ORE 654 Applications of Ocean Acoustics Lecture 3b Doppler shift and example sound levels Bruce Howe Ocean and Resources Engineering School of Ocean and Earth Science and Technology University of Hawai’i at Manoa Fall Semester 2011 4/26/2017 ORE 654 L3b

Doppler shift or effect Apparent change in signal frequency after propagation caused by the relative motion of a source and receiver 4/26/2017 ORE 654 L3b

Doppler frequency shift Consider repetitive pulse every T seconds If distance D constant, receive time is D/c and apparent frequency remains f0 = 1/T Distance decrease between s and r because of relative speed vr, arrival time changes Length of time between pulses will change/decrease, and apparent frequency changes too As distance decreases (vr +), frequency increases, wavelength decreases T – time of second pulse transmission 4/26/2017 ORE 654 L3b

Doppler and ASW Acoustic source passing a fixed receiver δf goes to zero at x=0 δf/f can be large (0.7%) for relative speed of 10 kts (18.5 km/hr) – 5 m/s Characteristic signature - pick out of clutter, track over time δf/f >> radar 4/26/2017 ORE 654 L3b

NPAL / ATOC Kauai source 260 W M-sequence coded signals 75 Hz, 35 Hz bandwidth 28 ms peak 27.28 s period 2 hour transmissions, 1 per day Red segments = ARS recordings 79 30 DIVES 25 and 56 - examples

} Kauai example } } } Example time series 1/75 Hz = 13.3 ms zoom PSD 4/26/2017 } Example time series 10.8 ms 14.7 ms 1/75 Hz = 13.3 ms 13.0 ms } } } zoom PSD Kauai example Example PSD

Coherent processing of M-sequence coded signals 4/26/2017 Arrival times (72.7195) (72.282) (72.8654) (72.9153) (73.4143) Relative travel time – 27.28 s Relative travel time – 0.4 s Peaks in each block shift due to changing s/r range Measured travel time changes ~3.7 ms per 27.28 s block Match glider kinematics 0.204 m/s, 136 m horizontally, 33 m vertically, in 12 minutes Process 1st block only – peaks of M sequence processor clearly show arrival times Relative travel time – 0.3 s

Coherent gain 4/26/2017 Relative travel time – 0.4 s Even with glider motion, coherent processing was possible, with 9.4 dB of gain – Doppler consistent Theoretical gain is 14 dB: peaks still not properly aligned – more to do 1 Block 26 Blocks Pk = 1.42 Mean = 0.026 SNR = 34.9 Pk = 32.15 Mean = 0.20 SNR = 44.2 Relative travel time – 0.16 s Time – 12 minutes

~ 5 cm/s differences The dots are estimates from the internal glider velocity and heading records. The plusses are from taking the derivative of the positions (lat,lon,depth) from the glider The solid lines are from the Doppler value of the IAP peak.

Doppler - other Doppler velocimeters Scatters – plankton, bubbles (ideally passive tracers) Basic limits on maximum unambiguous range Rm and velocity Vm Coherent and incoherent systems Moving (ocean) surface induces Doppler shift in scattered signal Measure velocity of platform relative to fixed seafloor – “Doppler velocity log” 4/26/2017 ORE 654 L3b

Sound levels Remember 1 W = 170.8 dB re 1 μPa at 1 m, water 4/26/2017 ORE 654 L3b

Sound levels In air? 1 W =? dB 4/26/2017 ORE 654 L3b

Sound levels Remember 1 W = 170.8 dB re 1 μPa at 1 m, water Remember that air ref is 20 μPa =>20 log(20) = 26 dB (re 1 μPa) Remember that impedance difference => 20 log(1000 * 1500 / 1.3 * 330) = 35.8 dB (re ρc water) So net difference between air and water is 61.5 dB and 1 W air = 109.3 dB re 20 μPa at 1 m, air 4/26/2017 ORE 654 L3b

Broadband Source Level (underwater dB at 1 m) Sound levels Source Broadband Source Level (underwater dB at 1 m) Lightning Strike on Water Surface ~260 Seafloor Volcanic Eruption ~255 Sperm Whale Clicks 163 - 236 Beluga Whale Echolocation Click 206-225 (peak-to-peak) White-beaked Dolphin Echolocation Clicks 194-219 (peak-to-peak) Spinner Dolphin Pulse Bursts 108-115 Bottlenose Dolphin Whistles 125-173 Blue Whale Moans 155 - 188 Humpback Whale Song 144 - 174 Humpback Whale Fluke and Flipper Slap 183 - 192 Snapping Shrimp 183 - 189 (peak-to-peak) 4/26/2017 ORE 654 L3b

Sound levels Source Broadband Source Level (underwater dB at 1 m) Tug and Barge (18 km/hour) 171 Supply Ship (Kigoriak) 181 Large Tanker 186 Icebreaking 193 Airgun array (32 guns) 259 (peak) AN/SQS-53C (U. S. Navy tactical mid-frequency sonar, center frequencies 2.6 and 3.3 kHz) 235 SURTASS-LFA (100-500 Hz) 215 underwater dB for a single projector, 18 in vertical array Heard Island Feasibility Test (HIFT) (Center frequency 57 Hz) 206 underwater dB for a single projector, 5 in vertical array Acoustic Thermometry of Ocean Climate (ATOC)/North Pacific Acoustic Laboratory (NPAL) (Center frequency 75 Hz) 195 4/26/2017 ORE 654 L3b

Sounds in air – DOSIT web site 4/26/2017 ORE 654 L3b