Uncalibrated High-Energy Neutron Detector (HEND) Spectra

High-Energy Neutron Detector (HEND) spectral data is obtained by the High-Energy Neutron Detector instrument, and consists of HEND records and associated timing and spatial information. HEND records, also called frames, may be one of three types:
  1. Nominal, or spectra, frames consist of six spectra with sixteen channels each at two bytes per channel.

  2. Profile, or time series, frames consist of the six spectra pus two time profiles. The inner scintillator profile is thirty seconds in duration, with a count for each second. The outer scintillator profile is also thirty seconds in duration, but has a time resolution of 0.25 seconds, with a count for each interval. Note: This is not related to Profile, or Gamma-Ray Burst data.

  3. Status frames, or HEND instrument commands.
The timing and spatial data provided with the HEND data 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.

For more information on uncalibrated (raw) HEND and other GRS data, please see the EDR Dataset Description document.

Overview of Uncalibrated Data

Uncalibrated data are raw data that has had associated timing and spatial information added. A full description may be found in the 2001 Mars Odyssey Gamma Ray Spectrometer EDR NASA Level 0 Software Interface Specification (EDR SIS).

Gamma-Ray Spectrometer Instruments Background

The Mars Odyssey Gamma-Ray Spectrometer (GRS) is a suite of three instruments working together to collect data that map the elemental concentrations on the surface of Mars. The three instruments are:
  1. The Gamma Subsystem (GS), or gamma sensor head, which obtains raw uncalibrated gamma spectra

  2. The Neutron Spectrometer (NS), which obtains the uncalibrated Neutron Spectra, and

  3. The High-Energy Neutron Detector (HEND), which collects the raw HEND data.

These three instruments work differently but are complementary. 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 instruments may be found in Boynton, et. al, 2004.