AIPS HELP file for ATLOD in 31DEC24
As of Thu Apr 18 19:36:48 2024
ATLOD: Task which reads RPFITS format uv data into AIPS.
INPUTS
INTAPE 0.0 9.0 Tape drive number (0 -> 1)
No REMOTE capability
NSKIP * 0.0 Number of tape files to
skip (0 -> 0)
NFILES * 0.0 1000.0 Number of tape files to
load (0 -> 1)
BCOUNT * 0.0 First scan to read (0 -> 1)
NCOUNT * 0.0 No. scans to read (0 -> all)
DATAIN Disk file name
OUTNAME Output uv file name (name)
blank -> source name
OUTCLASS Output uv file name (class)
blank -> UVDATA
OUTSEQ 0.0 9999.0 Output uv sequence number
0 -> highest unique AND a
new file for EACH pass
OUTDISK 0.0 9.0 Output disk drive number
OPTYPE 'LOAD' load data (default)
'LIST' scan summary
'SUMM' file summary
'SYSC' dump syscal info
see CPARM(9)
SOURCES * Source selection list
TIMERANG * Time range selection
FREQSEL * Frequencies to select (MHz)
IFSEL * IFs to select
CHANSEL 0.0 8192. Channel selection array:
(1,n) start channel group n
(2,n) end channel group n
(3,n) incr. channel group n
IFMAP True to map on-line IF chain
to AIPS IF axis.
NIF 0.0 4.0 Length of IF axis,
0 => ATLOD decides.
DOUVCOMP -1.0 1.0 Use compressed data?
APARM 1) If > 0, convert to Stokes
if < 0, kludge RR,LL,RL,LR
if = 0, don't change the
polarizations
2) If true, keep flagged data
3) If true, retain
autocorrelations
4) Shadowing diameter (m)
5) max NX time gap (min)
0 -> 10 min
6) max NX scan length (min)
0 -> 60 min
7) CL entry interval (min)
0 -> 5 min
8) Number of integrations
over which to average Tsys
0 -> 1 See HELP/EXPLAIN
9) Number of integrations
over which to average XY
phase diff if APARM(1) = 1
0 -> 1 See HELP/EXPLAIN
10) If non-zero drop data on
quality of XY phase diff.
See HELP/EXPLAIN
BPARM Baselines to be rejected,
(see HELP)
CPARM Further control parameters:
1) System cal. info. print
level. See HELP/EXPLAIN
2) If true negate system XY
cal phase difference
3) If true, negate phases
4) If true, use XYPHASE array
instead of on-line values
5) If true, apply XY phase to
the Y gain
6) If 1, report antennas for
which sampler stats bad
If 2, drop baselines with
bad sampler statistics
If 3, do 1 and 2
If 4, correct data for
bad statistics.
7) Sampler tolerance
8) If true, DATAIN will be
read as lower case. This
is intended for reading
from VAX disks mounted
under unix via multinet.
9) If OPTYPE='SYSC' then the
3 text files contain:
1 => XY phase, Tx & Ty
2 => X sampler stats
3 => Y sampler stats
0 => 1
10) If 1, Tsys from IF 1 is
applied to IF 2, if
APARM(8) is > 0
XYPHASE Enter XY phase difference for
each antenna & FQID (degrees)
DPARM 1) If > 0, then the scan
based source number of all
sources is set to 1.
2) If > 0, the spectra are
3-point Hanning smoothed.
3) If > 0 -> set weights to
D(3) instead of integration
time in units of 15s
HELP SECTION
ATLOD
Type: Task
Use: To read and load or list a summary of an RPFITS format uv
data file into AIPS. The RPFITS file can be on tape or
disk. If OUTNAME, OUTCLASS, and OUTSEQ specify an
existing file the data will be appended to it.
Adverbs:
INTAPE.....Tape drive number. 0 -> 1 Note that ATLOD does not
function with the AIPS remote tape system.
NSKIP......Number of tape files to skip from current tape
position before starting to load data.
NFILES.....The number of tape files to load (see OUTSEQ)
BCOUNT.....The first scan to read (same in each file). 0 -> 1
NCOUNT.....The number of scans to read (same in each file).
