研究目的
To evaluate the use of Pléiades tri-stereo data for generating high-resolution digital elevation models (DEMs) and assessing glacier surface changes in mountainous regions, specifically in the European Alps and Khumbu Himal.
研究成果
Pléiades tri-stereo data, processed with SGM and photogrammetric techniques, produce DEMs with sufficient relative accuracy (sub-meter) for detecting glacier surface elevation changes in remote mountainous areas. The method is effective for annual and seasonal assessments, revealing that glaciological processes primarily occur in summer. However, absolute accuracy is lower without GCPs, and terrain-specific challenges (e.g., snow cover, steep slopes) must be considered.
研究不足
Challenges include cloud cover, fresh snow reducing contrast and causing noise/gaps in DEMs, unfrozen water bodies affecting matching, steep terrain (>40°) leading to higher noise and gaps, and the need for assumptions in converting volume to mass changes (e.g., snow density). In the Khumbu Himal, lack of GCPs limits absolute accuracy, and mosaicking issues arise from multiple image acquisitions over time.
1：Experimental Design and Method Selection:
The study uses Pléiades tri-stereo optical imagery processed with semi-global matching (SGM) algorithms to generate DEMs. Photogrammetric techniques are applied, including orientation and georectification using rational polynomial coefficient (RPC) files, tie points, and ground control points (GCPs) where available.
2：Sample Selection and Data Sources:
Study areas include the Hochjochferner glacier in the Austrian Alps and five glaciers (Ngozumpa, Khumbu, Nuptse, Lhotse Nup, Lhotse) in the Khumbu Himal of Nepal. Data sources are Pléiades satellite images from multiple acquisitions (2014-2016), ALS data for the Alps, and dGNSS measurements for GCPs in the Khumbu Himal.
3：List of Experimental Equipment and Materials:
Pléiades satellites (PHR 1A and PHR 1B), ERDAS IMAGINE software with IMAGINE photogrammetry suite, Trimble Geo7X with Zephyr antenna for dGNSS, ALS equipment (not specified), and IMCORR software for image correlation.
4：Experimental Procedures and Operational Workflow:
Images are processed to generate point clouds using SGM, filtered for outliers, merged, and gridded to 1m resolution DEMs. Co-registration is performed using Berthier's method. DEM differencing is used to calculate surface elevation changes, and image correlation for glacier velocity.
5：Data Analysis Methods:
Statistical analysis of DEM accuracy (e.g., mean absolute differences, standard deviations), volume change calculations, and interpretation of glaciological processes based on elevation changes and velocity maps.
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