The AUV ‘‘SeaCat’’ needs less energy for propulsion due to the
use of only one main engine and fins for maneuvering, to extend
the mission time. There are additional thrusters illustrated in Fig. 4
to improve the vehicle maneuverability during slow speed or when
the vehicle is hovering. With the horizontal bow thruster, the
vehicle can turn on its current position. The elevator fins are used
for depth control supported by vertical thrusters for slow speed,
which can also be used for descent on the spot.
The additional thrusters provide maneuverability during low
speed required by the sensor constraints and by the complex
structured harbor environment.
Navigation sensors. A laser gyroscope is used for navigation and
positioning supported by a Doppler velocity log (DVL), a pressure
sensor and when not submerged a GPS receiver. Additionally, a
scanning sonar provides data for collision avoidance. This sonar is
mainly used for the reactive vehicle control by the vehicle guidance
system (VGS) and for detection of the inspection objects. The
guidance of the vehicle and the interoperation with the collision
avoidance sonar will be described in this article later in Section 4.
Inspection sensors. The sensors for inspection are mounted on the
bow of the vehicle. It is a head with a pan–tilt-unit for adjusting the
sensors in the right position to the inspection object independent
from the vehicle position as seen in Fig. 5. The used sensors are
a video imaging system with laser illumination and a multi beam
echo sounder (MBES), which are used for the anomaly detection.
The sensor head is shown in Fig. 6.
The inspection sensors also provide the VGS with distance
values to the inspection object. The anomaly detection system can