Laboratory model for radio-star scintillation and other diffraction phenomena

Abstract

The diffraction of a radio-star signal by a thin, weak, random phase-changing screen such as the earth's ionosphere or the solar wind has been modeled in the laboratory by using 40-kHz airborne ultrasonic sound and a diffracting screen of warm turbulent air. A phase-coherent system and temperature probes mounted in the diffracting region have provided information not available in typical radio-star observations. The experiment was designed with the idea of exploring more complicated screen geometries, particularly thick or strong diffracting screens or both. Considerable difficulties encountered in producing a satisfactory model even for the thin weak screen precluded the study of more complex geometries. Agreement with theory was obtained for the thin weak screen, and an on-line laboratory computer allowed a full application of a number of signal processing techniques, particularly for the determination of the screen drift velocity. It is concluded that further progress by modeling cannot be accomplished without unreasonably large investments of time and money.