Transcript PSU-FORA_KOS

An Overview And Lessons Learned From The
Five Octave Research Array (FORA) With Some
Perspectives For Future Towed Array
John R. Prestona, Kyle M. Beckerb, Paul T. Shultzc, Jeffrey R. McIlvainc, George M. Ruhlmannd
aARL,
Penn State University, P.O. Box 30, MS 6110D, State College, PA 16804
bNURC, Viale San Bartolomeo 400, 19126 La Spezia, Italy
cL-3 Chesapeake Sciences Corp., 1127B Benfield Blvd., Millersville MD 21108
dWaveTech Engineering, LLC., 3200 Dunbratton Court, Waldorf, MD 20601
Purpose/Background
• Built to support the ONR Ocean Acoustics
Program’s 6.1 experimental research efforts.
• MACE program at ONR was also a
sponsor/user of this system.
• After its shakedown cruise in 2002, FORA
has completed ten very successful sea trials
as of Sept. 2010.
FORA System
Module Layout*
Towed Array
Test Set (TATS)
TATS
Controller
Deck Cable
Array & Winch
Wt: 22,000 lbs.
Tow Cable
30 m long, 15 mm dia
950 m long, 27.4 mm dia.
Nas Nodes
Fore VIM
Forw.
VIM
25 m
Triplet
Module
25.0m
Fore LF/MF
Forw.
LF/MF
33.5m
MF/HF
Aft LF/MF
(Aft)
ULF
ULF
Aft VIM
30.0m
45.0m
88m
30.5m
277 m (triplet 89 mm dia, linear 77 mm. dia.)
*not the same as acoustic apertures
Drogue
305 m long,
11 mm dia.
FORA with new level wind
FORA Acoustic Apertures
Acoustic
Apertures
ULF
No. of phones
Design freq (Hz)/
spacing (m)
64
250 / 3.0
LF
64
500 / 1.5
MF
64
1000 / 0.75
HF
64
2000 / 0.375
Triplet section
78*3
3750 / 0.2
FORA SAMPLING CONFIGURATIONS
(Total channels =396)
Config.
number
Fwd
Triplet
Aft Triplet All Linear
Apertures
1
2
3
4
5
25 kHz
12.5 kHz
16.0 kHz
8.0 kHz
2.0 kHz
12.5 kHz
12.5 kHz
8.0 kHz
8.0 kHz
2.0 kHz
6.25 kHz
6.25 kHz
8.0 kHz
8.0 kHz
2.0 kHz
FORA on R/V KNORR
Deployment
FORA Overboard Sheave
FORA Capabilities
• Large frequency coverage 50 - 3750 Hz with beamformer
• Very high dynamic range 24 bit A/D, 19 bits actual
• 4 NAS suites - each with heading, pitch, roll, depth and
temperature
• Removable ULF section (88 m)
• Can also operate as short/long vertical array suspended
from own ship (drifting or moored only)
• Five sampling configurations from 2 kHz - 25 kHz
• Highest frequency aperture is a triplet array for left-right
ambiguity resolution
• Desensitized phone to capture direct arrival waveforms
Limitations/Considerations
• Drogue was designed for 4-5 kt tows but the split drogue
mod. allows tows up to 10 kts.
• Maximum depth at 3 kts is ~350 m (cable limit).
• Array uses ATM/Sonet fiber optic data link so input data
rate fixed at 155 mb/s but recording is done separately for
triplet or linear sections.
• The FORA acquisition system can record all 4 linear
sections or the full triplet section without problems.
• Acquisition system is based on archiving to SATA disks
from Linux workstations.
Newer Sea Trial Summaries
• NPAL//SPICE/LOAPEX 04 - long range propagation and azimuthal
scattering studies: FORA operated for the entire experiment without
any days lost but ~1s one-way timing errors were later discovered.
• OREX 05 - scattering and inversion studies: FORA weather +
equipment problems caused 1-2 days of data loss (for first time). New
FORA limit is SS4 for operations.
• Gulf of Maine 06 - remote sensing of fish schools: FORA operates
without equipment failures for entire trial.
• Clutter07/BASE07 FORA operates without major problems again (all
desired data collected successfully).
• During the course of FORA’s ten sea trials, it was requested to collect
data for a total of 138 days and missed only 3.5 days due to FORA
equipment problems (including the winch).
Summary of FORA Sea Trials
Sample of Reverberation from the FORA LF
aperture on the New Jersey Shelf
Sample reverberation from the FORA cardioid
aperture on the New Jersey Shelf
Triplet BF Near Mud Volcanoes
FORA Acquisition Software Problem History/Fixes
• The original FORA acquisition software was adapted from other active
systems and worked well in active experiments.
• In 2006-2007, post analysis of the NPAL04 experiment showed oneway timing errors of >=0.5 s with no way of correcting them.
• In 2008-2009 several improvements reduced one-way error to ~8ms.
• In 2010 the acquisition system was completely rewritten. In the course
of improving the FORA acquisition system for the LRAC10
experiment, GPS time tags have been added for each data block, and
all data dropouts are logged with location and duration.
• The new acquisition software worked flawlessly during the remainder
of the LRAC10 experiment recently completed (no dropouts). Now
one-way timing errors are down to approximately 1 ms.
Acknowledgements
•
ONR Ocean Acoustics Program
•
ONR MACE Program
•
Chesapeake Sciences Corp. & Teledyne Inst.
•
Digital Systems Research (DSR) Inc.
•
Lillimar (Lillie) Rulhmann, Nick Makris (MIT)
•
R. Hollett (SACLANTCEN), Eddie Scheer (WHOI)
•
A. C. Hill (Hill Consulting)
• WaveTech Engineering, LLC (George Ruhlmann)
New Array Technologies