P034-0003
Photometric Modeling of Bennu at 1064-nm with the OLA Normal Albedo
Thursday, 10 December 2020
Poster
Michael Kenneth Barker, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Gregory A Neumann, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA, Greenbelt, MD, United States, Erwan Mazarico, NASA Goddard Space Flight Center, Code 698, Greenbelt, MD, United States, Michael G Daly, York University, Centre for Research in Earth and Space Science, Toronto, ON, Canada, Olivier S Barnouin, JHU Applied Physics Lab, Laurel, MD, United States, Erica R Jawin, National Museum of Natural History, Department of Mineral Sciences, Washington, DC, United States, Manar Al Asad, University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, Beth Clark, Ithaca College, Ithaca, NY, United States and Dante S Lauretta, University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ, United States
Abstract:
The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission to the dark and primitive asteroid Bennu carries a laser altimeter, OLA, as part of its suite of instruments. OLA is an active-sensing instrument designed primarily for determining global shape and preparing for sample acquisition. OLA also records the return intensity of its pulses, from which we derived the surface albedo at zero phase angle (normal albedo) at 1064-nm wavelength. The data were collected with the Low Energy Laser Transmitter (LELT) during the Orbital B mission phase at ~600–740 m range at nearly nadir pointing as Bennu rotated beneath the polar-orbiting spacecraft. The LELT operated at a 10-kHz firing rate, collecting ~3 billion intensity measurements with ~7-cm-diameter footprints.
The laser spot returns provide uniform measurements globally of normal albedo, as has been done by laser altimeters at other airless bodies. For example, our previous work demonstrated the utility of the normal albedo measured by the Lunar Orbiter Laser Altimeter in studying geologically related variations in the lunar phase function (Barker et al. 2016). Such variations may be related to physical properties of the surface and regolith grains. Here, we take a similar approach, exploring how the OLA normal albedo can inform photometric modeling of Bennu with globally distributed data at 1064-nm from the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS). We report preliminary results on the absolute radiometric calibration of the OLA normal albedo, as well as on photometric modeling incorporating the normal albedo as a spatially variable constraint to reduce the number of free parameters in the models. We compare several photometric models (e.g., Minnaert, Lunar-Lambert, Hapke, etc.) with and without the model normal albedo fixed to the OLA normal albedo. Preliminary results suggest that incorporating the normal albedo map, smoothed to the OVIRS footprint size, generally improves the model RMS residuals. Future work will consider spatial variations in other model parameters and the derivation of parameter error estimates. We will examine geologically related variations in model parameters and model-data residuals to better understand the factors affecting the surface scattering behavior.
