Ya = (RA - (Zn - 531172 (7)
3. The Interferometric Side-Scan-Sonar Equipment
The equations (8) and (7) are valid only for the case of an absolute vertical baseline D
between the two transducers. This is not given because of the dynamic towing situation.
Mainly rolling in w changes the effective direction of the coordinate reference plane
and leads to a wrong determination of the water depth Z4, if this parameter is not recor-
ded and taken for correction. Pitch (4) and Yaw («) have more influence on Xn7 and Your
coordintes and falsify water depth only little. Nevertheless, synchronous recording of
all angular parameters is necessary for further evaluations.
3.1 The Interferometric Side-Scan-Sonar Sensor ([18855-F ish]
Realisation of the theoretical fundamentals of Interferometric Sonar was made at Han-
nover University (Kolouch in SFB, 1979). Based on the electronic components and the
original transducers of the system Mark1B from EG«G a new tow fish was built, which
carries both transducers on one side.
Fig.5: Interferometric Side-Scan-Sonar Fish (closed)
The depression of the transducers can be adjusted up to 35° down for different water
depth. The fish-length is about 1.30 m and its weight 72 kg. The transducers baseline can
be varied from 10 to 25 cm, which allows the processing of 17 interference lines at a
frequency from about 105 KHz. The fish is made of aluminium hollow sections, which
are flooded while surveying. Inside the fish a water-tight tube is mounted, which con-
tains the standard electronic elements, a three-axis rate transducer and a telemetry sy-
stem. that makes a transmission of the rate signals possible using a standard tow cable
(Figure 7 and Figure 8).
ee eee eme EE
i In deviation from the concept mentioned before the interference patterns are produced
d indirectly. Because of loss of coherence of the two outgoing signals from the two trans-
ducers only the lower one is transmitting. The returning echos are received by both and
the interference signals is processed by electronic signal mixing. In addition this proce-
dure has the advantage of synchronous processing of standard and interferometric sonar
image, which are in this system recorded on the original port and starboard channels.
