AIPS HELP file for CLVLB in 31DEC24
As of Wed Dec 6 23:42:43 2023
CLVLB: Corrects CL table gains for pointing offsets in VLBI 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 #
FREQID 0.0 Frequency ID number: 0 -> 1
SUBARRAY 0.0 Subarray: 0 -> 1
GAINVER Input CL table version
GAINUSE Output CL table version
CUTOFF -1.0 Minimum allowed beam
Text file containing antenna
TT -1.0 1.0 > 0, use alternative geometry
computation (Enno), else use
BIF DEBUG: print BIF when > 0
ANTENNA DEBUG: print ANTENNA(1) if >0
Task: DiFX correlators are capable of correlating the same input data
at multiple phase stopping positions, each separated from the
direction in which the antennas of array were pointed. For the
tiny fields of view surrounding the antenna pointing position,
the single-dish beam is essentially constant (spatially)
although it will vary in time due to beam squint and other
causes. This task reads an input CL table, computes the
corrections in amplitude for the separate polarizations and IFs,
and applies them to the CL data as a function of time.
Single-dish beam patterns are notoriously hard to compute. This
task assumes a simple model of them. The R polarization and L
polarization beams are assumed to be each circularly symmetric
and separated by equal distances in opposite directions from the
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.
FREQID.....Frequency ID number to do 0 => 1
SUBARRY....Subarray to do 0 => 1
GAINVER....Input version number of the CL table to be used.
GAINUSE....Output version number of the CL table to be written.
CUTOFF.....beam values < CUTOFF cause the solutions to be blanked.
CALIN......Text file giving in order:
1. antenna number (0 -> a default to use for those not
specified in some other way)
2. Azimuth squint (arc min (R - L)
3. Elevation squint (arc min (R - L)
4. Frequency at which 2 and 3 were measured (MHz)
5. Antenna effective diameter (meters)
6. Frequency at which 5 measured (MHz)
7. Change of effective diameter with frequency
Some of these can be recorded in the ANtenna file, but
usually are not. The values for VLBA antennas at L band
are known by the task.
Azimuth squint = V(2) * V(4) / Freq(IF)
Elevation squint = V(3) * V(4) / Freq(IF)
D_effective = V(5) * (Freq(IF)-V(6)) * V(7)
and the beam pattern is a J1(x) / x function where
x = pi * D_effective / lambda * sin(offset)
Some of these must be given to have the task work.
TT.........In order to find the primary beam level, Eric's algorithm
adds the squints to the pointing position (linearly) and
then computes the separation of the 2 squinted positions
and the target (fully non-linearly). TT <= 0.0
Enno's finds the separation and angle from the pointing
position to the target (fully non-linearly) and then adds
the squint parameters (linearly) before finding the
separation (also linearly). TT > 0.0
BIF........If > 0, then do debug print out with IF = BIF
ANTENNA....If ANTENNA(1) > 0, then do debug print out with
ANTENNA(1) and BIF only.
The debug print out shows antenna #, polarization, time number,
elevation (degrees), azimuth (degrees), separation (degrees), and
beam power factor.