The approximation of a sea surface using a shore mounted X-band radar with low grazing angle

Abstract

The ability to measure real time surface elevation over a large spatial domain offers large benefits to multiple industries, including offshore operations and marine renewable applications. In combination with a real time short-term wave prediction model safety related marine operations windows can be increased. This focuses on Quiescent Period Prediction during large sea states, and the ability of pre-emptive wave-by-wave tuning of marine energy converters leads to improved efficiencies. This study presents a new method of converting X-band radar sequence into approximate surface elevation in near real time using synthetic wave trough profile estimations, forgoing the use of a linear stochastic model. The artificial wave trough method applies a second order Stokes wave to trough regions where radar shadows occur, these shadows are caused as a result of high surround wave crest height where no surface information is gathered. The calculated surface elevation is validated against in situ sensor data at two locations, a correlation (r) of 0.69 is shown for the Signature 1000 sensor location, while a lower correlation of 0.56 is observed at the wave buoy location. When the phase-averaged wave parameters (Hm0 and Tp) derived from 20min wave spectra for the entire duration of the measurement campaign are compared, a reasonable agreement of 0.62 and 0.41 for the AD2CP and wave buoy location is achieved. The presented method shows a good approximation of wave profile shape, where the swell component is predominantly measured, indicating the potential of X-band radar surface elevation measurements in near real time for nearshore inhomogeneous seas.