Evaluating PolInSAR Tree Height and Topography Retrievals in Glen Affric
The University of Edinburgh,
EH8 9XP Edinburgh,
(2) AEL Consultants, Unit 3.3, KY15 5YQ Cupar, United Kingdom
(3) DLR German Aerospace Center, Oberpfaffenhofen, D-82230 Wessling, Germany
In this paper we present new results evaluating the retrieval of tree height and bald earth topography from polarimetric interferometry. We present a comparison of results from L-band repeat pass SAR imagery with detailed in-situ measurements of forest height and ground topography across the test site. The data was acquired over Glen Affric in Northern Scotland as part of the NERC/BNSC SAR and Hyperspectral Airborne Campaign (SHAC) in June 2000. The DLR E-SAR data comprises fully polarimetric L-band SAR data in repeat-pass interferometry mode with two baselines, and two look directions. The Glen Affric data set is unique within the UK in that it contains polarimetric and multi-baseline interferometric L-band data in an area of varied topography and heterogeneous landscape. This paper will comprise a description of recent field measurements that include a detailed survey of almost 400 trees, and a quantitative comparison between this survey data and retrieved parameters. The paper will assess both the accuracy of tree height retrievals derived from single baseline polarimetric interferometry, and surface topography derived from dual-baseline PolInSAR using coherence optimisation. Within certain limits of canopy geometry and topography the tree height derivation has proven to be more successful than expected in areas of heterogeneous forest cover. A RMS error of 6m was found when comparing the trend between retrieved and field survey topography, despite canopy heights of 20m or more. As expected, the greatest errors are mainly in areas of high canopy density.