Unit installation

Theory of Operation
974-24007001/4.1 11
2.5.4 Pulse Length Control
The FS 70 Trawl Sonar Heads are capable of changing the acoustic
pulse length that is transmitted. The surface processing unit sets the
pulse length based on the operating range of the sonar head. It is
generally better to use a longer pulse as the operating range
increases. However, the actual value can be optimized to enhance
the details in the sonar image (Optimize Resolution) or to increase
the target visibility at long distance away from the sonar head
(Maximum Range).
Optimize Resolution - The pulse length selection can be
optimized to enhance the detail of the targets. It has been
experimentally determined that the pulse length corresponding to
40% of the sample period can increase the image resolution and
details for targets that are generally larger than a few samples.
Maximize Range - The pulse length calculation can be optimized
to increase the detection range of the sonar head. Generally, the
longer the pulse length, the more energy is transmitted into the
water which could then travel a longer distance and get reflected
from the targets that are further away from the sonar head. It has
been determined that the pulse length corresponding to 80% of
the sample period can increase the detection distance of the
targets without a major drain on the sonar head power supply.
The pulse length increases linearly with increasing operating range.
The system will automatically set the pulse length to match the
range, unless manually adjusted by the operator.
2.5.5 Peak Detection
Depending on the operational settings, the combination of small
target size, short pulse length and long sample period could result in
the acoustic return from the target falling between two samples and
therefore not beings seen on the sonar image.
To remedy this, it was decided to take additional samples in the
interval between two displayed samples and select the strongest
echo target during that interval for the sonar image display. This is
generally referred to as Peak Detection because we are detecting the
peak value of signal in between two samples. The user can enable
the Peak Detection and select the number of additional samples that
the system takes in order to detect the peak value in order to
optimize the detail in the image while maintaining an acceptable
signal to noise ratio.