The underwater environment: a challenge for planning

Abstract

This paper reviews the applications and challenges of robotic

systems in the underwater domain. It focuses on the challenges

for achieving embedded situation awareness, adaptive

trajectory planning and adaptive mission planning. These are

required elements for providing true autonomy for delegation

of tasks to unmanned underwater vehicles. The paper analyses

current approaches to tackling these challenges and how

planning plays a vital role in overcoming them. It includes a

description of some key applications and future concepts of

operations.

Introduction

In the last few decades, increasing interest in oceans has resulted

in unprecedented attention being focussed on them.

Although they cover 71% of the Earth’s surface, humankind

has sent more astronauts to the Moon than scientists to the

deepest parts of our seas. It was almost 10 years after reaching

the surface of the Moon, that the deepest parts of the

oceans were finally reached. Since then, goverments and

industry have become more and more interested in understanding

and managing our planet and they have realised

how important the underwater regions, two thirds of the total

Earth’s surface, are. Nowadays, it is not only the need

to discover, but also to observe, map and protect our oceans

that motivates further exploration of underwater regions.

Unfortunately, access to these regions is not straightforward.

The underwater environment is a hostile environment

for humans and human technology. It can challenge some of

the capabilities that are now taken for granted in other domains

such as the Earth’s surface, the atmosphere or outer

space. Some of the most representative and specific challenges

underwater are high pressure, corrosion and signal

processing issues related to data transmission and sensing.

Even though the underwater domain presents such challenges,

several maritime disciplines still require access to

this environment. The most relevant ones are:

Oceanography: Scientists are faced with the need of

gaining access to the most remote parts of the oceans,

The study reported in this paper is partly funded by the

Project RT/COM/5/059 from the Competition of Ideas and by

the Project SEAS-DTC-AA-012 from the Systems Engineering

for Autonomous Systems Defence Technology Centre, both established

by the UK Ministry of Defence.

from deep trenches to fresh water lakes under the polar ice

caps. They have to collect information in order to be able

to understand issues such as climate change, the melting

of the polar ice caps and to forecast weather conditions,

hurricanes and tsunamis.

Energy industry: In current offshore oil fields the tasks

of Inspection, Repair and Maintenance (IRM) comprise

up to 90% of the related field activity. This inspection is

dictated by the vessels availability and the weather conditions.

Additionally, the deep sea is still un-exploited.

Gaining access to these deeper levels can provide access

to new sources of minerals and energy.

Military: A priority to current Navy operations is to

maintain clear access to ship passages and to protect vessels,

harbours and coastal waters. Achieving these capabilities

without compromising personnel safety due to foe

actions is still unsolved.

For all these disciplines, robotic platforms are proven to

be very useful in de-risking human activity in the hostile

underwater environment. The main challenges that robotic

systems have to deal with underwater are:

Power : Robots are highly dependant on their battery life

in a domain without possibility of extending it from other

external sources.

Communication : Sound is the media use for sensing and

communicating underwater. Low bandwidth, long delays

and high-power requirements impose many restrictions.

Perception : Visual methods are poor while acoustic

methods come with many false positives. They are affected

by temperature, pressure and salinity making them

very noisy. Range is inversely related to the frequency

and normally quite reduced (see Fig. 1).

 Additionally, raw

sensor data has to be ultimately processed into conceptual

knowledge in order to build the awareness of the environment.

Navigation : The underwater environment is a GPSdenied

area. Existing underwater maps are still quite innacurate.

Together, these make localization and orienteering

for navigation a very hard problem.

Delegation: Autonomous adaptation of different tasks

to changes in the environment has not yet been fully

achieved. Without it, it is necessary that the operator remains

in the loop, observing and taking decisions. Autonomous

adaptation to sensed changes is necessary to

gain the operator’s trust and acceptance and for them to

delegate tasks to the robotic platform (Johnson, Patr´on,

and Lane 2007).

Although new solutions are already being developed to

extend power autonomy and communication requirements,

the other three issues (perception, navigation and delegation)

are still a real challenge for achieving true autonomy

in robotics in the underwater environment. This paper describes

each of these challenges and provides an overview on

how reasoning tools and autonomous planning approaches

can contribute to overcoming them.

Robotic platforms