Version 9.0 of the ISO Off-Line Processing (OLP) software released on 18 July 2000

The OLP v9 (including Cal-G v6) has been made available to the community through the on-the-line-reprocessing facility of the ISO Data Archive. The improvements are in three areas: 1) CAM, 2) PHT, and 3) Pointing which are described in more detail below.

1) CAM

The major CAM changes of the ISO pipeline version 9 which have implications for the science data are:
  1. Improved compact status generation. For the ISO archive user this means:

    1. proper recognition of ISOCAM configuration for archive queries also for CUS observations (after the database entries will be updated)

    2. more CUS observations are reduced up to the final image level by Auto Analysis

  2. Derive-SPD will produce more data records.

  3. Improvements in the CUFF (Auto Analysis information file):

    1. the message "Saturation problems detected" warns about detector saturation, which affects the photometry,

    2. better explanations why no images are produced by Auto Analysis (this could be due to, e.g. a dark or clean configuration)

    3. to ease the understanding of Auto Analysis' data reduction for mixed LW/SW observations, the name of the used detector was added

  4. Improvement in the pointing information in raster observations. For cases where pointing information was lacking for parts of a raster measurement this is now recovered (see for further description the section on Pointing in this note).

  5. Improvement in the corrected coordinates of the IIPH file (see for further description the section on Pointing in this note). This does not impact the Auto-Analysis products but can be used in CIA processing.
Stephan Ott (IDC Vilspa)
Joris Blommaert (IDC Vilspa)

2) PHT

OLP 9.0 and CALG 6.0 introduce the following upgrades and new features for ISOPHOT data processing:
 calibration upgrade                       |  affects AOT
 1. dynamic spectral response function     |  PHT40 point & extended sources
    for staring PHT-S measurements         |  in staring mode
 2. refinement of flux dependent           |  all AOTs, except PHT40
    signal linearization                   |
 3. refinement of FCS characterization     |  all AOTs, except PHT40
 4. refinement of signal correction of     |  PHT03, PHT22 in chopped mode
    chopped photometry measurements        |
 5. consistent handling of different       |  PHT17/18/19 & PHT37/38/39
    calibration filters for start and end  |
    modules of sparse maps                 |
 6. complementary flux units for point     |  all AOTs, except PHT40
    and extended source products           |
 7. color correction tables                |  (color correction factors for
    PCCMBBONE and PCMBBTWO                 |  modified black bodies)
  1. Dynamic spectral response function correction for staring PHT-S measurements

    The previous spectral response function calibration of staring ISOPHOT-S measurements was limited in accuracy by transient effects which could not be corrected for using the static average spectral response function as stored in CalG file PSPECAL.

    The main idea behind the dynamic spectral response calibration is that a standard star spectrum of similar brightness as the target spectrum suffers the same transient effects. By taking into account the same temporal evolution of the signals for both standard and target spectrum, the transient effects cancel out by dividing the target spectrum by the standard spectrum, without having to derive "infinite values" with a sophisticated transient correction. Since target and standard spectrum can be quite different in shape, a library of standard stars is necessary to calibrate each PHT-S pixel individually in this way. For the automatic approach in the OLP, the transient behaviour with time for the different flux (signal) regimes was characterized by surfaces stored in the new CalG file PSDYNAMIC constructed from the library of standard stars. The software will determine for each ramp the appropriate transient dependent correction factor.

    There are new SPD products, PSSD and PSLD, containing the dark measurements, which precede each sky measurement.

    Due to the calibration scheme, which determines directly the flux in Jy, the units of the main SPD products, PSSS and PSLS, changed from V/s to Jy. In order to have consistent data products for all PHT40 submodes, the processing for chopped observations (implemented with OLP 8.4) and raster observations (still using the default RSRF in CalG PSPECAL) had to be adapted, too.

  2. Refinement of flux dependent signal linearization

    The signal linearization tables P%%SLINR, introduced with OLP V8.4 have been upgraded with regard to the following aspects:

    1. the new linearisation tables have been re-normalised with respect to the median responsivity per bandpass to avoid filter-to-filter corrections at the signal level.
    2. the shape of the curves among the pixels in the C100 and C200 arrays for a given filter has been homogenized. The curves of the individual pixels have now similar shape based on fine-tuning by eye.
    3. the curves of responsivity as a function of signal smoothly become constant in the extrapolations to very small and very strong signals where no calibration observations are available.

