Towed M-Sequence/ Long HLA Data Analysis

Transcription

1 Towed M-Sequence/ Long HLA Data Analysis Harry DeFerrari University of Miami Last experiment of CALOPS I Five hour tow at 6 Knots (M-sequence 255 digit, 4.08 sec., 250 Hz center frequency, 36Hzcbw) Thanks to Theo Koji and Jeff Vuono

2 North Towed source HLF-1 5 hrs at 6 Knots Receiver array 230 m SW06

3 6.1 ONR Basic Environmental variability Internal waves Minutes to hours 6.3 NAVSEA Applied Motion Seconds Temporal averaging Spatial averaging Fixed M-sequences Pulse compression Towed Moving target Array grams

4 6.1 ONR Basic Temporal processing Fixed system 6.3 NAVSEA Applied Spatial Processing Moving systems Channel pulse response time fluctuations Beam signal levels fluctuations Arrival Time (sec)

5 Objective: Combine Acoustic Observatory (21 db) array gain with M-sequence pulse compression gain (24 db) Steps: 1. General purpose broadband array processor 2. M-Sequence spectrum matched array processor 3. Linear temporal Doppler search algorithm 4. Hadamard Transforms for pulse compression 5. Hilbert Transform - low pass- threshold detector

6 Combine Temporal and Spatial Processing 1. Intensity (moments): 2. Arrival time 3. Experimental time 4. Frequency 5. Range and depth 6. Beam angle 7. Doppler (expanded parameter space) Beyond any combination of three: Movies Slices

7 Signal Processing: 1. Time delay beamformer F( ) e i t FT s 2 F beam ( ) Plot

8 25 km

9 Signal Processing: 2. M-seq band beamformer FT W f ( )* F( ) F i t s 2 ( ) e F beam ( ) Plot W f ( )* F( )

10 M-Sequence spectrum matched beam former 25 km

11 Signal Processing: 3. M-seq band beamformer and pulse compression FT i t s W f ( )* F( ) F( ) e IFT TS TS Dop1 PR Dop 1 LTDS TS Dop 2 HT PR Dop2 Detecter TS Dop60 PR Dop6 Detecter HilbertT Lopass Threshold

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13 Data 1. Start 432x125x4096 looks x phones x points 2. Beamformer 62x432x4096 beams 3. Doppler Search 59x62x432x4096 Dop lines (6 G-data) 4. Detector 62 beams 432 time samples Computations bit MATLAB 32-bit only access 4 G-data 2. Use MATLAB Matrix instructions no indices and loops! Beamformer First try seconds/sample 40 hrs. Optimized 6 seconds/sample ½ hr.

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17 Expanded scale Doppler -3.5 m/sec

18 Down Doppler (neg.) Opening Range Pulses arrive later in time 2.6 minute time history movies

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20 Up Doppler (pos.) Pulses arrive earlier in time! Range 58 km Range 45 km

21 Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime

22 20 km m-sequence reception Time slice

23 80 km m-sequence reception Time slice

24 1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival

25 Observations Low loss inshore path by 30 db. Low loss and high Doppler go together High Doppler echoes Micro-multipath formation at long ranges

26 6.1 Experiments Focusing effects of continental rise and slope. Focusing effects of whispering gallery Fluctuations and coherence for moving source. Effects of Internal waves on moving source fluctuations. Low frequency active with M-sequences. Statistics of 3-D fluctuations Micro-multipath formation with range

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29 Conclusions: Consistent picture emerges from observations alone. No 3-D propagation models yet. Doppler, paths and angles consistent with out-of-plane anomalous propagation at the SWAP site. Time compression gain may be part (or all) of the observed anomalous TL for the long range arrivals. Next: Build a time compress, processor to search for long range targets

30 Expanded scale Doppler +3.0 m/sec

31 Up Doppler Down Doppler

32 Positive (Up) Doppler Opening range Pulses arrive earlier in time Source appears to be moving towards receiver as ship moves away. Travel time path 2 less than path 1 Anomalous propagation Possible causes: Path 2 Path 1 1. warm fast water inshore 2. basin bathymetry Need a 3-d Model

33 Down (-) Doppler angle decreases with range r 3 r 2 r 1 t 3 >t 2 >t 1 time time

34 Up (+) Doppler angle increases with range r 3 r 2 r 1 t 3 <t 2 <t 1 time

35 Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime

36 Observations Low loss inshore path by 20 db. Low loss and high Doppler go together High Doppler echoes

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38 Towed or Fixed Source C sound speed V tow speed Down Doppler (-) Fixed or moving source - normal propagation Zero Doppler Moving source anomalous SWAP propagation Time Compression Gain SHOCK WAVE! Low frequency, slow motion SONIC BOOM Up Doppler (+) Time reversal Time Compression Gain

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40 Broadband beam output M-SEQ band beam output

41 20 km m-sequence reception Time slice

42 80 km m-sequence reception Time slice

43 1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival

44 6.1 Experiments Focusing effects of continental rise and slope. Focusing effects of whispering gallery Fluctuations and coherence for moving source. Effects of Internal waves on moving source fluctuations. Low frequency active with M-sequences. Statistics of 3-D fluctuations Micro-multipath formation with range

45 Conclusions: Consistent picture emerges from observations alone. No 3-D propagation models yet. Doppler, paths and angles consistent with out-of-plane anomalous propagation at the SWAP site. Time compression gain may be part (or all) of the observed anomalous TL for the long range arrivals. Next: Build a time compress, processor to search for long range targets

46 20 km m-sequence reception Time slice

47 80 km m-sequence reception Time slice

48 1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival

49 Signal Amplitude Data t p (t) p ( t ) COH t, p( t) p( t)* p( t ) 2 t, T 2 p( t ) t, T 2 t, T Change tau to dx - distance along the array Same calculation yields spatial coherence for every arrival of the pulse response!

50 Steering the Array Small shifts in travel time without distortion of the waveform Fourier Time Shifting Theorem p( t) FT F( ) F( ) e i IFT p( t ) r /C

51 Not aligned with wavefront Phase changing along the array causing the coherence calculation to cycle.

52 1. Lower order modes are more spatially coherent than higher order modes 2. All modes have same angle of arrival

53 80 km m-sequence reception Time slice

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55 10 km 80 km

56 Winter CALOPS 20 km 300 m Source Depth Time Dx Along array

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59 10 km 80 km

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69 Up (+) Doppler angle increases with range r 3 r 2 r 1 t 3 <t 2 <t 1 time

70 Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime

71 Down (-) Doppler angle decreases with range r 3 r 2 r 1 r 1 t 3 >t 2 >t 1 time time

72 1 m/sec= 3.6 km/hr 1 m/sec = knots 3.5 m/sec = 12.6 km/hr r 3 r 2 t 3 >t 2 >t 1 time time time

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74 Towed or Fixed Source C sound speed V tow speed Fixed or moving source normal propa Moving source anomalous SWAP propagation Zero Doppler Time Compression Gain Time reversal SHOCK WAVE! Low frequency, slow motion SONIC BOOM

75 Doppler + 2 m/sec

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