Abstract
One of the threats that has a significant impact on the conservation status and on the preservation of non-forest Natura 2000 habitats, is secondary succession, which is currently analyzed using airborne laser scanning (ALS) data. However, learning about the dynamics of this phenomenon in the past is only possible by using archival aerial photographs, which are often the only source of information about the past state of land cover. Algorithms of dense image matching developed in the last decade have provided a new quality of digital surface modeling. The aim of this study was to determine the extent of trees and shrubs, using dense image matching of aerial images. As part of a comprehensive research study, the testing of two software programs with different settings of image matching was carried out. An important step in this investigation was the quality assessment of digital surface models (DSM), derived from point clouds based on reference data for individual trees growing singly and in groups with high canopy closure. It was found that the detection of single trees provided worse results. The final part of the experiment was testing the impact of the height threshold value in elevation models on the accuracy of determining the extent of the trees and shrubs. It was concluded that the best results were achieved for the threshold value of 1.25–1.75 m (depending on the analyzed archival photos) with 10 to 30% error rate in determining the trees and shrubs cover.
Highlights
All of the European Union Member States are obliged to monitor the conservation status of natural habitats and species, as well as to undertake active protection measures to prevent deterioration of the status of habitats (EEA) [1]
The verification of the correctness of the height of individual trees, distinguishable in archival photographs in dense image matching (DIM)-digital surface models (DSM) compared to the height recorded in the airborne laser scanning (ALS) data;
The verification of the correctness of the height of individual trees growing in high canopy closure in DIM-DSMs, compared to the height recorded in the ALS data
Summary
All of the European Union Member States are obliged to monitor the conservation status of natural habitats and species, as well as to undertake active protection measures to prevent deterioration of the status of habitats (EEA) [1]. Due to the increasing potential of photogrammetric and remote sensing technologies, the availability of remote sensing sensors and airborne platforms, and the intensive development of data analysis methods (data mining, machine learning), it is reasonable to develop tools to optimize current methods of identification and assessment of the conservation status of Natura 2000 habitats. One of the threats to non-forest Natura 2000 habitats, significantly affecting their conservation status and prospects for their preservation in Poland, is secondary succession. This is related to the gradual cessation of the use of agricultural land that has occurred since the early 1990s. The process of secondary succession can be analyzed using airborne laser scanning (ALS) data [4,5], obtaining knowledge about the past dynamics of this phenomenon (e.g., from the 1960s onward) is only possible using archival materials—mainly aerial photographs, which are often the sole reliable source of information about the condition of land cover in the past
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