0 -> read all scans from file
DATAIN.....Name of an RPFITS format uv data disk file to be
loaded into AIPS. If this name is blank, ATLOD
assumes that input is to come from tape as
specified by INTAPE, and NFILES. If DATAIN is not
blank, INTAPE and NCOUNT are ignored.
OUTNAME....Output uv file name (name). Standard behavior with
default is source name.
OUTCLASS...Output uv file name (class). Standard behavior
with default is 'UVDATA'.
OUTSEQ.....Output uv file name (sequence number).
0 -> highest unique. If NFILES > 1, all the tape
files go into one output file. To make different
tape files go into different AIPS files, use
successive applications of ATLOD and NFILES=1.
OUTDISK....Output uv file disk drive number.
OPTYPE.....'LOAD' to read the data into an AIPS file (default)
'LIST' to list a summary of each scan
'SUMM' to list a summary of each file (very brief)
'SYSC' to write XY phases and Tsys values into text
files in the FITS area
SOURCES....List of sources to select. ' ' -> all. A "-" before
ANY source name means ALL EXCEPT any source named.
TIMERANG...Time range selection, 0 -> all.
FREQSEL....Frequencies of data to be selected (MHz), 0 -> all.
IFSEL......IFs of data to be selected, 0 -> all.
CHANSEL....Channel selection array: 0 => Load all channels
Up to 10 groups of channels may be selected.
CHANSEL(1,n) selects the begin channel, CHANSEL(2,n)
selects the end channel, and CHANSEL(3,n) selects the
channel increment for group n. Generally, unselected
channels are loaded but flagged. However, if only
one group of channels is specified, channels are
dropped rather than flagged.
IFMAP......If true, then the IF chain number defined by the on-line
system is mapped to the AIPS IF axis value one-to-one
NIF........Length of IF axis. 0 -> ATLOD chooses
DOUVCOMP...If true (DOUVCOMP >= 0) the output data is written
in compressed format which can result in a
substantial reduction - about a factor of 3 - in disk
space needed, but some tasks may not be able to
handle this format. Data are stored as 16-bit
integers with a different scaling for each visibility
spectrum. ATLOD will warn you if there is a loss of
accuracy due to some channels (interference?) being
much higher than the average.
APARM......Control parameters:HH,VH,HV
1) If > 0, convert VV, to Stokes IQUV.
If < 0, ignore the actual polarization order and
type and call them RR,LL,RL,LR.
If = 0, don't change the polarizations.
2) If true, retain data flagged on-line as bad.
3) If true, retain autocorrelations in the output
uv file.
4) Antenna diameter to adopt when rejecting data due
to shadowing effects. The physical diameter of
the AT antennas is 22 meters, so setting APARM(7)
smaller than 22 relaxes the shadowing constraint,
while making it larger tightens it.
The default is 22m.
5) Start a new index entry if a gap longer than
APARM(5) minutes occurs in the scan.
The default is 10 min., mininum 1 min.
6) Start a new index entry if an uninterrupted
section of data on the same source longer than
APARM(6) minutes occurs in the scan.
The default is 60 min., mininum 1 min.
7) A new CL (calibration) table will be created with
empty entries every APARM(7) minutes.
The default is 5 min., mininum 1 min.
8) If = -1 Undo the on-line correction and redo with
nominal 50 K system
If = 0 No additional corrections
If > 0 Undo the on-line correction and redo with
a Tsys correction averaged over APARM(8)
integrations
9) If APARM(1) = 1 then Stokes conversion is
requested and the XY phase difference per antenna
is used.
If A(9) = 0 no averaging of XY phases us done
If A(9) > 1 average XY phases for A(9)
integrations
10) If A(10) > 0, drop visibilities if one of the
antennas has a bad XY phase differences.
If A(10) < 0, apply additional absolute XY phase
tolerance as well as usual clipping algorithm.
See EXPLAIN for clear explanation!
BPARM......Baselines to be rejected, specified as 10*I + J
where I and J are the antenna numbers, order
being irrelevant unless the value is negative.
If I is 0 all baselines containing antenna J will
be dropped. Examples
12 Drop baselines 1-2 and 2-1
-31 Drop baseline 3-1 (but not 1-3)
4 Drop all baselines involving antenna 4
CPARM......Control parameters for experts only.
