Sea ice thickness spatial extent, and open water within

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

packs can vary rapidly in response to weather and climate.

Sea ice concentration Sea ice concentration is a useful variable for climatology, climate scientists and nautical navigators. It is defined as the area of sea ice relative to the total at a given point in the ocean. This article will deal primarily with its determinati ...

are 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 8th 2010. CryoSat-2 is dedicated to measuring polar sea ice thickness and monitoring changes in ice sheets. Its primary objective is to measure the thinnin ...

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 Sea ice is a complex composite composed primarily of pure ice in various states of crystallization along with air bubbles and included pockets of brine. Understanding its growth processes is important both for climate scientists for use in simula ...

. It is also important for

navigators A navigator is the person on board a ship or aircraft responsible for its navigation.Grierson, MikeAviation History—Demise of the Flight Navigator FrancoFlyers.org website, October 14, 2008. Retrieved August 31, 2014. The navigator's primar ...

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. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ic ...

and measuring it or more efficient 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 vesse ...

) 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 navigation, navigate, measure distances (ranging), communicate with or detect o ...

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

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 In sailing and boating, a vessel's freeboard is the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship. In commercial vessels, the latter criterion measured relativ ...

'' is the difference between the height of the surface of sea ice and the water in open leads. Since 7/8ths of the ice is 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 Soil Moisture and Ocean Salinity (SMOS) is a satellite which forms part of ESA's Living Planet Programme. It is intended to provide new insights into Earth's water cycle and climate. In addition, it is intended to provide improved weather foreca ...

(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 flow of electric current creates a magnetic field around the conductor. The 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. The unit itself, consist of a control box, and an adjustable shaft, ...

—and a

laser altimeter A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

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