REMOTE SENSING OBSERVATIONS OF WAVE DISSIPATION · 2014-03-05 · USA Mexico OSU WIMR specs: •...

1
Correlation of p(σ o p = -60dB ) vs wind speed R = -0.27 -0.64 -0.14 -0.72 lag xCorr = n/s n/s n/s n/s Correlation of p(σ o b = -4dB ) vs wave height R = -0.03 0.68 0.68 0.75 lag xCorr = n/s 0.00 0.00 5.00 Approach: Assess the Normalized Radar Cross Section (NRCS or σ o ) of the ocean surface from New River Inlet Experiment data. Identify NRCS associated with different stages of wave breaking (non-breaking waves, non-breaking steep waves, active breaking and remnant foam). Discriminate NRCS associated with active breaking σ o b [Haller & Lyzenga, 2003] following the PDF approach (i. e., normalized histograms) of Catalán et al., [2011]. Estimate fraction of breaking waves Q b from: where N b is the number of breaking waves, f p is the peak frequency, and τ is the length of the radar record. REMOTE SENSING OBSERVATIONS OF WAVE DISSIPATION School of Civil & Construction Engineering Oregon State University, Corvallis OR Abstract Ref. Number: 17369 Poster number: 453 Guillermo M. Díaz Méndez, Merrick C. Haller, David A. Honegger & Randall W. Pittman [email protected], [email protected], [email protected], [email protected] INTRODUCTION NRCS ANALYSIS New River Inlet, NC Atlantic Ocean USA Mexico OSU WIMR specs: commercial SiTEX/Koden marine radar electronics modified by ISR Inc. 9.45 GHz (X-band) peak power 25 W 2 KHz - PRF 50 MHz - sampling frequency 9' HH-polarized antenna 48 RPM Sampling scheme: half-hourly runs (May 7—15, 2012) range = 512 (1024 May 9—15, 2012) azimuth = 512 rotations = 1024 Δ range = 3 m; Δ azimuth = 0.57 o Δ t = 1.2 s (Δ f = 0.83 Hz ) Coverage: r 3 km; azi 290 o ; t 20 min 2. OSU WAVE IMAGING MARINE RADAR 3. WORK RATIONALE 1. STUDY AREA 10.2 m NAVD88 photo by D. Honegger North Topsail Beach, NC WIMR/CORrad Correlation of p(σ o b = -4dB ) Q b = N b τ f p Normalized histograms (PDFs) of optical pixel intensity (left) and marine radar NRCS (right) [Catalán et al. 2011]. Objectives: To understand the characteristics of the radar backscatter associated with bottom- and current-induced wave breaking. To estimate radar-derived nearshore wave dissipation associated to bottom- and current-induced breaking. R. Pittman gutting the radar pedestal 7. CORRELATION WITH WIND & WAVES 5. TIDAL DEPENDENCE OF THE PDF 4. TIME & SPACE FRAMEWORK non-breaking steep waves active breaking foam New River Inlet, NC, May 7, 2012 Summary & future work Time-average of calibrated RCS sequences are a proxy for wave-breaking dissipation. PDFs of NRCS agree with previous studies and show strong dependence on η, particularly at high σ o values. A high-NRCS peak σ o b =-4 dB, associated with active breaking, correlates well with η at South beach, and with Hs at the other locations, especially offshore where higher R values occur. Dependence of NRCS on environmental conditions through an EOF approach is in progress. Radar-derived Q b is estimated by applying σ o b as a breaking threshold similar to Catalán et al. [2011]. Future work: comparison of radar-derived Q b to calculated and modeled dissipation of Zippel & Thomson and Moghimi et al., respectively (this Meeting). Four different areas (~0.01 km 2 ) selected for the analysis: 1. South beach depth-induced breaking @ High tide 2. Navigation channel current-induced breaking @ Low tide 3. South ebb-shoal depth-induced breaking @ Low tide 4. Offshore no breaking expected Period of analysis: May 7—15, 2012 6. CORRELATION WITH THE TIDE Correlation of σ o p spring tides neap tides WAVE DISSIPATION Computation of Q b using radar-derived f p 56 57 WHOI ADVs 76 4 1 2 3 σ o [dB] High-tide conditions Time-average of calibrated radar intensity σ o [dB] (9 May 2012 @ 2:30h UTC) 56 57 WHOI ADVs 76 4 1 2 3 σ o [dB] Low-tide conditions Time-average of calibrated radar intensity σ o [dB] (10 May 2012 @ 9:00h UTC) σ o [dB] σ o [dB] 56 57 WHOI ADVs 76 4 1 2 3 56 57 WHOI ADVs 76 4 1 2 3 High-tide conditions Low-tide conditions R lag xCorr +0.86 0 -0.57 0 -0.67 0 0.04 N/S R lag xCorr +0.44 2 -0.40 N/S -0.43 N/S -0.03 N/S σ o p = low-RCS peaks non-breaking σ o b = high-RCS peaks active breaking High NRCS values during ebb conditions f p = 143Hz (T p = 6.9s) f p = 177Hz (T p = 5.6s) References Catalán, P. A., M. C. Haller, R. A. Holman & W. J. Plant (2011), Optical and microwave detection of wave breaking in the surf zone, IEEE Trans. Geosci. Remote Sens., 49(6), 1879—1893, doi:10.1109/TGRS.2010.2095864. Haller, M. C. & D. R. Lyzenga (2003), Comparison of radar and video observations of shallow water breaking waves, IEEE Trans. Geosci. Remote Sens., 41(4), 832—844, doi:10.1109/TGRS.2003.810695. Acknowledgements The authors would like to thank D. Trizna from ISR, Inc. for his assistance during the NRI experiment. We thank B. Raubenheimer & S. Elgar from WHOI for kindly providing access to AWAC data; J. Thomson from APL-UW, for access to Met station data; and R. Holman & J. Stanley from CIL-OSU, for access to ARGUS data. We thank as well the staff from the FRF for kindly providing buoy and bathymetry data. This work has been supported by the Office of Naval Research under award number N00014-10-1-0932. 8. σ o b = -4dB AS BREAKING THRESHOLD

