The Effects of Surface and Subsurface Structural Anomalies on the Detectability of Shallow Aquifers on Europa by Sounding Radar

Abstract:

Clutter from surface topography can compromise the sounding radar capability to detect shallow subsurface features in several planetary environments. Herein we investigate the effect of surface and subsurface structural anomalies on the detectability of potential shallow aquifers for the case of Europa ice penetrating radars. We investigate the surface and volume scattering effects arising from the cratering, geothermal and ice tectonic structural elements associated with Europa’s geological evolution. Using the Finite Difference Time Domain (FDTD) method we modeled the radar wave propagation through Europa’s subsurface in the frequency range from 9 to 30 MHz for two Europa geoelectrical models representing the thermally conductive and convective subsurface models. These geoelectrical models are then meshed to match the subsurface structural models for the most common two types of terrains on Europa, i.e. the Double Ridges and the Chaos Terrain, represented. Our simulations suggest that shallow aquifer detection in the first 3 km of the Europa subsurface can be achieved in most types of terrains for the conductive models and derive the constraints for its detectability in the terrains that are hypothesized to be formed from convective thermal activity. Both the large subsurface fractures and the brittle-ductile interface and their slopes variation are also possible to detect in the simulated radargrams for various surface roughness conditions. Our results suggests that quantifying the surface and volume scattering effects arising respectively from topographic and roughness conditions and subsurface structural anomalies through FDTD simulations is crucial to optimize the future sounding radar orbital data acquisitions. We will also present the added value of using interferometric and passive acquisitions to reduce the ambiguities of the complex clutter and maximize subsurface detectability of aquifers.