A High-Power, Dual-Frequency Monostatic Acoustic Sounder for Studying the Atmospheric Boundary Layer

Abstract

Microwave propagation conditions in the lower marine troposphere are evaluated using gradients of radio refractivity profiles. An inexpensive, weather-resistant system for Continuous monitoring of radio refractivity conditions in the lower marine troposphere would be useful for deciding when more detailed measurements should be made. Radio refractivity is largely dependent on vertical profiles of water vapor pressure. A high-power, dual-frequency, monostatic acoustic sounder was constructed to investigate the possibility of measuring water vapor pressure profiles in the marine boundary layer by acoustic means. These water vapor pressure profiles may be combined with surface measurements of atmospheric temperature and pressure to obtain estimated radio refractivity profiles. A fundamental assumption for this technique is that the pair of frequencies used should observe the same atmospheric backscatter. That is, the scattering coefficients of the two frequencies should remain a constant ratio. Measurements made with this acoustic sounder at the Boulder Atmospheric Observatory demonstrate that the 6- and 10-kHz frequencies used do not always observe the same atmospheric phenomena. Therefore, a different pair of frequencies should be sought to derive water vapor pressure profiles.