Error determination in the photogrammetric assessment of shoreline changes
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Error determination in the photogrammetric assessment of shoreline changes Laura Del Rı´o • F. Javier Gracia
Received: 26 May 2011 / Accepted: 11 September 2012 / Published online: 27 September 2012 Springer Science+Business Media Dordrecht 2012
Abstract The evaluation of error or uncertainty in shoreline change studies is an issue of prime importance for providing an adequate framework for calculated rates of change and to allow the establishment of threshold values above which the rates would be significant. In this note, a practical, easy-to-use method is presented to estimate error involved in the calculation of shoreline changes on aerial photographs, including the three most used types of shoreline indicators: high water line, dune/cliff toe and cliff top. This approach takes into account the specific characteristics of each shoreline proxy, such as relief in the case of the cliff top or tidal oscillations in the case of the high water line. At the same time it includes the error components that are independent from the proxy, basically related to the technical aspects of the process such as photo scanning and georeferencing. A practical example of application of the method is provided for several types of data inputs, based on shoreline changes around the Bay of Ca´diz (SW Spain). Keywords Error
Photogrammetry Coastal erosion Shoreline changes Aerial photography
1 Introduction Shoreline erosion constitutes one of the most serious natural hazards in many coastal areas worldwide. It can be considered an essentially natural process, but the increasing occupation of the coast has led to an increased risk, due to the growing exposure and the strong human influence on the stability of coastal systems. As a consequence of this, the assessment of shoreline change trends is an issue of prime importance for coastal scientists and managers worldwide. In this regard, several authors have highlighted the need for adequate methods that can be used to estimate the amount of error or uncertainty in calculated rates of shoreline change (Anders and Byrnes 1991; L. Del Rı´o (&) F. J. Gracia Earth Sciences Department, CASEM, University of Ca´diz, Av. Repu´blica Saharaui s/n, 11510 Puerto Real, Ca´diz, Spain e-mail: [email protected]
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Nat Hazards (2013) 65:2385–2397
Crowell et al. 1993; Moore 2000). These estimations provide an adequate framework for calculated rates of change and allow the establishment of threshold values above which the rates would be significant. The analysis of vertical aerial photographs is the most commonly used technique in coastal erosion studies, especially for quantifying medium-term shoreline recession rates (Moore 2000), due to the generally wide availability and low cost of the materials. The use of photogrammetry in the assessment of shoreline change involves diverse sources of error or uncertainty that must be taken into consideration: errors in the original data, interpretation errors, measurement errors, etc. (Coyne et al. 1999; Moore 2000; Morton et al. 2004). In t
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