Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) data processing and atmospheric temperature and trace gas retrieval

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRI STA) experiment aboard the Shuttle Pellet Satellite (SPAS) was successfully flown in early November 1994 (STS 66) and in August 1997 (STS 85). This pa per focuses on the first flight of the instrument, which was part of the At mospheric Laboratory for Application and Science 3 (ATLAS 3) mission of NAS A. During a free flying period of 7 days, limb scan measurements of atmosph eric infrared emissions were performed in the 4 to 71 mu m wavelength regio n. For improved horizontal resolution, three telescopes (viewing directions ) were used that sensed the atmosphere simultaneously. Atmospheric pressure s, temperatures, and volume mixing ratios of various trace gases were retri eved from the radiance data by using a fast onion-peeling retrieval techniq ue. This paper gives an overview of the data system including the raw data processing and the temperature and trace gas profile retrieval. Examples of version 1 limb radiance data (level 1 product) and version 1 mixing ratios (level 2 product) of ozone, ClONO2, and CFC-11 are given. A number of impo rtant atmospheric transport processes can already be identified in the leve l 1 limb radiance data. Radiance data of the lower stratosphere (18 km) ind icate strong upwelling in some equatorial regions, centered around the Amaz on, Congo, and Indonesia. Respective data at the date line are consistent w ith convection patterns associated with El Nino. Very low CFC-11 mixing rat ios occur inside the South Polar vortex and cause low radiance values in a spectral region sensitive to CFC-11 emissions. These low values are a resul t of considerable downward transport of CFC-11 poor air that occurred durin g the winter months. Limb radiance profiles and retrieved mixing ratio prof iles of CFC-11 indicate downward transport over similar to 5 km. The accura cy of the retrieved version 1 mixing ratios is rather different for the var ious trace gases. In the middle atmosphere the estimated systematic error o f ozone is similar to 14%. Ozone data of correlative satellite measurements are well within this error bar. CRISTA agrees, for example, with Atmospher ic Trace Molecule Spectroscopy Experiment (ATMOS) sunset measurements typic ally within 5%. The random error of version 1 ozone mixing ratios is 4%. Si milar values apply to other trace gases. These low random errors allow the identification of small and medium scale horizontal and vertical structures in the measured trace gas distributions. Examples of structures in mixing ratio fields of ozone, ClONO2, and CFC-11 are given.