Forest Height Estimation with X-band InSAR: Phase Centre Location versus RVoG

Abstract

Recent experiments indicated the potential of X-band SAR interferometry as a valuable information source for forest monitoring. One important forest parameter in terms of forest monitoring is forest height which can be estimated using the RVoG model [1]. Compared to low frequencies like L- and P-band where the ground is an essential contribution, at X-band for ordinary forest systems, the ground contribution in the signal can be (and has been) assumed to be negligible low [2]. In this case, the X-band signal is dominated by the volume contribution. Assuming this, and using a priori knowledge about the phase related to the underlying ground, forest height can be estimated from a single interferomtric acquisition at a single polarisation. Of course the ability of estimating height in terms of X-band interferomtry depends on the capability of X-band to penetrate into and through the forest layer –that directly depends on the density and hence the extinction of the volume layer. In this paper we address both questions by analysing, inverting and validating two data sets acquired by the ESAR system from the German Aerospace Centre (DLR). The first data set was acquired during the INDREX campaign and covers the Mawas peat swamp forest, while the second data was acquired over a temperate forest in upper Austria. Acquisitions have been performed in VV polarisation in a single path mode. For both data sets, beside the Radar measurements also Lidar measurements are available for validation purposes. and to provide a reliable estimation of the ground phase under vegetation. In a second step we discuss the applicability of the discussed approaches to spaceborn X-band systems as the TerraSAR-X and TanDEM-X configurations. For this we analyse and discus dual polarised repeat pass acquisitions (11 days) [1] R.N. Treuhaft, S.N. Madsen, M. Moghaddam, and J.J. van Zyl, “Vegetation Characteristics and Underlying Topography from Interferometric Data”, Radio Science, vol. 31, pp. 1449-1495, 1996. [2] I. Hajnsek, F. Kugler, S. Lee, K. Papathanassiou, “Tropical Forest Parameter Estimation by means of Pol-InSAR: The INDREX II Campaign, IEEE Transactions on Geoscience and Remote Sensing, accepted