TGO CaSSIS Calibrated Data

Instrument: CASSIS

PDS4 Collection: urn:esa:psa:em16_tgo_cas:data_calibrated

PDS4 Bundle: urn:esa:psa:em16_tgo_cas

CaSSIS Calibrated data are produced by an IDL pipeline created and maintained by UBE (the University of Bern). The steps to convert raw data into calibrated data are performed in the following order:

  • Bias calibration.

  • Flat calibration.

  • Bad pixel calibration.

  • Expand binned data.

  • Perform absolute calibration.

  • Straylight calibration.

  • Framelet to framelet offset correction.

A detailed description of the calibration steps can be found in the CaSSIS Calibration Report which is planned to be archived during 2020. An overview of the on-ground calibration can also be found in the CaSSIS Calibration Programme (EXM-CA-PLN-UBE-10000) archive document. A summary of each part of the calibration procedure is given in the Section 4.3.4 of CASSIS EXPERIMENT TO ARCHIVE INTERFACE CONTROL DOCUMENT.

Calibrated data are stored as data files for each framelet with a corresponding xml header file. The data files are 4-byte floating points in a 2D array, where the data file is an unformatted binary. The xml header files for calibrated data produced by UBE are not PDS4 compatible. Similarly to the raw data, calibrated data are delivered to ESAC (European Space Astronomy Centre), where the xml files are put through a parser to make them PDS4 compatible.

The calibrated framelet data files produced by UBE and corresponding PDS4 compatible xml header files are ingested into the PSA (Planetary Science Archive). All individually calibrated framelets are not cataloged in ODE due to their large volume. However, the calibrated framelets are accessible from the PSA site at https://archives.esac.esa.int/psa/ftp/ExoMars2016/em16_tgo_cas/data_calibrated/.Calibrated framelets from a specific filter of a given image are stitched together to make a stitched full image using geometrical information from the SPICE kernels. Stitched image data is stored as data file, with associated data being 4-byte floating points that are stored in a 2D array. The corresponding header file for each framelet is stored as a XML file. Browse products are generated for the stitched image data, which are stored as .jpg files. Validators use the stitched browse products to check that the straylight and the framelet brightness offset calibration have performed as expected. Validators also check that the image is of an acceptable contrast (i.e. whether the exposure of the image gives an acceptable signal to noise in the image). Validators also check how well individual framelets have stitched together, which in turn allow validators to check the alignment of the telescope. Validators also check the report file generated for stitched products which contains information about which images were acquired and the corresponding meta information of acquired images. Checks are made to see if all expected images have been acquired and whether the meta information of acquired images reflects what was planned. The stitched calibrated science data are accessible in ODE.

 

CaSSIS Calibrated science data stored on the PSA follow the LID naming convention:

cas_cal_sc_YYYYMMDDThhmmss-YYYYMMDDThhmmss-CCC-NN-FFF-UID-SEQ-WIN.<ext> - individually calibrated framelet

cas_cal_sc-YYYYMMDDThhmmss-YYYYMMDDThhmmss-CCC-FFF-UID-STI.<ext> - stitched calibrated science data (University of Bern file naming convention)

where:

YYYY = year, MM = month, DD = day, hh = hour, mm = minute, ss = second. The two times are the beginning and end time in UTC of the full image sequence respectively. So for the stitched calibrated science data, the first time is the beginning time in the filename of the first framelet used in the stitched product. The second time is the end time in the filename of the last framelet used in the stitched product.

CCC = orbit number

NN = observation number (from science file name)

FFF = filter used (BLU, RED, NIR, PAN)

UID = image unique id

SEQ = sequence number (sub-exposure in sequence)

WIN = Window number (filter used 1-6). Note window 1 and 6 are the control windows described in Section 3.4. of

CASSIS EXPERIMENT TO ARCHIVE INTERFACE CONTROL DOCUMENT

<ext> = dat, xml, tab for the data, xml, and table file respectively.

The beginning and end time in the filename is given to second resolution. However, the time between CaSSIS exposures is roughly 0.3 seconds. The sub-second beginning time of a framelet observation is not used in the filename. The end time in the filename is always taken to be 4 seconds after the beginning time for the individually calibrated framelet. This difference is included for consistency across all datasets only, it is not representative of the actual end time of a given framelet exposure.

The times used in the filename should therefore not be used for fine time calculations of when a framelet exposure began and finished. The xml file for a given data product contains the actual framelet observation start time to the milli-second level.