Data Set Information
DATA_SET_NAME ODY MARS GAMMA RAY SPECTROMETER 5 SGS V1.0
DATA_SET_ID ODY-M-GRS-5-SGS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The Mars Odyssey Gamma-Ray Spectrometer (GRS) is a suite of three instruments working together to collect data that will permit the mapping of elemental concentrations on the surface of Mars. The suite of three instruments, the gamma sensor head (GS), the neutron spectrometer (NS) and the high-energy neutron detector (HEND), are a complementary set of instruments in that the neutron instruments have better counting statistics and sample to a greater depth than the GS, but the GS determines the abundance of many more elements. A full description of the Mars Odyssey Gamma-Ray Spectrometer instrument can be found in [BOYNTONETAL2003]. The ODY MARS GAMMA RAY SPECTROMETER 5 SGS (SGS) data set is a collection of data tables that contain a gamma spectrum and the associated engineering data that has been summed over 5-degree by 5-degree latitude longitude cells on the surface of Mars and over a time period of 15 degrees of solar longitude (Ls). The SGS are produced because the individual gamma spectra collected during an approximately 19.7 second collection interval do not contain enough counts to be statistically significant. The SGS are summed over large enough and long enough spatial and temporal intervals to provide a statistically meaningful spectrum that can be used for scientific data analysis. The GRS collects a new spectrum (pixel) approximately every 20 seconds, 360 times per orbit. Approximately 4200 spectra are expected to be received every day. The data (both science and engineering) are downloaded from the spacecraft by the Jet Propulsion Laboratory (JPL) into the Telemetry Data System (TDS). The TDS sends data to a process that translates data packets and examines instrument health via messages. Data are output to a spooler that passes them to the University of Arizona (UA) database ingest process. The ingest process inputs raw data into the UA database. Gamma data are processed through a number of programs to yield corrected gamma spectra. The corrected gamma spectra are retrieved from the UA database and are summed into 5x5 degree grids for a time interval of 15 degrees of Ls. The resulting sums are the SGS data products. The SGS is intended to be the second 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. Parameters : The SGS data set is composed of a single data type (SGS). The objective of compiling the SGS is to create a table of summed gamma data that contains enough gamma counts per channel to be a scientifically useful product. Because there are relatively few counts in each individual spectrum, it is necessary to sum spectra in order to accumulate enough counts to separate the signal peaks from the background. A correction algorithm places each gamma spectrum on a common energy scale. Once the spectra have a common energy scale, they can be summed to produce an SGS. Each 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 degrees of Ls there will be one data directory with 36 data files representing full planet data coverage. Processing : A full description of the gamma data processing can be found in the Mars Odyssey Gamma-ray Spectrometer Gamma Data Processing document located in the document folder that accompanies this release. The following paragraphs are a summary of how the data are processed from data receipt through summation. GRS gamma data are downloaded from the Mars Odyssey spacecraft by JPL into the Telemetry Data System (TDS). The TDS sends the data to a process called GRS_tl, which translates GRS packets from any source to any destination and examines instrument health via messages. The data is checked for packet types, header information, messages, errors, engineering and channelized data values and is output to a spooler, which passes data to the UA database ingestion process. The ingestion process inputs raw data into the database. All data packets are processed for timing and spatial information. Once time data is extracted from the data packet, UTC time is calculated from the spacecraft event time (sc_ev_time) by a SPICE function. The UTC time is then inserted into the database. The spatial portion of the data packet is calculated using other SPICE routines. The returned values are all the spatial elements of an observation, including latitude and longitude at the mid-point of the observation. Engineering values have an additional step of processing. Raw engineering values (digital) are converted to engineering unit values by scaling the raw value with a stored polynomial. The polynomials were derived through hardware calibrations, and are calculated by a series of database functions. Once raw gamma data, with associated timing, spatial and engineering data is entered into the database, a series of processing steps are started to prepare the data for correction. The processing begins with Engineering Smoothing. The Engineering Smoother uses a gaussian-weighted smoothing algorithm to remove noise from engineering data, and inserts the results into the engineering database tables. The next process