4. HOW TO REDUCE SWS DATA

Getting started with SWS AAR data can be broken down into the following steps:

1

Reading the data from CD-ROM into your analysis package

2

Having a quick-look at the data
This usually involves plotting the AAR data as flux against wavelength

3

Selecting data
SWS observations of a source result in data products containing one or more wavelength regions observed in several scans mixed in with internal calibration measurements. The regions of interest must be selected and then checked to ensure they are not contaminated, e.g. by glitches.

3

Re-bin onto equidistant wavelength grid
The assigning of wavelengths to the grating or FP detectors does not involve any re-binning or interpolating. Hence the wavelengths are not on an equidistant grid.

4

Process up-down scans
No combining of up-down scans is carried out by the pipeline. This is because the up part of the scan may have a different zero level from the down part, or a line may have a different shape in the two scans. All scans should be checked to ensure features are present in all and that the scans are not behaving differently. If they do behave differently care should be taken analysing the data and in some cases it may be necessary to throw away any affected data.

5

Join AOT bands together
AAR data spanning two or more AOT bands can be joined together. No attempt is made to do this in the pipeline as the data in different bands may have a different zero level or may be affected differently by memory and pointing effects. Note that observations of extended sources through different apertures are not corrected for the different aperture sizes.

5

Smooth data
Smoothing may be the best option if the AAR data is badly affected by noise or fringes.

ISAP users may also de-fringe and further process their data. The ISAP on-line help should be accessed for further details.