Goals

To create and demonstrate a long-term, reactive survey system, capable of remote unattended deployments in harsh environments. We refer to such a system as an Autonomous Ocean Sampling Network (AOSN).

Objectives

The MIT Sea Grant team is the lead member of the Multi-disciplinary University Research Initiative (MURI) AOSN effort. Other institutions include Woods Hole Oceanographic Institution, Scripps, Northeastern University, and the Applied Physics Laboratory at the University of Washington.

MIT Sea Grant AUV Laboratory Objectives

1. To develop create a class of small, high performance AUVs capable of deployments several months in duration.
2. To create an internet based communication infrastructure for controlling, obtaining data from, and distributing decision making processes during such an AOSN deployment.
3. To combine the observational capability so created with established modeling and data assimilation systems to make best used of obtained data and plan optimal sampling strategies.

Approach

To focus AOSN development, and convincingly demonstrate new capabilities, the effort has been coupled to a series of science-driven experiments. The first deployment, during June-July 1996 as a participant of the Ocean Frontal Dynamics Primer Initiative in Haro Strait, focused on coordinated platform operations, adaptive sampling, and communications. The second deployment, in January-April 1998 in support of the Labrador Sea ARI, will demonstrate long-term deployment and remote communication. The final phase of the effort will integrate the resulting operational capabilities with modeling systems in an extended deployment experiment in coastal waters.

Present activity is focused on the approaching Labrador Sea deployment, the objective of which is to observe and characterize convection plumes. AUVs developed under prior ONR funding (the Odyssey IIb vehicles) are being employed to create a platform with robust docking, acoustic communications, and navigation capabilities. Extended deployment capability is being achieved by developing a docking capability with high efficiency power coupling and high bandwidth data link so that the vehicles can use appropriately equipped moorings as 'fuel stations' and communication relays. The vehicles are made reactive by providing moorings with a two-way satellite rf communication capability thus allowing the command and retrieval of data from deployed vehicles. To develop docking and acoustic communication, MIT is collaborating with the Woods Hole Oceanographic Institution, the Naval Research and Development Center, and Electronic Design Consultants.

The Labrador Sea experiment will provide the first long term deployment of AUVs for a science operation. The scenario envisioned is described below.

Deployment:

In January or February of 1998, a cruise will deploy the moorings, an array of LBL beacons, the AUVs, and the gliders in the approximate vicinity of Bravo in the Labrador Sea. On confirmation that moorings are working properly, the vehicles will be deployed, and will dock with the docking stations. Functionality of the AUVs will be confirmed by commanding a mission with each of the three vehicles.

Monitoring:

Conditions in the Labrador Sea will be monitored with an array of assets. Their data will be telemetered back to shore by satellite each time the vehicles are at the surface side of a profiling cycle. At the same time, atmospheric conditions will be monitored by satellite, shore stations, and sensors on the mooring(s) surface expression(s).

Convection event prediction:

Convection will occur when the water column has been sufficiently conditioned that an Arctic cold front can initiate sinking of surface waters. It may prove possible to predict convection, or at least conditions favorable for convection with the combination of water column and meteorological assets. In this case, the vehicles will be commanded to run surveys during the predicted event.

Convection event detection:

If prediction is impossible, uncertain, or communications fail, sensors on the vehicle docking moorings will be used to trigger vehicle missions. Options include using sensors on a surface expression to detect conditions favorable to a high buoyancy flux, or subsurface sensors to detect the convection process itself, probably via its vertical velocity signature.

Communication:

Satellite communication with the moorings should provide the ability to reprogram and extract data from docked vehicles.

Vehicle Missions:

Two classes of vehicle missions are envisioned. The first objective will be to determine the general statistics of a convection field. These vehicle runs will cover as much distance as possible. The second objective will be to map a plume. These missions will be more complex, attempting to localize and map a localized down welling region. Vehicles will return to the moorings they are launched from, and download mission data to the moorings.

Recovery:

A cruise in May 1998 will recover the vehicles, gliders, and moorings.

Following the Labrador Sea experiment, activity will shift to creating an integrated observation/modeling system. An extended field deployment in a logistically convenient location is envisioned. The New England shelf, with the large variety of oceanographic processes, provides a promising venue. Promising collaborations with modeling researchers, including the Harvard University physical oceanography group, will play a key role in this effort.

Results

A series of field experiments in FY 1996 focused on docking and on creating the communications infrastructure required for AOSN. Experiments in Buzzards Bay in collaboration with the Woods Hole Oceanographic Laboratory, the Naval Research and Development Center, and Electronic Design Consultants (North Carolina) accomplished the following.

1. Demonstration of three classes of homing systems, including acoustic homing (WHOI), optical homing (NRaD), and electromagnetic homing (EDC).
2. Demonstration of two types of docking methodologies, docking with a cone (EDC and NRaD) and latching with a pole (WHOI).
3. Multiple AUV operations with two Odyssey vehicles (collaboration with WHOI) in which one vehicle followed a 'lead' AUV.

In Haro Strait, four weeks of operations with two Odyssey vehicles generated scientifically unique observations of frontal processes. It also yielded tremendous insight as to the integration of AUVs with complementary sensing systems for reactive oceanographic survey operations. While the Haro Strait experiment was mainly funded under the Primer initiative, AUV involvement was also supported under the MURI.

Accomplishments include:

1. Multiple AUV surveys under acoustic control from the surface.
2. Moving source tomography using an AUV as the moving source (with H. Schmidt, MIT acoustic group).
3. AUV - drifter operations in which AUV surveys were coordinated with the drifter (in collaboration with D. Farmer at IOS).
4. Coupled sampling system - circulation model (in collaboration with Alan Robinson, Harvard University).
5. Fast synoptic mapping with coordinated ship - AUV surveys.
6. More than 80 vehicle missions by two Odysseys in the four weeks of operations, with no days lost due to vehicle failure.

In addition, a number of new sensors and navigation systems have been integrated into the Odyssey vehicles, including: side scan sonar, Acoustic Doppler Current Profiler (in collaboration with RDI), acoustic tomography source, and Acoustic Doppler Velocimeter.

Impacts

The benefits of AOSN will ultimately be manifested in a dramatic reduction of the cost of certain types of oceanographic surveys. Use of multiple vehicles will allow synoptic surveys which would otherwise be prohibitively expensive. Operation of AUVs from fixed moorings will provide an extended presence otherwise unobtainable. Demonstration of the capabilities for oceanography should generate interest for military applications of AOSN.

Transitions

The Odyssey AUVs have been licensed to Oceaneering for manufacture and sales. Since Oceaneering operates systems both for the Navy and for offshore oil companies, this should result in both military and commercial spin-off.

Lockheed-Martin funded MIT to develop a vehicle for mine-countermeasures applications (CETUS®) employing Odyssey design and construction techniques. This system has been delivered to Lockheed-Martin.

While AOSN development presently focuses on oceanographic applications, the fundamental concepts apply to military missions as well.

Other Projects

1. In the Ocean Frontal Dynamics experiment, supported under the ONR Vertically Integrated Research Initiative, used the AUVs developed under this project to map an ocean front in Haro Straits, British Columbia.
2. The observational effort in the Labrador Sea is coupled with the Oceanic Deep Convection ARI.