On the use of satellite information to detect coastal change:
Demonstration case on the coast of Spain
Abstract
Recent developments in satellite processing tools allow noncost, fast
and automatic processing of a large amount of information from Earth
observation, enhancing the capability of detecting coastal changes from
space at different temporal scales. However, these automatic procedures
are usually based on processors calibrated with information from a
limited set of beaches, and the application of these tools to areas with
different conditions may lead to significant errors in coastal change
assessment. In this work, we evaluate the capability to monitor changes
in coastal morphology at various temporal and spatial scales using 1D
(coastlines) and 3D (bathymetry) satellite-derived data obtained from
site-specific processing methods. Local characteristics were included in
several phases of the development of the satellite products used here:
i) VHR images from each pilot site were used in the coregistration
process to guarantee high geolocation accuracy in images from different
missions, ii) different spectral indices were tested at each pilot site
to guarantee reliable detection of the coastline at all sites and iii)
measured topobathymetry data were used to obtain datum-based satellite
shorelines and bathymetry. The accuracy and skill of those satellite
products were assessed at several pilot sites in Spain. The results
indicated high horizontal accuracy, with errors on the order of half of
the pixel size. Time-series analysis using satellite-derived shorelines
showed that coastal change processes can be detected at several temporal
and spatial scales, such as short-term erosion and accretion events on a
small beach, seasonal beach rotation, and long-term trends at local and
regional scales. However, the results from satellite-derived bathymetry
indicated that the quantitative assessment of the coastal morphology
with 3D products is still limited. Some in situ measurements are
necessary to obtain satellite data that represent site-specific
conditions. However, the quantity of required data measured in situ is
significantly lower than the quantity required by traditional monitoring
methods.