ITAC

Ice-Tethered Acoustic Current Profiler

APPLICATION

  • Velocity profiles from 10 m under the ice
    down to 600 m
  • Data transmission via Iridium
  • Up to 3 years operation
  • Remote control of the ADCP and the Surface Unit settings possible

Instrument design

OPTIMARE developed within the EU-project Damocles in collaboration with the Alfred Wegener Institute (AWI), both in Bremerhaven Germany, the prototype of an Ice-Tethered Acoustic Current profiler (ITAC). The ITAC was recently successfully deployed and measures ocean current velocity profiles from 10 m under the ice down to a depth of maximum 600 m. The system includes a RDI 75-kHz Acoustic Doppler Current Profiler (ADCP) which is mounted at least 0.5 m under the ice floe. The ADCP is attached to a wooden beam on the surface of the ice floe using a stainless steel pole. A cable provides the electrical connection from the ADCP under the ice to the surface unit with a GPS receiver (Navman Jupiter 20) and an IRIDIUM-9522-modem. A second GPS is positioned about 100 m away in line with the wooden beam and the ITAC surface unit. This allows the definition of the ADCP orientation, especially close to the magnetic pole where flux gate compass systems do not work very accurately.

All data are transferred daily via the IRIDIUM satellite Short Burst Data (SBD) message service to an e-mail address at OPTIMARE. In addition, all ITAC surface unit data, which also include temperature and horizontal tilt measurements, are transferred via the ARGOS satellite system once a week. The ARGOS system serves as a backup and allows position finding and recovery of the ITAC in case of IRIDIUM failure. The surface unit also allows the adjustment of various parameters (e.g. ADCP and GPS sampling rates) using SBD messages. The system is designed for a lifetime of three years.

Deployment and operation

The ITAC prototype was deployed during the Arctic Ocean expedition of the German RV Polarstern on Sep 13th/14th, 2007. The system is currently configured to acquire ADCP data in two-hour and GPS positions in hourly intervals. It transmits three to five SBD-messages per day to OPTIMARE with a total of five to nine kB. OPTIMARE decompresses the data and transfers them to the AWI for further processing and analyses. The last data were received on Dec 29th, 2007. Most probably, the complete „superstation“-floe crushed in the north of Greenland together with other buoys (three ITPs and one OFB). All stopped sending data almost at the same time.

 

Project no. 018509
The Damocles project is financed by the European Union in the 6th Framework Programme for Research and Development.