Aspects of thermal modeling using digital terrain models

Abstract

Context. Our thermal model is adapted and extended in this study. Specifically the aspect of handling indirect radiation, the solar limb darkening effect, and depth profiles are addressed. Aims. Our goal is to improve the existing thermal model to handle terrain scattering and re-radiation in an adaptive way. In addition, we aim to change previously fixed and manually chosen discretization of the solar limb darkening effect and depth profile to be adaptive and applicable for various planets and purposes. Methods. The temperature was modeled based on digital terrain models (DTMs) using data of the Mercury Laser Altimeter (MLA). New implementations to handle terrain scattering and re-radiation were introduced using level-of-detail techniques. The solar disk was discretized into a variable number of rings and the depth profile was introduced as an exponential function for which the number of nodes and the maximum depth can be chosen. Results. We present results for the ideal window size and degree of level-of-detail for thermal studies of the Hermean north pole. Further we show that the previous discretization of the solar limb darkening effect proved insufficient for Mercury, and we updated the implementation accordingly. Similarly we improved the implementation for the depth profile. For the first time, we derived depthto-ice, as well as average and maximum temperature maps based on thermal modeling of the complete north polar MLA DTM.

Highly Resolved Topography and Illumination at Mercury’s South Pole from MESSENGER MDIS NAC

“…Modeling surface illumination also constitutes the first step toward retrieving the thermal evolution at or near the surface. In turn, knowledge of near-surface temperature over time is key to determining the nature of radar-bright deposits observed at Mercury poles (Harmon et al 2011;Chabot et al 2018), as previously shown at Mercury's north pole (Paige et al 2013;Chabot et al 2018b;Hamill et al 2020;Barker et al 2022;Gläser 2022). For instance, an accurate modeling of near- surface maximum and average temperature is necessary to assess whether water ice (or other volatiles) can survive near the surface over geological timescales.…”

“…Early simulations of the north polar region's illumination conditions and thermal environment were described in Neumann et al (2013) and in Paige et al (2013), using the first year of MLA data. More accurate simulations, based on the complete MLA data set, were first published in Chabot et al (2018b), and more recently by Gläser (2022). Other studies (Deutsch et al 2016;Rubanenko et al 2018;Susorney et al 2021) have also focused on the north polar region leveraging the MLA elevation models (see, e.g., Zuber et al 2012;Hamill et al 2020;Barker et al 2022), in part because no reliable high-resolution elevation data for the southern polar region are available.…”