Simulation of laser travel-time on Mercury for BELA

TL;DR

This paper simulates how surface microtexture, especially on ice-covered areas, affects laser pulse shapes in planetary altimetry, aiding in interpreting BELA measurements for surface characterization.

Contribution

It introduces the first simulation of surface microtexture effects on laser pulse shapes for Mercury, using WARPE software to model different textures and assess detectability.

Findings

Microtexture influences laser pulse shape in measurable ways.

Simulation results suggest BELA can detect surface microtexture variations.

Different microtextures produce distinguishable pulse shape signatures.

Abstract

Recent laser altimeters are able to not only measure the ranging distance between the spacecraft and the surface but also the full time-of-flight of the photons or pulse shape. This new capabilities allows to measure the intra-footprint properties: surface slope distribution and surface microtexture. Here we simulate and discuss for the first time the effect of surface microtexture, especially for ice covered surface with longer penetration depth. Using the WARPE simulation software, two kind of microtextures are simulated: compact slab and granular. Laser pulse shape for an ideal instrument is simulated using physical properties such as the grain size, material composition, thickness, compacity (filling factor, porosity) rather than radiative properties. The effects of these parameters on the pulse shape are discussed as well in the range that could be possibly be observed with actual BELA measurement. Finally, examples of WARPE's simulated pulse shapes are used as input in the precise simulation chain of the BELA measurement output, to further assess the capability to detect variation in surface microtexture.