High-resolution InSAR image simulation for forest canopies

High-resolution interferometric airborne synthetic aperture radar (SAR) images of Indonesian tropical rain forests have been acquired during the European Space Agency (ESA) Indonesian Radar Experiment (INDREX) 1996 campaign. Research efforts are directed toward development of automated canopy reconstruction algorithms. In this paper, interferometric synthetic aperture radar (InSAR) image simulation is discussed as one of the tools to support development of such inversion algorithms. First, the relevant physics, observation geometry, and radar characteristics are described. It is assumed that a forest can be modeled as a cloud of uniformly distributed isotropically scattering elements located within crown volumes. These volumes were measured during a field experiment for a 7.2 ha plot. Simulated data comprise intensity, phase, as well as coherence images. These are compared, in a statistical sense, with real data acquired in C- and X-bands. The canopy attenuation was simulated over a range of values. The normalized second intensity moment, the mean coherence magnitude, the coherence histogram, and the autocorrelation function of coherence were taken as measures for comparison. It can be concluded that simulated and real C-band images compare well for an extinction coefficient in the range of 0.15-0.3 m^-1. For X-band, the selected measures of agreement lead to contradictions, indicating that the physical assumptions made may be less valid than for C-band.