Extracting tree heights using JPL TOPSAR DEM data

The accuracy of the digital elevation model (DEM) generated by the JPL TOPSAR for extracting canopy height is evaluated. For this purpose an experiment using C-band TOPSAR at the Michigan Forest Test Site (MFTS) in Michigan´s Upper peninsula was conducted. For the chosen tree stands, extensive ground data were collected. The most important and difficult-to-characterize ground truth parameter was the forest ground level data which is required for extracting the height of the scattering phase center from the interferometric SAR (INSAR) DEM. To accomplish this, differential GPS (Global Positioning System) measurements were done to accurately (±5 cm) characterize the elevation in selected areas. Significant discrepancies between GPS and TOPSAR DEMs and between the two TOPSAR DEMs of the same area were observed. The discrepancies are attributed to uncompensated aircraft roll and multipath. After correcting for these as best as the authors could, an average periodic height discrepancy along the cross-track direction of about ±5 m remained, Recommendations are provided for the extraction of the best estimate of the scattering phase center height and a model is provided to estimate actual tree height. It is accurate to within 1 meter or 10% for the red pine test stands used