Mass Balance: Instruments

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The IMB is an autonomous, ice-based system, designed to measure and attribute thermodynamic changes in the mass balance of the sea ice cover. The instrumentation of the autonomous mass balance buoys typically consists of a Campbell scientific datalogger, an Argos transmitter, a thermistor string,  and above ice and below ice acoustic sounders measuring the positions of the surface and bottom within 5 mm. In addition to the mass balance instrumentation the buoys also have a GPS, a barometer, and an air temperature sensor.

Thermistor strings were PVC rod with YSI thermistors spaced every 10 cm. These rods could easily be connected to assemble strings that extended from the air through the snow and ice into the upper ocean. The thermistor accuracy is better than 0.1 C.

A picture can be worth more than 1000 words, in that some of the mass balance buoys have web cams. Images from the cams are transmitted via the Iridium satellite communication network. Images from these cameras provide information on ice surface morphology including melt pond coverage.

   
1. Thermistor string - PVC rod with YSI thermistors (accuracy of 0.1 C).
2. Above ice acoustic rangefinder - a sonic rangefinder made by Campbell Scientific (model SR-50) specifically for measuring snow depth. The sensor is mounted on a pole, frozen into the ice, looking down at the snow surface. It measures distance between the instrument and the snow surface, thus recording the changes in the snow depth. When the snow melts in the summer, the instrument then measures surface ice ablation.
 3. Underice acoustic rangefinder - a Benthos (Model PSA-916) underwater sonar altimer is mounted on a pole, frozen into the ice, looking up at the underside of the ice sheet. It measures distance between the instrument and the ice bottom, thus recording ice bottom growth and ablation.
4. Barometer - sea level pressure is measured using a Vaisala barometers (model numbers PTB220A, PTB101B, and PTB210A).
5. The Datalogger - a Campbell Scientific CR10X datalogger is the brains of the buoy system. It collects information from each instrument, processes and organizes the data, adds the date/time stamp to the data, and sends it on to the ARGOS transmitter for transmission to the satellite.
 6. ARGOS transmitter – data is send to the ARGOS satellite system using a transmitter built for Campbell Scientific (SAT ARGOS).
7. Buoy housing - the buoys are typically housed a sealed 20 cm diameter aluminum tube.
8. GPS - a Global Positioning System sensor records position to an accuracy of better than 25 m.