microwave: Electromagnetic radiation with a wavelength of between 0.3 and 30 centimeters (between infrared and radio), corresponding to frequency of 1 to 100 gigahertz (GHz). Favored for radar because of its cloud-penetrating properties.

practical salinity unit (psu): Used to describe the concentration of dissolved salts in water, the UNESCO Practical Salinity Scale of 1978 (PSS78) defines salinity in terms of a conductivity ratio, so it is dimensionless. Salinity was formerly expressed in terms of parts per thousand (ppt) or by weight (parts per thousand or 0/00). That is, a salinity of 35 ppt meant 35 pounds of salt per 1,000 pounds of sea-water. Open ocean salinities are generally in the range between 32 and 37.

radiometer: An instrument that measures radiance, or the radiation emitted by an object.

salinity: A measure of the quantity of dissolved solids in ocean water. In general, salinity reflects the total amount of dissolved solids in ocean water in parts per thousand by weight after all carbonate has been converted to oxide, the bromide and iodide to chloride, and all the organic matter oxidized. Salinity is now measured as practical salinity units (psu).