calculates the temperature for the 170k board, an electrical component used for signal amplification in the GS. This temperature must be modeled as the temperature of the board is not directly measured. The modeled temperature is then inserted into the database. The third process extracts and deciphers digital housekeeping information that identifies the state of various components on the spacecraft. The digital housekeeping data is needed for the corrections. The engineering interpolator queries the database for uncorrected gamma spectra records where the associated engineering data fields are NULL. The program queries the engineering tables for one record on each side of the record of interest and does a linear interpolation from the two engineering records to fill in the engineering fields in the record of interest. The next process, fill_apps_gain, uses the digital housekeeping information to insert the shaping amp gain values into each spectrum record. The gain values are then used by the corrector. The correction process calculates the gain, offset, and linearity of the uncorrected spectra based on measured temperatures of various spacecraft subsystems. Because there are not enough counts in any given collection interval to establish a calibration, the correction process uses a spectrum shifting algorithm to re-bin the counts in each spectrum, aligning the channels in all of the spectra to a common energy scale. The corrected spectra are then binned by space, 5-degree latitude and 5-degree longitude bins, and by time, 15-degree Ls bins. The latitude portions of the spatial bins are calculated from 90N to -90S. Therefore the first latitude band of sums calculated are centered on 87.5N. The sum is inclusive of the northern boundary and exclusive of the southern boundary, e.g. less than or equal to 90N and greater than 85N. The longitude portion of the sum is calculated eastward from 0 to 360. The western boundary is inclusive and the eastern boundary is exclusive, e.g. greater than or equal to 0 and less than 5. The temporal bins are calculated from 0-degrees Ls, which is the vernal (spring) equinox within the northern hemisphere. The lower Ls boundary is inclusive and the upper boundary is exclusive, e.g. greater than or equal to 0 and less than 15. See the Time Conversion Tables in the document directory for more information on how Ls relates to spacecraft and Earth time. Once the spectra are binned, they are summed to produce a single SGS for each spatial and temporal bin. Any corrected spectrum with a bad_code greater than 0 (i.e. suspect data) is not included in the sum. Data : The SGS data set is composed of a series of data tables labeled with Mars year, starting Ls, ending Ls and 5-degree latitude band number (0 centered on 87.5N, 35 centered on -87.5S). Each files contains one data table with 72 rows of data, corresponding to the 72 5-degree longitude bins in the latitude band. Summed Gamma Spectra ------------- Summed Gamma Spectra products are composed of summed gamma spectra and the associated timing, spatial and engineering information. The SGS consists of the cumulative counts of gamma rays at the detector over the 5x5 degree latitude longitude, 15-degree Ls interval binned into 16384 channels based on energy. Please refer to the Corrector section of the Gamma Processing document located in the documents directory that accompanies this release for a full description of how gamma counts in a channel are mapped to energy. Note that the counts in Channel 0 are all the counts that would have been shifted to 0 or less than 0 by the spectrum shifting algorithm employed by the correction algorithm. The counts in Channel 16383 are all the counts with energies greater than 10MeV, and counts in Channel 16382 are all the counts that belong in either 16382 or would have been shifted to 16383 by the correction algorithm. The timing and spatial data provided with the spectra include the time and spatial range over which the sum was generated. Ancillary Data : Ancillary data needed to understand the gamma data processing, can be found in the Mars Odyssey Gamma-ray Spectrometer Gamma Data Processing document located in the document folder that accompanies this release. Coordinate System : The coordinate system used for all GRS data is a Mars areocentric system following the IAU convention [SEIDELMANNETAL2002], with east longitudes from 0 to 360. Software : A library of source code to parse the SGS data product files is included in the software directory. This library allows a programmer to build applications that display or manipulate SGS data. This source is written in the Java language, and requires version 1.3 of the Java Runtime Environment (JRE) or Java Software Development Kit (SDK). Documentation for the code is located in the software directory in the file GRS_DR_CODE_DOC.ZIP. The contents of this file are described in the label GRS_DR_CODE_DOC.LBL and the source and the binary classes that make up the library are in the file DR_CODE.JAR. Media/Format : The SGS will be delivered electronically. Formats will be based on standards established by the Planetary Data System (PDS) [PDSSR2001].
