A progress report on initial ground demonstrations of a new climate monitoring instrument: the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS)

A key in climate change monitoring and research is the ability to precisely and accurately measure the evolving state of the climate system. A truly global perspective can only be achieved from orbit. A complete and unbiased characterization of the climate state requires very accurate and precise all-weather observations that can be inverted to key climate state variables independent of climate models. Stability is required to detect subtle changes in climate while high precision and resolution are needed to constrain processes. This combination of requirements is very difficult to achieve in practice. IR and shorter wavelengths cannot penetrate through clouds and therefore yield clear-sky biased estimates of the climate state. Passive radiance observations are non-uniquely related to the thermodynamic state and therefore cannot determine the climate state without additional constraints such as those from atmospheric models which contain (unknown) biases. While GPS occultations have many features well suited to climate, it is limited by information that is insufficient to determine both water vapor and temperature. To address these observational needs, we have been developing the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS) with funding from NSF. ATOMMS is a cross between GPS RO and the Microwave Limb Sounder (MLS) that will actively probe absorption lines probed by MLS and other passive sounders via satellite to satellite occultations. We are progressing toward an aircraft to aircraft demonstration of the ATOMMS capabilities. Over the past year we have completed our development of the prototype ATOMMS instrument at the University of Arizona sufficiently to perform a series of demonstration experiments on campus and on local mountaintops and begin evaluating the ATOMMS instrumentation and demonstrate a number of its important remote sensing capabilities. We have measured the spectra of the 22 and 183 GHz water vapor absorption line spectra and used these to precisely determine variations in water vapor along the signal path in both clear and cloud/rain conditions. We have also begun evaluating spectroscopic models of these lines. Our measurements of the 203 GHz absorption line of H2-18O provide the first demonstration of ATOMMS' ability to profile water isotopes in the troposphere and stratosphere and provide much needed unique constraints on the cycling of atmospheric water for climate models. We have measured changes in propagation speed through the atmosphere that will be used to profile atmospheric temperature and pressure in the aircraft measurements. ATOMMS is also a large scale scintillometer that we have used to determine several properties of turbulence as well as wind speed in the boundary layer. We will present an overview of the ATOMMS concept and summarize our results to date.