Image Reconstruction Techniques in Neutron and Gamma Ray Spectroscopy: Improving Lunar Prospector Data

Abstract

We present improved resolution maps of the Lunar Prospector Neutron Spectrometer thermal, epithermal, and fast neutron data and gamma ray spectrometer Th‐line fluxes via global application of pixon image reconstruction techniques. With the use of mock data sets, we show that the pixon image reconstruction method compares favorably with other methods that have been used in planetary neutron and gamma ray spectroscopy. The improved thermal neutron maps are able to clearly distinguish variations in composition across the lunar surface, including within the lunar basins of Hertzsprung and Schrödinger. The improvement in resolution reveals a correlation between albedo and thermal neutron flux within the basins. The consequent increase in dynamic range confirms that Hertzsprung basin contains one of the most anorthositic parts of the lunar crust, including nearly pure anorthite over a region tens of kilometers in diameter. At Orientale, the reconstructed epithermal neutron data show broad overlap with circular polarization ratio but there remains a mismatch between measures of regolith maturity that sample the surface and those that probe the near subsurface, which is consistent with a complex layering scenario.

Potassium and Thorium Abundances at the South Pole‐Aitken Basin Obtained by the Kaguya Gamma‐Ray Spectrometer

“…Our results based on the unambiguous gamma‐ray counts with low interference from surrounding gamma‐ray lines are reliable as improved elemental maps obtained by direct observation of corresponding gamma ray. It will be interesting to apply estimation and deconvolution methods by Hagerty et al (), Lawrence et al (, ), and Wilson et al () to our data set in order to refine the distributions of lunar radioactive elements. Our Th maps are available to refine by their methods.…”

“…Then, Lawrence et al (2003) obtained the absolute Th abundance using Th abundances given by Prettyman et al (2002Prettyman et al ( , 2006 for the calibration of their count rates. Significant works have been conducted for increasing the spatial resolution of Th maps based on deconvolution of Lawrence et al (2003) data set (Hagerty et al, 2011;Lawrence et al, 2007;Wilson et al, 2018). One possible limitation of such statistical methods is that they rely on their models and primary data set of Lawrence et al (2003).…”

Distinguishing the Origin of Asteroid (16) Psyche

“…This altitude corresponds to an effective spatial footprint of to 150 km, which is a spatial scale of a large “province” on Psyche; this footprint may be reduced using spatial deconvolution techniques (Wilson et al. 2018 ). In a practical sense, the spatial resolution of the metal-to-silicate measurement will be similar to the gamma-ray and neutron measurements achieved with the Dawn mission at the asteroids Vesta and Ceres (Prettyman et al.…”

Global Hydrogen Abundances on the Lunar Surface

“…Finally, Wilson et al. (2018) performed an image reconstruction analysis on the LP neutron data sets from Maurice et al. (2004) to reduce the uncertainties in the mapped data and remove the effect of instrumental blurring, within the limits of the statistical uncertainties in the data, improving their spatial resolution.…”

“…Figure 10. Regional maps of the Aristarchus crater and plateau region: ( a ) hydrogen abundances ( this work ); ( b ) thorium abundances( Wilson et al, 2018 ); and ( c ) FeO abundances ( P. G Lucey, Blewett, & Jolliff, 2000 )…”