The Reflectivity of Mars at 1064 nm: Derivation from Mars Orbiter Laser Altimeter Data and Application to Climatology and Meteorology

TL;DR

This study derives a reliable reference reflectivity of Mars at 1064 nm from MOLA data, accounting for atmospheric and geometric effects, enabling improved atmospheric and climate analysis of Mars.

Contribution

It introduces a method to accurately estimate Mars surface reflectivity at 1064 nm, correcting for atmospheric opacity and calibration issues, and validates it against HST data.

Findings

Achieved <10% agreement with HST reflectivity measurements.

Provided a calibrated reflectivity reference for atmospheric studies.

Enabled detection of mesoscale cloud and aerosol structures.

Abstract

The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS) made $> 10^{8}$ measurements of the reflectivity of Mars at 1064 nm ($R_{1064}$) by both active sounding and passive radiometry. Past studies of $R_{1064}$ neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry. Therefore, as yet, there exists no acceptable reference $R_{1064}$ to derive a column opacity product for atmospheric studies and planning future orbital lidar observations. Here, such a reference $R_{1064}$ is derived by seeking $R^{M,N}_{1064}$: a Minnaert-corrected normal albedo under clear conditions and assuming minimal phase angle dependence. Over darker surfaces, $R^{M,N}_{1064}$ and the absolute level of atmospheric opacity were estimated from active sounding. Over all surfaces, the opacity derived from active sounding was used to exclude passive radiometry measurements made under opaque conditions and estimate $R^{M,N}_{1064}$. These latter estimates then were re-calibrated by comparison with $R^{M,N}$ derived from Hubble Space Telescope (HST) observations over areas of approximately uniform reflectivity. Estimates of $R^{M,N}_{1064}$ from re-calibrated passive radiometry typically agree with HST observations within 10%. The resulting $R^{M,N}_{1064}$ is then used to derive and quantify the uncertainties of a column opacity product, which can be applied to meteorological and climatological studies of Mars, particularly to detect and measure mesoscale cloud/aerosol structures.