Is Arctic Sea ice thickness decreasing as rapidly as suggested by recent investigations ? Some scientists claim that ice thickness may have decreased as much as 40 % over the last 4 decades. However, there are very few observations documenting this reduction, which might very well be an indication of ongoing global warming. Sea ice area and extent, which has been observed by passive microwave satellite data for more than 20 years, has decreased by about 3 % per decade in the Arctic indicating that the total volume of sea ice has been reduced. The multiyear fraction of the ice area has decreased much more, about 7 % per decade.

The major unknown parameter is the ice thickness due to lack of systematic observations. There are several measurement techniques for ice thickness, but few of them are developed into regular monitoring systems. The most important data for ice thickness in the Arctic are provided by US and British submarines through the SCICEX Programme, however the future access to submarine data is expected to decline. In this proposal a team of European research, space agency and industry partners will develop and validate some of the most promising techniques in order to establish new operational monitoring methods for polar oceans. These techniques are foreseen to be important elements of European components of global observing systems.

The Europan Space Agency is developing a new satellite, CRYOSAT, which will have sea ice thickness measurement as a main objective. CRYOSAT, scheduled for launch in 2004, will observe the surface height of glaciers and sea ice using a beam limited altimeter. For sea ice the principle is to observe freeboard height and translate this to ice thickness. Specific studies on this problem are urgently needed to validate if basin-scale thickness distributions can be derived from freeboard data provided by CRYOSAT. Through several field experiments, SITHOS will provide new data to establish the relations between ice freeboard and ice thickness for summer and winter conditions, which is needed to derive ice thickness from CRYOSAT data. In addition to satellite data, it is important to have robust and cost-effective in situ and non-space measurement systems to be operated from different platforms. SITHOS will develop and test techniques which are feasible for use on automatic buoys, fixed-wing aircraft, helicopter and ice-going vessels.

Technologies which are under investigation within SITHOS are:

Electromagnetic induction (ELM) combined with laser altimeter, mounted on helicopter or from a beam mounted in the bow of an ice-going vessel. In the future the method can also be used on fixed-wing aircraft. The method can be made operational by putting it into a “black box” which can be installed on ships and aircraft on “opportunity basis”.

Automatic ice station (AIS) which can measure ice thickness using surface wave information or other techniques and send data via ARGOS. The AIS will be deployed on ice floes and operate for months and years, similar to the IABP. AIS is a further development of existing robust measurement systems developed by no. 3 and no. 6, with long records in polar environment.

Upward-Looking Sonar (ULS)and sidescan sonar data from submarines.

Autonomous Underwater Vehicle (AUV Autosub) with several instruments including ULS.

Airborne laser profiling and scanning combined with kinematic GPS from aircraft (AL-GPS). Ice freeboard can be measured along the flight tracks in single-beam mode, giving a profile of ice thickness. In scanning mode a swath of ice heights is obtained, giving detailed information on ice ridging, lead geometry and ice rafting in a band along the aircraft trajectory, typically 300 m wide.

In situ measurement of ice thickness, freeboard, snow cover, etc. from expeditions and ice camps.