ADDCLO

ADDCLO creates a copy of a MERGE-format file, computing the closure phases from the visibility phases in the input file. If the input file already includes closure phases, they are ignored. Alternatively, the program can be used to delete the closure phases from a file (specify OPCODE=D).

Algorithm: The program computes closure phases for all possible station triangles LMN (L < M < N) for which baselines LM, MN, and LN are present in the input file. The closure phase CLPHS(LMN) for triangle LMN is defined in terms of the visibility phases PHS(LM), PHS(MN), and PHS(LN) on the constituent baselines by

      CLPHS(LMN) = PHS(LM) + PHS(MN) - PHS(LN),

and the error estimate for the closure phase is the quadrature sum of the error estimates of the visibility phases. The closure phase is reduced modulo 360° to the range -180° to +180°. The closure phase is undefined if any of the constituent visibility phases is absent or deleted (flagged).

This program can be used to generate the closure phases for programs that need them (e.g., VISPLOT). Most programs use only the baseline visibility phases; exceptions are programs AVERAGE and PHASE. AVERAGE should be used with great care: it averages both the visibility phases and the closure phases (separately), and this operation can produce visibility phases that are no longer consistent with the closure phases, if for example the visibility phases run through a large fraction of a cycle in the averaging period. Assuming that the closure phases have been correctly averaged, and are self-consistent, program PHASE can be used to generate a set of visibility phases that are consistent with the closure phases.

Example

% addclo
INPUT  = T1.MRG
OUTPUT = T2.MRG
OPCODE = D
/

Parameters

Parameters INPUT and OUTPUT must be specified; the others are optional. The parameters names can be abbreviated to uniqueness (minimum match). All the parameters are character strings, but they need not be enclosed in quotation marks unless they include commas or blank spaces. End the list of parameters with a slash (/).

INPUT = "filename": the name of the input merge-format file. This parameter must be specified; there is no default. e.g., INPUT = /citscr/tjp/b2/T1.MRG
OUTPUT = "filename": a name for the output file created by ADDCLO. This parameter must be specified; there is no default.
OPCODE = "C" or "D": specify "C" to calculate closure phases, "D" to delete closure phases. The default is "C".
HISTORY = "text": a character string to be written in the "history" section of the output file; this is optional. e.g., HISTORY = "Closure phases deleted to conserve space"

Limitations

The maximum number of stations is 40; otherwise, all MERGE files with format 1 or 2 should be acceptable.

History

Version 1.0: 1986 Mar 17 - new program (T. J. Pearson).
Version 1.1: 1986 Apr 1 - correct error in output parm REC1(7).
Version 1.2: 1986 Nov 15 - omit unnecessary history records.
Version 1.3: 1987 Dec 3 - use MKHIST subroutine.
Version 1.4: 1988 Jun 21 - use VLBOPE subroutine.
Version 1.5: 1990 Nov 13 - remove unused variables.
Version 1.6: 1991 May 15 - increase to 40 stations.

Tim Pearson, California Institute of Technology
tjp·astro.caltech.edu