Assessment of Value of Multiple Signals of Opportunity (SoOp) for Estimating Root-Zone Soil Moisture (RZSM) Directly

Signals of Opportunity (SoOp) in P-band (200-400 MHz) offers a new remote sensing approach with the potential of estimating rote-zone soil moisture (RZSM) directly under all weather conditions day and night. SoOp Reflectometry can benefit from using small satellites since the use of a dedicated transmitter is abandoned for the exploitation of existing satellite transmitters through separating direct and reflected signals. Because of this trait, SoOp reflectometry can achieve low size, weight, power, and cost (SWaP-C) solutions for remote sensing problems. Additionally, the use of free transmitters allows for measurements to maintain high spatial resolution on the scale of 1-to-10-km as well as to the high temporal resolution provided by the numerous communication/navigation transmitters. Finally, intelligent use of SoOp for remote sensing conserves the limited bandwidth available in the radio frequency spectrum. The benefits of using SoOp for land remote sensing directly address many of the concerns expressed by hydrologists for improving soil moisture data products.

The challenges that lie ahead for SoOp methodology to realize these advantages lay in the realm of robust forward and inverse modeling simulation environment. In this study, we utilize the described advantages of SoOp to develop high quality realistic simulated data for exercising inversion algorithms for such systems at multiple frequencies/polarizations, and incidence angles. To this end, we will use our forward model, titled the SoOp Coherent Bistatic Scattering (SCoBi) model, which is recently open-sourced. It simulates fully polarimetric, bi-static response from vegetated and bare-soil terrains where the ground structure can be modeled as multi-layered complex dielectric structure. In this talk, we will present our recent simulated studies to address two questions: How does the specular reflection coefficient change in response to RZSM changes? What can inversion techniques tell us about SoOp sensitivity to RZSM changes? Our recent findings indicate that dielectric contrast will largely determine the contributions of subsurface scattering to the total measured reflectivity. In addition, in many conditions, SoOp sources can detect large changes in reflectivity several times deeper than that suggested by the penetration depth.