A releasable data capsule for the deep ocean

There is a need to make continuous measurements of variations in sea pressure and temperature in the deep ocean for periods of five years or more. However it is important to recover data each year. Instrumentation has been developed using glass spheres as releasable data capsules (RDCs), capable of storing an entire observational series. Any capsule can be retrieved on command, leaving the sensors and main instrument on the sea bed. Whilst on the sea bed, data is telemetered to the capsules via an infra-red link. Each capsule can be released without the need to cut electrical cables or to part connectors. The datum of the measurements is presented and the sensors are not subject to large hydrostatic pressure changes which normally occur during recovery and redeployment. The capsule electronics have been designed using very low power electronic circuits to give a long deployment time with a limited power source. A prototype instrument has been built and is presently deployed at a depth of 3690 metres at the southern end of the Drake Passage. Three capsules have been successfully recovered during this deployment providing over 2 years of continuous bottom pressure records. An objective of the project has been to incorporate satellite telemetry into the RDCs. This will supply the data at scheduled intervals and reduce costs associated with recovery.