Abstract
Signals of opportunity (SoOp) reflectometry (SoOp-R) is a maturing field for geophysical remote sensing as evidenced by the growing number of airborne and spaceborne experiments. As this approach receives more attention, it is worth analyzing SoOp-R's capabilities to retrieve subsurface soil moisture (SM) by leveraging communication and navigation satellite transmitters. In this research, the CRLB is used to identify the effects of variable SoOp-R parameters on the best achievable estimation error for root-zone soil moisture (RZSM). This study investigates the use of multiple frequency, polarization, and incidence angle measurement configurations on a two-layered dielectric profile. The results also detail the effects of variable SM conditions on the capability of SoOp-R systems to predict subsurface SM. The most prevalent observation is the importance of using at least two frequencies to limit uncertainties from subsurface SM estimates. If at least two frequencies are used, the CRLB of a profile is retrievable within the root-zone depending on the surface SM content as well as the number of independent measurements of the profile. For a depth of 30 cm, it is observed that a CRLB corresponding to 4% RZSM estimation accuracy is achievable with as few as 2 dual-frequency-based SoOp-R measurements. For this depth, increasing number of measurements provided by polarization and incidence angle allow for sensing of increasingly wet SM profile structures. This study, overall, details a methodology by which SoOp-R receiver system can be designed to achieve a desired CRLB using a trade-off study between the available measurements and SM profile.
Highlights
S IGNALS of opportunity (SoOp) reflectometry (SoOp-R) within remote sensing refers to the process of leveragingManuscript received July 30, 2020; revised September 11, 2020; accepted September 27, 2020
While there is clearly increased performance when the root-zone soil moisture (RZSM) value increases from 10% to 20%, this behavior is caused by the interaction of the signals with the provided multilayer dielectric structure
This research presents the study of the Cramer–Rao lower bound (CRLB) for soil moisture (SM) within a two-layer SM profile by means of SoOp-R measurements
Summary
S IGNALS of opportunity (SoOp) reflectometry (SoOp-R) within remote sensing refers to the process of leveraging. 370 MHz, Global Navigation Satellite System sources which feature publicly available codes at 1575.42 MHz, and the XM Satellite Radio constellation at 2338 MHz. While simulations have clearly shown that SoOp-R measurements observe the effects of RZSM when simulating multilayered dielectric structures [20], it is helpful to determine the estimation accuracy of differing SoOp-R configurations on RZSM profiles. While simulations have clearly shown that SoOp-R measurements observe the effects of RZSM when simulating multilayered dielectric structures [20], it is helpful to determine the estimation accuracy of differing SoOp-R configurations on RZSM profiles Such studies can help design future SoOp-R experiments as well as provide insight on the potential uncertainty embedded within inversion algorithms.
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