1) If = 1 list system calibration information
If = 2, you are told when the XY phases or Tsys
values appear to have drifted or jumped.
If = 3, then the information from 1 + 2 is printed
2) If true negate the system XY phase difference
3) If true, negate the visibilty phase as it is
read in (to fix data taken in 1989).
4) If true, use the XYPHASE array rather than the
on-line values
5) If true, apply the XY phases to the Y gains.
6) If 1, report antennas for which the sampler
statistics are out of range
If 2, drop baselines involving antennas with
bad sampler statistics
If 3, do 1 & 2
If 4, correct data for bad sampler statistics.
7) If > 0, use this as the sampler statistics
tolerance instead of the internal default
(5 percent for C(6)=1,2,3 12 percent for C(6)=4)
8) If true, DATAIN will be read as lower case.
This is intended for reading from VAX disks
mounted under unix via multinet.
9) If OPTYPE='SYSC' then the text files contain:
1 => XY phase, Tx & Ty
2 => X sampler stats
3 => Y sampler stats
0 => 1
10) Apply Tsys from IF 1 to IF 2 if (A8) > 0
XYPHASE....Array of XY phases (degrees) for each antenna
and FREQID. See EXPLAIN
DPARM......1) If > 0, all sources are given source number 1.
This is for mislabelled single source per scan
data taken in March 1992 following intial
mosaicing experiments.
2) If > 0, the spectra are 3-point Hanning smoothed
3) By default, the weight of each visibility is set
to the integration time in units of 15 sec.
If DPARM(3)>0 then the weight for each visibility
is set to DPARM(3)
EXPLAIN SECTION
ATLOD: Task to read RPFITS format uv data into AIPS.
DOCUMENTERS: Mark Calabretta and Neil Killeen
RELATED PROGRAMS: FILLM, FILLR, UVLOD, IMLOD, FITTP
The uv file produced by ATLOD is in the multi-source format,
that is, it includes the SOURCE and FREQSEL random parameters,
and has SU, FQ, and NX extension files associated with it. The
SU extension file contains information which associates each
source with a set of identifiers (name, ra, dec, etc.), and
other information. The FQ extension file records information
for each IF used (frequency, bandwidth, sideband, etc). The NX
file records the index of visibility records associated with
each scan.
BCOUNT,NCOUNT Each RPFITS file has multiple scans. These
specify the first scan and number of scans to read. If
reading from tape, then these numbers are the same for each
file. Thus, they probably useful only for single file input.
DATAIN If blank, ATLOD assumes that input is to come from
tape as specified by INTAPE, and NFILES. Use the AIPS verb
AVFIL to skip files on the tape to reach the one of interest.
If DATAIN is not blank, INTAPE and NCOUNT are ignored. The
DATAIN, when used for disk file input, must be of two forms:
1) 'AREA:FILENAME' where AREA is an upper case environment
variable (e.g., percentsetenv AREA /scratch/data) pointing
to the location of the file called FILENAME. The file
name must also be upper case.
2) 'FITS:MYDIR/FILENAME' FITS is a pre-defined environment
variable and MYDIR is a directory (upper case) below the
FITS area. This can be shortened to 'MYDIR/FILENAME'
and the FITS area will be assumed as the route. Note
if you use DATAIN='SCRATCH/FILENAME' then the files are
assumed to reside in /scratch/aips which is symbolically
linked to the directory FITS/SCRATCH.
3) We recommend that you simply put your data in the FITS
area, and then DATAIN='FILENAME' will work by default.
OUTNAME, OUTCLASS, OUTSEQ, OUTDISK Specify the output file
name. If they specify a file that already exists, then the
new data are appended to it.
OPTYPE
'LOAD' means load the specified data into an AIPS UV file
'LIST' resticts ATLOD to reporting summaries of the contents
of each scan
'SUMM' restricts ATLOD to reporting summaries of each file
'SYSC' causes ATLOD to write text files in the FITS area
The contents depend upon what value you give
CPARM(9). By default, you get files containing
the XY phases (degrees) for each antenna (XYPHS_UID)
and the system temperatures (TSYSX_UID) and TSYSY_UID)
where UID is your AIPS user number in decimal.
