Transcript Slide 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.
The Basics: Estimating the Motion of a Sea Surface Particle
z
z
dz/dx,
dz/dy
y
x
w
The Big 3
v
u
X, Y, Z
Pressure Sensors
Accelerometers
Tilt sensors
Angular Rate Sensors
Acoustic Sensors
Radar
Lidar
In-Situ and Remotely Sensed Waves
Method
O(cm) X,Y,Z
Accuracy
Spatial
Coverage
Time
Coverage
In situ
SAR,LIDAR
HF, X-Band Radar
In situ and remote sensing systems are complimentary, NOT redundant.
The Big 3: X, Y, Z  Time Series Analysis  The Fab 5: S(f),a1(f),b1(f),a2(f),b2(f) !!
S
- 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
a1
1
Wave Energy Density
The Directional Spectrum
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]
Data Users & Measurement Accuracy
Dominant Wave
Users
S(f),
θ 1 @ f-peaks
Wave Component
Users
Fab 5
Generally tolerant
of errors.
Need a wave component
approach to evaluating
instrument performance.
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….