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1 School of Civil & Construction Engineering .... via 3D FFT analysis [Young et al. 1985]. Camp Lejeune. North. Topsail .... High tide (May 10 @ 2:30h UTC).
RADAR REMOTE SENSING ESTIMATES OF WAVES AND WAVE FORCING THROUGH A TIDAL INLET Alt. tit. Rapid Assessment of Wave Height Transformation at a Tidal Inlet via Radar Remote Sensing

Guillermo M. Díaz Méndez1, Merrick C. Haller1, Britt Raubenheimer2, Steve Elgar2 & David A. Honegger1 [email protected], [email protected], [email protected], [email protected], [email protected]

Abstract ID: 17712 Poster number: OS11B-1270 Session: Nearshore processes II

1

School of Civil & Construction Engineering Oregon State University, Corvallis OR

Met Station & CORAR (APL)

6

5

CH

8 68

7

TB

ES

b)

9

non-breaking

Topsail Beach (TB)

OSU WIMR

Inlet channel (CH)

σ0p = -48 dB σ0b = -4 dB σ0p = -74 dB σ0b = -4 dB

Ebb shoal (ES)

σ0p = -60 dB

σ0p = -64 dB

σ0p = -56 dB

σ0p = -60 dB

σ0p = -62 dB σ0b = -8 dB

σ0p = -56 dB

Atlantic Ocean

APL Met

photo by D. Honegger

NRCS [dB]

h [m]

hs56 = 2.2 m 3.6 m

hs57 = 1.7 m 3.0 m

hs58 = 5.1 m 5.1 m

R = 0.96; bias = -0.26 m; rmse = 0.61 m

h [m]

b) South transect

hs06 = 2.7 m 2.7 m

hs07 = 2.3 m 2.7 m

hs08 = 2.9 m 3.3 m

hs68 = 6.1 m 5.3 m

for additional info, see the poster (OSB11B-1271) by D. Honegger in this session!

R = 0.95; bias = -0.54 m; rmse = 0.89 m

surveyed cBathy

NRCS [dB]

balance equation is solved through a forward differencing scheme in space as:

NRCS [dB]

2.2. Maps of Qb:

x [m]

hs05 = 3.7 m 4.9 m

Assuming stationarity, and neglecting currents U (consistent with Chen et al. 2014), the α and fp are derived from radar-data via 3D FFT analysis [Young et al. 1985]

High tide (May 10 @ 2:30h UTC)

1.2. Radar-derived bathymetry via cBathy [Holman et al. 2013]

where wave dissipation Dw is estimated through [Janssen & Battjes 2007]

H rms 3 π fQb Bρg Dw = h 16

OS

North Topsail Beach

hs55 = 2.6 m 3.5 m

Offshore (OS)

∂ E  ∂  E  Dw   +  {U + c g }  = ∂t  σ  ∂x  σ σ

3

NRCS [dB]

a) North transect

2D wave-action balance equation [Svendsen 2006]:

p(σ0)

10.2 m NAVD88

y [m]

New River Inlet

57

56

55

58

3. 1D cross-shore model of wave transformation

2.1. PDF analysis:

1.1. Study site & sensor location

a)

Woods Hole Oceanographic Institution Woods Hole, MA

2. Estimating the fraction of breaking Qb

1. Radar observations at New River Inlet, NC Camp Lejeune

2

Camp Lejeune

where cgx = cgcosα. The local wave hight Hrms is predicted by

Low tide (May 10 @ 9:00h UTC) Camp Lejeune

where and the cross-shore wave forcing is estimated as the gradient of the radiation stress Sxx [Longuet-Higgins & Stewart 1964]:

x [m]

4. Model validation - time series of wave transformation R = 0.96; bias = 0.12 m; rmse = 0.13 m

a) North transect

St. 57

R = 0.77; bias = 0.02 m; rmse = 0.07 m

St. 58

R = 0.77; bias = 0.04 m; rmse = 0.07 m

St. 5

R = 0.95; bias = 0.01 m; rmse = 0.06 m

St. 6

R = 0.69; bias = 0.15 m; rmse = 0.19 m

x [m]

b) South transect x [m]

R = 0.87; bias = -0.05 m; rmse = 0.08 m

a) North transect

x [m]

