Overview:
There are many instances when surface mounted equipment if preferable. Typically, the current profiler will be deployed in a purpose-built surface buoy or attached to a buoy of opportunity such as a Coast Guard Aid to Navigation (ATON). Velocity data are transmitted through radio frequency modems, GSM or Iridium phones to a site on shore. The Aquadopp Profiler is a common choice for making velocity profiles from a surface buoy when wave measurements are not required.
Advantages:
- Surface buoys do not require divers for deployment or maintenance
- Ability to profile the upper portion of the water column in deep-water applications where a bottom mounted profiler would not have the required range
- Radio Modem, GSM or Iridium telemetry provides relatively high bandwidth for data transmission
- Opportunities for charging batteries with solar or wind power
Limitations:
- Possible damage by ships, storms, ice and vandalism
- Must perform accurate compass calibration if mounting on steel buoy
- Cannot measure waves from surface buoy
- Local RF “noise” may cause communication difficulties
- GSM coverage may be lacking at offshore sites
Technical considerations:
Once a careful compass calibration has been performed with the instrument mounted on the surface buoy, most of the technical considerations relate to data telemetry techniques. Radio modems, cell phones and Iridium satellite links are common modes of transmitting data from the current profiler to the shore station. Radio modems are inexpensive, free to use and can have a line-of-sight range to a shore station or repeater of up to 20 km. However, choosing the proper radio modem is critical and is a function of distance, antenna height, topography, transmit power, receiver sensitivity and local RF “noise.” Cell and Iridium phones are often robust communication tools if the coverage is available and fits within the project budget.
An ActiveX toolbox with current velocity processing commands is supplied for real-time data conversion. These processed data are then ready for display on the users web site in real-time.
Examples:
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