Microwave sensing encompasses both active and passive forms of remote sensing. The microwave portion of the spectrum covers a wavelength range of approximately 1 cm to 1 m. Compared to visible and infrared radiation, the longer wavelength of microwave radiation offers special properties that are important for remote sensing. Longer wavelength microwave radiation can penetrate through cloud cover, haze, dust, and rainfall as the longer wavelengths are not susceptible to atmospheric scattering, which does affect shorter optical wavelengths. This property allows detection of microwave energy under almost all weather and environmental conditions so that data can be collected day or night and in all kinds of weather.

Passive microwave sensors detect the naturally emitted microwave energy within its field of view, unlike active microwave sensors that provide their own illumination. Passive microwave sensors are typically radiometers or scanners in which an antenna is used to detect and record the microwave energy. For specific details regarding the passive microwave data at NSIDC, please refer to the instrument descriptions below.

AMSR-E: The AMSR-E instrument aboard Aqua provides measurements of land, oceanic, and atmospheric parameters for the investigation of global water and energy cycles, including precipitation rate, sea surface temperature, sea ice concentration, snow water equivalent, soil moisture, surface wetness, wind speed, atmospheric cloud water, and water vapor.

AMSR: The AMSR instrument aboard ADEOS-II measured geophysical variables such as atmospheric water vapor, precipitation, sea surface wind speed, sea surface temperature, soil moisture, sea ice extent, and snow water equivalent.

SMMR: The primary purpose of the SMMR instrument was to measure sea surface temperature and near-surface winds under all weather conditions for developing and testing global ocean circulation models and other aspects of ocean dynamics. Additional parameters were also measured using SMMR, such as winds, water vapor, liquid-water content, mean cloud droplet size, rainfall rate and sea ice.

SSM/I: The primary purpose of the SMM/I instrument is to measure sea surface temperature and near-surface winds under all weather conditions for developing and testing global ocean circulation models and other aspects of ocean dynamics. Additional parameters may also be applied, such as winds, water vapor, liquid-water content, mean cloud droplet size, rainfall rate and sea ice.