Abstract
Abstract. A statistical analysis of the results obtained by the tool SELI (Shoreline Extraction from Landsat Imagery) is made in order to characterise the medium and long term period changes occurring on beaches. The analysis is based on the hypothesis that intraannual shifts of coastline positions hover around an average position, which would be significant when trying to set these medium and long term trends. Fluctuations around this average are understood as the effect of short-term changes -variations related to sea level, wave run-up, and the immediate morphological beach profile settings of the incident waves- whilst the alterations of the average position will obey changes relating to the global sedimentary harmony of the analysed beach segment. The goal of this study is to assess the validity of extracted Landsat shorelines knowing whether the intrinsic error could alter the position of the computed mean annual shoreline or if it is balanced out between the successive averaged images. Two periods are stablished for the temporal analysis in the area according to the availability of other data taken from high precision sources. Statistical tests performed to compare samples (Landsat versus high accuracy) indicate that the two sources of data provide similar information regarding annual means; coastal behaviour and dynamics, thereby verifying Landsat shorelines as useful data for evolutionary studies.
Highlights
One of the most characteristic features of beaches is their intense dynamism
In this study we use the information from Landsat images registered by the TM and ETM+ sensors on the Landsat 5 and Landsat 7 series; the largest useable database of medium resolution images for studying the dynamics of coastal areas
Testing the accuracy from these extracted annual mean shorelines against other more precise data sources, we evaluate if the inherent Landsat error alters the correct average position or it remains compensated among the successive averaged images in one year
Summary
Movements in the shoreline position are defined by Kraus et al (1991) as meso-macro changes If these succeed during few hours or days will be known as meso changes and, if occur during some years or decades and affect long segments of coast (hundreds of meters or kilometres) will be called macro changes. In this study we use the information from Landsat images registered by the TM and ETM+ sensors on the Landsat 5 and Landsat 7 series; the largest useable database of medium resolution images for studying the dynamics of coastal areas. It takes worldwide images since March 1984 every 16 days until November 2011. In 2008 the United States Geological Survey (USGS) enabled free access to multiple images with less than 40% cloud cover, facilitating substantially the possibility of carrying out these kinds of evolutionary works
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