Temperature profile retrieval from surface to mesopause by combining GNSS radio occultation and passive microwave limb sounder data

A theoretical study on the combination of a passive microwave and a GNSS ra dio occultation instrument, mounted on the International Space Station (ISS ), was performed. Both instruments allow to deduce the atmospheric temperat ure profile. We combined realistically simulated data of the two highly syn ergistic sensors with the optimal estimation method (OEM) and retrieved sin gle joint temperature profiles from 0 to 90 km altitude for which we found accuracies < 1 K below 35 km and < 4 K in the mesosphere, respectively. In addition, we performed simultaneous tropospheric water vapor and temperatur e retrievals leading to a water vapor accuracy < 10 to 20 % at altitudes be low 5 to 8 km. The OEM allows to optimally exploit the synergy in the data and maximizes retrieval accuracy over the full range from surface to mesopa use. It seems worthwhile to install this type of instrument combination on the ISS or other low-Earth-orbit (LEO) platforms.