EXTINCTION - Remove the effect of atmospheric extinction from a SCUBA observation

Description:

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.

Usage:

extinction in sub_instrument first_tau first_lst second_tau second_lst out

Parameters:

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.

Examples:

extinction flat long 0.24 '01 00 00' 0.3 '02 00 00' corr

Process the LONG sub-instrument from flat.sdf using the knowledge that the 850 tau (assuming LONG refers to the 850 micron filter) was 0.24 at 1h LST and 0.3 at 2h LST. The output is written to corr.sdf

extinction test short 0.6 0 0.6 0 test2

Process the SHORT sub-instrument from test.sdf assuming a constant tau of 0.6 (since FIRST_LST = SECOND_LST) and write the result to test2.sdf

Related Applications

SURF: rebin, scuphot, skydip, scuquick