TGO CaSSIS Raw Data

Instrument: CASSIS

PDS4 Collection: urn:esa:psa:em16_tgo_cas:data_raw

PDS4 Bundle: urn:esa:psa:em16_tgo_cas

CaSSIS Raw science data is extracted from science files queried from the EDDS (Electronic Data Dissemination System) by an IDL pipeline created and maintained by UBE (the University of Bern). The individual CaSSIS packets are first extracted from a given science file, where each packet contains the image data and header information for a single framelet. Image data from each packet is subsequently extracted and stored in a data file. The data files are 4-byte floating points in a 2D array, where the data is stored as an unformatted binary. De-compression of image data is performed during this step if required. The header information from each packet is also extracted and stored as an xml file. This header information contains HK (housekeeping) data pertaining to that acquisition and geometry information taken from SPICE kernels, amongst other general meta information.

A single piece of CaSSIS raw data is therefore the image data for a single framelet in a given filter with a corresponding xml header file. The xml header files produced by the CaSSIS team are not PDS4 compatible. Instead, a parser has been written and is maintained by ESAC (European Space Astronomy Centre) to convert the xml files produced by UBE to have labels that are PDS4 compatible.

ESAC also extracts raw data from science files in the same way as UBE and produces a PDS4 compatible xml file for each framelet data file. An example of a PDS4 compatible label for CaSSIS data is shown in Section 7 of CASSIS EXPERIMENT TO ARCHIVE INTERFACE CONTROL DOCUMENT.

Raw science products (framelet data file and corresponding XML header file) produced by UBE are supplied to ESAC. Upon delivery to ESAC the xml header files for each framelet are put through the parser by ESAC to convert them into being PDS4 compatible.

The raw framelet data files and corresponding PDS4 compatible xml headers produced by ESAC are ingested into the PSA (Planetary Science Archive). However, regular comparisons are made by ESAC between the xml header files delivered by UBE (once made PDS4 compatible by the parser) and the header files produced by ESAC to make sure they are consistent. If the CaSSIS team update the xml header file for raw data, ESAC regenerate all xml headers of raw data in the PSA to reflect this change. This regeneration is done roughly every 6 months if needed.

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

cas_raw_sc_YYYYMMDDThhmmss-YYYYMMDDThhmmss-CCC-NN-FFF-UID-SEQ-WIN.<ext>

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 (see below for details).

CCC = orbit number

NN = observation number (from science file name)

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

UID = image 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. 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.

For example, a raw data product with the filename "cas_raw_sc_20190728T214441-20190728T214445-7489-16-BLU-552206384-48-2.dat",

data type = raw, the beginning time of the observation was at 21:44:41 UTC on July 28th 2019 with the end time being 21:44:45 UTC on July 28th 2019 (subject to the above caveat). The orbit number of the observation was 7489, with an observation number of 16. The BLU filter was used for the observation with an image id of 552206384. The framelet was the 48th in a complete image acquisition using window number 2 (BLU filter). Finally, the file is image data, from the dat extension.

Rare cases where a CaSSIS image has a missing framelet (both in the Raw_Data and Calibrated_Data collections) can be identified by the filename of framelets. Images with missing framelets are ingested into the PSA and maintain the expected filename description. That is, is a framelet is missing, this will result in a sequence number being skipped. For example therefore, if the following framelet data files are present in Data_Raw collection:

cas_raw_sc_20190728T214438-20190728T214442-7489-16-BLU-552206384-40-2.dat

cas_raw_sc_20190728T214438-20190728T214442-7489-16-BLU-552206384-41-2.dat

cas_raw_sc_20190728T214439-20190728T214443-7489-16-BLU-552206384-43-2.dat

cas_raw_sc_20190728T214439-20190728T214443-7489-16-BLU-552206384-44-2.dat

The jump in sequence number from 41 to 43 indicates that framelet 42 is missing in the BLU filter for this image acquisition. The above example is for data in the Data_Raw collection. However, the same applies for data in the Data_Calibrated collection.

The HK TM (telemetry) stored on the PSA has the following naming convention:

cas_raw_hk_hk<TM_type>_YYYYMMDDThhmmss-YYYYMMDDThhmmss.<ext>,

where:

the dates are the same format used for science products and describe the date range of contained HK TM data.

The <TM_type> refers to the hexid of the integer describing each of the CaSSIS HK frame types described in Section 4.3.1 of

CASSIS EXPERIMENT TO ARCHIVE INTERFACE CONTROL DOCUMENT. Broadly speaking, HK TM can be separated into 7 different types:

1 = CaSSIS temperature

2 = CaSSIS zone temperature

3 = voltages and currents

4 = proximity electronics HK and motor rotation status

5, 6, 7 = FSW status

The <ext> can be either xml or tab, referring to the xml definition file and the ASCII-format content file respectively.