Observation of tropical rain forest trees by airborne high-resolution interferometric radar

The Indonesian Radar Experiment (INDREX) Campaign was executed in Indonesia to study the potential of high-resolution interferometric airborne radar in support of sustainable tropical forest management. Severe cloud cover limits the use of aerial photography, which is currently applied on a routine basis to extract information at the tree level. Interferometric radar images may be a viable alternative once radar imaging at the tree level is sufficiently understood. It is shown that interferometric height images can contain large height and displacement errors for individual trees but that this problem can be solved to a large extent using models for the vertical distribution of backscatter intensity and an extension of the Van Cittert-Zernike theorem. The predicted loss of coherence in lay-over regions of emergent trees is shown to be in good agreement with the loss of coherence as observed in the high resolution radar data (Pierson correlation coefficient=0.94). Several correction methods for height and displacement errors are proposed. It is shown that a simple approach already gives a good correction. Semi-empirical correction models, which can be calibrated for forest structure, perform even better.