 1 => simple vector averaging (7) Output type 0 => average coherence 1 => current coherence times ready for BLING (8) expected coherence time (min), max for all basel. 0 => 5min BADDISK Disk #'s to avoid TIMERANG Time: start day,hr,min,sec; stop day,hr,min,sec. BIF 0.0 100.0 IF number; 0 => 1 BCHAN 0.0 4096.0 Lowest channel number 0=>1 ECHAN 0.0 4096.0 Highest channel number 0 => last available ANTENNAS Antennas to be selected BASELINE Baselines with ANTENNAS See explanation. SOURCES Source list. See explanation. FREQID Freq. ID to select. 0 => 1 DOCRT -3.0 132.0 > 0 means use the terminal. < 0 use the line printer OUTPRINT Disk file name in which to save the line printer output. SUBARRAY 0.0 9999.0 Subarray; 0 => 1. ---------------------------------------------------------------- COHER: Task to measure coherence time NB: data must be sorted to 'BT' or 'TB' order before running. NOTE: this task does NOT apply flagging or calibration tables to the input UV data. Run SPLIT first if that operation is desired. Adverbs: INNAME.....Input UV data file (name). Standard defaults. INCLASS....Input UV data file (class). Standard defaults. INSEQ......Input UV data file (seq. #). 0 => highest. INDISK.....Input UV data file disk #. 0 => any. APARM.....Task enrichment parameters. (1) Maximum time interval for a source or selected time interval, in minutes. 0=> 10*APARM(8) Comparison of vector and scalar average for each source is terminated having reached a next source or when time (starting from the beginning of the source or the beginning of a sequent time interval) reaches APARM(1). This parameter should be selected several times more expecting coherence time. If the output file created for BLING, this interval is desirable to have as long as possible. It is limited by the buffer size. APARM(1)<2000*PREAVE, where PREAVE is the preaverage time. (2) Max SNR deviation to pass. While calculating the coherence time, the scalar mean and rms of each baseline is calculated. If the value of a visibility exceeds APARM(2) times the RMS, the visibility is flagged (in buffer; not in the data). (3) Min Vector/Scalar amplitude ratio. The ratio of the vector to scalar averaged amplitude is calculated. The coherence time for each try is defined as the time interval for which the ratio falls below APARM(3). 0 => 0.8 (4) Print level: 0 => print tables of coherence times for selected baselines and antennas for each selected time interval and source. Print tables of coherence times averaged for all selected time interval and sources. Print minimum and mean coherence time through all antennas 1 => print additional information useful for debugging (5) Step in time in minutes; 0 => infinite So if zero, then the only time interval is selected. Introducing this parameter you can estimate the coherence time variance versus time. The less APARM(5) the more data at the time axis you get, but the more computing time is required. If output file for BLING is prepared (APARM(7)=1), APARM(5) is forced to be equall APARM(1). It is allowed continuously increasing the analysis time. (6) 0 => provide delay search, averaging frequencies 1 => not provide the search. Generally speaking it is necessary to search for the delay to average frequency channels. But if signal/noise ratio is not high enough, an error in the solution of the delay can occur. As a result phases of the frequency average data become random from time to time, and COHER find a low vector averaging and therefore low coherence time. However sometimes delay is known in advance close to zero. In this case APARM(6)=1 allows to exclude the delay search providing actual vector averaging at the frequency axis. If you are sure that delay is close to zero, APARM(6)=1 is more preferable because the task ran faster. (7) Output type. 0 => average coherence. This option gives idea about the coherence property of the baselines and antennas. 1 => current coherence times ready for BLING. BLING will use this data (infile) to find solution for the given variable solution intervals. (8) Expecting coherence time in minutes. Maximum for all baselines. 