Estimation of forest properties in the treeline zone using TanDEM-X and airborne laser scanning data

• Main Authors: Antonova, Sofia, Thiel, Christian, Höfle, Bernhard, Marx, Sabrina, Anders, Katharina, Boike, Julia
• Format: Conference Object
• Language: unknown
• Published: Bibliothek Wissenschaftspark Albert Einstein 2018
• Subjects: Arctic; Northwest Territories; Canada; Mackenzie Delta; Valley Creek; Trail Valley Creek; Tundra
• Online Access: https://epic.awi.de/id/eprint/48094/; https://hdl.handle.net/10013/epic.c51aa216-53cd-41a3-a0d6-3fe7b6ca7926

Northward shift of the treeline is expected circum-Arctic and has been observed in a number of locations in response to Arctic warming. The transitional zone between forest and tundra is, therefore, a vulnerable region that requires systematic monitoring. Currently, radar remote sensing is hardly employed in the treeline zone. The unique constellation of the TanDEM-X satellites with its bistatic mode and unprecedented spatial resolution opens new opportunities for monitoring of the treeline zone. We focus on an area near the Trail Valley Creek research basin in the east of the Mackenzie Delta in the Northwest Territories, Canada. The area lies at the northern edge of the treeline zone. Erect vegetation there is characterised by deciduous shrubs up to 3 m in height and isolated patches of sparse coniferous forest. We evaluate the potential of TanDEM-X bistatic data to characterise the structural properties of the forest patches. The TanDEM-X data were acquired during the TanDEM-X Science Phase in 2015, when the effective baseline was large and constant (approximately 540 m). We employ interferometric coherence from multitemporal bistatic pairs and compare it with standard vegetation metrics obtained from airborne LiDAR data. The full-waveform airborne LiDAR data were captured in September 2016, covering an area of about 20 km x 6 km with a point density of approximately 5 points per square meter. LiDAR metrics include vegetation height percentiles and vegetation ratio. The preliminary analysis shows a high agreement between TanDEM-X bistatic coherence and LiDAR vegetation metrics. The relation between coherence and LiDAR metrics, averaged for each forest patch, yields in a strong inverse correlation, varying from -0.81 to -0.88 for different LiDAR metrics. On sub- atch scale, spatial patterns of coherence and LiDAR metrics also show high inverse correspondence. Thus, a pixel-by-pixel comparison gives a first-shot correlation between tree height 99 percentile and coherence from -0.45 to -0.63 for different forest patches. Taking into account the global coverage of multiple bistatic TanDEM-X data acquired for the global digital elevation model, our results provide a basis for the quantification of the treeline properties circum-Arctic.