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