AIPS HELP file for UVCRS in 31DEC21
As of Wed Oct 27 23:45:15 2021
UVCRS: Task to find crossing points of UV-ellipses
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 #
BIF IF number; 0 => 1
BCHAN Channel number; 0 => 1
STOKES Stokes parameter; Recognized
values are: 'RR ', 'LL '
ANTENNAS The well calibrated antennas
whose gains are forced to 1
and not corrected
SNVER SN table number;
<0 => SN table is not made
0 => highest
OUTTEXT Name of the file to write the
crossings and ampl. ratios
APARM Control parameters
APARM(1) UVRADX in megalamda;
0 => 0.5
APARM(2) UVRADY in megalamda;
0 => 0.5
APARM(3) 0 => rect. area;
1 => elliptical area
APARM(4) 0 => no print
1 => print results
Task: This task finds the crossing points of UV-ellipses,
calculates the average ratios of the amplitudes at the
crossing points and finds the solution for the gains of
antennas by a least squares approach minimizing the
deviation of the ratios from 1
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.
BIF........IF number; 0 => 1
BCHAN......Channel number; 0 => 1
STOKES.....Stokes type. Recognized values are: 'RR ', 'LL '
ANTENNAS...The numbers of well calibrated antennas whose gains
are forced to 1 and not corrected
SNVER......SN table number; <0 => SN table is not made;
0 => highest;
OUTTEXT....Name of the file in which to write the crossing
points and ratios. Standard form, e.g 'MYAREA:OUT'
where OUT is the name of the file to be created,
and MYAREA is an environment variable defined
before starting up AIPS.
APARM(1)...UVRADX at megalamda; 0 => 0.5
APARM(2)...UVRADY at megalamda; 0 => 0.5
APARM(3)...Type of crossings region; 0 => rectangular;
1 => ellipse
APARM(4)...To print or not some intermidiate results on the
screen; 0 => no print;
1 => print
The program finds all crossings points of UV-ellipses.
The two points from two UV-ellipses are defined as 'crossing'
if the vector connecting them is located inside a given region.
The region can be rectangular or elliptical. The type of the
region and its size are determined by the input parameters
APARM. The logarithm of a ratio of an amplitude of a given point
and the amplitudes of all 'crossing' points of a neighbouring
UV ellipse is calculated. Then the average logarithm of the
ratios for a given point is constructed. Finally all these
logarithms for all crossingspoint of a given UV-ellipse are
averaged. This final average logarithm of the amplitude ratio
is associated with the given pair of baselines. The logarithm
of the amplitude ratios is preferable than the ratios themselves
for several reasons:
1..We have to consider the ratios 0.1 and 10 to be equally bad
rather than 0.1 and 1.9
2..Averaging of logarithms (for ratios close to 1) is equivalent
to averaging of deviations of the ratios from 1.
3..Averaging of logarithm excludes the ambiguity occuring when
we are using the reciprocals of ratios. For example
0.5(1 + 3)=2. But 0.5(1/1 + 1/3)=2/3; And 1/2 is not equal
The same example when averaging logarithms:
0.5(log(1)+log(3))=0.5log(3); average ratio = exp(0.5log(3))=
sqrt(3); reciprocal case: 0.5(log(1)-log(3))=-0.5log(3);
average ratio = exp(-0.5log(3))=1/sqrt(3);
4..The use of logarithms produces a linear system of equations
connecting logarithms of antennas gains and ratios. So we
can use a linear least square method to determine the
solution for the antennas gains minimizing the deviation
of the ratios from 1.
The program prints the results in the OUTTEXT. The sign '?'
before a ratios lines indicates the case of too large a
deviation of the ratios from 1 (RATIO > 2; or RATIO < 0.5).
The second column's integer indicates the number of crossings
that occured for a given pair of baselines. The last two
columns in the table represent the original ratios and the
ratios after applying the solution found for the antennas
If you desire to use the solution for different IFs and
different polarizations you have to run the program for
the first IF and polarization from your list with
'snver'=0 and then repeat the program in consecutive order for
all the polarizations and IFs in your data using the same
number of 'snver'.
1.Number of visibilities less than 50000.
2.Duration of an experiment has to be less than 24 hours