Probing Soil Moisture Up to Root-Zone by Using Multiple Signals of Opportunity

Routine, repeatable radar measurements of soil moisture are expected to be achievable through the use of frequencies with penetration depths that reach the root-zone of given vegetation structures within soil. Due to the size, weight, power, cost, and legal constraints of creating spaceborne radar transmitters, the practice of reutilizing existing satellite navigation/communication systems for spaceborne radar applications is gaining attention from research communities under the title "Signal of Opportunity" (SoOp). The use of SoOp transmitters as a free source of illuminators is expected to be a viable tool for the remote sensing of soil moisture at depths below 5 centimeters. However, the returns of a radar signal can be representative of many types of soil moisture profiles, and the returned radar signals do not indicate the depth of the contained soil moisture. To this end, this paper is intended to better understand the various effects that radar parameters have on a returned radar signal given a known, simple soil moisture profile in order to help determine the feasibility of using multiple (SoOp) transmitters to determine soil moisture profiles. In order to accomplish this, the recently developed SoOp Coherent Bistatic (SCoBi) scattering model is used to determine the relative permittivity of a given soil moisture profile as well as determine the complex reflection coefficients of the incident signals upon the surface.