Routing Strategies for Underwater Gliders
Russ E. Davis, Naomi E. Leonard and David M. Fratantoni Deep-Sea Research II,
vol. 56, 173-187, 2009.
Gliders are autonomous underwater vehicles that achieve long operating range by moving at
speeds comparable to those of, or slower than, typical ocean currents. This paper addresses routing
gliders to rapidly reach a specified waypoint or to maximize the ability to map a measured field,
both in the presence of significant currents. For rapid transit in a frozen velocity field, direct
minimization of travel time provides a trajectory "ray" equation. A simpler routing algorithm that
requires less information is also discussed. Two approaches are developed to maximize the mapping
ability, as measured by objective mapping error, of arrays of vehicles. In order to produce data
sets that are readily interpretable, both approaches focus sampling near predetermined "ideal tracks"
by measuring mapping skill only on those tracks, which are laid out with overall mapping skill in mind.
One approach directly selects each vehicle's headings to maximize instantaneous mapping skill integrated
over the entire array. Because mapping skill decreases when measurements are clustered, this method
automatically coordinates glider arrays to maintain spacing. A simpler method that relies on manual
control for array coordination employs a first-order control loop to balance staying close to the
ideal track and maintaining vehicle speed to maximize mapping skill. While the various techniques
discussed help in dealing with the slow speed of gliders, nothing can keep performance from being
degraded when current speeds are comparable to vehicle speed. This suggests that glider utility
could be greatly enhanced by the ability to operate high speeds for short periods when currents are
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