ORE 654 Applica.ons of Ocean Acous.cs. Lecture 3b Doppler shi< and example sound levels

Transcription

1 ORE 654 Applia.ons of Oean Aous.s Leture 3b Doppler shi< and example sound levels Brue Howe Oean and Resoures Engineering Shool of Oean and Earth Siene and Tehnology University of Hawai i at Manoa Fall Semester /25/14 ORE 654 L3b 1

2 Doppler shic or effet Apparent hange in signal frequeny acer propagakon aused by the relakve mokon of a soure and reeiver Change in path length during finite transmission Kme 9/25/14 ORE 654 L3b 2

3 Doppler frequeny shic Consider repekkve pulse every T seonds If distane D onstant, reeive Kme is D/ and apparent frequeny remains f 0 = 1/T Distane derease between s and r beause of relakve speed v r, arrival Kme hanges Length of Kme between pulses will hange/derease, and apparent frequeny hanges too As distane dereases (v r +), frequeny inreases, wavelength dereases t 1 = D(t 1) D(t) = D(t 1 ) v r t t 2 = T + D(t 2 ) t 2 t 1 = T v rt f = 1 T 1 v r = T+ D(t 1) v r T = = T 1 v r δ f = f f 0 = f 0 v r δ f = 2 f 0 v r ; f 0 1 v r two-way eho f 0 1+ v r 9/25/14 ORE 654 L3b 3

4 AousK soure passing a fixed reeiver δf goes to zero at x=0 δf/f an be large (0.7%) for relakve speed of 10 kts (18.5 km/hr) 5 m/s CharaterisK signature - pik out of luber, trak over Kme δf/f >> radar Doppler and ASW v r = 9/25/14 ORE 654 L3b 4 δ f f 0 = v xv x 2 + H 2 x x 2 + H 2 = v osθ

5 NPAL / ATOC Kauai soure 30 Red segments = ARS reordings W M- sequene oded signals 75 Hz, 35 Hz bandwidth 28 ms peak s period 2 hour transmissions, 1 per day DIVES 25 and 56 - examples

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

7 Coherent proessing of M-sequene oded signals ( ) Arrival times ( ) ( ) (72.282) ( ) Relative travel time s Relative travel time 0.4 s Peaks in eah blok shift due to hanging s/r range Measured travel time hanges ~3.7 ms per s blok Math glider kinematis m/s, 136 m horizontally, 33 m vertially, in 12 minutes Relative travel time 0.3 s

8 Coherent gain Relative travel time 0.4 s 1 Blok 26 Bloks Pk = 1.42 Even with glider motion, oherent proessing was possible, with 9.4 db of gain Doppler onsistent Theoretial gain is 14 db: peaks still not properly aligned more to do Pk = Relative travel time 0.16 s SNR = 34.9 SNR = 44.2 Mean = Mean = 0.20 Time 12 minutes

9 ~ 5 m/s differenes

10 Doppler - other Doppler veloimeters Sabers plankton, bubbles (ideally passive traers) Basi limits on maximum unambiguous range R m and veloity V m Coherent and inoherent systems Moving (oean) surfae indues Doppler shic in sabered signal Measure veloity of plaiorm relakve to fixed seafloor Doppler veloity log 9/25/14 ORE 654 L3b 10

11 Sound levels Remember 1 W = db re 1 μpa at 1 m, water 2 p 1m = ρ A 4π P a ; P a = aousti power W SL(dB) = 10log 10 (P a ) + 10log 10 ( ρ A 4π ) + 20log 10 SL(dB) = 10log 10 (P a ) + [( ) = 170.8]; 10 6 µpa 1 Pa re 1 µpa at 1 m 9/25/14 ORE 654 L3b 11

12 Sound levels In air? 1 W =? db 2 p 1m = ρ A 4π P a ; P a = aousti power W, air SL(dB) = 10 log 10 (P a ) + 10 log 10 ( ρ A 4π ) + 20 log 10 SL(dB) = 10 log 10 (P a ) + [( ) = 109.3]; 10 6 µpa 1 Pa 1 20 re 20 µpa at 1 m 9/25/14 ORE 654 L3b 12

13 Sound levels Remember 1 W = 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 impedane differene => 20 log(1000 * 1500 / 1.3 * 330) = 35.8 db (re ρ water) So net differene between air and water is 61.5 db and 1 W air = db re 20 μpa at 1 m, air 9/25/14 ORE 654 L3b 13

14 Sound levels - DOSITS Soure Broadband Soure Level (underwater db at 1 m) Lightning Strike on Water Surfae ~260 Seafloor Volani ErupKon ~255 Sperm Whale Cliks Beluga Whale EholoaKon Clik White- beaked Dolphin EholoaKon Cliks Spinner Dolphin Pulse Bursts Boblenose Dolphin Whistles (peak- to- peak) (peak- to- peak) Blue Whale Moans Humpbak Whale Song Humpbak Whale Fluke and Flipper Slap Snapping Shrimp /25/14 ORE 654 L3b (peak- to- peak) 14

15 Soure Sound levels Broadband Soure Level (underwater db at 1 m) Tug and Barge (18 km/hour) 171 Supply Ship (Kigoriak) 181 Large Tanker 186 Iebreaking 193 Airgun array (32 guns) AN/SQS- 53C (U. S. Navy takal mid- frequeny sonar, enter frequenies 2.6 and 3.3 khz) SURTASS- LFA ( Hz) 259 (peak) underwater db for a single projetor, 18 in verkal array Heard Island Feasibility Test (HIFT) (Center frequeny 57 Hz) 206 underwater db for a single projetor, 5 in verkal array AousK Thermometry of Oean Climate (ATOC)/ North Paifi AousK Laboratory (NPAL) (Center frequeny 75 Hz) 9/25/14 ORE 654 L3b

16 Sounds in air DOSIT web site 9/25/14 ORE 654 L3b 16