Estimating Tropical Aboveground Biomass from Fourier Transforms of Vegetation Profiles from TanDEM-X Phase Heights

This paper explores the information content of few-look phases from TanDEM-X (X-band) for the vegetation profile and aboveground biomass (AGB) over 50 x 50 m stands in tropical moist forests in Brazil. The formalism for modeling the interferometric phase of interferometric SAR (InSAR) is examined before taking the look, or ensemble average. It is suggested that it is the look averaging that confines the Fourier profile information to one Fourier frequency per baseline. Before the look averaging, a histogram of InSAR phases seems related to the radar power profile, which, in turn, is related to the vegetation density profile. This is only true, however, if the the number of participating scatterers is very small. After a simulation of small-scatterer-number profiles from few-look phases, 2-look phase histograms are shown along with lidar waveform profiles and modeled field profiles. A regression of field biomass versus Fourier transforms of the look-height distribution shows about 15% improvement over using traditional single-baseline coherence and phase.