Satellite Occultation Measurements-Contributions to Middle Atmosphere Science

Solar occultation measurements from earth-orbit began with two orbits of data from aboard Apollo during the Apollo-Soyuz test project flight in 1975. The instrument was called SAM for the Stratospheric Aerosol Measurement. It was a simple proof-of-principle, one-spectral channel experiment that led to the long-duration occultation measurement series beginning in 1978 with the launch of SAM II aboard Nimbus 7. SAGE I, II, and III followed with increasing instrument complexity and capability. SAGE II and III are presently in orbit providing excellent high vertically-resolved measurements of aerosol, ozone, and other constituents. Other occultation sensors for long-duration measurements were launched in the 1990s including HALOE and POAM. This paper will present a historical overview of satellite occultation missions from 1975 to the present. The fundamentals of the occultation technique will be presented along with its advantages and comparison with other remote sensors. The occultation sensors, to-date, have produced exceedingly important measurements that have contributed to atmospheric and climate science. These have included such measurements as: the naming and characterization of Polar Stratospheric Clouds; aerosol and ozone associated with the wintertime polar vortex phenomena; ozone, HCl and HF trends associated with the effects of CFCs; the impact of volcanic aerosols; and aerosol and cirrus cloud distributions and trends. As the lead-off paper in this session, examples of the above data will be presented. Finally, some "lessons-learned" from these occultation missions will be discussed.