Title: Autonomous Instrumentation for Oceanography

The Small Autonomous Underwater Vehicle - Maya

Autonomous Underwater Vehicles (AUVs) are free swimming marine robots that can be used as mobile platforms to collect data and explore the ocean on programmed mission tracks.

This propelled robot platform (AUV) is mounted with on-board computer, power packs and vehicle payloads which enable automatic control, navigation and guidance of the vehicle and acquire data from onboard sensors to sense physical, biological and chemical properties in the ocean, lakes, estuaries, rivers and dams. They can be programmed to dive and to maintain control at any given depth layer in a water body, to navigate by changing course at a chosen depth, to follow seabed terrain, and when a mission is accomplished to return ‘home’.Without disturbing the environment data has to be acquired for example shipboard profiling and towed instrument packages and samplers can cause disturbances and can introduce errors in measurements, even there are situations and places where divers are at risk and in these cases AUVs and ROVs equipped with appropriate sensors, power packs and propulsion capability are able to address these problems to a large extent.There are more than 58 on-going developments of AUVs of different classes and sizes around the world (see www.ausi.org/auvs/auvs.html)  some of the best known being REMUS, Gavia and Autosub [1].A significant step in developing a prototype small AUV, called Maya, was achieved at the National Institute of  Oceanography (NIO), Goa, India, in May 2006. The project received initial seed funding from NIO in 2003 and a subsequent full grant (2004-2006) from the Ministry of Communications and Information Technology (MIT), New Delhi, India. In addition, co-operative work was also carried out under the scope of the Indo-Portuguese Co-operation Programme in S&T with the group headed by Professor Antonio Pascoal, Institute of Systems and Robotics/ Instituto Superior Técnico, Lisbon, Portugal. This programme was funded through an exchange visit programme by the Department of Science & Technology, New Delhi, and GRICES (Gabinete de Relações Internacionais da Ciência e do Ensino Superior), the International Relations Unit of the Portuguese Ministry for Science, Technology and Higher Education.Here we give you the short description of Maya AUV’s mechanical design, control systems, navigation, on board sensors and safety aspects. Field results of Maya use in a confined freshwater ecosystem, and in open ocean water are also presented to demonstrate its use in an oceanographic setting

.Mechanical design (Click here for Mechanical details) Main specifications of the Maya AUV

The Maya AUV [2] follows a classical submarine design consisting of a low drag, slender ellipsoid removable nose cone on which scientific sensors can be mounted, a main hull bored from a single bar of aluminum alloy which has been pressure tested to depths of 200 metres, and a tapered Myring profile rear cone with a single DC motor at the extreme end for propulsion. It has two stern planes and two rudders to control diving and heading manoeuvres respectively. The nose section can accommodate different sensors for specific missions at sea. The AUV can receive commands from the shore over a high-speed UHF radio link or download data over the same link. Underwater navigation uses a Doppler velocity log (DVL) to measure speed and a navigation filter that estimates its position below sea surface. Surface navigation is based on GPS.

Mission specific removable nose cones

Design considerations have made it necessary to fabricate a series of removable nose cones which have mission specific sensors. For example, physical properties of the ocean are best studied with a conductivity, temperature, depth (CTD) sensor customised to fit within the available volume offered by the nose. All nose cones are free flooding and can be fitted on to the front pressure endplate of the main hull. Other missions incorporating biogeochemistry require a combination of dissolved oxygen (DO), chlorophyll and turbidity sensors fitted on an identical nose cone.

Scientific sensor payloads

The choice of scientific sensors was primarily constrained by size, weight, low power consumption and the need to lower cost. Most sensors used here are placed within or external to the nose volume. Table 2 lists the sensor payloads that have been used on the Maya AUV.

Scientific sensors used on Maya AUV

Data logging of science based sensors

Sensor payloads of Dissolved Oxygen (DO) , Chlorophyll, Turbidity, Temperature, Conductivity were interfaced to a Rabbit Core micro-conntroller through RS 232 serial ports. The data records of each sensors are stamped with date, time, and GPS  values which are transmitted from the MZ 104 main controller.  The DO and chlorophyll cum turbidity sensors are mounted on a nose cone. A separate nose accommodates the larger CTD sensor.