Abstract
Abstract. Terrestrial photography is a cost-effective and easy-to-use method for measuring and monitoring spatially distributed land surface variables. It can be used to continuously investigate remote and often inaccessible terrain. We focus on the observation of snow cover patterns in high mountainous areas. The high temporal and spatial resolution of the photographs have various applications, for example validating spatially distributed snow hydrological models. However, the analysis of a photograph requires a preceding georectification of the digital camera image. To accelerate and simplify the analysis, we have developed the "Photo Rectification And ClassificaTIon SoftwarE" (PRACTISE) that is available as a Matlab code. The routine requires a digital camera image, the camera location and its orientation, as well as a digital elevation model (DEM) as input. If the viewing orientation and position of the camera are not precisely known, an optional optimisation routine using ground control points (GCPs) helps to identify the missing parameters. PRACTISE also calculates a viewshed using the DEM and the camera position. The visible DEM pixels are utilised to georeference the photograph which is subsequently classified. The resulting georeferenced and classified image can be directly compared to other georeferenced data and can be used within any geoinformation system. The Matlab routine was tested using observations of the north-eastern slope of the Schneefernerkopf, Zugspitze, Germany. The results obtained show that PRACTISE is a fast and user-friendly tool, able to derive the microscale variability of snow cover extent in high alpine terrain, but can also easily be adapted to other land surface applications.
Highlights
Oblique terrestrial photography has become a more and more frequently used observation method in various research disciplines, such as vegetation phenology (Richardson et al, 2007; Ahrends et al, 2008; Crimmins and Crimmins, 2008; Migliavacca et al, 2011), land cover studies (Clark and Hardegree, 2005; Zier and Baker, 2006; Roush et al, 2007; Michel et al, 2010) and volcanology (Major et al, 2009)
We focus on glaciology and snow hydrology where, for example, investigations of the snow albedo on glaciers were realised by Corripio (2004), Rivera et al (2008) and Dumont et al (2009)
Terrestrial photography is used for these monitoring applications with an increasing frequency
Summary
Oblique terrestrial photography has become a more and more frequently used observation method in various research disciplines, such as vegetation phenology (Richardson et al, 2007; Ahrends et al, 2008; Crimmins and Crimmins, 2008; Migliavacca et al, 2011), land cover studies (Clark and Hardegree, 2005; Zier and Baker, 2006; Roush et al, 2007; Michel et al, 2010) and volcanology (Major et al, 2009). PRACTISE is that the new features form a flexible, fast and This method only needs one GCP (T ), but 13 camera param- user-friendly processing tool for analysing spatially and temeters have to be set. If these parameters are not accurately porally distributed land surface variables. Several new optional routines are im- 2 Data plemented in PRACTISE This includes the dynamically dimensioned search (DDS) algorithm (Tolson and Shoemaker, 2007) to automatically identify the camera location and orientation using GCPs if the exterior and interior orientation parameters are not precisely known. The GCPs of each photograph were determined by using the orthophoto in combination with the DEM for the longitude, latitude and altitude as well as the photograph with the row and column information
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