Page 6 - Ranger Demo

Underwater Gliders – A Welcome Addition
for Ocean Measurements
Timothy Clarke, Defence Science and Technology Laboratory (Dstl)
Stephen Woodward and Philip Bagley, National Oceanography Centre (NOC) Sam Jones, Scottish Association for Marine Science (SAMS)
Clare Munson, Royal Navy (RN)
The contents include material subject to Dstl © Crown Copyright 2020
Introduction
The world’s oceans and seas cover over 70% of the earth’s surface area and extend to depths of several kilometres, with the deepest known area being in the Mariana Trench in the Pacific Ocean at over 10km depth. The ocean is home to many aquatic species, is a critical element of the earth’s climate, is the main route for global transport of goods and is used by many nations for power projection. Even so, many parts of the world’s ocean remain un-measured, resulting in a limited understanding of ocean physics and biology. The advent of underwater gliders has allowed academic oceanographers to access high quality and high quantity ocean measurements in near real-time, which has revolutionised the understanding and forecasting of the ocean. The Royal Navy is now in the process of evaluating whether the same revolution is available for military oceanography as an enabler for more effective naval operations.
How Does an Underwater Glider Work and What is Measured?
Gliders are just one of many types of Autonomous Underwater Vehicle (AUV) used around the world for scientific, commercial and military purposes. Gliders are uniquely powered by a buoyancy engine comprising a pump that changes the volume of the vehicle, either by displacing water or by moving oil between internal and external reservoirs. Reducing volume at the surface causes the glider to dive, and pumping out at depth, increases volume and returns it to the surface. A typical glider is shown in (Figure 1), a SLOCUM GX just being recovered, which sometimes attract the attention of the local wildlife.
The glider’s fixed wings convert this
buoyancy-driven vertical velocity into
horizontal movement. A rudder (or in
some cases a rolling internal weight)
steers the glider on its course, resulting
in a vehicle which ‘glides’ slowly and
almost silently up and down through the
ocean in a sawtooth pattern, communicating with shoreside pilots to upload data and download new instructions via satellite when surfacing (Figure 2). This efficient means of propulsion combined with modern battery technology gives gliders an endurance of up to a year and a range of several thousand kilometres in ideal conditions.
Figure 1 Glider recovery after completing a successful mission during a Dstl trials programme. An Atlantic wreckfish in attendance!
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