Transcript of REMOTE SENSING OBSERVATIONS OF WAVE DISSIPATION · 2014-03-05 · USA Mexico OSU WIMR specs: •...

Page 1: REMOTE SENSING OBSERVATIONS OF WAVE DISSIPATION · 2014-03-05 · USA Mexico OSU WIMR specs: • commercial SiTEX/Koden marine radar • electronics modified by ISR Inc. • 9.45

Corr

elat

ion

of p

(σo p

= -6

0dB)

vs

win

d sp

eed  

R = -0.27 -0.64 -0.14 -0.72 lagxCorr = n/s n/s n/s n/s

Corr

elat

ion

of p

(σo b

= -4

dB)

vs w

ave

heig

ht  

R = -0.03 0.68 0.68 0.75 lagxCorr = n/s 0.00 0.00 5.00

Approach:

•  Assess the Normalized Radar Cross Section (NRCS or σo) of the ocean surface from New River Inlet Experiment data.

•  Identify NRCS associated with different stages of wave breaking (non-breaking waves, non-breaking steep waves, active breaking and remnant foam).

•  Discriminate NRCS associated with active breaking σob

[Haller & Lyzenga, 2003] following the PDF approach (i. e., normalized histograms) of Catalán et al., [2011].

•  Estimate fraction of breaking waves Qb from:

•  where Nb is the number of breaking waves, fp is the peak frequency, and τ is the length of the radar record.

REMOTE SENSING OBSERVATIONS OF WAVE DISSIPATION

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

Abstract Ref. Number: 17369 Poster number: 453

Guillermo M. Díaz Méndez, Merrick C. Haller, David A. Honegger & Randall W. Pittman [email protected], [email protected], [email protected], [email protected]

INTR

OD

UCT

ION

N

RCS

AN

ALY

SIS

New River Inlet, NC

Atlantic Ocean

USA

Mexico

OSU WIMR specs: •  commercial SiTEX/Koden marine

radar

•  electronics modified by ISR Inc.

•  9.45 GHz (X-band)

•  peak power 25 W

•  2 KHz - PRF

•  50 MHz - sampling frequency

•  9' HH-polarized antenna

•  48 RPM

Sampling scheme: •  half-hourly runs (May 7—15, 2012)

•  range = 512 (1024 May 9—15, 2012)

•  azimuth = 512

•  rotations = 1024

•  Δrange = 3 m; Δazimuth = 0.57o

•  Δt = 1.2 s (Δf = 0.83 Hz )

Coverage: •  r ≈ 3 km; azi ≈ 290o; t ≈ 20 min 2.

OSU

WAV

E IM

AG

ING

MA

RIN

E RA

DA

R

3. W

ORK

RAT

ION

ALE

1. S

TUD

Y A

REA

10.

