SCULIB_CALC_CLOCKERR - Calculate start up time and error in system clock

Description:

Checks the self-consistency of the FITS headers by calculating the expected LST from the Azimuth and Elevation values stored in the header and comparing this with the supplied reference LST. Returns the difference between the two values and the LST calculated from the headers.

Invocation:

CALL SCULIB_CALC_CLOCKERR( N_FITS, FITS, RA_CEN, LST_REF, CLOCK_ERR, LST_AZEL, STATUS )

Arguments:

N_FITS = INTEGER (Given)

Number of items in the FITS array

FITS() = CHAR$*$80 (Given)

FITS array

RA_CEN = DOUBLE (Given)

Apparent RA corresponding to the Az/El defined in the FITS header. In radians.

LST_REF = DOUBLE (Given)

Local sidereal time at the start of data acquisition. This usually comes from the LST_STRT array. In radians.

CLOCK_ERR = DOUBLE (Returned)

The time difference (in radians) between the times stored in the data file (header items and LST_STRT) and the actual time of the observation derived from the azimuth and elevation of the observed source. The value is the number that must be added to the supplied LST_REF in order to correct it.

LST_AZEL = DOUBLE (Returned)

Local Sidereal time calculated from the azimuth, elevation and apparent RA/Dec (radians)

STATUS = INTEGER (Given & Returned)

Global status. An error will be returned if the observation was not done in a tracking frame (eg NA or AZ) since those frames can not be used to determine the time from the telescope az and el.

Notes:

Requires the following FITS headers to be defined:

• LAT-OBS

• STRT_ELD

• STRT_AZD

• CENT_CRD

The clock error returned must be added to all times read from the data file in order to make those times correct.

The centre coordinates of the observation must corresponde to an astronomical frame. AZ can not be used (for obvious reasons).

Copyright

Copyright (C) 2000 Particle Physics and Astronomy Research Council. All Rights Reserved.