The CORSAR project: Can polarimetric SAR interferometry improve forest biomass estimation?
Centre for Ecology and Hydrology,
Huntingdon PE28 2LS,
(2) University College London, 26 Bedford Way, London WC1H 0AP, United Kingdom
(3) University of Zurich-Irchel, Remote Sensing Laboratories, CH-8057 Zurich, Switzerland
The main limitation in the application of spaceborne SAR to large-scale forest biomass mapping is the variability in canopy structure and vegetation density. It causes signal saturation and a large residual error in the parameter estimates. A problem in defining retrieval algorithms for forest biomass is that microwaves respond to the shapes, sizes, orientations and dielectric properties of all the illuminated scatterers including the ground. Microwave backscatter models have revealed that the effect of variation in canopy structure on the signal can be higher than the effect of biomass. Polarimetric SAR interferometry potentially offers a means of improving SAR-based estimates of forest biomass by quantifying canopy structural variability. The polarisation information is dependent on the scattering mechanisms, and the interferometric information can be used to determine the vertical location of these scattering events in the canopy. The CORSAR project (Carbon Observation and Retrieval from SAR), which is supported by the UK Natural Environment Research Council (NERC), has the objective to examine polarimetric decomposition and polarimetric SAR interferometry methods for estimating the effects of canopy structure in biomass-backscatter relationships. We present results of the polarimetric coherence optimisation of L-band E-SAR data acquired during the SAR and Hyperspectral Airborne Campaign (SHAC 2000), and compare the InSAR DEMís with a LIDAR derived DEM that was acquired concurrently. The effect of polarisation on the height estimation is discussed, and illustrated by coherent microwave modelling results from the model CASM. The expected rmse of the interferometric phase is modelled and its implications for defining useful sensor configurations discussed.