Salinity observation by satellite

That’s where satellites come in.

Satellites use electromagnetic waves to remotely acquire various information on the sea level．

For example, southern water, such as the Kuroshio, has a clear blue color, while northern water has a greenish color with low transparency. By observing the difference in the sea color in the visible range with satellites, the distribution of the chlorophyll a concentration contained in phytoplankton can be obtained.

The infrared range, which has a longer wavelength than visible light, is used for water temperature observations. For example, thermography installed at an airport measures the intensity of electromagnetic waves radiating from the body surface of a person passing through a gate, converting it into body temperature. Based on the same principle, the sea surface water temperature is measured by satellites.

 Microwaves, which have long wavelengths, are used for the observation of sea surface salinity．

Microwaves are widely used in the radio waves of mobile phones, microwave ovens, and radar, as well as in the field of communication.

Electromagnetic waves radiated from the sea surface are known to have “sensitivity” to salinity in the low-frequency micro band (sensitivity means that the intensity of the electromagnetic waves changes corresponding to the changes in salinity). Therefore, the sea surface salinity can be back-estimated based on the change in the intensity of the electromagnetic waves from the sea surface received by satellites．

However, due to its extremely weak signal, the technical level required for salinity observation is extremely high and could not be achieved until recently.