2 m

NAV

D88

photo by D. Honegger

North Topsail Beach, NC

WIMR/CORrad

Corr

elat

ion

of p

(σo b

= -4

dB)  

Qb =Nb

τ fpNormalized histograms (PDFs) of optical pixel intensity (left) and marine radar NRCS (right) [Catalán et al. 2011].

Objectives:

•  To understand the characteristics of the radar backscatter associated with bottom- and current-induced wave breaking.

•  To estimate radar-derived nearshore wave dissipation associated to bottom- and current-induced breaking.

R. Pittman gutting the radar pedestal

7. C

ORR

ELAT

ION

WIT

H W

IND

& W

AVES

5. T

IDA

L D

EPEN

DEN

CE O

F TH

E PD

F

4. T

IME

& S

PACE

FRA

MEW

ORK

non-breaking steep waves

active breaking

foam

New

Riv

er In

let,

NC,

May

7,

2012

Summary & future work

•  Time-average of calibrated RCS sequences are a proxy for wave-breaking

dissipation.

•  PDFs of NRCS agree with previous studies and show strong dependence on η,

particularly at high σo values.

•  A high-NRCS peak σob=-4 dB, associated with active breaking, correlates well

with η at South beach, and with Hs at the other locations, especially offshore

where higher R values occur.

•  Dependence of NRCS on environmental conditions through an EOF approach

is in progress.

•  Radar-derived Qb is estimated by applying σob as a breaking threshold similar

to Catalán et al. [2011].

•  Future work: comparison of radar-derived Qb to calculated and modeled

dissipation of Zippel & Thomson and Moghimi et al., respectively (this Meeting).

Four different areas (~0.01 km2) selected for the analysis: 1. South beach

depth-induced breaking @ High tide 2. Navigation channel

current-induced breaking @ Low tide 3. South ebb-shoal

depth-induced breaking @ Low tide 4. Offshore

no breaking expected

Period of analysis: •  May 7—15, 2012

6. C

ORR

ELAT

ION

WIT

H T

HE

TID

E

Corr

elat

ion

of σ

o p  

spring tides neap tides

WAV

E D

ISSI

PATI

ON

Com

puta

tion

of

Qb

usin

g ra

dar-

deri

ved

f p  

56 57

WHOI ADVs

76

4 1

2

3

σo [dB]

Hig

h-ti

de c

ondi

tion

s

Time-average of calibrated radar intensity σo [dB] (9 May 2012 @ 2:30h UTC)

56 57

WHOI ADVs

76

4 1

2

3

σo [dB]

Low

-tid

e co

ndit

ions

Time-average of calibrated radar intensity σo [dB] (10 May 2012 @ 9:00h UTC)

σo[dB]  

σo[dB]  

56 57

WHOI ADVs

76

4 1

2

3

56 57

WHOI ADVs

76

4 1

2

3

Hig

h-ti

de c

ondi

tion

s Lo

w-t

ide

cond

itio

ns

R lagxCorr

+0.86 0 -0.57 0 -0.67 0 0.04 N/S

R lagxCorr

+0.44 2 -0.40 N/S -0.43 N/S -0.03 N/S

σop = low-RCS peaks non-breaking

σob = high-RCS peaks active breaking

High NRCS values during ebb conditions  

fp = 143Hz (Tp = 6.9s)

fp = 177Hz (Tp = 5.6s)

References Catalán, P. A., M. C. Haller, R. A. Holman & W. J. Plant (2011), Optical and microwave detection of wave breaking in the

surf zone, IEEE Trans. Geosci. Remote Sens., 49(6), 1879—1893, doi:10.1109/TGRS.2010.2095864.

Haller, M. C. & D. R. Lyzenga (2003), Comparison of radar and video observations of shallow water breaking waves, IEEE Trans. Geosci. Remote Sens., 41(4), 832—844, doi:10.1109/TGRS.2003.810695.

Acknowledgements The authors would like to thank D. Trizna from ISR, Inc. for his assistance during the NRI experiment. We thank B.

Raubenheimer & S. Elgar from WHOI for kindly providing access to AWAC data; J. Thomson from APL-UW, for access to Met station data; and R. Holman & J. Stanley from CIL-OSU, for access to ARGUS data. We thank as well the staff from the FRF for kindly providing buoy and bathymetry data. This work has been supported by the Office of Naval Research under award number N00014-10-1-0932.

8. σ

o b =

-4dB

AS

BREA

KIN

G T

HRE

SHO

LD