The first column in each file is the UT in days.
The second column is the frequency.
An integer follows each quantity for each antenna.
A zero indicates that value is good, anything else
indicates that that value was flagged by the on-line
system (e.g. if the telescope was not on source).
If you have multiple frequencies in the data, you can
use FREQSEL and IFSEL to select only one, otherwise data
from all frequencies will be put into the one file.
Note however, that the utility program ``pltsys''
provided at the ATNF for plotting the text files
produced by the 'SYSC' option, has frequency selection,
and it is quicker to load all frequencies with ATLOD and
then select the ones you want to plot with ``pltsys''.
Use SOURCES to select the desired sources (note that
Tsys will vary from source to source).
Use TIMERANG to select by time.
All other selection parameters are inactive in this mode
See CPARM(9) for more details of other possible
output files.
FREQSEL Allows you to select a number of frequencies. They
should be specified in MHz. This apples to simultaneous
and time cycled frequencies. They are matched to the actual
frequencies in the data with a 1 KHz tolerance.
If you select frequencies that come from data with different
numbers of channels or polarizations, they cannot all go in
the one AIPS file. ATLOD will discard any frequencies that
are inconsistent with the attributes of the AIPS uv file.
You will be notified as this happens. You will have to run
ATLOD as many times as you need output files to deal with
this sort of data.
IFSEL Allows you to select a number of IFs. The combination of
FREQSEL and IFSEL should offer sufficiently flexible selection criteria
to deal with all cases. The ATCA produces one or two IFs.
Generally, spectral-line observers will use 1 IF, and continuum
observers two. It is possible, although not recommended, to
observe both IFs at the same frequency. If your correlator setup
was such that you had different numbers of channels in the two
IFs, then the two IFs would need to go into separate AIPS files.
In this case, FREQSEL would be insufficient to discriminate between
the two IFs and you would need IFSEL to pick out one or the other.
It may also be useful if you are time switching frequencies
but only want one IF to be loaded. With just FREQSEL you
would need to list all the desired frequencies, with IFSEL
you just select the IF number, 1 or 2.
Data are selected accroding to FREQSEL *and* IFSEL.
CHANSEL Channel selection array: 0 => Load all channels. Up to
10 groups of channels may be selected. CHANSEL(1,n) selects
the begin channel, CHANSEL(2,n) selects the end channel, and
CHANSEL(3,n) selects the channel increment for group n. If
all of CHANSEL(1:3,n) are 0, then no more groups are accepted.
Otherwise, the defaults are CHANSEL(1,n)=0 -> 1, CHANSEL(2,n)=0
-> NCHAN, CHANSEL(3,n)=0 -> 1.
Generally, unselected channels are LOADED but FLAGGED.
An important case in point is when you also set DOUVCOMP = 1
which means the visibilties are stored as scaled 16 bit integers.
If you have a strong birdie in a certain channel, you can deselect
it with the CHANSEL array. E.g., the bad channel is 10. Set
CHANSEL=1,9,1,11,33,1 to load channels 1-9 and 11-33. What this
really means is that all channels are loaded but channel 10 is
flagged. In addition, channel 10 is not used to work out the scale
factors for the visibilty on conversion to 16 bit integers, so that
your dynamic range is not compromised in the good channels.
Note that if only one group of channels is specified, channels
are actually dropped rather than flagged. Thus, CHANSEL=7,29,2
would load only the odd channels from 7 to 29. In the FQ table,
you would see that the channel increment has been doubled to
reflect this selection. However, the total bandwidth would reflect
only the actual channels that were loaded. Really, there should
be a channel separation AND a channel increment, but AIPS does
not support this. You will also note in the header (IMHEAD)
that the frequency reference pixel will also have changed
to reflect the new size of the frequency increment.
IFMAP AT data may have up to four simultaneous frequencies, but
generally you will see only two. Let us call these ``IF chains''.
Contemporaneous data is located within the AIPS uv file on the
IF axis (if the number of channels and polarizations is equal).
