Mitigation of Faraday rotation effect for long-wavelength synthetic spaceborne radar data

The focus for geophysical parameter retrieval from space, such as soil moisture, is shifting towards lower frequencies allowing better penetration through vegetation (rendering it less visible) and into the soil (allowing soil moisture sensing into depth). But the ionosphere becomes increasingly opaque at lower frequencies, which intensifies the need for mitigation of ionospheric effects to allow the use of spaceborne radar signals. This work focuses on a radar-only method to predict and mitigate the Faraday rotation effect, which is considered to be the remaining dominant effect. A novel method to retrieve the Faraday rotation angle by using three different optimization techniques in the presence of other system distortion terms with no external targets is presented. The retrieval performance with synthetic spaceborne radar data is very promising; it allows a successful retrieval of the Faraday rotation angle if it is initiated within ±25° of the ground truth.