Despite the importance of diffraction of irregular ocean waves, there is a lack of reported measurements over scales larger than a few tens of wavelengths. In the coastal zone, Satellite Altimetry is hindered because the backscatter characteristics of waveforms deviate from Brown's theoretical model, specially up to 20 km from the coastline. Here, we combine a novel set of retracked — reprocessed — altimeter data with directional buoy spectra and simulations with a spectral numerical model where diffraction is computed with an approximation based on the Mild Slope Equation. The Channel Islands, off the coast of California, is an ideal spot for the analysis because of the sharp variations in bathymetry in the vicinity of the archipelago, increasing the relative importance of diffraction over refraction. Spatial variations of wave energy in the lee of the islands are investigated along and across the wave propagation direction. For the first time the lateral rate of energy spreading — across the wave propagation direction — was computed in oceanic conditions and are of the same magnitude as those found in previously published experiments in a wave tank. The importance of diffraction as a non-dissipative process during wave propagation in situations normally encountered in the ocean is also discussed.

尽管不规则海浪的衍射很重要，但缺乏超过几十波长尺度的测量报告。在沿海地区，卫星测高受到阻碍，因为波形的后向散射特性偏离了布朗的理论模型，特别是距海岸线长达 20 公里。在这里，我们将一组新的重新跟踪 - 重新处理 - 高度计数据与定向浮标光谱和模拟与光谱数值模型相结合，其中衍射是通过基于温和斜率方程的近似计算的。加利福尼亚海岸附近的海峡群岛是进行分析的理想地点，因为该群岛附近的水深变化剧烈，增加了衍射与折射的相对重要性。沿着和穿过波浪传播方向研究了岛屿背风处波浪能量的空间变化。首次在海洋条件下计算了能量横向传播率——跨越波传播方向——与先前发表的波浪池实验中发现的幅度相同。还讨论了在通常在海洋中遇到的情况下波传播过程中衍射作为非耗散过程的重要性。