ASCA Science Data Processing Steps

Revision 1
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The steps involved in the standard processing of ASCA data are outlined below along with links to more detailed information about each step.

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I. Get, Unpack and Verify Data

  1. Get and Check Telemetry and Attitude Files
    Find, uncompress, and verify files containing scientific data as well as information about the spacecraft pointing and condition. This is the rawest data in a format close to that in which it was telemetered to the ground.

  2. Get Orbit Files
    Find a file containing the spacecraft's orbital elements at the time of the observation.

  3. Read Pointing Information from the Attitude Files
    Interpret the attitude files to determine the mean pointing of the spacecraft while the observation was being made.

  4. Split Telemetry Files by Mode and Create Housekeeping Files
    Read the raw telemetry information from the spacecraft and convert it to a more accessible format. Scientific information is put into a set of files with a separate file created each time the instruments change mode. A separate housekeeping file is also created for each instrument.

II. Apply Corrections and Calibrations to the Raw Data

  1. Create SIS Rate Files
    Create files containing selected housekeeping information for both SIS instruments. Set the telemetry saturation flag correctly in these files.

  2. Determine Temperature-Dependent Gain Corrections for the GIS
    Read the spacecraft temperature as a function of time from the original telemetry files. Calculate the effect this has on the GIS photon energy calibration and record the information in a gain history file.

  3. Create Filter Files
    Create files which record various aspects of the spacecraft condition as a function of time. These files are later used to reject data which is not scientifically useful.

  4. Linearize the Raw Telemetry
    Interpret the raw telemetry from the spacecraft as scientifically usable information. Detector coordinates are mapped onto the sky and the GIS gain corrections (calculated above) are applied.

  5. Fix GIS3 Telemetry for Some Observations
    Between Feb. 10 and Apr 8, 1994 there was a spacecraft-related problem with the GIS3 data sent to the ground. This problem is fixed with some loss of information.

  6. Convert FAINT Mode Data to BRIGHT and BRIGHT2 Modes
    FAINT mode data cannot currently be used in the standard data analysis routines. BRIGHT mode versions of the FAINT mode files are therefore created. This is done both by the on-board BRIGHT mode algorithm and by a method which corrects for dark frame error.

  7. Put PI Values into Modally Split SIS Telemetry Files
    Calculate the pulse invariant (PI) values for the SIS and record them in the SIS science files.

III. Create Standard Data Products

  1. Group Science Files by Mode
    Make a list of the science files for each mode. These lists are later used to reduce the data and to make the catalog files distributed to the observer.

  2. Do Standard Reduction of Data
    Merge groups of science files with the same mode. Create filtered (reduced) versions of these files with bad data removed. Also, produce images from the reduced data.

  3. Make Quick-Look Plots
    Make rough plots of the reduced image, spectrum, and time history for each observation mode.

  4. Make GIF Format Image Files
    Convert the image files created above into a format which can be easily viewed.

IV. Create Record-Keeping Files

  1. Create Catalog Files
    Create FITS format files which catalog the various types of event files.

  2. Create Summary of Data Products by Mode
    Make a file which lists the unfiltered event files along with information about those files.

  3. Create Summary of FRF Telemetry Files
    Make a file which lists the FRF telemetry files along with information about those files.

  4. Make ASCII Dumps of GIS Housekeeping Files
    Translate housekeeping information about the GIS into human-readable form.

  5. Make Files Summarizing the Observation and Processing
    Create files which briefly summarize the observation, the processing of the data, and the files involved.

  6. List and Verify the Files to Go on Tape
    List the files which are to be included on the tape which is sent to the guest observer. This is done in three different ways. The listed files are then checked for correct FITS format.

  7. Create Error Log
    Extract the error messages from the job log.