Odyssey GRS Corrected Gamma Spectra (CGS)

CGS – Corrected Gamma Spectra

Instrument: Odyssey Gamma Ray Spectrometer

PDS Data Set ID: ODY-M-GRS-4-CGS-V1.0DOI: 10.17189/1519469

For more information about GRS CGS products, see the Data Set Catalog File.

For more information about GRS CGS processing, see the Gamma Data Processing document.

For more information about GRS IDR products, see the GRS IDR Product SIS.

The Gamma Ray Spectrometer Intermediate Data Record (GRSIDR) Corrected Gamma Spectra (CGS) data products are composed of corrected gamma spectra and the associated timing, spatial, and engineering information. The CGS consists of the cumulative counts of gamma rays at the detector over one collection interval is approximately 19.7 seconds, but may vary over the course of mapping. The CGS are corrected for gain, offset, and linearity. The end result of the correction is that all the corrected spectra have a common energy scale, which allows the direct comparison of individual spectra.

The counts in Channel 0 are all the counts that would have been shifted to Channel 0 or less by the spectrum shifting algorithm. The counts in Channel 16,383 are all the counts with energies greater than 10MeV, and counts in Channel 16,382 are all the counts that belong in either 16,382 or would have been shifted to 16,383. The timing and spatial data provided with the spectra includes spacecraft clock values and spacecraft geometry data. The sc_ev_time, UTC time, and spatial fields are all recorded at the center of the collection interval.

The raw gamma data (GAMMAS) is processed in the following way to produce the CGS products. Detailed processing information can be found in the Gamma Data Processing document.

  1. A Gaussian-weighted smoothing algorithm is used to remove noise from the GS engineering data (e.g. temperatures, currents, and voltages), and inserts the results into the smoothed column of the engineering tables.

  2. The temperature is calculated for an electrical component in the GS, (170K board) that is not measured directly. The modeled temperature, which is used in later processing, is then inserted into the database.

  3. GS electronic settings information known as digital housekeeping is extracted from the raw data and is stored in the database.

  4. The database is queried by the engineering interpolator for all gamma spectra records where the associated engineering data fields have not yet been computed by previous runs of the interpolator (i.e. the engineering fields are null). The engineering tables are queried for the closest engineering records within an hour before and hour after the gamma record of interest and does a linear interpolation between the two engineering records to fill in the engineering fields in the gamma record of interest. If an engineering record does not exist within the hour before or the hour after the gamma record of interest, then the gamma record is marked as having no engineering readings, and is not processed further.

  5. The shaping amp gain setting from the previously extracted digital housekeeping information is inserted into each spectrum record. The shaping amp gain is the setting of the variable gain stage in the electronics. The gain values are used by the correction process.

  6. Any gamma spectrum records that do not meet particular criteria are identified, flagged, and not processed further.

  7. The correction process is used to calculate the gain, offset, and linearity of the individual spectra based on the measured temperatures of the various spacecraft subsystems. Since there are not enough gamma counts in any given collection interval to establish a calibration, the correction process re-bins the counts in each spectrum to align the channels in all of the spectra to a common energy scale.

  8. The SPICE calculated spacecraft vectors and the position on the surface of Mars being sampled during a collection interval is checked.

The CGS is intended to be the first intermediate data product available for the gamma portion of the GRS. These data should be useful to those scientists who are experienced in gamma spectroscopy.

GRS CGS products have the following file names:

CGS_yyyymmdd_hh_kk.DAT (with detached PDS label)

where:

yyyy = year

mm = month (01-12)

dd = day (01-31)

hh = start hour (00-24)

kk = end hour (00-24)

In ODE, CGS products have the following Product IDs:

CGS_YYYYMMDD_HH_KK