GNSS Reflectometry for Earth Remote Sensing

Reflectometry is one of many new applications made possible by freely available global navigation satellite system (GNSS) signals. Reflectometry measurement geometry has some features that are significantly different from conventional radar or radiometry. To understand the potential utility of GNSS reflectometry (GNSS-R), first this chapter reviews some of the broader principles of remote sensing and their application to Earth observation. Following a brief history of the field, it describes the fundamental principles and basic observables used in GNSS-R. This is followed by applicable scattering models and their numerical evaluation. Before developing a comprehensive electromagnetic model for the Delay-Doppler map (DDM), the chapter explores the basic geometry of bistatic radar, showing the relationship between the DDM and surface coordinates. This is used to define the essential features of the DDM which can be used to extract information about the roughness and reflectivity of the surface.