Seasonality in the Angular Dependence of ASAR Wide Swath Backscatter

The analysis of multitemporal synthetic aperture radar (SAR) images requires normalization to a common incidence angle when the images are acquired in varying view geometry. The dependence of radar backscatter on the incidence angle is known to vary with vegetation cover and will therefore change throughout the year. This letter tries to quantify the effect of neglecting this seasonal variability in an empirical incidence angle normalization for a region under Mediterranean climatic conditions. A methodology is presented to assess, at monthly intervals, the seasonal variability of the angular dependence of ASAR Wide Swath (WS) backscatter over Calabria, Italy. It is observed that the angular dependence of backscatter strongly fluctuates temporally, depending on the land cover. The angular dependence of ASAR WS backscatter has a similar seasonal behavior as that of the Advanced Scatterometer for large parts of the study site when both are resampled to a common spatial and temporal resolution. It is found that errors that are larger than the radiometric accuracy of the sensor may be introduced when this temporal variability is ignored in an angular normalization.