When IFMAP is true, (+1) then IF chain 1 will ALWAYS turn up on
the IF axis in location 1, and IF chain 2 at location 2. However,
you might select, with FREQSEL, only the IF chain 2 frequencies.
In this case, you would want them to go to IF axis location 1,
otherwise you would waste a lot of disk space by having an empty
IF axis location 1, followed by your data in IF axis location 2.
When IFMAP is false (-1), then ATLOD will put the next frequecy
it encounters in the next available IF axis location, regardless
of the on-line IF chain that it came from.
I suggest generally you leave IFMAP as false (-1). See the
example after the discussion of NIF below for an example
where you might set it to true (+1).
NIF Normally, ATLOD will work out the length of the IF axis
based upon the information present in the first scan header that
is consistent with the user's selection crteria. However, it
may be you know more than ATLOD and need to tell it the length
of the IF axis.
Consider the case where you have an observation such as
IF chain 1 IF chain 2
Scan 1: 4700 8300
Scan 2: 4600 8000
Let us say you set FREQSEL=4700,4600,8000, thus omitting
the 8300 frequency on IF chain 2. Now, you MUST set NIF=2
to get all these frequencies loaded. ATLOD notes that you
want one frequency from the first scan, and that it would
go to IF axis location 1. But this is the only information
it has when it reads the header for the first scan, which
is when it must build the attributes for the output file.
It doesn't know that the other specified frequencies are
is succeeding scans and that they will need an IF axis of
length 2. Thus, you must set NIF=2. IF axis location
2 for the first scan will get filled with dummy visibilities
of zeros.
Note, that if you set FREQSEL=8300,4600,8000 instead, and
IFMAP=-1, then the 8300 frequency would be put onto IF axis
location 1. However, if IFMAP=1 then it would go to
location 2, and location 1 would be zero filled instead.
DOUVCOMP For large data sets, you may wish to compress the
data format. This saves disk space, but loses dynamic range.
The task UVCMP can switch between compressed and uncompressed
formats. Uncompressing compressed data does NOT recover
that lost dynamic range
APARM(1) If > 0, convert VV, HH, VH, HV, polarizations to Stokes
IQUV. The format of raw AT data is linear polarizations.
At some stage this must be converted to the Stokes parameters
IQUV for imaging. Because AIPS does not deal very well with
linear polarization data at present, and for other reasons too,
we encourage you to use this option and convert to IQUV.
Note that the VV and HH gains must be roughly equal (< 10 percent)
for this to work properly if any of your sources are
polarized. Check this by loading an unpolarized and strong
source (e.g. 1934-63) with no Stokes conversion and compare
plots of VV and hh for individual baselines (to do this you
need APARM(1)=-1. See below.
If < 0, ignore actual polarization order and type and call
them RR,LL,RL,LR. This is for cases where you actually want
to load the data in their raw form, but in order to get many
of the plotting functions in AIPS to work, we need to trick
AIPS and call them something it knows how to recognize.
Calibrating VV and HH independently assumes that the
calibratirs are unpolarized.
APARM(1)=0 means load the data as they are with no Stokes
conversions or naming tricks.
See also APARM(10) for a bit more fiddling about.
APARM(2) If > 0 then retain all visibilites that the on-line
system flagged as bad. These usually occur for data taken
when the system is not yet on source, or for errors detected
by the correlator. You would want to be desperate for
visibilites to turn this one on.
APARM(3) If > 0 then autocorrelations are retained. At
present, these contain nothing useful and there is no point
to hanging on to them. When they become useful, the default
will be change to retain them.
APARM(4) The shadowing criterion is currently fairly simple and
is a geometric calculation for sources at the pointing
centre. For a given shadowed baseline, the shadowed antenna
is found, and all visibilities involving that antenna
dropped. Note the EW nature of the ATCA is used for
the shadowing calculation, so you must disable the shadowing
check for LBA data (see below).
If = 0 the shadowing is computed for 22 m diameter dishes
If > 0 the shadowing is computed for A(4) m diameter dishes
If < 0 the shadowing check is disabled
Increasing A(4) above 22 provides as more conservative
criterion.
APARM(5) The index (NX) table contains information about
where scans begin and end (times and visibility numbers).
This allows rapid access to the data base. A new index
record is always started for a source change.
