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Wave Measurements from SeaSondes

Learn about wave measurements derived from SeaSondes, including significant wave height, wave period, peak wave direction, and wind direction. Second order peaks in Doppler spectra, their characteristics, and their origins are explored. The process of calculating radar spectra, separating 1st and 2nd order regions, and fitting measured radar spectra to models is explained.

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Wave Measurements from SeaSondes

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  1. Wave Measurements from SeaSondes

  2. Measurements • Significant Wave Height • Wave Period • Peak Wave Direction • Wind Direction

  3. Wave info • Derived from 2nd order peaks in Doppler spectra

  4. 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

  5. Example: 5MHz System

  6. Where Do Second Order Peaks Come From?

  7. Positive Doppler Negative Doppler Where Do Second Order PeaksCome From?

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

  9. 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

  10. Reading References • 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. • 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. • 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 221-231.

  11. 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

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