AIPS HELP file for SDLSF in 31DEC21
As of Wed May 5 16:54:06 2021
SDLSF: Least squares fit baseline and subtracts from SD data
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 #
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 #.
CHANSEL Select channels to fit: NOTE
this is start,end,increment
for each region
ORDER 0.0 1.0 Order of the baseline (0/1)
DOALL -1.0 1.0 > 0 => fit the average of all
spectra at a given time.
DOOUTPUT -1.0 1.0 > 0 => write fit baseline as
a continuum uv data base
CHANNEL 0.0 9999.0 Channel of fit to be written
as continuum: 0 -> reference
FLUX 0.0 Flag data if residual flux in
any fit channel is > FLUX
0 -> 10**20
CUTOFF 0.0 Flag data if RMS of residual
in fit channels > CUTOFF
0 -> 10**20
PRTLEV 0.0 Print summary of data flagged
> 0 => detail by channel
Task: This task does a spectral baseline subtraction. It fits a
straight line (with optional slope) to a set of selected spectral
channels using either each observation individually or the
average of all observations at a given time. It then subtracts
the fitted baseline from each spectrum used in the average.
Optionally, it can flag data having excess residuals in the
channels used for the baseline fitting. This is a good method
for detecting and deleting data damaged by RFI. The whole
process is useful for producing better initial data for the
imaging operations and may well eliminate the need for baseline
removal from the images (TRANS-IMLIN-TRANS). (If SDLSF is used
to remove the "weather" (estimated from the average of multiple
feeds pointing in different directions at any given time), then
some spectral baseline may well remain after the initial SDIMG.)
INNAME.....Input (SD) UV file name (name). Standard defaults.
INCLASS....Input (SD) UV file name (class). Standard defaults.
INSEQ......Input (SD) UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input (SD) UV file. 0 => any.
OUTNAME....Output (SD) UV file name (name). Standard defaults.
OUTCLASS...Output (SD) UV file name (class). Standard defaults.
OUTSEQ.....Output (SD) UV file name (seq. #). 0 => highest unique
OUTDISK....Disk drive # of output (SD) UV file. 0 => highest with
space for the file.
CHANSEL....Select up to 10 groups of channels to fit as sets of
(Start,end,inc), i.e., CHANSEL = 6,37,1, 92,123,1
Defaults: if CHANSEL(1,1) and CHANSEL(2,1) are <= 0,
use all channels. Else use CHANSELs until CHANSEL(1,i) and
CHANSEL(2,i) are both <= 0 ignoring ones >= i.
CHANSEL(1,j) defaults to 1, CHANSEL(2,j) < CHANSEL(1,j)
defaults to Nchan. CHANSEL(3,j) < 1 or > CHANSEL(2,j) -
CHANSEL(1,j) + 1 defaults to 1.
ORDER......Order of the baseline: 0 no slope, 1 a slope is also fit.
NCOUNT=1 is highly recommended unless the data are very
noisy and only a few channels available for the baseline
DOALL......> 0 => fit the average of all observations occuring at the
same time (and consecutively in the data set). <= 0 => fit
each observation individually.
If there is a single pointing position at a given time,
DOALL TRUE will get the average baseline for, for example,
the two polarizations at that time with somewhat greater
reliability than it would fitting the two individually.
For multiple pointing positions at a single time (e.g., the
8-beam system), DOALL TRUE obtains the average baseline for
several positions at once. This may be a good measure of
the "weather" at that time but may not be such a good
measure of the baselines at each of the 8 positions
(especially if one or more of the feeds has instrumental
offsets or other problems). If you use DOALL TRUE with
multi-feed data, you may anticipate the need for additional
baseline removal after the images are made.
DOOUTPUT...<= 0 => write out only the subtracted uv data.
> 0 => write also a data set with the fit baseline as a
single-channel (SD) UV data set.
CHANNEL....When DOOUTPUT > 0, write the continuum data with the fit
evaluated at spectral channel CHANNEL.
0 => reference channel.
FLUX.......If the residual flux in any channel used to fit the
baseline exceeds FLUX, then the spectrum for that time, IF,
and polarization is fully flagged. <= 0 => 1.0E20
CUTOFF.....If the RMS flux in the channels used to fit the baseline
exceeds CUTOFF, then the spectrum for that time, IF, and
polarization is fully flagged. <= 0 => 1.0E20
PRTLEV.....A summary of points flagged is printed. To print (in the
message file) any channel having >= PRTLEV samples flagged
for excess residuals, set PRTLEV > 0. = 0 => print only