1. SeaSonde Overview

2. HF RADAR Definition and Uses
What Is HF RADAR?
RADAR = RAdio Detection And Ranging
HF = High Frequency: MHz or m wavelength
VHF = Very High Frequency: MHz or 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)

3. What does an HF RADAR consist of?
Computer and Monitor
Transmitter
Transmit Antenna
Receiver
Receive Antenna
receive antenna
monopole (A3)
loop box
(A1 & A2)
radial whips
electronics
loop box
loop 2 (A2)
loop 1 (A1)

4. RF Modes of Propagation

5. 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
Air is almost like free space
D ∝ λ
Depth of measurement is related to ocean wavelength
(Can be linear or logarithmic)
Seawater is conductive

6. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

7. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

8. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

9. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

10. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

11. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

12. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

13. Bragg Sea Echo Freq λ λ/2 T λ λ λ/2 λ/2 5 60 30.0 4.4 13 23 11.5 2.7
mhz λ
meters
λ/2 T
seconds 5 60
30.0
4.4 13 23
11.5
2.7 25 12
6.0
2.0 42 7
3.6
1.5
Bragg Sea Echo
-The leading RADAR wave crest reflects some energy off of wave slope C
-The second RADAR wave crest passes A (with some energy lost to reflection)
-The second wave crest & the reflected energy of the leading wave crest meet at B
-The energy of the second wave crest reflected at B adds coherently with the reflected
energy of the leading wave crest. λ λ
λ/2
λ/2 A B C
SeaSonde Principles
SeaSonde Principles

14. Doppler Frequency (Hz)
Doppler Spectrum
Echo Strength (dBm)
-fB
+fB
Doppler Frequency (Hz)

15. Radial Currents 5 4 3 2 1

16. Doppler Frequency (Hz)
Radial
Currents
Echo Strength (dBm)
-fB
+fB
Doppler Frequency (Hz) 5 4 3 2 1

17. The Doppler Spectrum Noise Floor Loop 1 (A1) Loop 2 (A2) Monopole (A3)
Negative Bragg peaks
(Waves receding)
Positive Bragg peaks
(Waves approaching)
Noise Floor
Loop 1 (A1)
Loop 2 (A2)
Monopole (A3)
Negative Doppler:
Targets moving
away from Antennas
Positive Doppler:
Targets moving
towards Antennas
0 Hz
Doppler Offset
a.k.a. “DC”

18. First Order Regions are convolution of spectral energy from all velocities at a given range cell
Compare Phase, Amplitude of all three antennas to determine direction of velocity
Loop 1 (A1)
Loop 2 (A2)
Monopole (A3)
+30 cm/s
-45 cm/s
0 cm/s

19. What does an HF RADAR consist of?
Computer and Monitor
Transmitter
Transmit Antenna
Receiver
Receive Antenna
receive antenna
monopole (A3)
loop box
(A1 & A2)
radial whips
electronics
loop box
loop 2 (A2)
loop 1 (A1)

20. Loop 2
Loop 1

21. Direction Finding 15 45 75 90 120 Amplitudes Phases P1-P3 P2-P3 A1/A3
0.707 15
0.866
0.5 45 1 75
180 90
120
0.259
0.966

22. Direction Finding 15 45 75 90 120 Amplitudes Phases P1-P3 P2-P3 A1/A3
0.707 15
0.866
0.5 45 1 75
180 90
120
0.259
0.966
Something to think about: If loop 2 went out, where would all of the solutions tend to pile up? Probably in the bearings surrounding the null of loop 2

23. Direction Finding 15 45 75 90 120 Amplitudes Phases P1-P3 P2-P3 A1/A3
0.707 15
0.866
0.5 45 1 75
180 90
120
0.259
0.966
Amplitudes for both loops are exactly the same as 0˚ bearing - how do we distinguish them? Use Phases.

24. Radial Vector 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˚

25. SeaSonde Operational Performance vs. Frequency
Radar
Frequency
(MHz)
Radar
Wavelength
(m)
Ocean
Wavelength
(m)
Ocean
Wave
Period
(s)
Depth of
Current1
(m)
Typical
Range2
(km)
Typical
Resolution3
(km)
Typical
Bandwidth
(kHz)
Upper H1/3
Limit4
(m) 60 25
12.5 6 5 12 25 48 30
12.5 6 3
4.5
2.5 2
1.5 2
1-1.5
.5-1
<.5
60-75
35-50
15-20
6-12
2-5
1-3
0.25-1
15-30
25-100
50-300 25 13 7 3
1. Depth averaged current
2. 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 loss
4. Significant Waveheight at which 2nd order spectra saturates 1st order and no current measurements possible

26. SeaSonde Gated FMCW Waveform -- Time Domain Echo Range Determination from 1st FFT
Linear FMCW (frequency-modulated continuous wave) determines:
Range to target
Range resolution
Pulsing Only Used to Protect Receiver During Strong Transmission
50% duty factor (square wave) is optimal for signal-to-noise ratio
Pulse period determines maximum range and blind zones in coverage

27. SeaSonde Waveform
TSweep
TPulsePeriod
FSweepWidth

28. How We Achieve Simultaneous Synchronization via Modulation Multiplexing
Second transmitter's modulation start is shifted to t2
After demodulation in receiver, signal plus echoes shifted to beyond f2
First FFT puts these signals plus echoes in distant, unused "range bins"

29. [Refer to Controller Settings on Next Slide]
Radiated Waveform Parameters for SeaSondes at Sandy Hook in Their Three HF Operating Bands
[Refer to Controller Settings on Next Slide]
5 MHz Band (4.53 MHz center frequency)
Sweep Period TSweep : 1 second
Sweep Bandwidth FSweepWidth : 25.6 kHz
Pulsing Period TPulsePeriod : 1946 microseconds
13 MHz Band (13.46 MHz center frequency)
Sweep Period TSweep : 0.5 second
Sweep Bandwidth FSweepWidth : 49.4 kHz
Pulsing Period TPulsePeriod : 669 microseconds
25 MHz Band (24.65 MHz center frequency)
Sweep Bandwidth FSweepWidth : 101 kHz
Pulsing Period TPulsePeriod : 486 microseconds
Note
Sweep Direction Can
Either Be Up or Down
Figure Shows
Upsweep
All Three Sandy Hook
Radars Are Sweeping
Downwards