Calibration of geostationary satellites infrared radiometers using the vertical sounder of a polar orbiting satellite

A method for the calibration of infrared radiometers of geostationary satellites using calibrated infrared radiometers of an orbiting satellite is presented. This method relies upon similarities between the weighting functions corresponding to the radiometers on geostationary satellites like Meteosat or the GOES series and the weighting functions of some of the channels of the TIROS-N Operational Vertical Sounder (TOVS). It makes use of iso-secant observations of the same scene from both satellites. Many such observations are available every day resulting in a possibly daily calibration curve defined by several hundred of points. This calibration method is shown to be very sensitive, accurate and tractable. This method does not require to collect radiosonde data nor any kind of in-situ experiments and may be completely automatized.