Radio acoustic sounding of the atmosphere using a FM CW radar

Abstract

The use of a FM CW radar for the measurement of atmospheric sound velocity profiles is investigated. In contrast to particulate scatterers or clear air turbulence the sound waves represent a coherent scattering structure, and the consequences are examined. We derive the theoretical shape of the signal spectrum and present examples of velocity profiles of vertically propagating sound waves. As the sound and clear air echoes are separable by frequency, simultaneous measurements of atmospheric wind and temperature profiles should be feasible. Because of the excellent spatial and temporal resolution of the FM CW technique, these measurements perhaps offer a possibility of future remote heat flux measurements.

Effects of temperature gradient and radial range decay on the spectrum analysis of the radio acoustic sounding system using FM CW radar

“…Through a mixer in the receiver the return em signal that is scattered from the acoustic wave fronts is multiplied (mixed) with the reference signal, which is identical with the transmitted signal; the mixer output operates through a time window and low-pass filter and then utilizes a fast Fourier transform (FFT) analyzer to obtain the spectrum. Without introducing the window and after low-pass filtering the mixer output can be expressed as [Peters et al, 1988]…”

“…The radio acoustic sounding system (RASS) using a FM CW radar [Peters et al, 1988] is particularly useful for short range (lower than 1000-2000 m) and high time and space resolution (can be of the order of a few meters) remote sensing. This kind of radio acoustic sounding system (RASS) could be used as a surface-based system to monitor atmospheric boundary layer including the measurements of temperature, wind, and turbulence.…”

“…The position of its maximum in each range gate contains information about the sound speed, therefore, providing the temperature profile. However, the idealized spectral envelope deduced by Peters et al [1988] is a rectangular function with very narrow width, for instance, for the Hamburg RASS, the width, that is, the sensitive interval tSfa is only 11 Hz [see Peters et al, 1988, Table 1]. Apparently, the real atmosphere must modify the idealized derivation and the conclusions.…”

“…In discussing the effects of the temperature gradient, the simulation results and the algorithm with the approximate correction for temperature bias (caused by the nonlinear temperature distribution) will be provided in the text. Peters et al [1988] presumed that the effects of signal decay with range was so weak that it could be treated as a constant. This assumption, of course, is reasonable for the far-field aspects.…”

Development of radio acoustic sounding system (RASS) with Gadanki MST radar – first results

“…Over the past four decades RASS has been demonstrated to be a reliable ground-based remote profiling technique to obtain altitude profiles of atmospheric virtual temperature, T v (e.g. Marshall et al, 1972;Bonino et al, 1979;Kon, 1981;Makarova, 1980;Matuura et al,1986;Peters et al, 1988;May et al, 1990). Using RASS, continuous observations of T v with high temporal resolution have been conducted (e.g.…”