How well do we know the polar hydrogen distribution on the Moon?

TL;DR

This paper compares lunar polar hydrogen measurements from two neutron detectors, concluding that the collimator's flux is negligible and that pixon reconstructions of LPNS data provide the most spatially resolved hydrogen maps.

Contribution

It demonstrates that the LEND CSETN has a larger footprint than expected and validates pixon image reconstructions as the best method for high-resolution hydrogen mapping.

Findings

LEND CSETN footprint is at least as large as expected for an omni-directional detector.

Collimated flux into the collimator's field of view is negligible.

Pixon reconstructions of LPNS data yield the highest contrast hydrogen maps.

Abstract

A detailed comparison is made of results from the Lunar Prospector Neutron Spectrometer (LPNS) and the Lunar Exploration Neutron Detector Collimated Sensors for EpiThermal Neutrons (LEND CSETN). Using the autocorrelation function and power spectrum of the polar count rate maps produced by these experiments, it is shown that the LEND CSETN has a footprint that is at least as big as would be expected for an omni-directional detector at an orbital altitude of 50 km. The collimated flux into the field of view of the collimator is negligible. Arguments put forward asserting otherwise are considered and found wanting for various reasons. The maps of lunar polar hydrogen with the highest contrast, i.e. spatial resolution, are those resulting from pixon image reconstructions of the LPNS data. These typically provide weight percentages of water equivalent hydrogen that are accurate to 30% within the polar craters.