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AIPS HELP file for REWEIGHT in 31DEC18

#### As of Thu Jan 18 20:50:35 2018

### HELP SECTION

REWEIGHT
Type: Adverb (Real(2))
Use: All uv data have associated weights which express the
relative value of the data. Internally, these weights are
treated as statistical weights (i.e. 1 / variance
(amplitude)). These weights are used in making images but
are modified by uniform weighting and tapering. In
practice, the weights coming into AIPS from non-AIPS
calibration systems are in arbitrary units so a
renormalization of the weights may be necessary when data
sets are combined.
The adverb REWEIGHT can be used to modify the relative
weights of the two input data sets. The simplest way to
determine the appropriate relative weighting is to image each
set of data independently in the same fashion as the desired
final image (i.e. using the same IMSIZE, CELLSIZE, UVWTFN,
UVBOX, and UVTAPER but not necessarily doing a deconvolution).
All AIPS imaging tasks report the "sum of the gridding weights"
in the message file. This is the sum of the weights after all
corrections are applied (this value has been written into the
history file since 15JUL89). REWEIGHT is a pair of values to be
multiplied by the input weights for the first (1) and second (2)
input uv data file. These values should be set such that the
two data sets will have the desired relative sum of weights.
For example, if the two data sets before DBCON give a sum
of gridding weights of 1.0E5 and 2.0E2 when imaged by MX AND you
wish to make them contribute equally to the final image then
use: REWEIGHT = 1.0,1.0e5/2.0e2 (or 1, 500).
Null value: 0 will be interpreted as 1.0
Tasks:
DBCON Used to concatenate 2 uv data sets.

### EXPLAIN SECTION