If = 0 then begin a new index entry if a gap longer than
10 minutes occurs in the data.
If > 0 then then begin a new index entry if a gap longer than
A(5) minutes occurs in the data. Minimum allowed is 1
minute.
APARM(6) If = 0 then start a new index entry if an
uninterrupted section of data on the same source is longer
than 60 minutes.
If > 0 then start a new index entry if an uninterrupted
section of data on the same source is longer than A(6)
minutes. Minimum is 1 minute.
APARM(7) ATLOD will also create the pristine calibration (CL)
table. It consists of 1s (Real part of gain) and 0s
(imaginary part of gain). Later, as the calibration
procedes, new CL tables will be created by applying
corrections to CL table 1. The frequency of CL table entries
sets the fundamental time scale on which you can make gain
corrections, when you work entirely within multi-source
files. That is, when doing self-calibration, it would be
pointless having solution intervals smaller than the CL table
entry interval. If you split off single source files, the
fundamental gain change time scale that you can add is the
integration time (10 seconds). Self-cal is often done on
time scales of a couple of minutes or maybe less (depends on
the S/N), so you should bear this in mind.
If = 0 then a new CL table entry will be created every 3
minutes.
If > 0 then a new CL table entry will be created every
APARM(7) minutes. The minimum is 1 minute.
APARM(8) The Tsys correction attempts to correct for gain
changes that occur faster than you observe calibrators. It
is measured every integration by comparing the switched noise
source of known power with the total power for each X and Y
feed on each antenna. It is this number that is used to
normalize the signals before they are transformed into
digital signals in the samplers -- the samplers require input
signal levels that are steady. The correlation function is
the rescaled by Tsys. Since Tsys is worked out from a single
integration it is noisy. It is preferable to apply a less
noisy Tsys correction.
If APARM(8) = -1, the the on-line correction, if any, is
undone, and the Tsys correction is redone with a nominal
50 K system. This is the same as no on-line Tsys correction
If APARM(8) = 0, no additional changes are made to the Tsys
corrections.
If APARM(8) > 1, then APARM(8) integrations will be used to
determine the running Tsys mean.
Some data are too old for the offline Tsys correction
(earlier than 13-Aug-90), you will be warned if this is the
case. The algorithm attempts to deal with frequency and
source changes (Tsys may jump if the source is bright enough)
as well as unexpected drifts or jumps.
APARM(9) If you have requested Stokes conversion (APARM(1)=1)
then the phase difference between the X and Y feeds on each
antenna is used. Essentially, VV and HH must be summed in
phase to form Stokes I. These VH phases are noisy and
APARM(9) allows an averaged value to be used.
If APARM(9) = 0 then no averaging of the XY phases is done
and no checks for bad values are made
If APARM(9) > 1 then the XY phases are averaged over APARM(9)
integrations
APARM(10) The XY phase differences for each antenna are
measured from a noise diode every integration. Dropouts in
normal AT visibilities generally correlate with dropouts in
the XY phase difference for at least one of the antennas
involved in the baseline. If your source is very weak you
cannot detect these dropouts by visual inspection. However,
the XY phase difference is always measured.
If > 0 then visibilities are dropped when the XY phase
difference is bad. The XY phase is deemed bad by comparing
it with the running mean and the width of a stack of
accumulated phases (see APARM(9)).
If < 0, then in addition to first being marked as bad by the
algorithm which compares the current point with the stack
mean and width (see above), the point is finally only called
bad if it is greater than ABS(APARM(10)) DEGREES from the
stack mean as well. Note that if you are using the XYPHASE
array (CPARM(4)=1), then the values in it are used as the
stack mean instead of the on-line values. This provides for
a simple means of flagging on the basis of XY phases if you
have gone to the trouble of plotting them up.
If = 0 then no dropping of visibilities is done. If you have
also selected to convert to Stokes, ATLOD will replace what
it thinks are bad XY phases with the stack average (see
APARM(9) and below). However, visibilities involving the
antenna with the bad XY phase are likely to be bad.
CPARM(1) If = 1 then lots of information can be printed that
is used in the conversion to IQUV. XY phase difference,
Tsys and parallactic angles are listed.
