Sea ice thickness spatial extent, and open water within

sea ice Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...

packs can vary rapidly in response to weather and climate. Sea ice concentration is measured by satellites, with the Special Sensor Microwave Imager / Sounder (SSMIS), and the ''European Space Agency's''

Cryosat-2 CryoSat-2 is a European Space Agency (ESA) Earth Explorer Mission that launched on April 8, 2010. CryoSat-2 is dedicated to measuring polar sea ice thickness and monitoring changes in ice sheets. Its primary objective is to measure the thinning ...

satellite to map the thickness and shape of the Earth's polar ice cover. The sea ice volume is calculated with the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), which blends satellite-observed data, such as sea ice concentrations into model calculations to estimate sea ice thickness and volume. Sea ice thickness determines a number of important fluxes such as heat flux between the air and ocean surface—see below—as well as salt and fresh water fluxes between the ocean since saline water ejects much of its salt content when frozen—see sea ice growth processes. It is also important for navigators on

icebreaker An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice-breaking ships, it may also refer to smaller ...

s since there is an upper limit to the thickness of ice any ship can sail through.

Measurement

Ice thickness can be measured in various ways, directly by taking an

ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier ...

and measuring it, remotely using point measurements from ice mass balance buoys, or more efficiently with satellite measurements. Measurements of ice depth below the waterline (or

draft Draft, the draft, or draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a v ...

) by submarine

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects o ...

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

systems can give good estimates of ice thickness provided there isn't too much snow (which is less dense than ice) on top. ''Sea ice freeboard'' is the difference between the height of the surface of sea ice and the water in open leads. Since 85–95% of snow-free sea ice is usually located below the waterline, the computation of the thickness is fairly simple; however, accurate measurement of ice freeboard is hindered by several factors including snow cover, and modeling of this data is being constantly improved.

Satellites

The Ice, Cloud, and land Elevation Satellite (ICESat), measured ice sheet mass balance, cloud and aerosol heights, and land topography and vegetation characteristics, with an active service period from February 2003 to October 2009. The European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission is the first orbit mission to measure salinity of the Earth’s surface and able to show data through most clouds and during darkness. The sea ice volume is calculated with the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).

Other methods

The E-M Bird ice thickness meter, designed by the

Alfred Wegener Institute for Polar and Marine Research The Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (German: ''Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung'') is located in Bremerhaven, Germany, and a member of the Helmholtz Association ...

, is carried aloft by helicopter and measures ice thickness with a combination of a pair of inductance coils that measure the ice-water interface based

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the ...

variations—similar to a

metal detector A metal detector is an instrument that detects the nearby presence of metal. Metal detectors are useful for finding metal objects on the surface, underground, and under water. A metal detector consists of a control box, an adjustable shaft, and ...

—and a laser altimeter which measures the ice surface. It was used on a small scale in 2007 to supplement microwave radiometer measurements during the Pol-Ice campaign and on a much larger scale during the GreenICE (Greenland Arctic Shelf Ice and Climate Experiment) campaign conducted in 2004 and 2005.

References

{{Reflist, 30em Sea ice Climate Remote sensing Radiometry Climatology

Measurement

Satellites

Other methods

See also

References