Overview of Calibrated Products

Calibrated products are spectra which are calibrated and corrected, and ready for scientific use. These products have been through processing techniques that are documented in the section of the GRS PDS Query Tool. In particular, consult the GRS Intermediate Data Record Software Interface Specification (SIS).

Why do spectra have to be calibrated and processed? The energy levels detected by the GRS instruments are subject to the fluctuations of power in the spacecraft due to heating or cooling, sensitivity of the device, and other factors. By using engineering data provided by the spacecraft, GRS scientists are able to adjust spectra with a suite of processing applications so that the data are subject to a common energy scale with other corrected spectra. All raw spectra should be processed and adjusted to a common energy scale before use.

Final GRS calibrated map products (RDR) will not be ready for release until the end of the mission. The delay is due to the time needed to integrate enough data to properly separate the signal peaks from the background, and to reduce the data to elemental abundances and other derived values. To meet the scientific community's interest in analyzing the GRS data on a shorter timescale, the GRS Science Team has produced a series of interim intermediate data products:
  1. The first of these intermediate products are the Corrected Gamma Spectra (CGS). The CGS are gamma spectra that have been corrected for gain, offset and linearity. The end result of the correction is that all the corrected spectra have a common energy scale, allowing the direct comparison of individual spectra. Each CGS product data file contains corrected spectra collected over a 2-hour time period. The 2-hour data files will be grouped by Earth days, i.e. 12 data files per day.

  2. The second type of intermediate data products are the Summed Gamma Spectra (SGS). The SGS are sums of 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 season. In this nomenclature Mars season 0 is the time period between = 0 and = 15, where = 0 is the vernal (spring) equinox within the northern hemisphere. The SGS product data files will contain a 72-row data table of one 15-degree temporal bin, with one data record for each 5x5 degree spatial bin in a 5-degree latitude band around Mars. The 36 data files that complete data coverage over the planet will be grouped in directories labeled with Mars year and interval.

  3. The third type of intermediate data products are the Derived Neutron Data (DND). The DND products include a number of calculated quantities that describe the shape and location of peaks found in the NS prism histogram data. The calculated quantities are the first step in calculation of thermal, epithermal and fast neutron counting rates. Each DND product data file will contain neutron data collected over one Earth day, approximately 4300 data records.

  4. The fourth kind of intermediate data products are the Averaged Neutron Data (AND). The AND are averages of DND that have been binned both spatially and temporally. The spatial constraint on the AND 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 constrain on the AND is 3.75-degrees of (a Mars week). AND product data files will contain a table of one 3.75-degree of temporal bin, with a record for each spatial bin. The AND data files will be grouped by Mars year and .

  5. The Derived High-Energy Neutron Data (DHD) is the fifth intermediate data product, released on July 1, 2004. he Mars Gamma-Ray Spectrometer Derived High-Energy Neutron Detector (DHD) data set is a time series collection of counts and backgrounds for the five neutron signals obtained by the four HEND detectors.

  6. The Averaged High-Energy Neutron Data (AHD) dataset, the sixth intermediate data product which was released on July 1, 2004, is a collection of data tables that contain an average counting rate and the associated engineering data for each of the five neutron signals that are obtained by the High-Energy Neutron Detector's four individual detectors. These data have been summed by signal over 5-degree by 5-degree latitude and longitude cells on the Martian surface over a time period of 15 degrees of solar longitude (, or also called "L-sub-S" in the Data Interface).