DEVELOPMENT AND TESTING OF NAVIGATION ALGORITHMS

                 Cecilia Liljeberg

       Matematisk Statistik, Lunds Universitet


When traveling under water, a submarine has access to
measurements of position, speed, etc from different
measurement systems. The problem is that these
measurements are not as accurate as one would wish.
Therefore, the submarine is forced to go up to the
surface to get a GPS reading every once in a while,
to get back on track. It is desirable to spend as little
time as possible at the surface, since it involves a risk
of detection, and that is what this Master Thesis is about.
 
The passive measurement systems, inertial navigation system,
gyro compass, passive log and depth gauge, are in use all
the time and the active ones, GPS and active log, only when
necessary. The aim is to increase the precision of the
measurements, which is done in two steps. The first step is
to use all available measurements together. This is done
using a Kalman filter to cofilter the data. The second step
is to use good models for the ship and the measurement
systems.
 
In this thesis the David W. Taylor standard submarine
equations of motion are used as ship model. This means,
among other things, that the motion in all three dimensions
is considered. The results from the different simulations
are very good, for a while. After some time, however, the
results explode. It seems there is some kind of instability,
that leads to growth of the estimates. This problem has
however not been solved in this thesis.