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Abstract
It has been over a decade since COSI-Corr, the Co-Registration of Optically Sensed Images and Correlation, was first used to produce a raster map of sand dune movement, however, no studies have yet applied it to the full Landsat archive. The orthorectified and geolocated Landsat Level-1 Precision Terrain (L1TP) products offer the opportunity to simplify the COSI-Corr pre-processing steps, allowing an automated workflow to be devised. In the Bodélé Depression, Chad, this automated workflow has calculated average dune speeds of 15.83 m/year and an increase in dune movement of 2.56 m/year ±12.58 m/year from 1987 to 2009. However, this increase does not stem from a systematic increase in dune mobility. The fastest 25% of dunes from 1987 to 1998 reduced their speed by 18.16%. The overall increase stems from the acceleration of features previously moving under 13.30 m/year. While successfully applied to the Bodélé Depression, the automated workflow produces highly variable outputs when applied to the Grand Erg Oriental, Algeria. Variations within path/row scene pairings are caused by the use of mobile features, such as dune crests, as ground control points (GCPs). This has the potential to warp Landsat scenes during the L1TP processing, potentially obfuscating dune migration. Two factors appear to be crucial in determining whether a Landsat scene is suitable for COSI-Corr analysis. Firstly, dune mobility must exceed the misregistration criteria. Secondly, GPCs should be located on static features such as bedrock outcrops.
Highlights
Coupled with scarce water resources and poor land fertility, the encroachment of sand dunes remains a key hazard for the inhabitants of dryland desert areas [1]
Parts of the Sahara are already experiencing increased risks from sand dune migration accelerated by unsustainable development, over-cultivation, and poor irrigation practices [6]
Scheidt and Lancaster [30] found that the correlation engine struggled to accurately measure the migration of a dune which merged with an adjacent feature and was insensitive to small dunes
Summary
Coupled with scarce water resources and poor land fertility, the encroachment of sand dunes remains a key hazard for the inhabitants of dryland desert areas [1]. The Pairs of Source and Target Points [19] and Digital Shoreline Analysis System methods both remove user defined extractions and the subjectivity associated with manual measurements of dune displacement Their focus on dune crest extraction provides little information on morphological changes within the dune shape and sloss slope. At a coarser resolution than the 2.5 m SPOT-5 imagery, the global catalog of 30 m resolution Landsat data is freely available and consists of an archive stretching back to 1972 [39] In addition to this archival longevity, the pre-orthorectified and geolocated Landsat Level-1 Precision Terrain (L1TP) data products remove the requirement for the manual pre-processing steps of the COSI-Corr methodology.
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