Gamma Spectra

The gamma data are time series records taken over the course of a day. Data files are labeled with the date. Individual records are composed of raw gamma spectra and the associated timing and spatial information. The gamma spectra consists of the cumulative counts of gamma rays at the detector over one collection interval binned into 16384 channels based on energy. The collection interval is approximately 19.7 seconds, but may vary over the course of mapping. The timing and spatial data provided with the gamma 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.

Column Descriptions
Column Name Type Bytes Units
BAD_CODE MSB_UNSIGNED_INTEGER 4
If non-zero, the data has been flagged bad. Definitions in bad_code.txt.
COUNTER MSB_UNSIGNED_INTEGER 4
A spectra can come down in up to 8 packets. Each packet has its own counter. This counter is the combination of all eight possible counters, four bits for each.
FIRST_CHAN MSB_UNSIGNED_INTEGER 2
First valid channel in the spectrum.
LAST_CHAN MSB_UNSIGNED_INTEGER 2
Last valid channel in the spectrum.
LLD_CNTR MSB_UNSIGNED_INTEGER 2
Lower level discriminator count.
ULD_CNTR MSB_UNSIGNED_INTEGER 2
Upper level discriminator count.
L1_CNTR MSB_UNSIGNED_INTEGER 2
Total number of gamma events within the L1 energy range.
L2_CNTR MSB_UNSIGNED_INTEGER 2
Total number of gamma events within the L2 energy range.
L3_CNTR MSB_UNSIGNED_INTEGER 2
Total number of gamma events within the L3 energy range.
PHA_CNTR MSB_UNSIGNED_INTEGER 4
Pulse Height Analyzer counter.
PHA_TIMER MSB_UNSIGNED_INTEGER 8
Pulse Height Analyzer timer.
RAW_SPECTRUM MSB_UNSIGNED_INTEGER 32768
Raw uncompressed gamma spectrum.
SC_RECV_TIME MSB_UNSIGNED_INTEGER 8
The time this packet was received by the spacecraft, in ticks (256 per second).
SC_EV_TIME MSB_UNSIGNED_INTEGER 8
Spacecraft time at the middle of the pixel, in ticks.
CEB_TIME MSB_UNSIGNED_INTEGER 8 MILLISECOND
Clock count from the GRS Common Electronics Box at the beginning of the pixel.
UTC CHARACTER 23
SC_EV_TIME converted to UTC, stored as yyyy-mm-ddThh:mm:ss.sss.
GRS_PIXEL_NUMBER MSB_UNSIGNED_INTEGER 4
Sequential counter of accumulation intervals, starts with one as grs orbit begins. Special case on reboot when the the CEB is in orbit 0, pixel 0.
GRS_ORBIT_NUMBER MSB_UNSIGNED_INTEGER 4
Sequential counter of orbits from GRS CEB boot.
ODY_ORBIT_NUMBER MSB_UNSIGNED_INTEGER 4
Orbit number common to all instruments aboard Odyssey. This orbit number is incremented by one as the spacecraft passes through the orbital descending node.
LATITUDE IEEE_REAL 8
Sub spacecraft latitude in Mars fixed coordinates at the middle of the pixel.
LONGITUDE IEEE_REAL 8
Sub spacecraft longitude in Mars fixed coordinates at the middle of the pixel.
SCPOS_INERT IEEE_REAL 24 KILOMETER
The geometric position (x,y,z) of the spacecraft with respect to Mars in the 'MARSIAU' inertial frame at the input epoch 'et' at the middle of the pixel.
SCVEL_INERT IEEE_REAL 24 "KILOMETER/SECOND"
The geometric velocity (x,y,z) of the spacecraft with respect to Mars in the 'MARSIAU' inertial frame at the input epoch 'et' at the middle of the pixel.
MARSPOS_INSTR IEEE_REAL 24 KILOMETER
The (x,y,z) position of the sub-spacecraft point as seen from the spacecraft in the instrument frame at the middle of the pixel. If no spacecraft orientation data was available from the loaded CK files for the request time, then all elements of are set to zero.
MARSVEL_INSTR IEEE_REAL 24 "KILOMETER/SECOND"
Contains the inertial spacecraft velocity direction (x,y,z) rotated to the instrument frame at the middle of the pixel. If no spacecraft orientation data was available for the request time, then all elements are set to zero.
SCPOS_MARS IEEE_REAL 24 KILOMETER
Spacecraft position (x,y,z) in Mars fixed coordinates at the middle of the pixel.
INSTR_BORESIGHT_MARS IEEE_REAL 24 KILOMETER
Sub instrument boresight (x,y,z) in Mars fixed coordinates at the middle of the pixel.
SUB_SCPOS_MARS IEEE_REAL 24 KILOMETER
Sub spacecraft vector (x,y,z) in Mars fixed coordinates at the middle of the pixel.
SCALT IEEE_REAL 8 KILOMETER
Areocentric altitude of the sub-spacecraft point in Mars-fixed rotating frame at the middle of the pixel.
DELTA_ANGLE IEEE_REAL 8 DEGREE
Difference between instrument +y direction and true north at the middle of the pixel. Currently not computed for NEUTRON_SPECTRA and HEND_SPECTRA.
MARS_SOL IEEE_REAL 8
Longitude of the Sun at 0 hours UT on the date of the record. Taken from the Association of Lunar and Planetary Observers 'Ephemeris for Physical Observation of Mars'.
DAY_INDEX MSB_UNSIGNED_INTEGER 2
Day of Martian year.
LOCAL_HOUR MSB_UNSIGNED_INTEGER 1
Local Sun hour at the sub-spacecraft point.
LOCAL_MINUTE MSB_UNSIGNED_INTEGER 1
Local Sun minute at the sub-spacecraft point.
POINTING BOOLEAN 1
True if pointing data was available.
INTERSECTING BOOLEAN 1
True if the pointing vector intersects Mars.