Temporal Stability of Ground Notched Images

The problem of estimating above ground biomass in tropical regions has been recently tackled by using tomographic SAR data at low frequencies. The added value of tomography is the possibility of focusing on specific heights inside of the vegetation layer, rejecting the echoes coming from other elevations at the same time; in particular, the strong echoes coming from the ground level are greatly attenuated. Recently, a simpler algorithm aiming at this goal has been proposed: the interferometric ground notching. According to this algorithm, two InSAR images are coherently combined to cancel out the ground echo and emphasize the forest backscattering. However, any time lag between the two images introduces temporal decorrelation which, in turn, affects the effectiveness of the coherent subtraction. This work shows an analysis of the effect of the temporal decorrelation from a theoretical point of view and through experiments on real data; results from a boreal forest and a tropical one are presented. As predicted by the theory the impact on the radiometric stability results limited to within 0.5-1dB for taller forest where most of the biomass is stored.