    Due to the re-normalization also the default responsivity values in files P*RESP_01 and P*RESP_02 have been updated.

  3. Refinement of FCS characterization

    The CALG files P%%ILLUM, P%%FCSPOW, P%%FLAT, PPFTOF and PFLUXCONV have been upgraded to reflect the introduction of the new signal linearization corrections (P%%SLINR, see item 2 above). The physical FCS model was refined to give a better relation between the electrical FCS heating power and the FCS/TRS temperature and this was used to determine the extrapolated FCS powers outside the calibrated range.

  4. Refinement of signal correction of chopped photometry measurements

    Several deficiencies in the CalG files P%%CHOPSIG installed with OLP V8.4 were closed:

    1. signal loss correction for P2 detector
    2. chopper offset (residual signal difference for zero flux difference in both beams) corrections for all detectors
    3. the signal loss corrections were re-derived with the updated signal linearization calibration as described above under item 2.

    Chopped observations with the read-out data reduction flag being set are properly processed now. Refinements were also achieved in the chopped pattern processing and a bug omitting the filter-to-filter correction for chopped measurements was fixed.

  5. Consistent handling of different calibration filters for start and end modules of sparse maps

    So far it was assumed in the OLP processing that the FCS measurements of the start and end modules of sparse maps are done in the same filter. This needs, however not to be the case. This led to a mismatch of the responsivity values for the sparse map modules which are interpolated values in time between the two responsivity values from the bracketting FCS measurements. With the new version the correct filter information for the evaluation of both FCS measurements is used.

  6. Complementary flux units for point and extended source products

    Depending on the original observer definition whether the target was a point (P) or extended (E) source, different PHT photometry AAR products are generated, e.g. PPAP and PPAE for PHT-P or PCAP and PCAE for PHT-C pointed observations. P-type products are in unit Jy, E-Type products in unit MJy sr^-1. The comparison between both products, needed e.g. for background subtraction, where the on-source measurement may be in Jy while the off-source measurement is in MJy sr^-1, is not straight forward, since a conversion using the wavelength dependent effective solid angles and point spread function factors is necessary.

    For these products now complementary flux information in the respective units is provided, i.e. for P-type products in addition the surface brightness in MJy sr^-1 and for E-type products the flux in Jy/pixel. The same is true for the scan products PPAS and PCAS.

    For the OLP 9 version this additional information is restricted to the data records, corresponding information in the headers has to be postponed to a later version. This made it necessary to define new keyword fields for the AAR products.

  7. Color correction tables PCCMBBONE and PCCMBBTWO

    In the "What's New" note from 23 December 1999 "Wrong colour correction Cal-G tables for ISOPHOT" observers were warned about faulty contents of the CALG files PCCMBBONE and PCCMBBTWO providing the color correction factors for modified blackbodies. From this time to now the correct files were only available via the PIA homepage. The correct files are now available in the IDA with the OLP 9 delivery.

Ulrich Klaas (PHTNDC at Max-Planck-Institut für Astronomie)
Phil Richards (UK ISO Data Centre at Rutherford Appleton Laboratory)
Rene Laureijs (IDC Vilspa)

3) Pointing

OLP v9 has seen some recovery procedures introduced into the derivation of IIPH files. The IIPH gives real-time estimates of the pointing direction of the prime instrument every 0.5s derived from those parts of the telemetry reserved for the AOCS system. Very occasionally, for operational reasons, some parts of the pointing telemetry were not available, notably the RPID that shows which part of a raster is currently in execution. Any missing values are now recovered by comparison with the expected pointing schedule. There are also new allowances for unexpected delays in the schedule. Improvements have also been introduced to ensure the accuracy of individual 0.5s pointing data as the telescope's position is adjusted between the successive apertures or raster points in an observation. The combination of these measures was designed to guarantee, even under difficult circumstances, the completeness and reliability of the pointing files delivered with observers' data.

Andy Pollock (IDC Vilspa)