Polarization effects in radar reflection from surfaces with periodic roughness

Periodic roughness occurs due to both human activities and wind erosion processes. Data from the Jet Propulsion Laboratory´s Airborne Synthetic Aperture Radar (AIRSAR) have revealed that wind rippled surfaces produce a shift in the location of maximum co-polarized return away from the typical VV response of natural surfaces. It was also noted that these surfaces cause an imbalance between the two co-polarized circular polarizations. The wind ripples observed during in-situ observations were found to have wavelengths close to that of the radar wavelength in which these polarization effects were observed. A second-order small perturbation model is used to demonstrate that these polarization effects can be generated in radar echoes from nearly sinusoidal surfaces with dominate wavelengths dose to the wavelength of the radar. The shift of the co-polarized response and the change in the balance between the co-polarized circular returns depends on the orientation of the sinusoidal surface. This is extended to investigate more closely the dependence on incidence angle and on the relative wavelengths of the surface and of the radar being used to illuminate the surface. Another type of periodic surface that can occur in areas commonly imaged as part of remote sensing experiments is planting furrows on active, fallow and some recently abandoned fields. A particularly interesting example of this is the concentric furrowing sometimes used with center pivot irrigation. In remote sensing data collected over the Manix Basin Area of the Mojave Desert in Southern California, bright diameters were noticed on active and recently inactive fields. The most commonly occurring bright diameter is one parallel to the look direction that is easily explainable by specular reflection from the segments or the concentric furrows that are perpendicular to the look direction. However, them is a particularly interesting case of an active field that exhibits two other bright diameters oriented approximately 30 degrees from the look direction in the wavelength that most nearly matches the spacing between the furrows.