On the Imaging of Surface Gravity Waves by Marine Radar ...
Post on 04-Jun-2022
6 Views
Preview:
Transcript
On the Imaging of Surface Gravity Waves byMarine Radar: Implications for a Moving
Platform
*Björn Lund, Clarence Collins, Hans Graber,§Eric Terrill
*Rosenstiel School of Marine and Atmospheric Science, University of Miami§Scripps Institution of Oceanography, UC San Diego
October 28, 2013
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
Introduction
Marine radars were developed for ship detection → Sea clutterfirst analyzed as noise (e.g. Croney ’66)
Today, marine radar data are being used to determinefully-directional wave spectra (Young et al. 1985) as well asphase-resolved maps of the surface elevation (Borge et al. 2004)
Surface currents and bathymetry may be obtained as aby-product of the wave analysis (Senet et al. 2001, Bell 1999)
In addition, marine radar data have been used to study internalwaves (Watson and Robinson 1990, Lund et al. 2012), winds(Dankert et al. 2003, Lund et al. 2012), oil spills (Gangeskar2004), ...
Motivation
Previous studies, focused on fixed platform data (e.g. from lighthouses or oil rigs), established marine radar as reliable wave andcurrent sensor (Borge and Soares 2000, Wyatt et al. 2003)
Recent results suggest that shipboard marine radar wave heightestimates cannot be trusted (Stredulinsky and Thornhill 2011)
Wave and current retrieval from ships remains challenging due to:
Ship-motion-induced Doppler shift leads to aliased wave energyJittering wave signal due to changing ship headingResults’ dependency on angle between analysis box and waves
Study goals:
Develop new techniques that address ship-motion-related marineradar wave and current retrieval issuesDemonstrate possibility to reliably determine waves and currentsfrom shipborne marine radar data
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
System Specs
Radar antenna: Hardware diagram:
Scanner
Antenna
Radar
display
unit
Video
Trigger
Heading
Bearing
PC with
WaMoS
capture
board
Screen
Polar backscatterimage:
Furuno marine X-band radar operating at 9.4 GHz withHH-polarization and grazing incidence angle
Pulse length of 0.07 μs (short pulse mode) → 10.5 m rangeresolution
Antenna length of 8 feet → 0.75° antenna beam width
1.5 s antenna rotation period
Wave Monitoring System (WaMoS) sampling up to 4 km with cellsize of 0.2° in azimuth and 7.5 m in range
Hi-Res Experiment
High Resolution Air-Sea Interaction (Hi-Res), off San Francisco, 2010.
Map of Hi-Res experiment:
-124.40 -123.60 -122.80 -122.00
-124.40 -123.60 -122.80 -122.00
37
.80
38
.20
38
.60
39
.00
37
.80
38
.20
38
.60
39
.00
R/P Flip06/06, 19:00 UTC
06/10, 12:00 UTC
California
R/P Flip:
R/V Sproul:
Source: ucsd.edu
Marine Radar Image and Spectrum
Ramp-corrected marine radar image:
FLP, 06/11/2010, 00:00:01.3 UTC
-4 -2 0 2 4x [km]
-4
-2
0
2
4
y [km
]
Head N
Wind
0
2
4
6
8
10
Ram
p-d
ivid
ed r
etu
rn
Frequency-wavenumber slice throughcenter of 3D image spectrum:
-0.4 -0.2 0.0 0.2 0.4Wavenumber [rad m-1]
0.0
0.5
1.0
1.5
2.0
Angula
r fr
equency [ra
d s
-1]
First harmonic
Fundamentalmode
Group line
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
Marine Radar Image Data Concept
Traditional approach (snapshotsimplification):
Source: Borge et al. 1999
Accurate view (spiraling data stream):
Antenna Heading Correction
Pre-correction wave analysis windowat t = 0 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Pre-correction wave analysis windowat t = 6 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Antenna Heading Correction
Pre-correction wave analysis windowat t = 1.5 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Pre-correction wave analysis windowat t = 7.5 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Antenna Heading Correction
Extension of Bell and Osler’s (2011) wave-signature-based heading correction.
