The Standard Product Generation (SPG) (also known as Off-Line Processing (OLP) or simply the `pipeline') processes the raw data telemetered down from ISO (in terms of bits) into more conventional astronomical units of flux against wavelength in a purely automatic procedure. This chapter describes the pipeline and its error propagation. It should give the reader an understanding of what processing has been carried out on the data and why. The ISO Legacy Archive was processed with OLP Version 10.1.
The pipeline is composed of three parts:
Extracting from the raw data stream the instrument data and
placing it into Edited Raw Data (ERD)
files. For SWS this process is a
reformatting step only and will not be discussed further.
ERD to Standard Processed Data (SPD)
stage, known as
Derive-SPD (DSPD). This involves removing all instrumental
effects on time scales of less than 1 reset interval, converting
detector readouts (bits) into slopes
(
V/s) and assigning wavelengths, where possible. Pointing and
instrument status files are also read in at this stage. This
results in a table of corrected slopes, which should be proportional to
the flux density of the target under study, errors and wavelengths in
m. The table is still in time order.
SPD to Auto-Analysis Results
(AAR)
stage, known as Derive-AAR (DAAR). This further processes
the SPD removing instrumental effects on time scales of greater than 1
reset interval and converts slopes to fluxes (Jy). It results in fully
calibrated fluxes as a function of wavelength.
In the course of Derive-SPD and Auto-Analysis several files are used that describe the behaviour of the instrument and its performance. These calibration files are known, for historical reasons, as Cal-G files. They contain such things as the conversion between scanner position and wavelength, the relationship between voltages per second and fluxes, etc.
Examples of the data produced by these steps are given throughout this chapter. In previous chapters examples were given for each of the 4 observing modes of SWS (see Sections 3.3 to 3.6), in raw ERD format or processed to SPD or AAR.
Sections and subsections describe (compound) steps in the pipeline processing. They are in the order in which they occur in the pipeline. Sections 7.2 and 7.3 describe the DSPD and DAAR processing, together forming the complete pipeline. Section 7.4 describes the error propagation for SWS. The last Section 7.5 shortly describes the software elements the pipeline is built of. These elements are runnable procedures within OSIA.