IRFLAT-Generates a ripple spectrum from an IR spectrum

Description:

IRFLAT generates a ripple spectrum from an IR spectrum. In principle, the (raw or ratioed) data can then be divided by this ripple spectrum to take out the effects of different detector responses, which produces a periodic pattern on the continuum of the data (with period equal to the number of detectors).

Parameters:

SPECTRUM

Spectrum containing data.

CGS2

Flag indicating whether to operate in 'CGS 2' mode.

PERIOD

Period of the ripple (pixels).

OUTPUT

The name of resulting ripple spectrum.

XSTART

First X value for region to be used.

XEND

Second X value for region to be used.

MORE

Include additional ranges? (If TRUE the prompts for XSTART and XEND are repeated for another region.)

Source comments:

 I R F L A T

 Figaro function that produces a "flatfield" ripple
 spectrum from a infrared  spectrum, by averaging the data from
 regions of the spectrum uncontaminated with spectral features
 (i.e. assumed flat) to determine the relative response of each
 detector or scan. The output spectrum can be divided into the original
 spectrum using IDIV to flat field the data.

 The program is used to remove two kinds of ripple from spectra.
 In instruments which interleave a number of scan positions to give
 a fully sampled spectrum (such as CGS3 and CGS4), the program removes
 ripple which results from seeing or transparency fluctuations between
 scan positions. In an instrument such as CGS2 it can remove the ripple
 which results from the fact that the flatfield (i.e. relative detector
 responses) is different for extended and point sources. In the case of
 CGS2 data it makes use of a .MORE.PIXELS extension in the data which
 specifies the detector and scan position corresponding to each pixel.
 If this structure is not present it prompts for a period and assumes
 a periodic ripple. The period will normally be the oversampling factor,
 typically 2 or 3 for CGS4 or CGS3 data.

 If the program is run in batch only one region can be specified.
 Multiple regions can only be specified in interactive mode.

 Command parameters -

 SPECTRUM    (Character) The name of the file containing the
             spectrum to be used.
 CGS2        (Logical) Flag indicating whether to operate in 'CGS 2'
             mode.
 PERIOD      (Real) The period of the ripple (in pixels).
 OUTPUT      (Character) The name of the resulting ripple spectrum.
 XSTART      (Real) First X value for region to be used.
 XEND        (Real) Second X value for region to be used.

 Command keywords -

 MORE        If YES, the prompts for XSTART and XEND are repeated for
             another region.

 10th Dec 1990 - JAB / JAC