Towed M-Sequence/ Long HLA Data Analysis Harry DeFerrari University of Miami hdeferrari@rsmas.miamai.edu 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
North Towed source HLF-1 5 hrs at 6 Knots Receiver array 230 m SW06
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
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)
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
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
Signal Processing: 1. Time delay beamformer F( ) e i t FT s 2 F beam ( ) Plot
25 km
Signal Processing: 2. M-seq band beamformer FT W f ( )* F( ) F i t s 2 ( ) e F beam ( ) Plot W f ( )* F( )
M-Sequence spectrum matched beam former 25 km
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
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 1. 64-bit MATLAB 32-bit only access 4 G-data 2. Use MATLAB Matrix instructions no indices and loops! Beamformer First try - 341 seconds/sample 40 hrs. Optimized 6 seconds/sample ½ hr.
Expanded scale Doppler -3.5 m/sec
Down Doppler (neg.) Opening Range Pulses arrive later in time 2.6 minute time history movies
Up Doppler (pos.) Pulses arrive earlier in time! Range 58 km Range 45 km
Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime
20 km m-sequence reception Time slice
80 km m-sequence reception Time slice
1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival
Observations Low loss inshore path by 30 db. Low loss and high Doppler go together High Doppler echoes Micro-multipath formation at long ranges
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
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
Expanded scale Doppler +3.0 m/sec
Up Doppler Down Doppler
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
Down (-) Doppler angle decreases with range r 3 r 2 r 1 t 3 >t 2 >t 1 time time
Up (+) Doppler angle increases with range r 3 r 2 r 1 t 3 <t 2 <t 1 time
Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime
Observations Low loss inshore path by 20 db. Low loss and high Doppler go together High Doppler echoes
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
Broadband beam output M-SEQ band beam output
20 km m-sequence reception Time slice
80 km m-sequence reception Time slice
1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival
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
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
20 km m-sequence reception Time slice
80 km m-sequence reception Time slice
1. No recognizable modal structure 2. Burst of micro-paths 3. Different angles of arrival
Signal Amplitude Data t p (t)..1......2 p ( t )...3........... 240. 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!
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
Not aligned with wavefront Phase changing along the array causing the coherence calculation to cycle.
1. Lower order modes are more spatially coherent than higher order modes 2. All modes have same angle of arrival
80 km m-sequence reception Time slice
10 km 80 km
Winter CALOPS 20 km 300 m Source Depth Time Dx Along array
10 km 80 km
Up (+) Doppler angle increases with range r 3 r 2 r 1 t 3 <t 2 <t 1 time
Zero Doppler angle unchanged with range r 3 r 2 r 1 t 3 =t 2 =t 1 timetime
Down (-) Doppler angle decreases with range r 3 r 2 r 1 r 1 t 3 >t 2 >t 1 time time
1 m/sec= 3.6 km/hr 1 m/sec = 1.944 knots 3.5 m/sec = 12.6 km/hr r 3 r 2 t 3 >t 2 >t 1 time time time
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
Doppler + 2 m/sec