Design and operation of a long-duration mooring for ocean observations

Abstract

A new moored measurement system (ULTRAMOOR) has been developed whose aim is to reduce the cost and effort associated with making sustained in situ observations, especially in remote parts of the oceans. Present mooring technology, which typically requires annual, or at best biennial, maintenance and employs internally recording instruments, does not meet existing or future needs for timely, cost-effective data. ULTRAMOOR is designed for unattended deployments of five years or more with regular data updates from instruments positioned throughout the water column. It eliminates the requirement for frequently scheduled maintenance, which is an important factor in the total cost of long-term monitoring programs. While the initial ULTRAMOOR has been instrumented with current and temperature sensors, the design is compatible with a variety of low power instruments with digital data output. We envision the system as a prototype for a new generation of potentially expendable mooring types whose instruments spend almost all of their working lives at sea. ULTRAMOOR is a subsurface mooring equipped with a combination of modern acoustic current meters and current profilers. Each instrument transfers its data to an acoustic modem, which forwards these data to a central receiver. The central receiver then loads the data into an array of expendable data capsules, which release themselves at scheduled intervals throughout the deployment period and float to the surface. Once on the surface, they transmit their stored data via small satellite transmitters. The prototype ULTRAMOOR has been deployed successfully on two occasions. The long-term test mooring is instrumented with six acoustic current meters. Three of the ten data capsules have surfaced since the deployment and have provided high quality data from five of the six current meters. Remaining data capsules are scheduled to release at six-month intervals until November 2004. Preliminary results indicate that the acoustic links are working flawlessly, that eight of the ten data capsules are functioning normally, and that the data in the capsules are true representations of the data collected by the individual instruments.