Heading errors:
0 20 40 60 80Time [s]
-2
-1
0
1
2
Radar
puls
e h
eadin
g e
rror
[°]
Heading pre- and post-correction:
0 20 40 60 80Time [s]
110
111
112
113
114
115
116
Ship
headin
g [
°]
Before heading correction After heading correction
Antenna Heading Correction
Post-correction wave analysis windowat t = 0 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Post-correction wave analysis windowat t = 6 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Antenna Heading Correction
Post-correction wave analysis windowat t = 1.5 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Post-correction wave analysis windowat t = 7.5 s:
-0.5 0.0 0.5x [km]
-0.5
0.0
0.5
y [km
]
Dependency of Results on Analysis Box Position
Traditional analysis window setup:FLP, 06/11/2010, 00:00:01.3 UTC
-2 -1 0 1 2x [km]
-2
-1
0
1
2
y [km
]
Head N
Wind
0
1
2
3
4
Radar
retu
rn [
×10
3]
Test setup:FLP, 06/11/2010, 00:00:01.3 UTC
-4 -2 0 2 4x [km]
-4
-2
0
2
4
y [km
]
Head N
Wind
0
1
2
3
4
Radar
retu
rn [
×10
3]
Dependency of Results on Analysis Box Position
7
8
9
10
Pe
ak w
ave
pe
rio
d [
s]
-100 0 100Box − peak wave direction [°]
305
310
315
320
325
330
335
Pe
ak w
ave
dire
ctio
n [
°]
0
2
4
6
8
Sig
na
l-to
-no
ise
ra
tio
Downwave Crosswave Upwave Crosswave Downwave
Color legend:Near range,mid range,far range.
Signal-to-Noise Ratio Dependency on Box Orientation
-100 0 100Box − peak wave direction [°]
0
2
4
6
8S
ignal-to
-nois
e r
atio
Downwave Crosswave Upwave Crosswave Downwave
t = 0.5 h t = 1.6 h t = 2.7 h t = 3.8 h t = 4.9 h t = 6.0 h
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
Example of Marine Radar Wave Spectrum
Ramp-corrected radar image:FLP, 06/11/2010, 00:00:01.3 UTC
-4 -2 0 2 4x [km]
-4
-2
0
2
4
y [km
]
Head N
Wind
0
2
4
6
8
10
Ram
p-d
ivid
ed r
etu
rn
Marine radar frequency-directionspectrum:
Comparison with Datawell Buoy and ADCP Data
Time series of waves:Time series of currents:
Datawell buoy data courtesy ofThomas Herbers.
Comparison with Datawell Wave Spectra
Frequency spectrum at t = 0 h:
0.05 0.10 0.15 0.20 0.25 0.30Frequency [Hz]
0.0
0.2
0.4
0.6
0.8
1.0
Norm
aliz
ed w
ave e
nerg
y
Marine radar Datawell buoy
Frequency spectrum at t = 5 h:
0.05 0.10 0.15 0.20 0.25 0.30Frequency [Hz]
0.0
0.2
0.4
0.6
0.8
1.0
Norm
aliz
ed w
ave e
nerg
y
Marine radar Datawell buoy
Outline
1 Introduction
2 Data Overview
3 Moving Platform Challenges and Solutions
4 Preliminary Results
5 Conclusions
Summary / Outlook
Identified ship-motion-related marine radar wave and currentretrieval issues and proposed solutions:
Aliasing due to Doppler-shift from vessel motion→ Geo-referencingJittering wave signal due to Gyro compass errors→ Antenna heading correctionWave retrieval dependency on range and antenna look direction→ Correction function
Shipborne marine radar waves and currents are in goodagreement with measured and modeled reference data
Current research focuses on modeling of wave signal’sdependency on range and antenna look direction
Acknowledgment
This work was supported by theCenter for Southeastern TropicalAdvanced Remote Sensing (CSTARS)of the University of Miami and theU.S. Office of Naval Research (ONR)under grants N000140510758,N000140710650, N000140810793,and N000140910392.
top related