Summed Gamma Spectra (SGS)Gamma spectra are summed because an individual gamma spectrum taken over a pixel (a collection interval of about 19.7 seconds) does not contain enough counts to be statistically significant. Individual spectra over a particular time period may be summed on the fly over 5-degree by 5-degree latitude-longitude cells, and the date range will be adjusted to a time period of 15 degrees of solar longitude, or . Once data has been summed, it may be used for scientific data analysis.
The Summed Gamma Spectra (SGS), which are intermediate data products, are sums of Corrected Gamma Spectra (CGS) binned both spatially and temporally. The spatial constraint on the SGS is a 5-degree latitude by 5-degree longitude bin. Latitudes and longitudes are calculated for each pixel based on the spacecraft position at the midpoint of the collection interval. The temporal constraint on the SGS is 15-degrees of , referred to as a Martian season. In this nomenclature Mars season zero (0) is the time period between = 0 and = 15, where = 0 is the vernal (spring) equinox within the northern hemisphere.
Each GRS Data Interface SGS product data file will contain a 72-row table. The table will contain 1 data record (row) for each of the 72 5x5 degree latitude-longitude cells in a single 5-degree latitude band around the planet. The data files will be grouped by time, so that for each 15-degees of there will be one data directory with 36 data files representing full planet data coverage. The SGS data set is composed of a series of data tables labeled with Mars year, starting , ending and 5-degree latitude band number (band number 0 centered on 87.5 North, and band number 35 centered on -87.5 South). Each file contains one data table with 72 rows of data, corresponding to the 72 5-degree longitude bins in the latitude band.
OverviewMore complete information is contained in the SGS Data Set Overview.