Direct measurement of geopotential geight by the hirdls instrument

Abstract The HIRDLS instrument is an infrared limb sounder which will be part of the NASA EOS-Chem payload to be launched in 2002. It will measure temperature, various minor constitutents, polar stratospheric clouds, aerosols and geopotential height gradients in the upper troposphere and middle atmosphere with a much better combined vertical and horizontal spatial resolution than has hitherto been possible. The limb scanning technique provides pressure registration of the limb scans by means of radiometric measurement of emission from atmospheric carbon dioxide. By inclusion of a gyroscope on the instrument optical bench, it is possible to obtain very precise knowledge of variations of the instrument line-of-sight tangent height above the Earth's surface. Fields of geopotential height will be derived by combining this knowledge with the pressure information.