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)

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)

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

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

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

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

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

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

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

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

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

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

Radial Currents 5 4 3 2 1

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

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”

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

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)

Loop 2 Loop 1

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

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

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.

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˚

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 <.5 175-220 60-75 35-50 15-20 6-12 2-5 1-3 0.25-1 15-30 25-100 50-300 150-600 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

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

SeaSonde Waveform TSweep TPulsePeriod FSweepWidth

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"

[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