DATA_SET_RELEASE_DATE 2003-11-01T00:00:00.000Z
START_TIME 2002-02-19T12:00:00.000Z
STOP_TIME N/A (ongoing)
MISSION_NAME 2001 MARS ODYSSEY
MISSION_START_DATE 2001-01-04T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME MARS
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID ODY
INSTRUMENT_NAME GAMMA RAY/NEUTRON SPECTROMETER/HIGH ENERGY NEUTRON DETECTOR
INSTRUMENT_ID GRS
INSTRUMENT_TYPE SPECTROMETER
NODE_NAME Geosciences
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The data presented in the SGS is intended to be the second intermediate data set released for the GRS. Data presented here are a highly processed and re-binned representation of the GRS data. It is possible that changes will be made in the processing and correction procedures that the SGS products are based on if errors are found. If errors are found, the data will have to be regenerated from the corrected data set. Review : The SGS was reviewed internally by the GRS team prior to release to the PDS. PDS will also perform an external review of the SGS. Data Coverage and Quality : Data reported are the processed and re binned gamma data received from the spacecraft during the mapping mission stage. Data coverage and quality are addressed in the following sections. Primary Mapping --------------- The Mapping portion of the mission began February 19, 2002, and is expected to last until August, 2004. Primary mapping is broken into two phases: stowed mapping and deployed mapping. Stowed Mapping -------------- The stowed mapping configuration began on February 19, 2002 and lasted until June 1, 2002. The stowed mapping configuration is with the Odyssey spacecraft in a mapping orbit, with the GRS in data collection configuration without the 6-meter boom deployed. The reason for data collection in the stowed configuration is to measure the background signal from the spacecraft. During the stowed mapping portion of the mission, two anneals were performed on the gamma detector. The anneals were performed between March 8, 2002 to March 22, 2002 and May 6, 2002 to May 20, 2002. No science data was collected during these two periods. On June 1, 2002 the GRS was shutdown to prepare for boom deployment, which occurred on June 4, 2002. There may also be short periods of missing data due to missing telemetry that cannot be recovered. Deployed Mapping ---------------- Deployed Mapping began on June 5, 2002 and is expected to continue until at least August, 2004. Gamma data collected on June 19, 2002 are suspect due a number of temperature fluctuations in the gamma subsystem. A number of solar particle events have been recorded. Gamma Data collected during these times are suspect: 07/16/02 17:00:00 to 07/24/02 12:00:00 10/14/02 15:00:00 to 10/17/02 03:00:00 10/25/02 10:15:00 to 10/27/02 00:00:00 10/28/02 00:00:00 to 11/02/02 00:00:00 03/18/03 15:00:00 to 03/21/03 00:00:00 05/31/03 00:00:00 to 06/02/03 00:00:00 Gamma Data collected during solar flare events are also suspect: 07/16/02 15:54:02 to 07/16/02 16:05:13 10/14/02 14:25:39 to 10/14/02 14:38:29 10/27/02 22:58:30 to 10/27/02 23:24:00 03/29/03 11:45:16 to 03/29/03 11:47:54 04/06/03 22:36:53 to 04/06/03 22:39:51 04/21/03 13:09:17 to 04/21/03 13:14:34 04/25/03 15:48:08 to 04/25/03 15:58:00 05/28/03 00:26:59 to 05/28/03 00:37:31 Gamma Data collected over the time interval 11/05/02 01:48:04 to 11/28/02 08:00:00 are suspect due to a safe mode of the spacecraft, and the subsequent high temperature anneal of the gamma detector. There are short data gaps due to missing telemetry that cannot be recovered. Any single spectrum with a bad code greater than 0 should be treated with caution, as it may not be suitable for further processing. Refer to the Auto_Bad section in the Mars Odyssey Gamma-ray Spectrometer Gamma Data Processing document located in the documents folder that accompanies this release for further details. Limitations : The major limitation of this data set is that it is derived from the raw minimally processed data. The data is received from spacecraft telemetry, and ingested into a database. If gaps exist in the telemetry, data is lost. Timing and spatial components of the data set rely on the accuracy of the NAIF SPICE kernels. The validity of the corrected gamma spectra is based on the 'correctness' of each step in the processing. It is possible that changes will be made in the processing and correction procedure if errors are found. If errors are found, the data will have to be regenerated from the raw unprocessed data set. Data Compression : No compression is used on the SGS data set. Caveat : The SGS data products that have been released to the PDS in the November 1, 2003 release were created using CGS spectra that were produced with the original correction algorithm (in the same manner as the releases with data taken before January 1, 2003). The SGS data products will be re-released with the new correction once this correction has been fully validated for the entire data set and propagated through the GRS database. See the caveat in the CGS data set description for details on the differences between the old correction method and the new one.
CITATION_DESCRIPTION Boynton, W.V., Mars 2001 Odyssey Gamma Ray Spectrometer Summed Gamma Spectra V1.0, ODY-M-GRS-5-SGS-V1.0, NASA Planetary Data System, 2003.
ABSTRACT_TEXT The ODY MARS GAMMA RAY SPECTROMETER 5 SGS (SGS) data set is a collection of data tables that contain a gamma spectrum and the associated engineering data that has been summed over 5-degree by 5-degree latitude longitude cells on the surface of Mars and over a time period of 15 degrees of solar longitude (Ls). The SGS are produced because the individual gamma spectra collected during an approximately 19.7 second collection interval do not contain enough counts to be statistically significant. The SGS are summed over large enough and long enough spatial and temporal intervals to provide a statistically meaningful spectrum that can be used for scientific data analysis.
PRODUCER_FULL_NAME WILLIAM BOYNTON
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