Abstract
This paper presents a new methodological process for detecting the instantaneous land-water border at sub-pixel level from mid-resolution satellite images (30 m/pixel) that are freely available worldwide. The new method is based on using an iterative procedure to compute Laplacian roots of a polynomial surface that represents the radiometric response of a set of pixels. The method uses a first approximation of the shoreline at pixel level (initial pixels) and selects a set of neighbouring pixels to be part of the analysis window. This adaptive window collects those stencils in which the maximum radiometric variations are found by using the information given by divided differences. Therefore, the land-water surface is computed by a piecewise interpolating polynomial that models the strong radiometric changes between both interfaces. The assessment is tested on two coastal areas to analyse how their inherent differences may affect the method. A total of 17 Landsat 7 and 8 images (L7 and L8) were used to extract the shorelines and compare them against other highly accurate lines that act as references. Accurate quantitative coastal data from the satellite images is obtained with a mean horizontal error of 4.38 ± 5.66 m and 1.79 ± 2.78 m, respectively, for L7 and L8. Prior methodologies to reach the sub-pixel shoreline are analysed and the results verify the solvency of the one proposed.
Highlights
Coastal areas are a point of interest from several perspectives
The assessment is completed by comparing this against aLSM and sLSM solutions to show both the importance of the use of the adaptive window and the improvement produced by the Lagrange polynomial interpolation method
The two sets of shorelines compared only differ in the window of pixels chosen to adjust the polynomial surface using least squares. sLSM uses a 7 × 7 symmetric window whatever the polynomial degree (3 or 5) is used. aLSM uses an adaptive window (defined according to Equation (A4)) with 16 pixels when looking for third-degree and 36 pixels for fifth-degree
Summary
Coastal areas are a point of interest from several perspectives. These are the main spaces in which land, sea, and air interact. These are places of settlement, leisure, and economic activity. The sustainable and safe use of these spaces requires knowledge of their natural functioning. Acquiring this knowledge from biologists, geomorphologists, engineers and managers involves the acquisition of information that requires coastal mapping techniques [1]. The type of data and processing reflects the purpose [2]
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