0 => 5min. The task compares scalar average amplitude with estimated amplitude by FFT plus least square. The comparison starts with this time (APARM(8)). Then this interval is splitted for twice smaller intervals. This process continue while the maximum possible time is found satisfying condition: AMPVEC/AMPSCAL = APARM(3). This condition determines the first coherence interval. The search of the next interval starts at the end of the previous found interval using APARM(8) as the initial estimation. BADDISK...Disk #'s to avoid for scratch files TIMERANG..Time: start day,hr,min,sec; stop day,hr,min,sec. 0 => all BIF.......IF number; Only one (the specified) IF can be used; 0 => 1 BCHAN.....Lowest channel number 0 => 1 ECHAN.... Highest channel number, 0 => highest available ANTENNAS..A list of the antennas to be selected BASELINE...Baselines between antennas named in ANTENNAS and those named in BASELINE are selected.. There are four possible combinations of ANTENNAS and BASELINE: 1. ANTENNAS = 0; BASELINE = 0. All possible baselines are selected. 2. ANTENNAS <>0; BASELINE = 0. a)All ANTENNAS > 0 Baselines including an antenna in the ANTENNAS list are selected; b)Some ANTENNAS < 0 All baselines NOT including an antenna in the ANTENNAS list are selected; 3. ANTENNAS = 0; BASELINE <> 0. a)All BASELINE > 0 Baselines including an antenna in the BASELINE list are selected; b)Some BASELINE < 0 All baselines NOT including an antenna in the BASELINE list are selected; 4. ANTENNAS <> 0; BASELINE <> 0. a)All ANTENNAS>0 and all BASELINE>0 Baselines between antennas named in ANTENNAS and those named in BASELINE are selected. b)Some ANTENNAS<0 .OR. some BASELINE<0 Baselines between antennas named in ANTENNAS and those named in BASELINE are DE-selected, all others are selected. SOURCES....Source list. Blank => all If the first character of any source names begins with a "-", all sources EXCEPT those named will be returned. The "-" will be ignored in determining the source name. FREQID.....Freq. ID to select. 0 => 1. Use LISTR (OPTYPE=SCAN) to find list of FREQIDs of the data DOCRT......False (<= 0) use the line printer if OUTPRINT = ' ' else write named OUTPRINT file only. When OUTPRINT is not blank, DOCRT=-2 suppresses the page-feed character on page headers and DOCRT=-3 suppresses page headers and most other header information. True (> 0) use the terminal interactively. The task will use the actual terminal width as a display limit unless 72 < DOCRT < width. In that case, the display limit will be DOCRT characters. OUTPRINT...Disk file name in which to save the line printer output. ' ' => use scratch and print immediately for interactive jobs - batch jobs use OUTPRINT = 'PRTFIL:BATCHjjj.nnn' (jjj= job #, nnn = user #). When OUTPRINT is not blank, multiple outputs are concatenated, and the file is not actually printed. SUBARRAY...Subarray; 0 => 1. ---------------------------------------------------------------- COHER: Task to estimate coherence time NB: data must be sorted to 'BT' or 'TB' order before running. Related programs: COHER derived from PHASE Documentor: Leonid Kogan NRAO/Socorro. Comments Coherence time is determined by comparing vector and scalar averaged amplitudes. When the vector/scalar ratio becomes less than APARM(3) the coherence time is considered exceeded. A new coherence time is determined for the following time interval starting with the end of previously found coherence interval. This process is terminated when the time reaches the source end or APARM(1). This process begins again for a new source or new time interval (APARM(5)). The result is presented as a table of found coherence times for each source or time interval. The final coherence time is determined as an average over the selected sources. Complex amplitude for each time is determined using FFT analysis of the data at the selected frequency channels and fitting a complex exponent by non linear least square method. Vector averaging at the time axis is provided by fitting a complex exponent by non linear least square method. The first approach for the least square is given by FFT. The fitting of the complex exponents instead of simple vector averaging allows to estimate amplitude in the case of non zero value of delay and rate. But such a method required more computing time. The special methods were used to minimize the computing time. Now it is equal ~20 sec at SPARC station IPX for 5 antennas and four 5 minutes intervals. The task ran much faster if delay search is excluded (APARM(6) = 1).