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© GeoAcoustics 2008
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GeoChirp 3D
Standard System The standard system employs a rigid and robust but relatively lightweight towed array and cable lengths of up to 50m. The system includes the following:
Deck Unit The Deck Unit supplies power for each of the hydrophone pre-amplifiers as well as controlling multi-channel digital acquisition. Digitised raw data is stored and then processed in near real time. The deck unit is connected to the towed array using specially designed modular cabling. The Deck Unit also interfaces to the RTK GPS system, and stores this data with an absolute time stamp synchronised using the 1PPS GPS information. The Chirp processing, transmitter control, and data visualisation graphical interface runs on XP.
The Towed Array is a “just below surface” two dimensional array of hydrophone elements housed in a streamlined platform. The transmit electronics and transducers are also fitted to this platform. The transmitter emits an acoustic swept frequency signal of precisely controlled frequency, amplitude and phase. The signal bandwidth can extend from 1.5 kHz to 13 kHz, allowing high penetration and high resolution to be simultaneously achieved. The source levels can be user controlled to meet even the most environmentally sensitive requirements. Each receiver element consists of several hydrophones integrated with a low noise pre-amplifier. A standard array of 2.5m by 2.2m allows 60 receiver elements to be fitted. The array is modular allowing expansion to over 100 elements if required. Processing data from the array allows true 3-D data to be generated. Unlike pseudo 3-D systems which use multiple 2-D slices of
data and interpolation, the true 3-D system offers decimetre resolution in all
three dimensions down to depths below sea bed of several tens of metres. Unlike
sub-sea towed arrays, absolute positional accuracies to centimetre scale are
achievable.
Applications
Options
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The
3-D Chirp System is the result of collaborative research between National Oceanographic Centre
Southampton (NOCS) and GeoAcoustics Ltd. The system is based around the GeoChirp II Profiling System transmitter and transducers, using a 2-D grid of
receive elements fitted to a lightweight rigid hydrodynamically stable low noise
surface towed array. The 3-D Chirp is the first commercially available system
capable of generating high resolution (decimetric) true 3-D sub bottom data
volumes in “real time” for shallow water applications. The generation of true
3-D volumes requires absolute centimetric positional accuracy, and this problem
has been solved using a Real Time Kinematic (RTK) 3-D GPS system. The sonar
receive array consists of a large number of separate sub-arrays, each with built
in pre-amplifier, and a high bandwidth high resolution multi-channel digital
acquisition and processing system.
Towed
Array
