Browse the documentation available below to know more about the LWS. A lot of new information about the instrument calibration is constantly put on-line !

• Upcoming LWS Pipeline (OLP) Version 8; main changes with respect to previous versions:

• Improved glitch identification and removal
• The temporal responsivity drift is treated differently.
• Improved Fabry-Perot data processing
• Updated flux uncertainty estimates.


Click here for more detailed information about these changes.

Q. How these changes affect the data quality ? Should I reprocess my data ?
A. The Fabry-Perot data processing in the OLP is now approaching the quality of treatment done in LIA with routine FP_PROC. Since you have probably used LIA to analyse your OLP 7 Fabry-Perot data, doing the job again with OLP 8 reprocessed data will not significantly improve the final product.

The temporal responsivity drifts are now correctly estimated. This brings back a problem you may have with data from faint sources. Indeed, the drift is estimated after Dark Current subtraction, meaning that for a faint sources the signal is dangerously close to 0; this implies that the estimated drift correction might cross 0, and the calibrated fluxes may be incredibly (and erroneously) high in that case.  Again, this may impact you only in case of a faint source (less than 100 Jy).  If you analysed your OLP 7 data with LIA and reprocessed them with SHORT_AAL using the /nodrift or /newdrift options then there are no problems. If, against our recommendations, you worked on OLP 7 data (remember, this only applies for faint sources) without using LIA, OLP 8 data will continue to give you problems. In essence, the drift correction applied in OLP 7 was wrong, but the one applied in OLP 8 could corrupt the calibrated spectrum. Please, check the on-line LWS data reduction recipes for recommendations about LWS data processing.

• Flux Uncertainties in OLP 8. The flux uncertainties contained in the calibrated data file LSAN (which in ISAP are stored in the variable STDEV) only contain an estimate of the calibration uncertainties at the different wavelengths; they are not related to the statistical noise of the data. In particular, the calibration uncertainties

 
 

contain:
 

• the uncertainty in the dark current estimate during the observations of the primary calibrator (Uranus)
• the uncertainty in the responsivity estimate during the observations of the primary calibrator
• the statistical uncertainty of the data collected toward the primary calibrator
• for Fabry-Perot observations only, the uncertainty in the FP transmission and size of the FP spectral element.


do not contain:
 

• the uncertainty on the adopted calibrator model.


Important: In OLP 8 the flux uncertainties are expressed in the same units as the fluxes, i.e. W cm^-2 um^-1 . In OLP 7 the uncertainties were expressed as a squared percentages of the flux values, i.e. the values given as the uncertainties were [DF/F]² .

- Documentation

• The ESA LWS Intrument Page - Essential information about the instrument, its operating mode and its data. You will find documents like the ``LWS Instrument Manual'' (from pre-launch, but still useful for an overview of the instrument), the ``LWS Instrument Data User Manual'', and a lot of useful links to calibration reports and updates; you can view some of them here too:

 
• Instrument status. SPIE paper by B. Swinyard et al. 1998.
• The report on Fabry-Perot wavelength calibration, by S. Pezzuto.
• The report on Absolute Flux Accuracy for Grating observations, by T. Lim & M. Burgdorf.
• The report on Grating Wavelength Calibration, by C. Gry & E. Tommasi.
• Details about the performance of LWS detectors in space, by B. Swinyard et al.

• ISO Explanatory Library - Same information as above, organized by subject.
• Notes and comments about the LWS Fringes and about the detector glitches from Cosmic Ray impacts.
• On-line Notebook  from the IPAC ISO LWS Workshop (July 1997)

• LIA : The LWS Interactive Analysis Package - This is what you need to inspect and possibly improve the quality of your data. New LIA Version 10.3 released 1 Sept. 2003 Details here