If = 2, then the user is told when the XY phases or Tsys
values appear to have drifted since the last freq
or source/freq combination, respectively, was observed.
The accumulations of these quantities are reset when this
happens. Otherwise, the current accumulations would reflect
the wrong values.
If = 3, then the information from 1 + 2 is printed
CPARM(2) If the conversion to IQUV does not look correct, try
turning this on AND come and talk to me (NEBK).
CPARM(3) If true, negate the visibilty phase as it is read in.
There was a problem with early AT data sets which produced
inverted images. The phase had the wrong sign, so you can
change it here. Only data from 1989 is likely to be
affected.
CPARM(4) Use the XYPHASE array rather than the on-line values.
CPARM(5) When not converting to Stokes IQUV, you can optionally
apply the VH phase to the H gains. Thus, the HH phases would
be rotated to those of VV
******* NB ********
A trap here is that applying XYPHASEs of zero degrees, is different
from NOT applying any XYPHASE. Thus, let us say you use the 'SYSC'
option to plot up your XYPHASEs, and you see that they are all
close to zero. However, because, internally, ATLOD adds pi to the
XYPHASEs (to bring them to the same convention as Miriad), applying
an XYPHASE of zero is different from not applying them. If you
want to apply the XYPHASEs, you should ALWAYS do it, even if they
are apparently close to zero.
CPARM(6) The sampler statistics for each antenna have well
defined ideal values. The correct values are 50 percent for the
zero level statistic. For the positive and negative level
statistics, they should be 17.1 percent for data taken before
21/8/93, and 17.3 percent thereafter.
If the samplers are out of range, it indicates that the
data will be scaled incorrectly, although the spectrum
may look fine. A tolerance of about 5 percent is about all that
one should tolerate on these statistics.
A particular case is that of interference, which may drive
the samplers to their rails. This would produce
uncalibratable data but would be hard to flag otherwise.
If = 1, then when the sampler statistics are out of
range, a warning is issued to the user. The default
is that the samplers must be within 5 percent of the correct
value.
If = 2, then baselines involving antennas with out of range
sampler statistics are dropped. The default is that
the samplers must be within 5 percent of the correct value.
If = 3, then 1 and 2 above are done.
If = 4, then the data are CORRECTED for the error in the
sampler statistics when they are within the tolerance
of the correct value. The default is that the sampler
statistics must be within 12 percent of the correct value in order
that the correction can be made. Any visibilities outside
of this range will be dropped. In addition, the correction
can only be made of the zero statistic is within 5 percent of 50 percent
and if the difference of the positive and negative statistic
is within 5 percent. Data outside of this range will again be
dropped. Note also that the sampler correction is for
small correlation coefficients only. Thus, autocorrelations,
if loaded, are not corrected. Similarly, if you have visibility
amplitudes of the order of 50 Jy, they should not be corrected
either.
CPARM(7) The internal setting for the acceptable tolerance in
the sampler statistics is 5 percent if C(6)=1,2 or 3 and 12 percent if
C(6) = 4. If you want a different TOLERANCE, set CPARM(7)
to this value.
CPARM(8) AIPS normally converts adverbs to upper-case, so
reading files with lower-case names is impossible. Files on
VAX disks, available to unix via multinet, are seen by
default on a unix system as lower-case. If CPARM(8) is set
true, ATLOD converts the string in DATAIN back to lower-case,
before reading the file.
CPARM(9) If you set OPTYPE='SYSC' then information from
the SYSCAL group is written into three text files for
you to examine it (3 is the maximum number of text files
that can be open at one time in AIPS).These files go
to the $FITS area. Each file contains 14 columns, the
first is the time, the second the frequency, and the
next 12 are the quantity and a flag for each antenna.
A flagf of 0 means the data are good, a flag > 0 means
the on-line system flagged it bad (e.g. not on source
for Tsys)
If C(9) = 1 the files contain the XY phase differences
(XYPHS_UID), the X (TSYSX_UID) and the Y (TSYSY_UID)
feed system temperatures.
If C(9) = 2 the files contain the X sampler statistics.
The negative (XSSNEG_UID), zero (XSSZER_UID) and
positive (XSSPOS_UID) statistics are each put into
a separate file.
