Passive sounding experiments and experimental requirements for the determination of trace gas concentrations

Three classes of passive optical sounding experiments required to accomplish scientific research goals under the Middle Atmosphere Program (MAP) are outlined: absorption measurements utilizing occultation of the sun; thermal emission measurements (to detect either outgoing radiation from the earth's surface and atmosphere or atmospheric emission when the instrument is pointed limbward); nonthermal emission measurements of excited species (say, free radical OH). Advantages and limitations of these classes are indicated. Requirements for flying experiments of this type in future Spacelab missions are surveyed.