SeaSonde Overview. 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

SeaSonde Overview

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

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

λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5

SeaSonde PrinciplesSeaSonde Principles

λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


λ/2λ/2

λλ

Bragg Sea Echo

A B C

Freq mhz

λmeters

λ/2meters

Tsecond

s

5 60 30.0 4.413 23 11.5 2.725 12 6.0 2.042 7 3.6 1.5


Doppler Spectrum

Doppler Frequency (Hz)

Ech

o S

treng

th (

dB

m)

0 +fB-fB

11 22 3 4 5

Radial Currents

11 22 3 4 5

Doppler Frequency (Hz)Ech

o S

treng

th (

dB

m)

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

2

Direction Finding

Amplitudes

Phases

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

Amplitudes

Phases

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

Amplitudes

Phases

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

SeaSonde Operational Performance vs. Frequency

RadarFrequency

(MHz)

RadarWavelength

(m)

OceanWavelength

(m)

OceanWavePeriod

(s)

Depth ofCurrent1

(m)

TypicalRange2

(km)

TypicalResolution3

(km)

5

12

25

48

60

25

12.5

6

30

12.5

6

3

4.5

2.5

2

1.5

2

1-1.5

.5-1

<.5

175-220

60-75

35-50

15-20

6-12

2-5

1-3

0.25-1

Upper H1/3

Limit4

(m)

25

13

7

3

1. Depth averaged current2. Range based on 40W avg power output. Salinity, wave climate and RF noise may affect this. 3. Based on bandwidth approval only - no system limitations - higher resolution will cause some range loss4. Significant Waveheight at which 2nd order spectra saturates 1st order and no current measurements possible

TypicalBandwidth

(kHz)

15-30

25-100

50-300

150-600

SeaSonde Gated FMCW Waveform -- Time DomainSeaSonde Gated FMCW Waveform -- Time DomainEcho Range Determination from 1st FFTEcho Range Determination from 1st FFT

• Linear FMCW Linear FMCW (frequency-modulated continuous wave)(frequency-modulated continuous wave) determines: determines:

• Range to targetRange to target

• Range resolutionRange resolution

• Pulsing Only Used to Protect Receiver During Strong TransmissionPulsing Only Used to Protect Receiver During Strong Transmission

• 50% duty factor (square wave) is optimal for signal-to-noise ratio50% duty factor (square wave) is optimal for signal-to-noise ratio

• Pulse period determines maximum range and blind zones in coveragePulse period determines maximum range and blind zones in coverage

TSweep

TPulsePeriod

FS

wee

pWid

th

SeaSonde Waveform

• Second transmitter's Second transmitter's modulation start is modulation start is shifted to shifted to tt22

• After demodulation in After demodulation in receiver, signal plus receiver, signal plus echoes shifted to beyond echoes shifted to beyond ff22

• First FFT puts these First FFT puts these signals plus echoes in signals plus echoes in distant, unused "rangedistant, unused "range

bins"bins"

How We Achieve How We Achieve Simultaneous Simultaneous Synchronization via Synchronization via Modulation Modulation MultiplexingMultiplexing

Radiated Waveform Parameters for SeaSondes Radiated Waveform Parameters for SeaSondes at Sandy Hook in Their Three HF Operating at Sandy Hook in Their Three HF Operating BandsBands

• 5 MHz Band (4.53 MHz center frequency)5 MHz Band (4.53 MHz center frequency)

• Sweep Period Sweep Period TTSweepSweep : 1 second : 1 second

• Sweep Bandwidth Sweep Bandwidth FFSweepWidthSweepWidth : 25.6 kHz : 25.6 kHz

• Pulsing Period Pulsing Period TTPulsePeriodPulsePeriod : 1946 microseconds : 1946 microseconds


• Sweep Period Sweep Period TTSweepSweep : 0.5 second : 0.5 second

• Sweep Bandwidth Sweep Bandwidth FFSweepWidthSweepWidth : 49.4 kHz : 49.4 kHz



• Sweep Period Sweep Period TTSweepSweep : 0.5 second : 0.5 second

• Sweep Bandwidth Sweep Bandwidth FFSweepWidthSweepWidth : 101 kHz : 101 kHz


[Refer to Controller Settings on Next Slide]

Note

Sweep Direction CanEither Be Up or Down

Figure ShowsUpsweep

All Three Sandy HookRadars Are Sweeping

Downwards

Documents

SeaSonde Overview. 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