Spatial resolution in GNSS-R under coherent scattering

• Published in: IEEE Geoscience and Remote Sensing Letters
• Main Author: Camps Carmona, Adriano José
• Other Authors: Universitat Politècnica de Catalunya. Departament de Teoria del Senyal i Comunicacions, Universitat Politècnica de Catalunya. RSLAB - Grup de Recerca en Teledetecció
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Àrees temàtiques de la UPC::Enginyeria de la telecomunicació::Radiocomunicació i exploració electromagnètica::Teledetecció; Remote sensing; Coherent scattering; Fresnel zone; Global navigation satellite systems; Reflectometry (GNSS-R); Spatial resolution; Teledetecció; Sea ice
• Online Access: http://hdl.handle.net/2117/175851; https://doi.org/10.1109/LGRS.2019.2916164

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Global Navigation Satellite Systems Reflectometry can be understood as a multistatic radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas, even under dense vegetation, and in some cases, over land show a significant coherent component. Under coherent scattering conditions, it is usually stated that the coherent signal component comes from an area equal to the first Fresnel zone. This letter analyzes in more detail the spatial resolution in this forward scattering configuration, showing that, when coherent scattering is nonnegligible, the spatial resolution is mostly determined by the geometry and not by typical surface roughness values. As the scattering area around the specular reflection point increases and encompasses the first Fresnel zone, the received power increases and then it fluctuates as higher order Fresnel zones are included (rapid phase changes due to the spherical waves). These contributions may explain in part the large scattering encountered over inhomogeneous land regions, as these different contributions add or subtract, depending on the phase of the electric field, and are weighted by different scattering coefficients (i.e., changes in the dielectric constant and/or surface roughness, such in water ponds or some agricultural fields). Finally, over homogeneous targets, when all Fresnel zones are included, the received power tends asymptotically to the value obtained using the free-space propagation with a total path length equal to the sum of the path lengths, weighted by the reflection coefficient. This value can also be interpreted as coming from an ...