CODAR SeaSonde Principles

SeaSonde Overview

O C E A N S E N S O R S

Tuesday, October 8, 13

HF RADAR Definition and Uses

• What Is HF RADAR?• RADAR = RAdio Detection And Ranging

• HF = High Frequency: 3 - 30 MHz or 100 - 10 m wavelength

• VHF = Very High Frequency: 30 - 300 MHz or 10 - 1 m wavelength

• What Can Be Observed/Detected?• Currents

• Most robust environmental data product from HF RADAR systems

• First-order effect - sea echo from Bragg scattering

• Waves• Second-order effect

• Subject to perturbation theory limits - upper waveheight limitation

• Ionosphere Layers• Can cause interference with current measurements

• Discrete “Targets”• Ships: dual use w/ current mapping (under development)

• Ice Packs/Bergs (work done in 70’s - more being done currently)


monopole (A3)

radial whips

loop box(A1 & A2)

Computer and Monitor TransmitterReceiver

What does an HF RADAR consist of?

loop 1 (A1)loop 2 (A2)

receive antenna

loop box

Transmit Antenna

Receive Antenna

electronics


RF Modes of Propagation

Ionosphere

Earth

Line-of-sight (Horizon Limited)

Over-The-Horizon (OTH)

Ground Wave (Beyond Horizon)


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5

SeaSonde PrinciplesSeaSonde Principles


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tseconds

5 60 30.0 4.4

13 23 11.5 2.7

25 12 6.0 2.0

42 7 3.6 1.5



Doppler Spectrum

Doppler Frequency (Hz)

Echo

Str

engt

h (d

Bm)

0 +fB-fB


Doppler Spectrum


Echo

Str

engt

h (d

Bm)

0 +fB-fB


Doppler Spectrum


Echo

Str

engt

h (d

Bm)

0 +fB-fB


Doppler Spectrum


Echo

Str

engt

h (d

Bm)

0 +fB-fB


1 2 3 4 5

Radial Currents


1 2 3 4 5

Doppler Frequency (Hz)Ec

ho S

tren

gth

(dBm

)0 +fB-fB

RadialCurrents


The Doppler Spectrum

Loop 1 (A1)

Loop 2 (A2)

Monopole (A3)

0 HzDoppler Offset

a.k.a. “DC”

Positive Doppler:Targets moving

towards Antennas

Negative Doppler:Targets moving

away from Antennas

Positive Bragg peaks(Waves approaching)

Negative Bragg peaks(Waves receding)

Noise Floor


First Order Regions are convolution of spectral energy from all velocities at a given range cell

+30 cm/s-45 cm/s

Compare Phase, Amplitude of all three antennas to determine

direction of velocity

Loop 1 (A1)

Loop 2 (A2)

Monopole (A3)

0 cm/s


monopole (A3)

radial whips

loop box(A1 & A2)

Computer and Monitor TransmitterReceiver

What does an HF RADAR consist of?

loop 1 (A1)loop 2 (A2)

receive antenna

loop box

Transmit Antenna

Receive Antenna

electronics




Loop 1


Loop 1

Loop

2


Loop 1

Loop

2




Direction Finding

AmplitudesAmplitudes PhasesPhases

A1/A3 A2/A3 P1-P3 P2-P3

0 0.707 0.707 0 0

15 0.866 0.5 0 0

45 1 0 0

75 0.866 0.5 0 180

90 0.707 0.707 0 180

120 0.259 0.966 0 180

180 0.707 0.707 180 180


Direction Finding


A1/A3 A2/A3 P1-P3 P2-P3

0 0.707 0.707 0 0

15 0.866 0.5 0 0

45 1 0 0

75 0.866 0.5 0 180

90 0.707 0.707 0 180

120 0.259 0.966 0 180

180 0.707 0.707 180 180


Direction Finding


A1/A3 A2/A3 P1-P3 P2-P3

0 0.707 0.707 0 0

15 0.866 0.5 0 0

45 1 0 0

75 0.866 0.5 0 180

90 0.707 0.707 0 180

120 0.259 0.966 0 180

180 0.707 0.707 180 180


Output of MUSIC processing:radial vectors

Vectors are in polar coordinate system centered at receive

antenna

1 radial map per averaged cross spectra file

Typically, seven radial maps “merged” into one hourly map

Angular resolutions are 1 - 5˚

Radial Vector Output of MUSIC Processing


New Jersey

Long Island

Nested Ranges & Resolutions


Two (or more) Sites Used to Produce Total Current Vector Maps from

Single-Site Radials Where Coverages Overlap

Angle of incidenceGreater than 15°or less than 165°










Combining Radials into Totals










Surface Current Maps

[Paduan, J.D. and L.K. Rosenfeld, Journal of Geophysical Research, vol. 101, 1996]


Applications


Nyhamna Gas Terminal


Improving Search & Rescue

ModelDrifter

CODAR


http://www.uscg.mil/hq/g-o/g-opr/logohist.htm

http://www.uscg.mil/hq/g-o/g-opr/logohist.htm

Data courtesy of Japan Coast Guard

Vessel Traffic Safety

TextKurushio

Tokyo Bay

Typical Current = 170 cm/s


Planning Coastal Development


South North

Chevron’s Genesis Platform

Loop Current Detection


Loop Current Detection


Operational Oceanography in Norway


Data Assimilation


Fisheries Management


Washington State to Rosarita, Mexico

~2000 km of coastline

Continuous SeaSonde coverage

Nested grid resolutions

COCMP



Ground Wave Propagation & Depth of Measurement

• Requires interface between free space (air) and highly conductive medium (>8 ppt salinity sea water)

• Ocean surface exists as a free boundary allowing surface molecules freedom to conduct EM energy, much like a waveguide

• Allows vertically polarized EM energy to propagate w/ reduced energy loss for greater distances and beyond horizon

• Radar wave does not penetrate surface at all - depth of measurement comes from effective depth-averaged current “felt” by ocean wave

• 25 MHz measures to < .5 m, 5 MHz measures to 2 m deep

D ∝ λ

Depth of measurement is related to ocean wavelength(Can be linear or logarithmic)Seawater is conductive

Air is almost like free space


CODAR SeaSonde Principles

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