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Not just a matter of scale: measurement and comparison of coastline lengths derived from WVS, Landsat and Corona datasets for representative coast sections of the Lena Delta

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Kruse, J. E. , Lantuit, H. and Rachold, V. (2005): Not just a matter of scale: measurement and comparison of coastline lengths derived from WVS, Landsat and Corona datasets for representative coast sections of the Lena Delta , 2nd International Alfred Wegener Symposium, Bremerhaven, GermanyOctober - 02 November 2005. .
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Abstract:

To calculate long-term coastal erosion rates in the Laptev Sea and subsequent sediment release to the Arctic Ocean, a precise assessment of shoreline length is necessary since current estimates rely on rough worldwide-available shoreline datasets. In addition coastlines are rarely divided into morphometric subtypes to characterize their self-similarity. We therefore used World Vector Shoreline (WVS), Corona and Landsat datasets to measure, compare and characterize the length of four representative coast sections in the Lena Delta and at the Bykovsky Peninsula at different scales.The Bykovsky Peninsula lies NE of the town Tiksi and extends 40 km parallel to the mainland in NNW-SSE-direction. This 40 m high original surface, called Ice-Complex, has a very high volumetric ice content (i.e. 80%) and is subjected to thermal abrasion at the coast. At the Sardakh Channel mouth we find islands and peninsulas within accretional flood plains, 0-1m high and composed of silt, fine grained sand and peat with an ice content of 25-40% (Schirrmeister 2004). The NE coast of Arga Island is a sea dominated, erosional, 10m high coast composed of fine grained sands with low ice content (20-30%). About 100km of the Arga Island west coast is built up of a vast 10-20m high sand plain of the second terrace of the Lena Delta with a large number of deep thermokarst lakes. Submergence of these lakes has created an extremely embayed coast, divided from the sea by a 4-7km wide lagoon. The lagoon is separated from the sea by a chain of barrier islands (Pfeiffer et al. 2002).Coastlines were extracted from Landsat and Corona data digitising the shoreline between two distinct points of each section with constant length fragments (100 m) as described in previous studies (e.g. Mandelbrot, 1967). The lengths of these sections were then compared with those of the corresponding sections of the WVS, which was digitised from analogue maps at the scale of 1:250000 or smaller in the Russian Arctic (Soluri et al. 1990).As expected, the lengths of the coastlines measured on the satellite images are longer than the corresponding lengths of the WVS with exception of the north east coast of Arga Island. There are, however, considerable differences in the magnitude of the deviation with Landsat-lengths ranging from 96% of the WVS-length at the north east coast of Arga Island up to 124% for the coast of the Sardakh Channel mouth.The following reasons explain these deviations:1. The uncertain position of the WVS associated with the rough scale at which it was processed as well as the modifications inherited from ongoing coastal processes may have changed the start and ending points as well as the course of the shoreline within the investigated sections2. Despite the efforts to bring the satellite image and WVS in agreement, there are incoherencies due, for instance to the localization of the fresh water / sea water interface within the delta.3. Apart from these potential errors, we can consider that the complexity of the coastal sections is the main driver for the observed differences in length. The more complex the shoreline, the longer the measured coastal length.References:Mandelbrot, B. B., 1967. How Long is the Coast of Britain: Statistical Self-similarity and Fractal Dimension, Science 155, 636-38.

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