Water content in the upper 1 meter of the Martian regolith, estimated from FREND experiment data

This dataset contains a raw map of neutron suppression and a smoothed map of water content in the upper meter of the Martian subsurface derived from FREND instrument data, between latitudes 50° north and south. FREND is a high resolution neutron telescope onboard ExoMars’ TGO orbiter (see Mitrofanov, I. et al. Fine Resolution Epithermal Neutron Detector (FREND) Onboard the ExoMars Trace Gas Orbiter. Space Sci Rev 214, 86 (2018). https://doi.org/10.1007/s11214-018-0522-5).

Neutron Suppression is defined as ratio between neutron count rate (counts per second) at each pixel and a reference count rate (average count rate over Solis Planum area between -115° and -65° longitude and -55° and -15° latitude). It is a dimensionless parameter, showing how much the neutron flux is suppressed relative to the reference Solis Planum area, known to be one of the driest on Mars with water equivalent hydrogen (WEH) estimated as 2.78 weight percent (wt%, see Boynton, W.V. et al. Concentration of H, Si, Cl, K, Fe, and Th in the low- and mid-latitude regions of Mars. Journal of Geophysical Research 112, (2007) E12S99. https://doi.org/10.1029/2007JE002887). Statistical errors are given in each pixel. Map of neutron suppression can be used to locate regions of high or low water content.

Map of water is derived from the neutron suppression map in the following way: neutron suppression map is smoothed with a gaussian 12° (full width half maximum) filter, considering statistical errors in each pixel. Transition from smoothed neutron suppression values to WEH values is done through numerical modeling of all physical process from neutron emission from the Martian regolith to detection of neutrons by FREND instrument, depending on the WEH content in the regolith. Map of water contains three values for each pixel: minimum, mean and maximum WEH in wt%: mean values are derived from neutron suppression map, maximum and minimum values correspond to plus and minus error of the neutron suppression. These three values represent the range of WEH in each pixel within 1 error margin of neutron suppression values.