The MicroWave Radiometer (MWR) is a two-channel sensor aboard the SENTINEL-3 satellite. MWR measures water vapor, cloud water content, and thermal radiation emitted by Earth. The lower frequency 23.8 GHz channel is mostly sensitive to atmospheric water vapor and the higher frequency 36.5 GHz channel to cloud liquid water. MWR is used in conjunction with synthetic aperture radar (SAR) altimeters to measure sea-surface height, ocean-surface waves, the extent and height of sea ice, and the height of large inland rivers and lakes.