Abstract
The use of Unmanned Aerial Vehicles (UAV) for photogrammetric surveying has recently gained enormous popularity. Images taken from UAVs are used for generating Digital Surface Models (DSMs) and orthorectified images. In the glaciological context, these can serve for quantifying ice volume change or glacier motion. This study focuses on the accuracy of UAV-derived DSMs. In particular, we analyze the influence of the number and disposition of Ground Control Points (GCPs) needed for georeferencing the derived products. A total of 1321 different DSMs were generated from eight surveys distributed on three glaciers in the Swiss Alps during winter, summer and autumn. The vertical and horizontal accuracy was assessed by cross-validation with thousands of validation points measured with a Global Positioning System. Our results show that the accuracy increases asymptotically with increasing number of GCPs until a certain density of GCPs is reached. We call this the optimal GCP density. The results indicate that DSMs built with this optimal GCP density have a vertical (horizontal) accuracy ranging between 0.10 and 0.25 m (0.03 and 0.09 m) across all datasets. In addition, the impact of the GCP distribution on the DSM accuracy was investigated. The local accuracy of a DSM decreases when increasing the distance to the closest GCP, typically at a rate of 0.09 m per 100-m distance. The impact of the glacier’s surface texture (ice or snow) was also addressed. The results show that besides cases with a surface covered by fresh snow, the surface texture does not significantly influence the DSM accuracy.
Highlights
In recent years, Unmanned Aerial Vehicle (UAV) photogrammetry has emerged as an on-demand method to generate high-resolution datasets including Digital Surface Models (DSMs) and orthorectified images
In order to allow for the results of all campaigns to be compared, the number of Ground Control Points (GCPs) used for DSM georeferencing was divided by the surveyed glacier area
For Findelen- and Gries- gletscher, the vertical and horizontal accuracies increase when increasing the number of GCPs used for DSM generation
Summary
In recent years, Unmanned Aerial Vehicle (UAV) photogrammetry has emerged as an on-demand method to generate high-resolution datasets including Digital Surface Models (DSMs) and orthorectified images (orthophotos). This method offered a new range of application in many different research areas including forestry and agriculture (e.g., [1,2]), archeology (e.g., [3,4]) biology [5,6] and hydrology (e.g., [7,8]). Light detection and ranging has more recently emerged as an alternative for generating high resolution DSMs (e.g., [18,19]) Compared to these methods, UAV photogrammetry can be appealing due to the (i) portability of the required.
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