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On the Sensitivity of TanDEM-X-Observations to Boreal Forest Structure

1
Department of Space, Earth and Environment, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
2
Department of Forest Resource Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(14), 1644; https://doi.org/10.3390/rs11141644
Received: 7 May 2019 / Revised: 27 June 2019 / Accepted: 4 July 2019 / Published: 10 July 2019
(This article belongs to the Special Issue Remote Sensing of Boreal Forests)
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Abstract

The structure of forests is important to observe for understanding coupling to global dynamics of ecosystems, biodiversity, and management aspects. In this paper, the sensitivity of X-band to boreal forest stem volume and to vertical and horizontal structure in the form of forest height and horizontal vegetation density is studied using TanDEM-X satellite observations from two study sites in Sweden: Remningstorp and Krycklan. The forest was analyzed with the Interferometric Water Cloud Model (IWCM), without the use of local data for model training, and compared with measurements by Airborne Lidar Scanning (ALS). On one hand, a large number of stands were studied, and in addition, plots with different types of changes between 2010 and 2014 were also studied. It is shown that the TanDEM-X phase height is, under certain conditions, equal to the product of the ALS quantities for height and density. Therefore, the sensitivity of phase height to relative changes in height and density is the same. For stands with a phase height >5 m we obtained an root-mean-square error, RMSE, of 8% and 10% for tree height in Remningstorp and Krycklan, respectively, and for vegetation density an RMSE of 13% for both. Furthermore, we obtained an RMSE of 17% for estimation of above ground biomass at stand level in Remningstorp and in Krycklan. The forest changes estimated with TanDEM-X/IWCM and ALS are small for all plots except clear cuts but show similar trends. Plots without forest management changes show a mean estimated height growth of 2.7% with TanDEM-X/IWCM versus 2.1% with ALS and a biomass growth of 4.3% versus 4.2% per year. The agreement between the estimates from TanDEM-X/IWCM and ALS is in general good, except for stands with low phase height. View Full-Text
Keywords: TanDEM-X; ALS; height; vegetation density; above ground biomass (AGB); phase height; penetration depth; change detection TanDEM-X; ALS; height; vegetation density; above ground biomass (AGB); phase height; penetration depth; change detection
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Askne, J.I.H.; Persson, H.J.; Ulander, L.M.H. On the Sensitivity of TanDEM-X-Observations to Boreal Forest Structure. Remote Sens. 2019, 11, 1644.

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