Observations of Shoaling and Breaking Waves in Shallow Water With Different Coherent X-Band Radars

The study analyzes the microwave imaging of shoaling nearshore surface gravity waves during the process of steepening and breaking over two beaches for a wide range of environmental conditions. Data are sourced from two coherent X-band radars, operating under low-grazing angle conditions. Using automatic wave tracking on the radar images, the evolution of individual waves is followed over hundreds of meters. The extracted backscatter intensity and Doppler speed form distinct patterns that reveal a nonnegligible dependence on environmental conditions. Statistical representations of the backscattered signal are presented by conditional Doppler speed-intensity histograms. These are composed of ensembles extracted at the radar-facing fronts. This technique helps to focus on the steepening of the wave and minimizes the impact of extremely low-grazing angle imaging mechanisms that are still not well understood. The combination of wind speed and direction, as well as initial wave steepness, local depth, and degree of nonlinearity, contributes to the shapes and centroid positions of the histograms. The backscatter signature exhibited by breaking waves remained consistent and similar throughout all datasets. The results are consistent across radars. Before consolidating the findings, it is imperative to conduct a further investigation of radar imaging of nonlinear wave dynamics in shallow water to eliminate any possible influence of imaging mechanisms.