Quantifying migration rates of barchan dunes using radar and optical remote sensing imagery

Quantifying sand dune migration is an important aspect in analyzing desert dunes and in particular barchans dunes. Moreover, identifying the active barchans and estimating their migration rate are crucial steps for proper understanding and assessment of sand encroachment hazard. The increasing availability of remote sensing data for larger regions have made it possible to study (less)inaccessible regions such as large desert dune fields. Contrary to the detailed study on individual dunes, this has also made it possible to study the dynamics of entire dune fields. Multi-temporal analysis of remote sensing data offers to the potential to quantify dune migrations rates and sand fluxes. However, the reflectance properties of dune surfaces challenges the automatic detection and delineation of sand dunes, and thus also the automatic calculation of migration rates. In this study, barchan dunes in the South-Rayan dunefield (SRFD) in central Egypt were therefore examined through a combination of optical RS data(i.e. multi-temporal Landsat imagery) as well as with active RS data (i.e. Envisat ASAR SLC images). The method used for extracting dunes’ shape from radar imagery is easier, faster and requires minimum human interaction than their extraction from optical data, however, the latter are more readily available and require less preprocessing. The dune migration rate in m a-1 of 43 dunes was estimated based on the calculation of the movement of centroids (i.e. centroid displacement) corresponding to each dune. Fieldwork (i.e. GPS-surveyed dune boundaries) and a recent GeoEye image were integrated to assess the results. Results obtained with optical and radar imagery are similar and point towards an average migration rate of 4.4 m a-1, with values for individual dunes ranging from 1 m a-1 to 18 m a-1. Moreover, the dune migration was found to be mainly controlled by dune size and the interdune slope-aspect. The centroid displacement technique is a successful approach that enabled a fully automatic calculation of barchans dune migration. This abstracts fits within the APLADYN project: a Belgian Science Policy projection anthropogenic and landscape dynamics in large fluvial systems.status: publishe