Technical Note: Evolution, current capabilities, and future advance in satellite nadir viewing ultra-spectral IR sounding of the lower atmosphere

Infrared ultra-spectral spectrometers have brought in a new era in satellite remote atmospheric sounding capability. During the 1970s, after the implementation of the first satellite sounding instruments, it became evident that much higher vertical resolution sounding information was needed to be able to forecast life and property threatening localized severe weather. The demonstration of the ultra-spectral radiance measurement technology required to achieve higher vertical resolution began in 1985, with the aircraft flights of the High resolution Interferometer Sounder (HIS) instrument. The development of satellite instruments designed to have a HIS-like measurement capability was initiated in the late 1980's. Today, after more than a decade of development time, the Atmospheric Infrared Sounder (AIRS) and the Infrared Atmospheric Sounding Interferometer (IASI) are now operating successfully from the Aqua and MetOp polar orbiting satellites. The successful development and ground demonstration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS), during this decade, is now paving the way toward the implementation of the ultra-spectral sounding capability on the international system of geostationary environmental satellites. This note reviews the evolution of the satellite ultra-spectral sounding systems, shows examples of current polar satellite sounding capability, and discusses future advances planned for geostationary orbit.