Relationships between physical characteristics and polarimetric radar backscatter for Corsican pine stands in Thetford Forest, U.K.

Abstract

Global monitoring of forest extent and changes of extent with time are vital not just to provide a continuous assessment of a renewable resource essential to mankind but also to give an input to models of the global carbon cycle and of climate change. Microwave remote sensing is a potential means to accomplish this objective. However, to determine the optimum characteristics of a satellite synthetic aperture radar (SAR) for reliable forest monitoring it is first necessary to validate modelled microwave backscatter relationships in studies of relatively small areas using data from aircraft SAR systems and from detailed ground survey.

The Maestro 1 Campaign provided fully polarimetric SAR data in three wavelengths together with a large set of ground data for Thetford Forest. Calibrated microwave responses were averaged for more than 300 stands, primarily of Corsican pine. A georefercnccd database for the test site was built up from these mean responses combined with information on planting date, species and, for those stands fully sampled, characteristics such as height and timber volume. The radar backscatter at P and L bands, expecially the cross-polarized responses. correlate well with volume.

An analysis is made of the accuracy with which regression models can be used to predict timber volume over larger areas around the test site. The precision of this prediction can be improved by fuller use of the information contained within the measured data, specifically in the correlation between the HH and VV returns, and by the fuller use of theoretical models, which consider more comprehensively the complete polarimetric backscatter mechanisms relevant to the response of stands.