Nearshore Monitoring with X-Band Radar: Maximising Utility in Dynamic
and Complex Environments
Abstract
Data quantifying the nature and range of bathymetric changes in the
near-shore are required for coastal management and engineering works.
However, due to high costs and complex logistics, bathymetric surveys
are usually infrequent. This study demonstrates that ground-based X-band
radar offers a cost-effective alternative to monitor seabed changes at
relatively high frequency and over large near-shore areas. Through a
robust data processing and quality control framework developed to
validate radar-derived data and quantify uncertainties, bathymetric maps
were obtained using an 18-month radar installation at Thorpeness, U.K.
The analysis incorporates calibration of water levels and wave heights;
validation of radar-derived water depth using concurrent multibeam
surveys; the application of a method to reduce the influence of data
scatter and outliers; and assessment of spatio-temporal variability of
data quality due to varying wave heights and direction. For conditions
when the wave height is >1 m, and the angle of wave
approach relative to the radar is relatively small, the accuracy of the
radar-derived depths is shown to be {plus minus}0.5 m at 40x40 m
spatial resolution. At Thorpeness, quantification of changes exceeding
this error was possible at time-scales as short as three weeks, and
near-shore volume changes are seen to be of a comparable magnitude to
historical longshore transport rates in the area. The use of radar can
provide to coastal managers an early warning of changes in offshore
bathymetry likely to impact vulnerable coastal locations; thereby
allowing mobilisation of resources that may be required to protect lives
and property.