Observing operationally in situ ocean water parameters: the EMMA system

The need for a network of non manned instrumented platforms generating profiles of different types of water parameters over any ocean area, and transmitting the collected data in quasi-real time to operational computer facilities has been clearly expressed, for example by the OOSDP/OOPC commissions and by the GODAE project designers. To meet this demand, several types of platforms have been proposed, using either expendable drifters or reusable long line moorings. The authors have decided to investigate the technical and economical feasibility of a device adapted to another concept, named EMMA. The basic idea of this concept is to moor at each network node a group of expendable instrumented lighter-than-water probes equipped with RF Xmission equipment, to store them for long time periods on the sea bottom, to release them one by one at successive preprogrammed time intervals, to collect the profiling data during the probe ascent, and to transmit it to a data collection satellite after surfacing. During the sea bottom storage, the sensors are encapsulated for fouling protection and immersed in a standard liquid for calibration. The paper describes a new architectural approach for designing the device, which permits very important cost reductions.