1. 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

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

3. 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
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ORE 654 L3b

4. 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
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ORE 654 L3b

5. 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

6. } Kauai example } } } Example time series 1/75 Hz = 13.3 ms zoom PSD
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Example time series
10.8 ms
14.7 ms
1/75 Hz = 13.3 ms
13.0 ms } } }
zoom PSD
Kauai example
Example PSD

7. Coherent processing of M-sequence coded signals
4/26/2017
Arrival times
( )
(72.282)
( )
( )
( )
Relative travel time – 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 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

8. Coherent gain
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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

9. ~ 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.

10. 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”
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ORE 654 L3b

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

12. Sound levels
In air? 1 W =? dB
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ORE 654 L3b

13. 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 = dB re 20 μPa at 1 m, air
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ORE 654 L3b

14. 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
Beluga Whale Echolocation Click
(peak-to-peak)
White-beaked Dolphin Echolocation Clicks
(peak-to-peak)
Spinner Dolphin Pulse Bursts
Bottlenose Dolphin Whistles
Blue Whale Moans
Humpback Whale Song
Humpback Whale Fluke and Flipper Slap
Snapping Shrimp
(peak-to-peak)
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ORE 654 L3b

15. 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 ( 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
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16. Sounds in air – DOSIT web site
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ORE 654 L3b