Wave Measurements from SeaSondes

Measurements Significant Wave Height Wave Period Peak Wave Direction Wind Direction

Wave info Derived from 2nd order peaks in Doppler spectra

What Are Second Order Peaks? Secondary peaks caused by the orbital velocity created by passing waves Characteristics: Signal is an order of magnitude weaker May occur on both sides of 1st order peak May be present in both +/- Doppler Occasionally more than one peak is present

Example: 5MHz System

Where Do Second Order Peaks Come From?

Negative Doppler Positive Doppler

Ocean Wave Model Pierson-Moskowitz Spectrum Total ocean-wave spectrum: Pierson-Moskowitz model with cardioid directional factor Short wave spectrum

Process Calculate model radar spectra for wide range of total ocean-wave spectral parameters (using Pierson-Moskowitz model) Separate 1st order from 2nd order regions Determine short-wave ocean spectrum from 1st order to give direction (wave and wind) Fit measured radar spectra to models to give wave height, period and direction

Reading References Barrick, D. (1971), Dependence of second-order Doppler sidebands in HF sea echo on sea state, IEEE G-AP Internat. Symp. Digest Barrick, D. (1971), Dependence of second-order Doppler sidebands in HF sea echo on sea state, IEEE G-AP Internat. Symp. Digest Hasselman, K. (1971), Determination of ocean wave spectra from Doppler radio return from the sea surface, Nature. Hasselman, K. (1971), Determination of ocean wave spectra from Doppler radio return from the sea surface, Nature. Barrick, D. (1972), Remote sensing of sea state by radar, in Remote Sensing of the Troposphere Barrick, D. (1972), Remote sensing of sea state by radar, in Remote Sensing of the Troposphere Barrick, D. (1977), Extraction of wave parameters from measured HF radar sea-echo Doppler spectra, Radio Sci. Barrick, D. (1977), Extraction of wave parameters from measured HF radar sea-echo Doppler spectra, Radio Sci. Lipa, B. (1978), Inversion of second-order radar echoes from the sea, J. Geophys, Res. Lipa, B. (1978), Inversion of second-order radar echoes from the sea, J. Geophys, Res. Lipa, B.J., B. Nyden (2005), Directional wave information from the SeaSonde, IEEE Jour. Ocean. Eng., vol 30, no. 1, pp

Limitations 42MHz High-Res Sensitivity: 0.25m waves Saturation: 3m waves 25MHz High-Res Sensitivity: 0.5m waves Saturation: 4m waves 12MHz Standard Sensitivity: 0.75m waves Saturation: 7m waves 5MHz Long Range Sensitivity: 1m waves Saturation: 20m waves