"Angel-echo" in acoustics

Abstract

Investigation of the troposphere fine structure has been attracting attention of researchers since long ago. One source of information on the troposphere localized inhomogeneities (TLI) are the reflections called «angel-echo» observed on the radar screens. The angel-echoes are weak in the radio-frequency band. That is why the radar method of the tropospheric sounding requires the application of expensive high-potential radars with complicated highly-directive antennas.

As well known, acoustic waves interact with the atmosphere considerably stronger than electromagnetic ones. This circumstance enables one to observe clearly the angel-echo on recording devices of rather inexpensive and comparatively simple acoustic radars using small weakly-directive antennas. The authors have developed an acoustic radar of the decimeter wave band that had proven its high efficiency as an instrument for TLI remote sounding. Here, a parabolic reflector antenna of the radar was fed by a horn-type electro-acoustic transducer. Small size and weight of antenna ensured a good transportability of the radar, that enabled the authors to obtain a large statistics about the angel-echoes in various climatic zones. Based on these results, a number of important conclusions about the localized tropospheric inhomogeneities has been made, under conditions of stable boundary layer of the atmosphere and a well-developed atmospheric convection.

It is worth noting that the simplicity of antenna and its comparatively small size offer an easy way to perform a mechanical beam scanning in wide range. This will open new exciting opportunities of the analysis of transversal structure of the localized tropospheric inhomogeneities.