[daip] CLCOR

[Lynn D. Matthews]

I am having some difficulties in understanding what CLCOR is doing when it
makes a position correction.

I notice that there was a change back in March in how CLCOR does position
corrections, but I thought this should be a second order effect and not
explain what I'm seeing.

Previously I would expect to enter a position offset using CLPARM(5,6)
and OPCODE = 'ANTP' and find that those were the offsets that would appear
in the history file. However, now I notice that in at least some cases,
the numbers in the HI file are very different from the inputted values.
For example, the history file reports:

  1594  CLCOR   CLPARM(5,6) =   0.0214  -0.0087 / Source position error

when my inputs were as below:

AIPS 1: CLCOR     Task which applies various corrections to
CL tables.
AIPS 1: Adverbs     Values                 Comments
AIPS 1: ----------------------------------------------------------------
AIPS 1: INNAME     'BG118H'                Input UV file name (name)
AIPS 1: INCLASS    'CVEL'                  Input UV file name (class)
AIPS 1: INSEQ         2                    Input UV file name (seq. #)
AIPS 1: INDISK        4                    Input UV file disk unit #
AIPS 1: SOURCES    'BNKL-I'                Source list ' '=>all.
AIPS 1:            *rest ' '
AIPS 1: STOKES     ' '                     Stokes type to process
AIPS 1: SELBAND      -1                    Bandwidth to select (kHz)
AIPS 1: SELFREQ      -1                    Frequency to select (MHz)
AIPS 1: FREQID       -1                    Freq. ID to select
AIPS 1: BIF           1                    Lowest IF number 0=>all
AIPS 1: EIF           2                    Highest IF number 0=>all
AIPS 1: TIMERANG   *all 0                  Time range to use.
AIPS 1: ANTENNAS      1           2        Antennas to correct.
AIPS 1:               3           4           5           6
AIPS 1:               7           8           9          10
AIPS 1:              11        *rest 0
AIPS 1: SUBARRAY      0                    Subarray;  0 => 1.
AIPS 1: GAINVER      10                    Input CL table 0=>high
AIPS 1: GAINUSE      11                    Output CL table: not =
AIPS 1:                                    GAINVER -> high+1
AIPS 1: OPCODE     'ANTP'                  Operation code.
AIPS 1: CLCORPRM      0           0        Parameters (see HELP CLCOR).
AIPS 1:               0           0           0.1012    -0.0781
AIPS 1:            *rest 0
AIPS 1: BADDISK    *all 0                  Disks to avoid for scratch
AIPS 1: INFILE     *all ' '                OPCODE = 'ATMO' or 'TROP':
AIPS 1:                                     list of antennas, times and
AIPS 1:                                     relevant atmosphere vertical
AIPS 1:                                     delay.
AIPS 1:                                    OPCODE = 'SUND'
AIPS 1:                                     list of the planet(including
AIPS 1:                                     Sun and Moon) used in
AIPS 1:                                     the light deflection.
AIPS 1:                                     'BLANK' => SUN
AIPS 1:                                    OPCODE = 'EOPS'
AIPS 1:                                     The FILE can be picked up
AIPS 1:                                     from the webside
AIPS 1:                                     http://gemini.gsfc.nasa.gov/
AIPS 1:                                     solve_save/usno_finals.erp


In fact, for another data set that I corrected on Feb. 28 using a
different position offset, the exact same "Source position error" appears
in the history file:

CLCOR   CLPARM(5,6) =   0.0214  -0.0087 / Source position error

Yet in at least two other recent cases, the inputted offsets are indeed
the ones reported in the history file.

Can you help me understand what is going on?

Thanks,

Lynn Matthews