Deriving atmospheric water vapor and ozone profiles from active microwave occultation measurements

The GPS/MET experiment was the first active atmospheric microwave occultation experiment using the existing GPS L1 and L2 frequencies to measure the atmospheric refractive index. One major limitation to this technique is that the presence of water vapor in amounts typically found in the lower troposphere (below 5-7 km) causes an ambiguity between the contributions of dry air and moisture to the refractive index. Additionally the profiles of other gases, such as ozone, cannot be measured using the L1 and L2 frequencies. A new satellite remote sensing technique to independently monitor atmospheric water vapor and ozone is under development. It will include small satellites with both transmitter and receiver capabilities on each. The frequencies will be located around the 22 and 183 GHz water vapor and the 195 GHz ozone absorption lines. The receivers will also have the capability to observe the L1 and L2 GPS frequencies. Simulation studies show that this new active occultation technique has the potential to provide accurate profiles of water vapor and ozone, as well as refractivity, temperature and pressure.