Swell and Wind Wave Inversion Using a Single Very High Frequency (VHF) Radar

A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is presented

and evaluated using a single 48-MHz radar unit and in situ wave measurements. This hybrid approach greatly

reduces errors in radar wave inversion during swell seas. Our analysis suggests that, prior to the inversion, the

second-order spectrum should be normalized using Barrick’s weighting function because this process removes

harmonic and corner reflection peaks from the inversion and improves the results. In addition, the resulting

calibration constants for the wind wave component are not wave-frequency dependent and are

similar in magnitude to those found in previous studies using different operating-frequency radars. This

result suggests radar frequency independence, although additional experimental verification is required.

The swell component of the model presented here ignores the effect of swell’s propagation direction on

the radar signal. Although this approach has several limitations and may only be useful near the coast

(where swell propagates close to perpendicular to the coastline), the resulting wave inversion is accurate

even when swell is propagating close to perpendicular to the radar beam direction. RMS differences

relative to in situ wave height measurements range from 0.16 to 0.25m as the radar beam angle increases

from 22^o to 56^o.