HAWAII MR1 Technical Description

Towfish Instrumentation

The MR1 transducer arrays were custom built by Reson, Inc. to HMRG specifications. The arrays use an air based tonpilz design that features two rows of elements per array, 32 individual elements per row, and rows spaced 1/2 wavelength apart. Pitch and roll are measured using a Lucas Accustar II dual-axis clinometer that has a range of plus/minus 20 degrees and a resolution of 0.01 degrees. Heading is measured using a KVH C100 microprocessor-controlled fluxgate compass that has a resolution 0.1 degree and an accuracy of plus/minus 0.5 degree. Depth is measured using a Micron Instruments MP405-500-G pressure sensor that can be used to 500 PSI (~=3400 kPa or 340 m) with 0.25% error. The towfish is attached to the ship by a steel armored coaxial cable. Telemetry is accomplished using a half-duplex, frequency-shifted keyed datalink with a data rate of 422 kilobaud.

Additional new capabilities will include an upgrade of the system's programmable eletronics to permit operation with the swept-frequency (chirp) transmit signals for improved data quality, and faster pulse repetition rates for increased resolution in shallow water. This capability should be available by January 1, 1997.

Starboard Transducer Array

Sonar Transducers

The sonar transducers in the HAWAII MR1 were acquired in 1988 for use with SeaMARC II. They have been thoroughly tested and calibrated (near field) at the Navy's test facility in San Diego, and both beam pattern and phase response are well-determined. These transducers are rated to allow transmitted pulses of up to 10 kW per row (40 kW total power) in contrast to approxiamately 5 kW/row in the older SeaMARC II system. HMRG plans to upgrade HAWAII MR1 with new transducer arrays and reprogrammed eletronics, to improve data quality, during late 1996. The new arrays will provide enhanced bathymetry resolution by featuring wider row spacing, which improves the system's ability to measure the phase of returning acoustic signals. The modular design of the new arrays will also simplify system maintenance.

Electronics

HAWAII MR1 is designed around a network of up to 16 digital signal processors (DSPs). At present, three are used in the system - two located in the subsurface vehicle and one in the topside data acquisition workstation. These DSPs process the acoustic signals digitally. Earlier sonar designs performed much of the signal processing with analog electronics, subject to noise and component drift that would introduce artifacts into the data. Digital computations are not subject to drift, and the 24-bit word size of the present system allows a dynamic range of 144 dB. The software that implememts this signal processing is remotely loaded from the surface, and can be reloaded in a few seconds without recovering the tow vehicle.

 Subsurface Electronics

 This drawing illustrates one side only; electronics are identical
on port and starboard sides. Each block represents a single
printed circuit board.

 Surface Electronics

 The MR1 system sails with redundant topside systems that can be
interchanged on-the-fly to minimize data loss due to computer failure