Anders, Katharina

Antonova, Sofia

Boike, Julia

Helm, Veit

Höfle, Bernhard

Marx, Sabrina

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Bistatic coherence from CoSSC TanDEM-X data for tree height estimation in the Canadian SubarcticS. Antonova1,2, K. Anders1, V. Helm2, B. Höfle1, S. Marx1, J. Boike2IntroductionThe heterogeneous subarctic forest-tundra transition zone is a vulnerable ecosystem. Its response to current climate change trends is not well understood. Accurate mapping of the tree cover and tree height would provide the baseline for future studies aiming at monitoring vegetation changes in the Arctic.  Interferometric SAR coherence is sensitive to the vertical structure of vegetation and thus can be used in the estimation of tree height. Coherence from bistatic TanDEM-X data is highly valuable due to the lack of a temporal decorrelation factor. We use seven TanDEM-X bistatic pairs to evaluate their potential to distinguish pockets of sparse forest in the Canadian Subarctic to Arctic transition region. Moreover, we relate the coherence values with tree height obtained from Airborne Laser Scanning (ALS).1Heidelberg University, Heidelberg, Germany, 2Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Potsdam, GermanyStudy areaTrail Valley Creek,Northwest Territories, Canada68°45'N, 133°30'W1 June 2015 23 June 2015 15 July 2015 26 July 2015 6 August 2015 17 August 2015 28 August 2015PC 1, filtered and manually shiftedALS vegetation heightOrthophotographs(zoomed)ResultsCoherence for all individual CoSSC pairs for selected tree areasCoherence and vegetation heightNo sensitivity to shrubs• coherence does not show a sensitivity to shrubs• shrubs within these two areas are lower in height compared to trees within studied tree areas• this can be useful in case forests need to be mappedClassification trees/non-trees• for the classification, individual coherence images are not suitable due to noise• PC 1 is used instead of individual images and classification is performed using simple thresholding• most of the studied tree areas are classified correctlyALS vegetation heightData• TanDEM-X CoSSC pairs June-August 2015  coherence imagesincidence angle: ~46°; polarization: VV (single-pol); baseline: ~583 m; HoA: -14 m;cell size: 8 m• ALS from Polar 5 AIRMETH campaign 2016  vegetation height (preliminary results)cell size: 1 m• Orthophotographs: 2004-2008 from Northwest Territories Centre for Geomatics(open access) cell size: 50 cm• zone of continuous permafrost• transition from forest to tundra• pockets of spruce forestLeft: PC 1 of all coherence images; Middle: ALS vegetation height; Right: fragments of orthophotographswhere single trees can be identified.All individual coherence images are highly affected by noise. Tree areas are visually distinguishable with different levelsof confidence. Principal Component Analysis (PCA) enhances the signal and reduces the noise, which provides aclearer identification of the tree areas.• for single coherence images, correlationsbetween mean coherence and mean vegetation height are between -0.41 to -0.71• for the PC 1, the correlation is -0.64 and improves to -0.76 after manual shifting (to correct inaccurate georeferencing) and filteringmax. height: 0.9 m max. height: 0.85 m PC 1 ALS OrthophotographsClassification based on PC 1 of all coherence imagesOblique aerial photograph showing high landscape heterogeneityForest area on the backgroundIn the forest areaIn the frame of PermaSAR project (BMWi and DLR)Mackenzie DeltaLandsat mosaic19 tree areas

Bistatic coherence from CoSSC TanDEM-X data for tree height estimation in the Canadian Subarctic

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