Mass Balance: Instruments
The Seasonal Ice Mass Balance Buoy
Over the past decade, the Arctic sea ice cover has seen a dramatic increase in the relative amount of thinner, seasonal sea ice. This recent development has motivated researchers at CRREL to develop a new buoy that can survive in these thinner ice conditions. The result of their work is the Seasonal Ice Mass Balance buoy (SIMB). The SIMB has been designed around a single six inch diameter spar-buoy type hull that contains, protects, and positions the sensors. Unlike the Ice Mass Balance Buoy, all of the instrumentation of the SIMB are contained within or are mounted a single and external wires are reduced to an absolute minimum. Not only does this design make the SIMB more robust, it makes installation easier, as only one deployment hole must be drilled through the ice cover. The buoy hull is designed to float with a strong righting moment, which enables it to position the sensors accurately in relation to sea level without relying on the ice for support. Even when the buoy is completely detached from the ice and floating in open water, it is able to continue to provide valuable data from its instrumentation.
The SIMB (design sketch above, left) is modular and can be packed for shipping in three sections. The sections of the SIMB Buoy are sized to fit within typical air express shipping size limits and to allow for easy loading and transport to deployment sites using a helicopter. The hull is made almost entirely from off the-shelf PVC components, greatly reducing the hull's cost and providing a good thermal conductivity match to sea ice compared to using an aluminum hull.
The top section of the SIMB both protects the wires and serves as a support tower for the transmitting antenna, air temperature sensor, barometric pressure sensor, and downward looking acoustic sounder which measures the distance to the snow or ice surface. The middle section serves to provide buoyancy, support the top section, and provides an attachment point for the thermistor string, while the bottom section houses the data controller, satellite transmitter, and battery, and provides an attachment point for the underwater sensors. The bottom section also contains the ballast that adjusts the flotation level and righting moment to the buoy. Unused hull space is filled with closed cell foam to reduce the likelihood of sinking in the event of a leak.
The sensor package includes a barometer and air temperature sensor, a string of thermistors to measure the air-ice-ocean temperature profile, and a pair of acoustic rangefinders (sounders), one above the ice and one below the ice. Data from these acoustic rangefinders are used determining ice thickness, ice growth, and ablation. The SIMB also has an underwater pressure sensor, which provides information on the mass balance of the entire ice floe.
CRREL Researchers successfully tested a prototype Seasonal Ice Mass Balance Buoy in the fast ice off the coast of Barrow, Alaska in the spring of 2009. The researchers are currently preparing 3 Seasonal Ice Mass Balance Buoys for deployment this spring (2010). Once deployed, data from these buoys will be available through the data pages on this web site.
For information on obtaining/using an Ice Mass Balance Buoy or a Seasonal Ice Mass Balance Buoy for your research project contact Bruce Elder at Bruce.C.Elder@usace.army.mil.