DATASONICS SIS-1500, System Manual

Page: 82 / 110

4-14 DATASONICS
Volume I System Manual June 1998
of 40 dB. Once amplified, the received signals are mixed with a local oscillator
frequency and the difference frequency, or base band, which is the swept
frequency bandwidth, is output to the Digitizer board.
The Digitizer board is a six channel, 16-bit analog to digital converter that
inputs the amplified and filtered signals from the Receiver board. The four
additional channels can be used to input analog signals from the optional
sensors. The input signals from all six channels are sampled simultaneously
at 48 kHz and output to the T1 Interface board in an interleaved serial output
format.
The T1 Interface board, which inputs the serial data outputs from the Digitizer
board, is used to format the serial data in accordance with the T1
specification. The formatted data is output at 1.544 Mbits/sec to the Cable
Interface board. The T1 Interface board also generates the clock signals
required by the Digitizer board.
Transducer Arrays
There are two independent transducer arrays: one on the port side and one
on the starboard side of the TTV-195 Tow Vehicle. They are both
independently connected to the Transmitter board in the sonar electronics.
Each transducer array consists of six precisely spaced transducer elements
that are positioned in a straight line to form a linear array with specific beam
characteristics: a narrow horizontal beam, which contributes to the high
resolution imaging in the along-track dimension, and a wide vertical beam,
which provides wide bottom coverage in the cross-track direction. In addition,
the down-look angle of each transducer array is adjustable from 0
°
to 20
°
in
10
°
increments.
Standard and Optional Sensors
The standard sensors are the pitch, roll, and heading sensors, and the
optional sensors include a temperature sensor, a pressure sensor, and a
cesium magnetometer. All the sensors are installed within the tow vehicle or
mount externally to the tow vehicle, and they connect to the sonar electronics
either with an RS-232 interface or with a direct analog connection. In addition,
an optional responder, which is triggered by the responder key, can be
installed in the tow vehicle. The responder is used with an acoustic tracking
system to provide tow vehicle positioning. Both the responder’s transducer
and the temperature sensor are contained within the nose of the tow vehicle,
and the pressure sensor is contained within the nose end cap.