Signals of Opportunity Reflectometry at Multiple Frequencies and Polarizations: Simulation Studies and Instrument Validation

Signals of Opportunity reflectometry (SoOp-R) employs existing non-cooperative transmitters as sources of illumination in bistatic radar. In the typical application, these sources are communication satellites. Cross-correlation between a direct line of sight signal and a reflected path signal (or autocorrelation of the combined signal) can be used as an observation to estimate the surface complex reflection coefficient. SoOp-R enables microwave remote sensing observations to be made in bands allocated for communications and is thus not limited to frequencies protected for science use. P-band (<500 MHz) is of particular value as those frequencies are heavily used for communications and have no protected bands. Only P-band is capable of penetrating below the top few cm of the soil, to provide sensitivity to the root-zone soil moisture (RZSM). Presently no direct retrievals of RZSM are available from spaceborne instruments (although there are some data assimilation products using surface soil moisture from L-band observations).