The amount of salts in sea water is important because it affects ocean currents, which, in turn, affect the world’s climate. Sea water contains a variety of dissolved elements, including chlorine, sodium, magnesium, calcium, sulfur, and potassium. In the past, measurements of salinity were taken simply by going out onto the ocean, filling a bucket with sea water, and testing the salt levels by measuring electrical conductivity (the more salts, the quicker electricity flows through the water because there are more ions present). There are also techniques to measure chlorine or other dissolved elements.

More recently, sophisticated equipment has become available for measuring ocean salts remotely. Low-frequency radiometers mounted on C-130 aircraft can scan the ocean during flights, covering over 38 square miles (100 square kilometers) every hour. The European Space Agency plans to launch its Soil Moisture and Ocean Salinity (SMOS) satellite in 2009 to take readings from space using a two-dimensional interferometric radiometer, a new technology that captures images based on microwave radiation emitted at a frequency of 1.4 gigahertz (GHz).