In the Netherlands civil and hydraulic engineering have traditionally been important fields of research and development The TNO-Institute of Applied Physics has been involved in (instrumentational) research and development for more than 25 years. A large number of special measuring systems have been developed ranging from optical, echoacoustical and conductivity sensors to the design of large data-gathering networks for the measurement of hydrological and meteorological parameters in the Dutch coastal waters.
Over the last few years the demand for underwater acoustical instrumentation has evolved from simple transit time gauges to complex imaging and feature extraction systems The key phrase in this development has been ‘full wave analysis’ Instead of simply measuring the elapsed time between the transmit pulse and the first bottom return, the echos from the water column and the sub-bottom are also processed and analysed.
Figure 1 shows a typical received echoacoustical signal As can be seen, the same signal is used for a broad range of applications.
Fig. 1 Echoacoustic ‘reference’ signal
In the computer industry another revolution has taken place in the same period of time Computer systems with integrated signal processing and graphics capabilities, the so-called workstations, have become less expensive, gained in performance, and entered the personal computer market Array processors are now available as plug-in boards that can be added to standard Multibus, VME-bus, Q-bus and even PC-bus systems.
In this chapter a system architecture will be described in which state of the art developments of the computer industry are used as components to create an interactive, research environment with integrated data acquisition, processing and presentation facilities The system to be described is called the sonar workstation First the individual components within the sonar workstation will be described, next a few examples will be Sven of current applications.
The Sonar Workstation consists of three main parts a transducer unit, a data acquisition and processing unit, and a host computer system The data acquisition and processing unit is fully general purpose It is configured on an open computer bus structure to offer full flexibility with commercially available hardware Nevertheless special hardware modules had to be developed to create a useful instrument for different research purposes The entire unit is housed In a reinforced cabinet which is easily handled.
The host computer is an IBM-PCIAT computer with a high resolution graphics display that acts as a user-interface for the workstation and a laser-printer output for quality presentation A detailed block diagram of the sonar workstation is shown in Figure 2
The transducer unit consists of a cylindrical container with a removable transducer flange The cylindrical container houses the preamplifiers, the matching networks, and switching electronics for up to four individual transducers The preamplifiers typically yield 35 dB fixed linear gain over a frequency bandwidth which ranges from 100 kHz up to 10 MHz.
Two different transducer flanges have been constructed one with only one 200 kHz transducer looking vertically downwards and one with four l MHz transducers in a Janus configuration.
