Utilising a new laboratory BRDF dataset for Apollo regolith samples with known surface properties: Interpreting Diviner's visible off-nadir data and setting accurate scattering functions within thermal models.

An accurate description of how visible light scatters from the lunar regolith over a range of viewing anglesdefined as the Bidirectional Reflectance Distribution Function (BRDF)enables physical properties to be determined, by comparing laboratory or remote sensing data to a photometric model, such as Hapke [1]. It also enables more accurate scattering functions to be set within 3D thermal modelsi.e. the Oxford 3D Thermal Model (O3DTM)thus potentially improving the match between modelled surface temperatures and remote sensing measurements from thermal infrared (TIR) instruments, such as the Diviner Lunar Radiometer [2, 3]. At Oxford, a suite of BRDFs have been measured using the Visible Oxford Space Environment Goniometer (VOSEG), for Apollo regolith samples 10084 and 68810 with a range of porosity and RMS slope angle values (measured across 10-1000m size-scales) [4, 5, 6]. BRDFs have been measured over a wide range of viewing angles (0-60o incidence; 0-70o reflectance; 0/45/90/135 and 180o azimuth) and have been compared to Diviners broadband solar visible (300nm-3m) off-nadir data, for various targets such as Aristarchus, Kepler Ejecta, the Dufay Anomaly and equatorial and high-latitude Highlands and Mare regions [7]. Furthermore, by fitting Diviners visible off-nadir data to the Hapke model, estimates for various Hapke parameters can be deduced, as in [8]; thus shedding light on the physical properties of the lunar regolith in these regions. Finally, this dataset can be used to set more accurate visible scattering functions within the O3DTM, than by using Lambertian functions [2]. This presentation will detail the laboratory BRDF study; and it will show the latest results from off-nadir remote sensing and thermal modelling studies which utilise this new BRDF dataset. References: [1] B. Hapke (2012) Icarus [2] O. King et al. (2020) Planet. and Space Sci. [3] D. Paige et al. (2010) Science [4] R. Curtis et al. (2021) Rev. Sci. Instrum. [5] R. V. Morris (1983) Handbook of Lunar Soils [6] P. Helfenstein and M. K. Shepard (1999) Icarus [7] B. T. Greenhagen et al. (2017) AGU Fall Meet Abstr. [8] H. Sato et al. (2014) J. Geophys. Res.