If C(9) = 3 the files contain the Y sampler statistics
(YSSNEG_UID, YSSZER_UID, YSSPOS_UID).
Any other value => 1 UID is your AIPS user number
XYPHASE The on-line XY phases for each antenna, are still quite
often very poor, especially at 13 and 20 cm. We believe that
these phases shoudl be constant over the observation. If
you have a better estimate of the XY phase than the on-line
value, you can put it in here, and set CPARM(5)=1.
You might use OPTYP='SYSC' to write the XY Phases to a text
file and examine them. Then input into the XYPHASE array,
the mean value for each antenna. If you have more than one
frequenciy in the file, then you can input 6 XYPHASEs for
the first frequency and then the next 6 for the second
frequency.
We need to associate the correct XYPHASE with the correct.
frequency. The order in which to input the XYPHASEs is the
order in which they list in the FQ table.
Thus, first 6 phases for IF 1, FREQID 1, then IF 2 FREQID 1,
and so on to IF n FREQID 1. Then start on FREQID 2 and so on.
Note that if IFMAP=-1 the location of a frequency on the IF
axis does not necssarily reflect its on-line IF chain value.
You should know what you are doing here in the more complicated
cases. See me if unsure (NEBK).
You must always specify 6 values if you are going to specify
values for more than one frequency. This is true even if
antenna 6 is not in use for your observation.
SPace for up to 6 frequencies is provided. This would require
thirty numbers
DPARM(2) If > 0, then the spectra are three point Hanning smoothed.
The real and imaginary spectra are smoothed separately. The
smoothing occurs before channel selection, so that you can
smooth the data, and then drop every second channel say. This
is appropriate for spectral-line observations where adjacent
channels in the spectrum are intiially independent, but the
raw spectrum is still convolved by a SinC function which will
cause sidelobes about narrow spectral features.
DPARM(3) ATLOD has always written the weights for each visibility
as 1.0. However, as of ATLOD version 03/mar/94, and for data
taken after 22/feb/04, it now by default sets the weights
to the integration time divide by 15 sec. This includes
allowing for time losses such as the blank and hold times.
If DPARM(3) > 0 then the weights will be set to DPARM(3).
So if you wish the weights to still be unity, set DPARM(3)=1
If you wish to concatenate with some old data with weights=1,
you should use the REWEIGHT adverb of DBCON accordingly
SHOW and TELL are implemented for ATLOD. Type
AIPS> SHOW ATLOD
to see which adverbs you can change while ATLOD is running.
Set their values appropriately, and then type
AIPS> TELL ATLOD
to inform ATLOD of your intentions. ATLOD receives TELL
information in two places. The first is after each specified file
has been skipped (NSKIP). Thus you could change NSKIP if
you wish. The second is after each scan has been read into
AIPS. ATLOD will inform you when it receives a TELL command.
Here are the adverbs you can change.
OPTELL Operation ('CHAN', 'QUIT', 'ABOR')
NSKIP Number of tape files to skip
NFILES Number of tape files to load
BCOUNT First scan to read
NCOUNT No. scans to read
SOURCES Source selection list
TIMERANG Time range selection
FREQSEL Frequencies to select (MHz)
IFSEL IFs to select
set OPTELL='CHAN' to change them.
set OPTELL='QUIT' to have ATLOD finish cleanly at the next
available opportunity. VERY useful if
you suddenly find you asked ATLOD to read
many files from tape, but that you have not
selected any data from the last 10 and don't
want to wait while it finds this out.
set OPTELL='ABOR' to have ATLOD abort
The only one that can run you into trouble is IFSEL. Consider
loading data where you have set IFSEL=0 and IFMAP=-1. Let
us say IF 1 goes to IF axis 1, and IF 2 goes to IF axis 2.
Now, with TELL, you change IFSEL=2,0 ATLOD then finds on the
next scan that you don't want IF 1 any more, but that you do want
IF 2. It sees that IFMAP=-1, which means put the data on the
first available IF axis location. Thus, IF 2 will now arrive
in IF axis 1. Ths would be a bit of a mess.
However, if you set IFMAP=1 in this case, IF 2 would still go to
IF axis 2 and all would be well.