Impact of wave refraction due to environmental conditions on image processing quality in high resolution SAR

SAR signal processing is based on the range evolution of the different scatterers during the illumination time. The range is estimated using the time delay between the emission of the pulse and the reception of the echo. During processing, it is assumed that the wave travels through an homogeneous medium with uniform dielectric characteristics and that the optical path corresponds to the straight line between sensor and scatterer. In reality, waves travel through different media, like clouds or forest canopies which have a dielectric constant greater than 1 due to their water content. Refraction through those different media will lead to a longer optical path, combined with a smaller wave velocity. Both effects are then responsible for an overestimation of the target range, which is not constant during the whole illumination time, causing a degradation of the image quality. This paper analyzes the effect of the refraction of radar waves in the SAR signal processing.