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:
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.
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
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.
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
(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
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.
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).