Studies of phase center and extinction coefficient for boreal forest using X- and L-band polarimetric interferometry combined with LIDAR measurements
Jaan Praks(1), Martti Hallikainen(1) and Yu Xiaowei(2)
(1) Helsinki University of Technology, Otakaari 5 A, 02150 Espoo, Finland
(2) Finnish Geodetic Institute, Geodeetinrinne 2, 02431, Masala, Finland
In this work we study aspects of boreal forest remote sensing with L-and X-band POLinSAR and Random Volume over Ground (RVoG) model based methods. For this study, we complement interferometric L-band and X-band dataset with an accurate LIDAR measured terrain and canopy height model. With the help of this terrain model we calculate accurate ground and treetop phase estimates for interferometric SAR data and discuss several important issues connected to RVoG model based POLinSAR techniques.
We show that the interferometric phase center is deep inside the canopy even at X-band, and the phase center height follows rather well the treetop height. By inverting the RVoG model for extinction coefficient, we show that extinction coefficient for L- and X-band is rather low for boreal forest, but varies with forest type. We also discuss the ability of coherence tomography to reveal objects hidden inside the canopy.
The SAR data used in our study was collected during the FINSAR campaign, carried out in autumn 2003 in Finland over a boreal forest test site. The German E-SAR collected five L-band (1.3 GHz) repeat pass fully polarimetric images (5 m, 10 m, 12 m and 0 m baselines) and an X-band (9.6 GHz) single-pass single-pol (VV) interferometric image pair. The LIDAR scanning over part of the FINSAR test site was conducted by the Finnish Geodetic Institute on 12 July 2005 using Optech ALTM 3100 scanner, providing a 3-4 pts/m² point density on the object. Accurate Digital Surface Model (DSM) and the canopy height model (CHM) were derived from the LIDAR measurement