Absorptive and Refractive Stellar Occultation Techniques for Atmospheric Remote Sensing

Occultation methods have been used for many years to provide accurate measurements of species concentrations of planetary and terrestrial atmospheres. The technique is ideal for monitoring trends of species of global change importance because of its degradation-free nature. Stellar occultation has the advantage of source light selection flexibility and coverage, but suffers from weaker signals and stringent spacecraft/orbital requirements. Although space-borne stellar occultation has been discussed for over 30 years, its real applications have been very limited, especially for providing measurements of the lower atmosphere composition due to the presence of contaminating atmosphere emissions and scintillations. Recently, the UVISI instrument onboard the US MSX spacecraft and the GOMOS instrument onboard the ESA EnviSat satellite have both successfully implemented the stellar occultation technique to retrieve Earth's atmosphere ozone profiles. In this paper, we will present the stellar occultation technique, MSX observations and the assessment of the retrieval densities, especially of molecular oxygen and ozone from the lower stratosphere to the lower thermosphere. Potential future applications of stellar occultation technique will also be discussed.