Monitoring atmospheric turbulence with the ATOMMS active sounding system

We present measurements of amplitude scintillations of microwave signals of an active sounding system to infer atmospheric turbulence.

The Active Temperature Ozone and Moisture Spectrometer (ATOMMS) is a remote sensing instrument for climate that comprises a microwave transmitter and receiver system that actively probes the atmosphere. In this system, electromagnetic signals are propagated through the atmosphere from a source to a receiving system, which records the signals digitally. An inversion algorithm is then applied to recover the atmospheric temperature, pressure and the concentrations of water vapor and other trace gases from the digitized phase and amplitudes of the received signals.

ATOMMS transmits and receives signals at 13GHz for monitoring atmospheric temperature from the propagation delay of this signal, and eight monochromatic tones at selected frequencies in the18-25 GHz band and two tunable tones in the 176-208 GHz band, for monitoring the atmospheric moisture content from the changes in amplitude of the signals.

Atmospheric turbulence mixes air of different thermodynamic and moisture properties, changing the complex air index of refraction of the medium. These fluctuations in the index of refraction are the source of scintillations (amplitude fluctuations) in the propagation of electromagnetic signals through the atmosphere, and are a source of noise for the ATOMMS instrument. While the goal for ATOMMS is to remove the effects of turbulence in order to retrieve atmospheric temperature and moisture, these amplitudes fluctuations are also useful to monitor the strength of the atmospheric turbulence along the propagation path and could be useful to learn more about the processes responsible for the turbulence such as convection, wind shear, and frontal activity.

We are making field test measurements with the prototype ATOMMS instrument with the transmitting and receiving units located at the ends of baselines of 0.82 km, 5.4 km and 83.4 km. The shorter of the baselines is accomplished from the rooftops of two tall buildings located on the university of Arizona campus, while the longer baseline tests are done by placing the instruments on mountain peaks at about 2500 m elevation with signals propagation over the valleys.

In this work we present results on the temporal fluctuation and spectral characteristics of turbulence as monitored by ATOMMS at the various baselines setups during field-testing, and we show its potential for studying atmospheric turbulence in the boundary layer.