A novel method for noise equivalent sigma nought estimation

In Synthetic Aperture Radar, Noise Equivalent Sigma Nought (NESZ) is usually verified by measurements over targets with ideally null backscatter, like calm water, or flat surfaces. This condition is quite different from the normal one, in term of quantization, source temperature, ambiguities and received signal energy. We propose a novel method based on interferometry that estimates NESZ in presence of a significant source backscatter. It exploits the principle that noise is the ultimate and unavoidable factor limiting coherence. For each value of backscatter (say in an histogram), a search is made for the target with highest coherence. NESZ is then estimated by fitting the theoretical model of coherence versus signal-to-noise-ratio. The estimate is performed for different range by exploiting narrow strips. The method relies on the existence of some target whose coherence is limited only by thermal noise. Results of processing Sentinel 1A / 1B data over the'Salar de Uyuni' site are here compared with the classical measures over signal-free region.