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Directional Wave Observations

This comprehensive overview on directional wave observations discusses the fundamentals of wave motion estimation and instrument evaluation. It highlights the complementary roles of remote sensing and in-situ technologies, stressing measurement accuracy and user needs. The paper introduces the mathematical models essential for analyzing sea surface particle motion, as well as detailed methodologies for estimating directional wave properties. Key aspects include the exploration of various sensor technologies and their applications in wave observation, providing insights into the current state-of-the-art in the field.

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Directional Wave Observations

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  1. Directional Wave Observations 1) Da Basics 2) Remote Sensing v. In Situ : It’s all good. 3) Estimating directional wave properties. 4) Measurement accuracy and user needs. 5) A Recipe for instrument evaluation.

  2. The Basics: Estimating the Motion of a Sea Surface Particle z z y dz/dx, dz/dy The Big 3 x w v X, Y, Z u Pressure Sensors Accelerometers Tilt sensors Angular Rate Sensors Acoustic Sensors Radar Lidar

  3. In-Situ and Remotely Sensed Waves O(cm) X,Y,Z Accuracy Time Coverage Spatial Coverage Method In situ SAR,LIDAR HF, X-Band Radar In situ and remote sensing systems are complimentary, NOT redundant.

  4. The Big 3: X, Y, Z  Time Series Analysis  The Fab 5: S(f),a1(f),b1(f),a2(f),b2(f) !! S

  5. - mean direction - directional spread - skewness - kurtosis or, in NDBC format - first-moment mean direction (θ1) - first-moment spread parameter (r1) - second-moment mean direction (θ2) - second-moment spread parameter (r2) a1,b1,a2,b2 r1 b1 -1 θ1 1 a1

  6. The Directional Spectrum Wave Energy Density Wave Direction θ S(f,θ)=S(f)[a1·cos(θ)+b1·sin(θ) +a2·cos(2θ) +b2·sin(2θ) +a3·cos(3θ)+b3·sin(3θ)+ a4·cos(4θ)+b4·sin(4θ)+………………infinity and beyond]

  7. Data Users & Measurement Accuracy Wave Component Users Dominant Wave Users S(f), Fab5 @ f-peaks θ 1 Generally tolerant of errors. Need a wave component approach to evaluating instrument performance.

  8. Conclusion Let’s talk about the Fab 5 • This is the current state-of-the-art. • This is the bar modern wave instruments should have to clear. • This is the standard emerging technologies should try and achieve before pursuing the Fab 7, the Fab 9….

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