Improved measurements of cryospheric processes using advanced photogrammetry
AbstractThe cryosphere is defined as the areas of the Earth where water is found frozen. The notion of cryospheric processes relates to glaciers, ice caps, ice sheets, ice shelves, sea ice and permafrost. Cryospheric processes are often used as indicators of a changing climate since they respond relatively fast to climate change: sea ice extent decreases, ice shelves and glaciers retreat, permafrost thaws...Therefore, understanding these processes is critical to the understanding of the causes and effects of climate change. Photogrammetry, the science of making geometric and radiometric measurements using photographic imagery, has a century-long history of providing data for geoscience research. Indeed, it is an incredible tool to produce data for the study of processes of interest, in the form of digital elevation models to study their geometry, or in the form of orthoimages to study their texture. If imagery data of the same scene can be acquired at different moments in time, it is possible to create time series. Series of measurements allows for the study and understanding of the evolution of a process through time. This thesis presents work done in the development and application of leading edge photogrammetric methods to the measurement of cryopsheric processes, going through the different scales at which these processes are active, starting at the largest scale with the camera closest to the ground for the study of the meter scale and gradually getting a larger view. Close range photogrammetry was used for the study of the meter scale permafrost process of sorted circles, light airborne imaging was used for the study of a small glacier called Midtre Lovénbreen and its periglacial area, historical heavy airborne survey was used for a more regional survey of Prins Karl Forland and a satellite imaging processing workflow was developed to allow for the study of global scale changes. Thanks to recent developments in photogrammetry, including those presented in this thesis, data quality is on the rise. The key conclusions of this work are that (1) it is possible to push the limit of the precision of the elevation data obtained from imagery by applying modern, improved methods, and (2) that, with these methods, all sorts of image sources can be exploited in order to acquire data on various processes of interest. We used images that we acquired ourselves using consumer grade tools, images found by digging through historical airborne survey archives, and images obtained using spaceborne instruments. That second objective is complemented with the open-source availability of the software and methods developed in the context of this PhD in order to facilitate their use by the scientific community.
List of papers
|Paper I: Surface kinematics of periglacial sorted circles using structure-from-motion technology. Andreas Kääb, Luc Girod, and Ivar Berthling. The Cryosphere 2014, 8, 1041-1056. doi:10.5194/tc-8-1041-2014. The article is included in the thesis. Also available at: http://urn.nb.no/URN:NBN:no-48008|
|Paper II: Terrain changes from images acquired on opportunistic flights by SfM photogrammetry. Luc Girod, Christopher Nuth, Andreas Kääb, Bernd Ezelmüller, and Jack Kohler. The Cryosphere 2017, 11, 827-840. doi:10.5194/tc-11-827-2017. The article is included in the thesis. Also available at: http://urn.nb.no/URN:NBN:no-64742|
|Paper III: Precise DEM extraction from oblique imagery of Svalbard in 1936. Luc Girod, Niels Ivar Nielsen, Frédérique Couderette, Christopher Nuth, and Andreas Kääb. Manuscript. To be published. The paper is not available in DUO awaiting publishing.|
|Paper IV: MMASTER : improved ASTER DEMs for elevation change monitoring. Luc Girod, Christopher Nuth, Andreas Kääb, Robert McNabb, and Olivier Galland. Remote Sensing 2017, 9, 704. doi:10.3390/rs9070704. The article is included in the thesis. Also available at: http://urn.nb.no/URN:NBN:no-63812|