FET321-Extracts a spectrum from 1 detector from etalon mode FIGS data

Description:

FET321 takes a FIGS data cube, as produced by the FIGS data acquisition system running in etalon mode, and reduces it to a single spectrum, summing up the various cycles and performing the beamswitch and chopping subtractions. Data from only one detector is extracted.

Parameters:

CUBE

The name of a data cube produced by the FIGS data acquisition system. That is is should have the dimensions (wavelength steps,8,beamswitch cycles) The cube should have been taken in Etalon mode.

DETECTOR

In etalon mode, each of the FIGS detectors produces data over a different wavelength range. Rather than produce a single spectrum covering disjoint wavelength ranges, FET321 uses DETECTOR to specify a single detector to be used to produce the spectrum.

SPECTRUM

The name of the resulting single spectrum produced by collapsing down the FIGS data cube.

CUTOFF

Values more than CUTOFF times sigma away from the mean value for the spectral point will not be included in the final spectrum.

ADD

Disables the subtraction of the background beamswitch and chopping data. This is unusual (ADD=NO is the default) and is generally only required for test data.

BACK

Returns the background spectrum only, rather than the background subtracted source data.

NORM

Causes the data for each cycle to be normalized so that the mean value for each cycle is the same. This gives more reasonable errors when data are taken in the presence of cloud. It should not be used on very faint sources, as the mean level may go negative under these circumstances

Source comments:

 F E T 3 2 1

 Given a FIGS data cube as produced by the FIGS data acquisition
 system running in one of the etalon modes, processes it to produce
 a single spectrum, for one of the detectors only.

 Command parameters -

 'CUBE'     The name of the cube from which the planes
            are to be taken.  This should be a raw FIGS data
            cube.
 'DETECTOR' The number of the detector to be used.
 'SPECTRUM' The name of the resulting spectrum.
 'CUTOFF'   The level (in sigma) at which a point will
            be ignored (FIGS321 only)

 Command keywords -

 'ADD'      Add the data together rather than subtracting the
            beamswitch and chop backgrounds

 'BACK'     Return the background spectrum only

 'NORM'     Normalize data to mean level of each cycle.

 Input data -

 CUBE is assumed to have a structure with the actual
 cube data in CUBE.Z.DATA

 This routine assumes that the first axis of the cube data
 represents wavelength, that the second represents spectral
 scans in the order A1a,A1b,B1a,B1b,B2a,B2b,A2a,A2b, where
 A1,A2,B1,B2 represent the parts of the beamswitch ABBA cycle
 and a and b represent the signal and background chop positions
 respectively.  In etalon mode 2, there are no chop positions,
 and the second axis is just A1,B1,A2,B2. This means that the
 second dimension of the cube has to be either 4 or 8.  The
 cube third axis represents beamswitch cycle number.
 The data is normalized to give a figure in detected photons
 per second.  Along the wavelength axis, the data is assumed
 to be in order of etalon position, each etalon position having
 n values where n is the number of detectors used.

 Output data -

 IMAGE is created with the same structure as CUBE
 except that .Z.DATA will only have 1 dimension, and any
 .Y or .T sub-structures that CUBE has will be deleted.
 If a spectrum is produced the errors (derived from
 the cycle to cycle statistics) are placed in the .Z.ERRORS
 component

  5th May 1988  KS / AAO.   Original version, based on FIGS321.