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.


Phase I - Wavenumber Analysis Steps:(Tile-based phase and magnitude example)


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


Bad Example Raw Bathy EstimateEstimated depth Estimated error

January 13, 2010, early morning with sun glare


Kalman Filtering

P - estimate errorQ - process errorR - measurement errorK - time step ĥ - estimated depth - - prior value

h, cBathy est. , filtered


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


cBathy - Comparison With Ground Truth

• 2-year test

• 16 surveys

• 1000 x 500 m

• Turn-key (no tuning)


• Global bias 0.19 m

• Global rmse 0.51 m

Oregon State University

Ground Truth Tests, Egmond, The Netherlands

Leo Sembiring TU Delft - Shore


Ground Truth Tests, RIVET


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


Time Variations of Hourly Returns

Hs = 1.4 m


Wave Height Dependency


Wave Height Dependency

• Good performance limited to low wave conditions.

• Scientific interest focused on storms

• Fix unclear (to me).


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!)


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


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.


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).


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.


Questions?

cbathy on open beaches rob holman secnav/cno chair in oceanography update since 2011 shoreline...

Documents

eof phase of c

number of f

compute weighted cost

tilebased phase

resulting f

wavenumber analysis

crossspectral matrix

based q