The RCM 9 is built by use of parts and materials proven to be well suited for oceanographic instruments and according to a design philosophy that is the result of many years experience in the field. Thus it makes extensive use of an encapsulating technology for protecting electronic circuits. Further it employs the standard Data Storage Unit DSU 2990, which finds use in a large family of other oceanographic instruments.
Figure 1 shows the opened instrument from the side of the data storage unit and from the side where the internal control knobs are placed. By selecting various settings of these control knobs, various sampling intervals and various sensor ranges can be set. The battery shown is an encapsulated l5Ah alkaline battery that can power the instrument for 2 years when a sampling interval of one hour is selected.
The RCM 9 can find many uses for monitoring the conditions in ocean, sea, lakes, rivers and fresh water reservoirs. One reason for its many uses is that the conductivity cell of the instrument also has a range that can measure the conductivity of fresh water. Another reason is that the frequency modulated acoustic telemetry system used, designated FSK 4, allows data to be obtained in real time without an underwater cable from the instrument.
Large scale circulation
One of the main uses of the RCM 9 is for monitoring the large scale circulation in the depth of the water in the ocean. For this task information on the current speed and direction is essential. But the conductivity and the turbidity sensors can also give useful information. These sensors can usually tell the kind of water that passes and its origin.
For such applications of the RCM 9, a mooring as shown by figure 2 can be useful.
One or more instruments can be moored in-line from a surface or a sub-surface float. Owing to the fact that the instrument can operate correctly at an inclination up to 35 degrees from the vertical, it can tolerate a similar inclination of the mooring line. The RCM 9 will normally, when moored, operate every 10 minutes. Data is recorded inside but can also be obtained in real time by use of a hydrophone receiver.
For transmission of data ashore, a relay buoy furnished with a hydrophone receiver and a VHF/UHF transmitter can be moored near the instrument mooring. This arrangement allows data in real time over a distance of 10 to 20 km from land to be obtained. For longer distances data in near-real-time can be obtained by furnishing the relay buoy with an Argos transmitter.
Figure 2. In-line mooring
Arctic waters
What happens in the polar region is very important for the general circulation of the water masses on this planet and is likely to have a large influence on our climate. In these regions warmer water masses cool, sink and start on a long journey as cold deep water in our oceans. Knowledge of the currents and the water density in these regions is therefore very important. The RCM 9 is well suited for use in arctic water as it has a special arctic temperature range, that in combination with the con- ductivity readings, allow density of the water to be computed.
