When it comes to current speed, that can be up to 5 or 10 knots in narrow sounds and near river outlets, conventional mooring of the RCM 9 is not well suited. A catamaran type surface float with an upside down RCM 9 is better suited. With this arrangement the current speed at about 0.5 meter depth can be learned of. The conductivity sensor can tell the amount of fresh water being present and the turbidity sensor the amount of algae in the water.
As the oxygen content of the water near the surface is usually plentiful, there is in this case less need for an oxygen sensor. Therefore another type of optional sensor can be used, for instance a sensor for one of the trace elements of sea water. There is today great concern for the occurrence of harmful algae, that can kill fish in fish farms and elsewhere. Such "mad" algae tend to occur when the vertical mixing of the water is poor, and when there may be an excess supply of some nutrition elements and depletion of others. It may be that the depletion of trace elements such as copper or zinc, which often is the case in surface waters, may be one of the reasons that mad algae occur. If the RCM 9 could be furnished with a sensor for one of these trace elements, as optional sensor, it is possible that the occurrence of harmful algae could be warned of at an early stage. A catamaran carrying an RCM 9 can therefore provide many forms of useful data for surface waters. Since the data is usually wanted in real- time, or near-real-time, a VHF/UHF or an Argos transmitter can easily be fitted to the same catamaran.
Figure 5. Placed on a Catamaran(upside down)
Profiling
Another application of the RCM 9 is to obtain vertical profiles of its measured parameters. In fjords and lakes the water near the bottom can be stagnant and be depleted from oxygen. If an RCM 9 is fitted with a fast response oxygen sensor, it can be used for profiling and to find areas where depletion of oxygen is the case, and at what depth it occurs. Profiling in the open sea can also be of interest for many other reasons.
Knowledge of the actual current speed at various depths can, for instance, be of interest for diving operations, for laying cables and pipelines and for installing various underwater structures. For such operations the turbidity sensor can be useful as it indicates the visibility range under water. When profiling, the instrument can be set to operate continuously, providing a sensor reading every 4 seconds with a 2 second pause after each set of data. When an RCM 9 is set to read all 8 channels, the respective parameters are updated every 34 seconds. When profiling, data can be transferred to the ship in real-time by use of a one- conductor cable, or by acoustic telemetry.
