Experimental Demonstration of Soil Moisture Remote Sensing Using P-Band Satellite Signals of Opportunity

P-band Signals of Opportunity (SoOp) has great potential for remote sensing of root zone soil moisture (RZSM) from space. We have carried out a tower-based experiment with receivers to detect the reflected signals from the communications satellites at the Fraser Experimental Forests (FEFs), Colorado, in 2017. The measured reflectivity data at 260 MHz have a good correlation with in-soil moisture (SM) measurements. Retrieval of SM from the reflectivity data was also performed with results indicating accuracy of about 0.01 bias and 0.02 standard deviation (std) with respect to the average of SM in the upper 10 cm of soil. The experimental data and retrieval analyses lend support to the use of P-band SoOp for the remote sensing of SM. Our data also indicate the limitation of single frequency observations, suggesting the requirement of multiple frequencies to enable RZSM remote sensing because the surface SM plays a critical role on the change of reflectivity even at P-band frequencies.