Odyssey GRS Improved Derived Neutron Data (IDND)

IDND – Improved Derived Neutron Data

Instrument: Odyssey Gamma Ray Spectrometer

PDS4 Bundle: urn:nasa:pds:mesick_pdart19_odyssey_idndDOI: 10.17189/eh0p-qw34

The Mars Odyssey Neutron Spectrometer (MONS) instrument, part of the Gamma Ray Spectrometer (GRS) suite [Boynton et al., 2004], measures the leakage flux of neutrons from the surface of Mars in three energy bands: thermal (0 - 0.4 eV), epithermal (0.4 eV - 700 keV), and fast (0.7 - 5 MeV). These neutrons are generated by the bombardment of Mars by Galactic Cosmic Rays (GCRs) and measurement of these neutrons enables the study of near-surface water inventories of Mars (e.g. [Feldman et al., 2002, Prettyman et al., 2004, Feldman et al., 2011, Pathare et al., 2018]). The extended time-scale of continuous operation on MONS also allows for the study of changes in the seasonal CO2 cycle of Mars (e.g. [Prettyman et al., 2009, Maurice et al., 2011, Mesick et al., 2020]), which can provide important benchmarks of General Circulation Models that are used to study Mars’ climate history.

There are two types of raw data products produced by the MONS instrument that define what type of neutron was detected – Category 1 (thermal, epithermal) and Category 2 (fast). Processing of raw MONS data to a high-order “derived neutron data” (DND) product of corrected neutron counting rates requires removing bad data and applying numerous corrections to extract the time-series of corrected counting rates from the raw spectral histograms. The GRS Improved Derived Neutron Data (IDND) bundle contains high-order Category 1 DND time-series data and improved high-order Category 2 DND time-series data from the beginning of the mission to December 2020. The data were generated by Katherine E. Mesick and Dorothea M. DeLapp, LANL, and funded by the NASA Planetary Data Archiving, Restoration, and Tools program (PDART). For more information about GRS IDND processing, see Improved Derived Neutron Data User Guide.

IDND data products are archived using the PDS4 standard. The data products are in command separated value (CSV) format and meta data labels are PDS4 xml. The time-series data product is a CSV file with 22 fields/columns. The column name and description are documented in Table 1.

Column Name	Column Description
UTC	UTC timestamp of the data point
mars_year	Derived mars year of the data point
mars_solar_lon	Derived mars solar longitude of the data point
rot_flag	Flag indicating when the Mars Odyssey spacecraft was rotated off nadir (=1)
cat1_lat_p1	Latitude registration associated with Prism 1 (Epithermal)
cat1_lon_p1	Longitude registration associated with Prism 1 (Epithermal)
cat1_lat_p2	Latitude registration associated with Prism 2
cat1_lon_p2	Longitude registration associated with Prism 2
cat1_lat_p3	Latitude registration associated with Prism 3
cat1_lon_p3	Longitude registration associated with Prism 3
cat1_lat_p4	Latitude registration associated with Prism 4
cat1_lon_p4	Longitude registration associated with Prism 4
cat1_lat_p2m4	Latitude registration associated with Prism 2-4 (Thermal)
cat1_lon_p2m4	Longitude registration associated with Prism 2-4 (Thermal)
cat1_rate_p1	Category 1 corrected Prism 1 counting rate (Epithermal)
cat1_rate_p2	Category 1 corrected Prism 2 counting rate
cat1_rate_p3	Category 1 corrected Prism 3 counting rate
cat1_rate_p4	Category 1 corrected Prism 4 counting rate
cat1_rate_p2m4	Category 1 corrected Prism 2-4 (Thermal) counting rate
cat2_lat	Latitude registration associated with Category 2 data (Fast)
cat2_lon	Longitude registration associated with Category 2 data (Fast)
cat2_rate_p1	Category 2 corrected fast neutron counting rate from Prism 1 (Fast)

The UTC timestamp is the middle of the collection interval, stored as YYYY-MM-DDThh:mm:ssZ. The mars_year and mars_solar_lon are derived from the UTC based on the Mars calendar defined by [Piqueux et al., 2015].

Additional resources:

[Boynton et al., 2004] W.V. Boynton, W.C., Feldman, I. Mitrofanov et al. (2004), The Mars Odyssey Gamma-Ray Spectrometer Instrument Suite, Space Science Reviews 110, 37–83. https://doi.org/10.1023/B:SPAC.0000021007.76126.15
[Feldman et al., 2002] W. C. Feldman et al. (2002), Global distribution of Neutrons from Mars: Results from Mars Odyssey, Science 297, 5578. https://doi.org/10.1126/science.1073541
[Feldman et al., 2011] W.C. Feldman et al. (2011), Mars Odyssey neutron data 2. Search for buried excess water ice deposits at nonpolar latitudes on Mars, Journal of Geophysical Research: Planets 116, E11. https://doi.org/10.1029/2011JE003806
[Mesick et al., 2020] K.E. Mesick et al. (2020), New and Extended Processing of Mars Odyssey Neutron Spectrometer Data, Icarus 335, 113397. https://doi.org/10.1016/j.icarus.2019.113397
[Maurice et al., 2011] S. Maurice et al. E11 (2011), Mars Odyssey neutron data 1. Data processing and models of water-equivalent-hydrogen distribution, Journal of Geophysical Research: Planets 116, E11. https://doi.org/10.1029/2011JE003810
[Pathare et al., 2018] A.V. Pathare et al. (2018), Driven by excess? Climatic implication of new global mapping of near-surface water-equivalent hydrogen on Mars, Icarus 301, 97-116. https://doi.org/10.1016/j.icarus.2017.09.031
[Piqueux et al., 2015] S. Piqueux et al. (2015), Enumeration of Mars years and seasons since the beginning of telescopic exploration, Icarus 251, 164-180. https://doi.org/10.1016/j.icarus.2014.12.014
[Prettyman et al., 2004] T.H. Prettyman et al. (2004), Composition and structure of the Martian subsurface at high southern latitudes from neutron spectroscopy, Journal of Geophysical Research: Planets 109, E9. https://doi.org/10.1029/2003JE002139
[Prettyman et al., 2009] T.H. Prettyman et al. (2009), Characterization of Mars’ seasonal caps using neutron spectroscopy, Journal of Geophysical Research: Planets 114, E8. https://doi.org/10.1029/2008JE003275

GRS IDND products have the following file names:

IDND_YYYYQ#.CSV (with detached PDS label)

where:

yyyy = year

# = the quarter of the year

In ODE, IDND products have the following Product IDs:

IDND_YYYYQ1.CSV

IDND_YYYYQ2.CSV

IDND_YYYYQ3.CSV

IDND_YYYYQ4.CSV