Lipa Belinda, Nyden Bruce, Barrick Don, Kohut Josh
Codar Ocean Sensors, 125 La Sandra Way, Portola Valley, CA 94028 USA.
Codar Ocean Sensors, 1914 Plymouth Street, Mountain View, CA 94043 USA.
Sensors (Basel). 2008 Aug 6;8(8):4611-4635. doi: 10.3390/s8084611.
HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information) far more than first-order (which gives information on current velocities), the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements.
高频雷达系统被广泛且常规地用于测量海洋表面的洋流和波浪。目前使用的分析方法基于无限水深的假设，因此在雷达回波最强的近岸区域可能并不适用。在本文中，我们探讨了雷达回波来自与海底相互作用的海浪时的情况。文中描述了一些模拟，这些模拟展示了浅水对雷达海回波的影响。这些模拟被用于研究现有理论的局限性，并确定浅水效应变得显著时的水深。随着水深减小，二阶谱能量相对于一阶谱能量增加，当波高超过由雷达发射频率定义的极限时会导致谱饱和。这种效应在较低的雷达发射频率下尤为明显。浅水中波高的饱和极限较小。浅水对二阶谱（给出波浪信息）的影响远大于一阶谱（给出流速信息），只有在极低的雷达发射频率和极浅的水深情况下，一阶谱才会受到显著影响。我们描述了对罗格斯大学高频雷达系统测量的浅水雷达回波进行分析以获得海浪谱估计的过程。将雷达推导的波高、周期和方向与同步的浅水现场测量结果进行了比较。
