DATASONICS SIS-1500 System Manual
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Contents
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1-12 DATASONICSVolume I System Manual June 1998Sonar ElectronicsContained within the electronics housing in the tow vehicle is the sonarelectronics, which controls the tow vehicle’s functions, generates andtransmits the Chirp waveforms, and processes the received signals. Includedwith the sonar electronics in the electronics housing are the pitch, roll, andheading sensors. The sonar electronics receives power, downlinkcommands, and the sonar and responder keys from the Chirplink II DigitalMultiplexer, and transmits the sonar data, the tow vehicle status information,and the sensor data to the digital multiplexer.Optional SensorsSpare RS-232 and analog inputs are available for connecting optionalsensors and oceanographic instruments, including a temperature sensor, apressure sensor, and a cesium magnetometer. In addition, a responder inputis included, which allows for the installation of a responder for tow vehiclepositioning.Chirp TechnologyChirp technology uses digitally produced linear FM acoustic transmissions toproduce high resolution images of seafloor contours. In all sonar systems,higher frequency content is invariably associated with an increase inresolution, and in the case of a sidescan sonar, a decrease in range. Chirptechnology, as implemented in the SIS-1500 Seafloor Imaging System,reduces this trade-off, providing both high resolution and extended range.Across-Track ResolutionThe resolution of a sidescan sonar is measured by its ability to discern closelyspaced objects that lie in the direction that is 90 degrees to the path of thetow vehicle. This resolution is referred to as the across-track resolution. Asidescan sonar system with an across-track resolution of 10 cm will detectindividual objects that are at least 10 cm apart. Objects spaced closer than10 cm will be resolved by the sonar as a single object. In a conventionalsidescan sonar system, the limit of its resolution is determined by the pulselength of the transmitted waveform. In the SIS-1500 Seafloor ImagingSystem, which is a Chirp sidescan sonar system, it is the bandwidth of thetransmitted pulse that sets the system's theoretical resolution. The theoretical |
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