This application extracts from a demodulated-data file data for a specified
SCUBA sub-instrument and corrects it for the effect of atmospheric extinction. The airmass
at which each bolometer measurement was made is calculated, then multiplied by the
zenith sky extinction at the time of the measurement to give the extinction optical depth
along the line of sight. The data point in question is then multiplied by the exponential of
the optical depth to give the value that would have been measured in the absence of the
atmosphere.
The zenith optical depth is assumed to vary linearly with time between the values input in parameters
FIRST_TAU and LAST_TAU. If the measurement was taken at a time outside the range covered by
FIRST_TAU and LAST_TAU then the value closest in time will be used.
FIRST_LST =
CHAR (Read)
The local sidereal time at which FIRST_TAU was the zenith sky opacity,
in hh mm ss.ss format.
FIRST_TAU = REAL (Read)
The zenith sky opacity before the
observation. The default value is the zenith tau value accepted by the on-line system before
the observation.
IN = NDF (Read)
The name of the input file containing demodulated
SCUBA data.
MSG_FILTER = CHAR (Read)
Message filter level. Allowed values are
QUIET, NORM and VERB. Default is NORM. There are no verbose messages.
OUT =
NDF (Write)
The name of the output file to contain the extinction corrected data for the
specified sub-instrument.
SECOND_LST = CHAR (Read)
The local sidereal time at which
SECOND_TAU was the zenith sky opacity, in hh mm ss.ss format. The default value is that
of FIRST_LST (usually the case for a constant tau). If this value is less than FIRST_LST
it is assumed you are referring to the following day.
SECOND_TAU = REAL (Read)
The zenith sky opacity after the observation. The default value is that of FIRST_TAU.
SUB_INSTRUMENT = CHAR (Read)
The name of the sub-instrument whose data are to be selected
from the input file and extinction corrected. Permitted values are SHORT, LONG, P1100,
P1350 and P2000. This parameter is only used if more than one sub-instrument is present
in the file.