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Subsections
9. Getting started with LWS data
9.1 How to read to data
The files on the CD-ROM are ordered into subdirectories. For each
observation there is a separate subdirectory on the CD-ROM (see the
README file and the DATALIST file for more details). Many of the
products are written in Binary FITS extension format (see
chapter 8 for details on the file formats for LWS data).
To read the data products observers can use several tools.
- The IPAC first look tools
- These are available from IPAC
and allow the user to read in the FITS files, and create ASCII
files from them. These tools are available for Sun/Solaris 2.4,
Sun/SunOS 4.1.3, Dec/Ultrix 4.4, PC/Linux, Dec/Open VMS AXP V6.1.
The tools can be downloaded from IPAC, see their worldwide
web page:
http://www.ipac.caltech.edu/iso/iso.html
- The ISO Spectral Analysis Package (ISAP)
- This is an analysis
package that was specifically written for LWS and SWS data. It can
read in the product files and write a FITS file or an IDL save set.
This package requires IDL4 (for ISAP 1.4) or IDL5 (for ISAP 1.5).
The routines in ISAP have been tailored to reduce LWS data. The package
was written jointly by IPAC, the LWS instrument team and the SWS
instrument team. ISAP allows the user to flag or delete data points
that are clearly wrong (due to undetected glitches for instance), average
scans (using different averaging routines), to scale the detectors
to make smooth spectra, to rebin spectra to a standard wavelength
scale, and to subtract an off spectrum from an on source spectrum.
ISAP can be downloaded from one of the following websites:
http://www.ipac.caltech.edu/iso/isap/isap.html
http://www.mpe.garching.mpg.de/iso/isosdc.html
- The LWS Interactive Analysis (LIA)
- This package is written as
a set of IDL routines, to be used together with ISAP. The routines are
written to allow the user to redo all or part of the automatic processing
in an interactive way. It also allows some extra functionalities,
like the strong source correction and the interactive FP responsivity
correction. It also allows the user to tailor the processing somewhat
to his needs (for instance for darkcurrent removal). LIA can be downloaded
from the same sites as ISAP.
- IDL with the astronomy library
- Using IDL with the astronomy
library, the observer can write his own code to read the data files,
using the information in this IDUM (chapter 8).
Below are some IDL commands that can be useful.
To read the FITS primary header in variable hdr_prime:
hdr_prime=headfits('<filename>')
To read the binary header into variable hrd_bin:
fxbopen,unit,'<filename>',1,hdr_bin
To read the data from column N into variable X:
fxbread,unit,X,N
A longer note on the use of IDL and the Astro Library to read LWS
data can be found on the IPAC WWW pages (see above).
9.2 Where to find instrumental calibration parameters (SPD calibration)
The following table (9.1) gives the calibration files
where the observer can find the instrumental
calibration parameters that are used during the Derive-SPD process.
The table also gives the reference to the table that describes the calibration
file in this document. The descriptions of these calibration files are
given in section 8.2.6. The
list is given in alphabetical order.
Table 9.1:
List of instrumental
calibration parameters used in Derive-SPD.
Parameter |
File |
Table |
page |
Analogue amplification gains |
LCGA |
none |
|
Detector amplifier (JF4) capacitances |
LCJF |
8.21 |
|
Detector amplifier (JF4) gains |
LCJF |
8.21 |
|
Detector read out to voltage conversion |
LCVC |
none |
|
First level deglitching parameters |
LCD1 |
8.23 |
|
Maximum voltages on the detectors |
LCDB |
8.22 |
|
Readout limits of the electronics |
LCAL |
8.20 |
|
Time periods to be ignored after a reset |
LCDT |
8.19 |
|
|
9.3 Where to find astronomical calibration parameters (AA calibration)
The following table (9.2) gives the calibration files
where the observer can find the astronomical
calibration parameters that are used during the Auto Analysis process.
The table also gives the reference to the table that describes the calibration
file in this document. The descriptions of these calibration files are
given in section 8.2.9. The
list is given in alphabetical order.
Table 9.2:
List of astronomical
calibration parameters used in Auto Analysis.
Parameter |
File |
Table |
page |
FP wavelength calibration coefficients |
LCFW |
8.34 |
|
FPL positions for response curves |
LCLRZ |
8.36 |
|
FPL relative response curves |
LCLR_ n |
8.35 |
|
FPS positions for response curves |
LCSRZ |
8.38 |
|
FPS relative response curves |
LCSR_ n |
8.37 |
|
Grating relative response curves |
LCGR |
8.32 |
|
Grating spectral bandwidth correction |
LCGB |
8.39 |
|
Grating wavelength calibration table |
LCGW |
8.30 |
|
Standard Illuminator photo currents |
LCIR |
8.29 |
|
|
Next: 10. Post-processing
Up: ISOLWS DATA USERS MANUAL
Previous: 8. Guide to instrument
ISOLWS Data Users Manual, Issue 5.0, SAI/95-219/Dc