Abstract DGP2026-10

Surface reflectance of a planet provides fundamental information for understanding its geologic evolution. In the ESA-JAXA joint BepiColombo mission to Mercury, the BELA (BepiColombo Laser Altimeter) will obtain surface reflectance at 1064 nm as well as high-resolution topographic data [1]. This will spatially supplement information that previous Mercury explorations did not obtain. The MESSENGER mission’s MLA (Mercury Laser Altimeter) instrument provides a valid source of 1064-nm data only for the northern hemisphere because of its eccentric orbit [2]. Therefore, BELA presents an opportunity to provide the first global measurements of Mercury’s reflectance and topography with a laser altimeter. However, its performance still needs to be quantified using realistic reflectance distributions of Mercury at the wavelength of 1064 nm.

 

Laser altimetry provides surface reflectance at only a single wavelength and does not directly constrain surface composition, requiring comparison with broader-wavelength reflectance datasets to relate laser-altimeter measurements to geologic evolution such as space weathering [e.g., 3]. Comparative analysis between MLA and hyperspectral reflectance data may allow for interpretation of 1064-nm reflectance data in the context of surface composition. The MASCS (Mercury Atmospheric and Surface Composition Spectrometer) instrument onboard MESSENGER collected hyperspectral data of the Mercury surface in wavelengths that include 1064 nm with full global coverage and can be used to make comparisons with MLA data. Comparison between MASCS and MLA data can also provide global-scale expectation for 1064-nm surface reflectance, which can be used in BELA performance estimates.

 

In this study, we investigate the relationship between MLA and MASCS data. We compare reflectance data for instances where both instrument footprints overlap spatially on Mercury’s surface. Taking only high-quality data for each instrument based on observation geometry and instrument temperature, we compare MASCS reflectance with the average reflectance of MLA measurements located within the targeted MASCS footprint.

 

Throughout our comparison, reflectance values show a scattered but consistently positive trend with MLA values appearing three times brighter than those of MASCS due to differences in observation geometry. We found a weak correlation between the datasets, possibly being limited due to the resolution discrepancies between the instruments. Fitting a linear model to the measurement data, we quantify reflectance correlation between instruments to construct a simulated 1064-nm dataset based on global MASCS mosaic. This comparison may lead to better prediction of BELA measurements as well as improved analysis of its future reflectance measurements. In this presentation, we will discuss additional comparison of 1064-nm reflectance data with spectral curvature and color indices of hyperspectral datasets to demonstrate how laser altimeter data can be used to interpret surface material information.

 

[1] Thomas et al. (2021), The BepiColombo Laser Altimeter, Space Sci Rev, 217:25

[2] Cavanaugh et al. (2007), The Mercury Laser Altimeter Instrument for the MESSENGER Mission, Space Sci Rev, 131: 451–479

[3] Barraud et al. (2025), Impact of Thermal Weathering on Mercury's Reflectance, Geophysical Research Letters, 52, e2024GL113933.