Acoustic sounding

Abstract

Methods and apparatus for atmospheric sounding using acoustic chirps are disclosed, the transmitted and echo chirps being compared in a mixer that yields frequency sums and differences. Preferably, the mixing is performed as a complex multiplication in the Fourier domain. In one system ( ) a signal generator ( ) such as a PC sound card drives a loudspeaker ( ) that serves as a transmitter and echo pulses are detedcted by a microphone ( ) that serves as a receiver. Chirps transmitted by the loudspeaker ( ) travel by different paths ( and ) due to reflection from TILS or thermal inversion layers ( and ) at different altitudes. The transmitted and echo chirp signals are compared in a mixer ( ) from which various outputs ( and ) can be generated. One output ( ) might be the magnitude of the difference between the transmitted and echo chirp tones, instant by instant, which is indicative of the altitudes of the respective TILs. The other output ( ) might be the phase shift in an echo tone with transit time, which is indicative of vertical wind velocity at different altitudes. Such sounding methods and apparatus are useful for weather research, prediction of plume dispersal and the design of microwave links to minimize multipath fading.