  Global positioning systems can provide sufficient positioning accuracy for
large scale robotic tasks in open environments. However, in underwater
environments, these systems cannot be directly used, and measuring the position
of underwater robots becomes more difficult. In this paper we first evaluate
the performance of existing pose estimation techniques for an underwater robot
equipped with commonly used sensors for underwater control and pose estimation,
in a simulated environment. In our case these sensors are inertial measurement
units, Doppler velocity log sensors, and ultra-short baseline sensors.
Secondly, for situations in which underwater estimation suffers from drift, we
investigate the benefit of intermittently correcting the position using a
high-precision surface-based sensor, such as regular GPS or an assisting
unmanned aerial vehicle that tracks the underwater robot from above using a
camera.
