Abstract
Abstract. The project ‘Application of remote sensing for the early detection of drought stress at vulnerable forest sites (ForDroughtDet)’ is funded by the German Federal Agency of Agriculture and Food and aims to detect drought stress in an early phase using remote sensing techniques. In this project, three test sites in the south and middle part of Germany are selected. Three levels of observation and analyses are performed. In the first level, close-range stereo images and spectral information are captured with a research crane in Kranzberg forest. In the second level, three study sites are imaged twice in three years by airborne hyperspectral and stereo cameras. In the third level, the drought stress detection approach will be transferred to regional scale by satellite image. In this paper, we will briefly report our results from the first and second levels. In the first level, 3D models of the forest canopies are generated with the MC-CNN based dense matching approaches, with which the 3D shapes of the stressed and healthy trees are analysed. In addition, for the spectral analyses, different chlorophyll-sensitive indices are calculated and compared for the stressed and healthy trees. In order to further analyse the tree drought stress in the second level, a novel individual tree crown (ITC) segmentation approach is proposed and tested on the airborne stereo dataset.
Highlights
Climate change, especially global warming, is assumed to increase the frequency, intensity and duration of drought periods in Mid-Europe
We apply Semi-Global Matching (SGM) with matching cost based on convolutional neural networks (MCCNN) (Hirschmüller, 2008) (Zbontar and LeCun, 2016)
3.3 Spectral measurement maple to support the approach of identifying tree species via the "phenological fingerprint” from air- and spaceborne systems. (ii) Gonio-spectro-radiometric measurements of selected drought stressed – and control trees to develop a database for the approximation of the Bidirectional Reflection Distribution Function (BRDF) of the drought stress experiment tree species beech and spruce
Summary
Especially global warming, is assumed to increase the frequency, intensity and duration of drought periods in Mid-Europe. The system under development should identify forest sites with drought stress endangered trees in advance of a drop out, information required by forest management for the preferential start of restructure measures Both of the spectral and 3D structure changes of trees under drought stress are monitored and analysed in this project. In the KROOF project, trees under drought stress are located in an outdoor environment with novel, rain-controlled roof closure Another hypothesis of the investigation concept is that water deficit will result in a change of leaf and needle orientation and shape (shrinking, rolling, leaf angle and exposure change) which might be detectable by exploring anisotropy information from appropriated air- or spaceborne sensors. A new aspect of the ForDroughtDet project is the exploration of anisotropy features as additional, independent information source
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