Abstract
In this paper, an ocean wave measurement technique and a newly developed short-range K-band radar are tested. In previous work, the technique and its feasibility were studied based on numerical simulations and wave tank experiments, while its performance at sea was still unknown. Surface current, Stokes drift, and wave breaking can greatly complicate interpreting radar backscatters. The feasibility of the technique needed to be further investigated with sea experiments. Experiments were carried out at a stationary site and from a moving platform. The short-range K-band radar transmitted continuous wave and received backscatters at low-grazing angles. The Bragg-scattering from the radar’s effective footprint dominated the backscatters. The Doppler shift frequency of the Bragg-scattering was attributed to the phase velocity of Bragg waves and modulated by the surface motions induced by current, Stokes drift, platform, and gravity waves. These sources of the Doppler shift frequency were analyzed, and the components induced by wind waves were successfully retrieved and converted into wave spectra that were consistent with the measurements of wave rider buoy. The experimental investigation further validated the feasibility of using short-range K-band radar to measure ocean waves.
Highlights
Many microwave radar remote sensing techniques are available to measure ocean waves
Instead of distance measurements and the radar images in various types and scales, we developed a technique using a short-range K-band radar, which focuses on the Doppler shift caused by surface motions and retrieves wave spectrum based on the relationship among the Doppler shift, wave orbital velocity and wave characteristics [9,10]
The work presented in this paper supports the feasibility of using the short-range K-bang radar for measurement of the non-directional wind wave spectrum at sea surface
Summary
Many microwave radar remote sensing techniques are available to measure ocean waves. Downward looking frequency-modulated continuous-wave (FMCW) radars measure wave height and period by measuring the vertical distance from ocean platforms or ships to sea surface. Instead of distance measurements and the radar images in various types and scales, we developed a technique using a short-range K-band radar, which focuses on the Doppler shift caused by surface motions and retrieves wave spectrum based on the relationship among the Doppler shift, wave orbital velocity and wave characteristics [9,10]. Backscatter from the effective footprint dominates the backscattered power and carries various DSF components that originate from Bragg waves [13,14] but are modulated by surface current, Stokes drift, platform motion, and gravity waves. This paper is organized as follows: Section 2 includes the definition of the radar’s effective footprint, the analyses of the DSF sources, and the general processing of wave spectrum retrieval.
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