The Jason-1 Microwave Radiometer (JMR) was one of five instruments aboard the joint NASA/CNES (Centre National d'Etudes Spatiales) Jason-1 spacecraft. JMR measured atmospheric water vapor content to determine the impact of water vapor on radar signal propagation. JMR was a passive receiver that collected radiation reflected by the ocean at frequencies of 18.7, 23.8, and 34 GHz. The main 23.8 GHz frequency was used to measure water vapor; the 34 GHz channel provided the correction for non-rain bearing clouds, and the 18.7 GHz channel was highly sensitive to wind-driven variations in the sea surface. The water vapor signal was determined by combining the measurements from all three frequencies.