Abstract
Despite nearly complete coverage of the Martian surface with thermal
infrared datasets, uncertainty remains over a wide range of observed
thermal trends. Combinations of grain sizes, packing geometry,
cementation, volatile abundances, subsurface heterogeneity, and
sub-pixel horizontal mixing lead to multiple scenarios that would
produce a given thermal response at the surface. Sedimentary
environments on Earth provide a useful natural laboratory for studying
how the interplay of these traits control diurnal temperature curves and
identifying the depositional contexts those traits appear in, which can
be difficult to model or simulate indoors. However, thermophysical
studies at Mars-analog sites are challenged by distinct controls present
on Earth, such as soil moisture and atmospheric density. In this work,
as part of a broader thermophysical analog study, we developed a model
for determining thermal properties of in-place sediments on Earth from
thermal imagery that considers those additional controls. The model uses
Monte Carlo simulations to fit calibrated surface temperatures and
identify the most probable dry thermal conductivity as well as any
potential subsurface layering. The program iterates through a
one-dimensional surface energy balance on the upper boundary of a soil
column and calculates subsurface heat transfer with
temperature-dependent parameters. The greatest sources of uncertainty
stem from the complexity of how thermal conductivity scales with water
abundance and from surface-atmosphere heat exchange, or sensible heat.
Using data from a 72-hr campaign at a basaltic eolian site in the San
Francisco Volcanic Field, we tested multiple models for how dry soil
components and water contribute to thermal conductivity and multiple
approaches to estimating sensible heat from field measurements. Field
measurements include: upwelling and downwelling radiation, air
temperature, relative humidity, wind speed, and soil moisture, all
collected from a ground station, as well as UAV-derived surface
geometries. By mitigating Earth-specific uncertainty and isolating the
controls that are most relevant to Martian sediments, we can then
validate those controls with in situ thermophysical probe measurements
and ultimately improve interpretations of thermal data for the Martian
surface.