THERMOPHYSICAL MODELING OF MANTLED LAVA FLOWS ON MARS: EXTENDING THE KRC LEGACY AND THE PIONEERING WORK OF JOSH BANDFIELD

Mantling of Martian lava flows by dust and sand hinders thermal infrared (TIR) analysis of the underlying bedrock, particularly in the low thermal inertia Tharsis region. Because the dust is not uniformly thick, particularly at the sub-THEMIS pixel scale, it is important to identify the degree of mantling to accurately retrieve the underlying flow’s spectral signature. One approach uses thermophysical modeling to first derive the particle size and areal coverage of the mantling material and then extract the composition of the underlying rocks. To quantify the amount of dust, sand, and lava outcrops on the surface of mantled flows in Daedalia Planum, KRC was used to numerically model the diurnal and seasonal temperature curves of these layered surfaces. Using three ideal components (dust, sand, and rock), diurnal temperature curves were generated for layered units iteratively increasing the thickness of the upper layer. The modeled diurnal responses of the layered systems were linearly mixed to simulate complex flow surfaces. Supervised classifications of visible HiRISE data into lava flow and sand/dust classes also provided a qualitative estimate of the areal percentage of lava outcrops. The idealized single layer mixed model results were compared with the average THEMIS day and night brightness temperatures. Comparison of the model and classification results to the derived thermal response suggests a maximum presence of up to 40% rock (lava outcrops) on these rough (a’a-like) flows. This result corresponds to a maximum dust thickness over the outcrops of less than 0.2 mm and over the sand of 4-5 mm. The work demonstrates that lava flows in Daedalia Planum have a complex combination of vertical layering of dust and lateral mixing of sand, which can be quantified using this modeling approach. A combination of this methodology with a linear spectral deconvolution, both of which are significantly advanced by Josh Bandfield’s past work, may extract the spectral signatures of the least mantled lava outcrops. Results could allow retrieval of lava composition within these low dust windows to constrain any compositional change down flow and between flows with the goal of describing variations in the emplacement process over time.