Hrms [m]

b) South transect

kg s-2 m-1

R = 0.83; bias = 0.13 m; rmse = 0.15 m

Model skill [Willmott 1981] from prior results (Ch14, [Chen el al. 2014]), and skill and error metrics for model results using A) surveyed bathymetry and parametric Dw [Janssen & Battjes 2007], B) surveyed bathymetry and radar-derived Dw, and C) radar-derived bathymetry and Dw. Willmott Skill scores Ch14 A B

a) North transect 58 0.70 57 0.76 56 0.82 55 0.87

b) South transect 68 0.59 8 N/A 7 N/A 6 0.75 5 0.87

Radiation stress gradient,

b) South transect St. 7

6. Wave transformation assessment

stations

x [m]

Hrms [m]

St. 56

Radiation stress, Sxx

kg s-2 m-1

a) North transect

St. 55

measured | predicted

5. Time & space variation of wave forcing through the Inlet

C

A

R B

C

A

bias [m] B

C

A

rmse [m] B

C

0.85 0.95 0.85 0.82

0.85 0.86 0.79 0.80

0.85 0.88 0.83 0.80

0.97 0.91 0.92 0.91

0.97 0.83 0.64 0.66

0.96 0.87 0.77 0.77

0.12 0.00 0.07 0.08

0.12 -0.06 -0.02 -0.01

0.12 -0.05 0.02 0.04

0.13 0.05 0.08 0.09

0.13 0.09 0.08 0.08

0.13 0.08 0.07 0.07

0.97 0.66 0.56 0.54 0.46

0.97 0.71 0.70 0.68 0.59

0.97 0.71 0.68 0.63 0.57

0.96 0.63 0.75 0.60 0.60

0.96 0.70 0.85 0.79 0.78

0.95 0.69 0.83 0.73 0.75

0.01 0.18 0.18 0.20 0.23

0.01 0.15 0.12 0.14 0.16

0.01 0.15 0.13 0.16 0.17

0.05 0.23 0.20 0.23 0.25

0.05 0.20 0.15 0.16 0.18

0.06 0.19 0.15 0.18 0.17

Acknowledgements Data were collected as part of a joint field program, Data Assimilation and Remote Sensing for Littoral Applications (DARLA) and Rivers and Inlets (RIVET-1), funded by ONR and ASD(R&E). We gratefully acknowledge D. Trizna from Imaging Science Research, Inc. and R. Pittman from OSU for assistance on radar deployment and data collection, J. Thomson and G. Farquharson from APL-UW for MetOc data and installing the scaffolding structure, respectively; J. McNinch and the USACE-FRF for the LARC-2 bathymetry data, and the PVLAB field crew for deploying, maintaining, and recovering the in situ sensors in less-than-pleasant conditions.

References St. 8

R = 0.73; bias = 0.16 m; rmse = 0.18 m

St. 68

R = 0.75; bias = 0.17 m; rmse = 0.18 m UTC time (May 2012)

c) η [m] (@ Wrightsville Beach); Hs [m] (@ WHOI st. 9)

UTC time (May 2012)

Chen, J. L., T. J. Hsu, F. Shi, B. Raubenheimer, and S. Elgar, 2014: Hydrodynamic and sediment transport modeling of New River Inlet (NC) under the interaction of tides and waves, in review J. Geophys. Res. Holman, R., N. Plant, and T. Holland, 2013: cBathy: A robust algorithm for estimating nearshore bathymetry, J. Geophys. Res. Oceans, 118, 2595—2609, doi: 10.1002/jgrc.20199. Janssen, T. T., and J. A. Battjes, 2007: A note on wave energy dissipation over steep beaches, Coast. Engr., 54, 711—716, doi:10.1016/j.coastaleng.2007.05.006. Longuet-Higgins, M. S., and R. W. Stewart, 1964: Radiation stresses in water waves; a physical discussion, with applications, Deep Sea Res., Vol. 11, 529—562, doi: 10.1016/0011-7471(64)90001-4. Svendsen, I. A, 2006: Introduction to nearshore hydrodynamics: Advanced series on Ocean Engineering — Vol. 24, World Scientific, 722 pp. Willmott, C. J., 1981: On the validation of models, Phys. Geogr., 2, 184—194. Young, I. R., W. Rosenthal, and F. Ziemer, 1985: A three-dimensional analysis of marine radar images for the determination of ocean wave directionality and surface currents, J. Geophys. Res., 90(C1), 1049—1059.