AIPS HELP file for WTMOD in 31DEC22
As of Tue Jun 6 4:24:43 2023
WTMOD: Task to modify weights in a uv data set.
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 #.
SUBARRAY 0.0 Limit to subarray
APARM Control info:
1 = multiplier (0=>1)
2 = power (0=>1)
3 = Max. (0=>infty)
ANTWT -9999.0 9999.0 Replace weights (all ants.)
NOISE Scale weights by antenna
FQCENTER >= 0 -> center frequency axis
Task: This task will modify the weights of uv data as specified by
the user. The purpose is to adjust the weights so that data
from very sensitive baselines will not swamp the less sensitive
baselines. The maximum and minimum weights (in absolute value)
after the modifications will be reported. The output file may
be the input file. The weights of flagged data are also
modified, but they are not unflagged by this program. WTMOD
can flag data, however.
WTMOD can also be used to change system-temperature dependent
weights into constant ones for concatenation with old data
WTMOD handles compressed data finally (8-Feb-2001)! It is
particularly fast since it does not need to unpack and then
repack the data to change the weight.
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.
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #). 0 => highest unique
OUTDISK....Disk drive # of output UV file. 0 => highest with
space for the file.
SUBARRAY...Subarray number to which the operation should be limited.
0 -> do to all subarrays.
APARM......Weight modification control information (ignored if any
ANTWT is not 0.0):
1 = A multiplier for the weights. 0 => 1.0
2 = A power to which to raise the weights; 0 => 1.0
0.25 - 0.5 is a useful range for VLBI.
Weight_out = (APARM(1) * Weight_in) ** APARM(2)
3 = The maximum acceptable value of the weight.
Values higher that APARM(3) will be set to
APARM(3). 0 => infinity.
ANTWT......Replace vis. weights with constant values. A new weight
must be specified for all antennas. (If there are > 30
antennas, the average (abs) value is used for antennas >
30.) Negative values may be used to flag data. Note
that previously flagged data remain flagged, but
otherwise at the new weights.
Weight_out = SQRT (ANTWT(ant1) * ANTWT(ant2)) ignoring
Weight_in except for flagging information (sign).
NOISE......If all ANTWT are zero, then scale the output weights by
NOISE(i) where i is the antenna number. Thus
Weight_out = NOISE(ant1) * NOISE(ant2) *
min (APARM(3), (APARM(1)*Weight_in) ** APARM(2))
NOISE(i) <= 0 -> NOISE(i) = 1.0
and a value of 1.0 is used for all antennas numbered
greater than 64.
FQCENTER...> 0 => Change frequency axis reference pixel to
Nchan / 2 + 1
else => do not change reference pixel