CBathy on Open Beaches Rob Holman SECNAV/CNO Chair in Oceanography Update since 2011 Shoreline...
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Transcript of CBathy on Open Beaches Rob Holman SECNAV/CNO Chair in Oceanography Update since 2011 Shoreline...
cBathy on Open Beaches
Rob HolmanSECNAV/CNO Chair in Oceanography
• Update since 2011
• Shoreline problems
• Storm performance
• Camera seam problem
• Phase-locked harmonics
• Outliers
• Doppler
• Process error?
Updates Since 2011
Has been a game changer for nearshore remote sensing
• Published in JGR, 2013
• Toolbox implemented with docs and debug tools
• Disseminated to Netherlands, England, Australia
• Applied to radar by Honegger and Haller at OSU
• Being exercised in wide range of locations and
conditions
Oregon State UniversityOregon State University
Phase 1 - Wavenumber Analysis Steps
1. Compute normalized Fourier Transform, G = FT(I)/|FT(I)|
2. Compute the cross-spectral matrix,for a number of f-bands
3. Compute the first complex EOF, expressed as phase and amplitude maps
4. Model the EOF phase of C as
4. Compute weighted cost function,
where weighting wij is product of EOF magnitude and spatial Hanning filter
5. Use nonlinear least-squares to find kx, ky (or k-alpha) that minimize J.
Oregon State UniversityOregon State University
Phase I - Wavenumber Analysis Steps:(Tile-based phase and magnitude example)
Oregon State UniversityOregon State University
Analysis Steps – Add Phase 2
1. Compute normalized Fourier Transform, G = FT(I)/|FT(I)|
2. Compute the cross-spectral matrix,for a number of f-bands
3. Model the phase of C as
4. Compute weighted cost function,
where wij is the coherence
5. Use nonlinear least-squares to find kx, ky that minimize J.
6. From resulting [f, kx, ky], estimate depth using linear dispersion (or better alternate) using N most coherent f-bands
wave
nu
mb
er
bath
ymetr
y
Oregon State UniversityOregon State University
Bad Example Raw Bathy EstimateEstimated depth Estimated error
January 13, 2010, early morning with sun glare
Oregon State UniversityOregon State University
Kalman Filtering
P - estimate errorQ - process errorR - measurement errorK - time step ĥ - estimated depth - - prior value
h, cBathy est. , filtered
Oregon State UniversityOregon State University
Process Error, Q
• Variance of prior estimates degrades with time and wave energy.
• Based Q on SandyDuck daily survey variance (mean square abs dev.)
• Dependent on H and cross-shore location
Oregon State UniversityOregon State University
cBathy - Comparison With Ground Truth
• 2-year test
• 16 surveys
• 1000 x 500 m
• Turn-key (no tuning)
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
Oregon State UniversityOregon State University
• Global bias 0.19 m
• Global rmse 0.51 m
Oregon State University
Ground Truth Tests, Egmond, The Netherlands
Leo Sembiring TU Delft - Shore
Oregon State University
Ground Truth Tests, RIVET
Oregon State University
Shoreline Issues!
• Large errors common at shoreline
• Thought it was issue of merging phase content from waves and sand in single tile
• Appears to be more problem of runup appearing progressive
• Unclear fix
cBathy Performance During High Wave Conditions(10/17/11 – 11/08/11;
Becca Aiken, CIL)
~ y=925 transect
Survey 110/17/11
Survey 211/16/11
Mini-survey11/07/11
cBathy Performance During High Wave Conditions
Oregon State UniversityOregon State University
Time Variations of Hourly Returns
Hs = 1.4 m
Oregon State UniversityOregon State University
Wave Height Dependency
Oregon State UniversityOregon State University
Wave Height Dependency
• Good performance limited to low wave conditions.
• Scientific interest focused on storms
• Fix unclear (to me).
Oregon State UniversityOregon State University
Camera Seam Problems!
• Depth anomalies along camera seams (at times)
• Originally assumed geometry problem
• Recently discovered camera timing problems (one cam off by ½ s, etc)
• Requires cam timing pre-processing (easy!)
Oregon State UniversityOregon State University
Phase-locked Harmonics
•Narrow-banded nonlinear swell (like cnoidal waves) have fundamental and phase-locked harmonics
•Harmonics travel as same speed as fundamental, NOT like independent linear components
•Best estimate depth pulled too deep by these fast harmonics
• Issue with radar (nonlinear imaging physics)
•Unclear fix.
Massaguacu, Brazil
Oregon State UniversityOregon State University
Shallow Anomalies
• Occasion estimates that are clearly wrong but appear good (Max examples)
• Usually low signal areas, can be boat passage
• Dominate Kalman result until next good signal
• Unclear fix (Max?)
cBathy At Tidal Inlet Environments – Doppler!!!RIVET 2013 – Columbia River, OR
SELFEModel, Baptista
cBathy Variations With Tidal Currents
Tide-level corrected
flood
ebb
Histogram of Non-Doppler cBathy Depths, MCR
surveycBathymean
Ground Truth Tests, RIVET
floodebb
RMSE: 56 cmBias: 14 cm
G.V. ESTIMATES: Depth
Channel structure recovered
Estimate accuracy & precision deteriorates to the south
Honegger and Haller, X-band radar.
Oregon State UniversityOregon State University
Process Error, Q
• Process error represents expected decay of faith in estimate with time
• Standard cBathy formulation based on one set of daily CRAB surveys at Duck.
• Should vary with location, wave regime, bar configuration, etc.
• May have to bootstrap better estimates (assume form, do cBathy, use estimates to constrain bathy change, repeat until converged).
Oregon State UniversityOregon State University
Summary
• cBathy seems to be a game-changer
• Fabulous under small waves, unusable for storms.
• For VERY small signals sensitive to non-waves (boats??)
• Some technical issues with seams and shorelines
• More to be done on nonlinear waves (esp harmonics) and process error.
Oregon State UniversityOregon State University
Questions?