2020 CoastSat time-series.JPG

CoastSat - How to estimate beach slopes using satellite imagery

How steep a beach is can dictate the way the beach interacts with the incoming ocean waves; and is therefore of paramount importance for coastal scientists and engineers, coastal flood modellers and swim safety officers.

The CoastSat dashboardHowever, despite its importance, it is impractical to obtain reliable estimates of the “typical” beach‐face slope along large lengths of sandy coastlines (hundreds to thousands of km) because of the logistics that would be necessary to visit many sites repeatedly to obtain these measurements. 

CoastSat was developed by WRL PhD student Kilian Vos in 2019; and provides a streamlined package for mapping long-term sandy-beach shoreline positions using freely available satellite imagery. Satellite remote sensing provides a low-cost long-term shoreline data set where no in-situ field measurements are available. The CoastSat system enables users to extract shorelines from Landsat 5, Landsat 7, Landsat 8 and Sentinel-2 satellite imagery, providing analysis of long-term shoreline positional change and insights into beachface slope.

CoastSat data over Collaroy-Narrabeen

Kilian's latest research has recently been published in Geophysical Research Letters, where this novel approach to estimate beach slope from time series of satellite‐derived shoreline positions is presented. The technique uses a frequency domain analysis to find the optimum slope that minimises high‐frequency tidal fluctuations relative to lower‐frequency erosion/accretion signals. A detailed assessment of this new approach at eight locations spanning a range of tidal regimes, wave climates, and sediment grain sizes shows strong agreement (R 2 0.93) with field measurements. The automated technique is then applied across thousands of beaches in eastern Australia and California, USA, revealing similar regional‐scale distributions along these two contrasting coastlines and highlights the potential for new global‐scale insight to beach‐face slope spatial distribution, variability, and trends.


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