Nadir sensitivity of passive millimeter and submillimeter wave channels toclear air temperature and water vapor variations

The upwelling microwave-to-submillimeter wave brightness temperature observ ed from above the Earth's atmosphere is sensitive to parameters such as pre ssure, temperature, water vapor, and hydrometeor content, and this sensitiv ity has been successfully used for passive vertical sounding of temperature and water vapor profiles. To determine optimal satellite observation strat egies for future passive microwave instruments operating at frequencies abo ve those now used, a study of the potential clear-air vertical sounding cap abilities of all significant microwave oxygen and water vapor absorption li nes in the frequency range from approximately 10 to 1000 GHz has been perfo rmed. The study is based on a second-order statistical climatological model covering four seasons, three latitudinal zones, and altitudes up to simila r to 70 km. The climatological model was developed by comparing data from t hree sources: the Upper Atmosphere Research Satellite Halogen Occultation E xperiment (UARS HALOE) instrument, the TIROS Operational Vertical Sounder ( TOVS) Initial Guess Retrieval radiosonde set, and the NOAA advanced microwa ve sounder unit (AMSU) radiosonde set. The Liebe MPM87 absorption model is used for water vapor and oxygen absorption and considers the effects of ozo ne and isotope absorption. Variations in the vertical sounding capabilities due to statistical variations of water vapor and temperature with latitude and season around each line are considered, and useful channel sets for ge ostationary microwave vertical sounding are suggested.