1 SIMULATING X-BAND INTERFEROMETRIC HEIGHTS AND CANOPY PENETRATION USING AIRBORNE LIDAR

Forest health monitoring may be based on SAR interferometry (inSAR) heights, where variations over time in the height will represent defoliation and recovery, as well as other disturbances. SAR microwaves penetrate down into the forest canopy layer. The depth of this penetration depend on the amount of, and the 3D distibution of foliage scatterers, and this may be utilized for forest monitoring. We have developed a routine that simulates the X-band SAR backscattter and interferometric heights derived from it. We have used a combined data set og SRTM x-band interferometric heights and airborne laser scanning data for a 15 km2 forest area in South Norway. The 3D distribution of scatterers is described by voxels, or 3d pixels. The gap fraction and cover fraction of each of the 2.5 mill voxels is determined from near-vertical LIDAR data. We have modelled the SRTM 55 degrees inclination angle view through the voxels, assuming a direct northfacing azimuth view. The backscatter from each voxel is estimated, as is the interferometric height. The interferometric heights and the modelled heights were linearly related with a slope of almost 1:1 and R2=0.99. After subtracting the terrain heigts, the relationship was still close to 1:1 and had R2=0.76. This corresponds to a height measure in the forest canopy. The model will be further tested with Terrasar-X data being gathered in this year’s summer. 1