RETRIEVAL OF FOREST BIOMASS FROM SAR DATA

In recent years, there has been an increasing interest in the use of radar data for observations of forest ecosystems. In particular, it was shown that the intensity of SAR images at L band was proportional to the forest aboveground biomass. More recently, the analysis of NASA/JPL SAR data over the Landes forest (south-west France) revealed strong correlation between P-band backscatter and biomass of pine trees and related characteristics (tree age, height, diameter). Also, similar relations have been obtained on two different forests (maritime pine at Landes forest, France, and loblolly pine at Duke forest, U.S.A.). This paper presents a step further in the understanding of the observations, using theoretical modelling applied to calibrated SAR data to explain the radar backscatter from the forest canopy under study. The study is presented at P band, which was found to be an optimal frequency band for forest observations. It was found that the HH return is physically related to both trunk and crown biomass, whereas VV and particularly HV returns are linked to crown biomass. Through allometric equations, relations between radar backscatter intensities and most of the forest characteristics can thus be explained. The validated model has been used in a next step to simulate a diversity of forest and observation conditions. The results have been used for a preliminary assessment of the possibility of inverting SAR data into forest biomass.