Spot size of the radar return from a radar‐acoustic sounding system (RASS) due to atmospheric refractive turbulence

Abstract

We have calculated the intensity profile on the receiving plane of a radar‐acoustic sounding system (RASS) in the presence of varying amounts of atmospheric refractive turbulence. The results indicate that the refractive turbulence produces corrugations in the initially spherical acoustic wavefronts and these corrugations scatter electromagnetic energy over a large solid angle in the backward hemisphere. The net effect is to leave the scattered beamshape nearly unchanged from its form in the case of a homogeneous atmosphere. Of course the on‐axis intensity is reduced considerably but the energy is scattered into such a large solid angle that this produces only an increased background level or tails in the electromagnetic intensity profile.

Signal power for radio acoustic sounding of temperature: The effects of horizontal winds, turbulence, and vertical temperature gradients

“…The corresponding reduction in signal power is similar to that associated with an optical system when the transverse coherence length of the optical wave becomes smaller than the diameter of a receiving lens [Fried, 1967]. The ratio of the transverse coherence length to the transverse dimension of the radar beam, which characterizes the extent to which turbulence affects the performance of a RASS, continues to decrease with range for a uniform turbulence strength profile resulting in an R-26/5 range depen-dence [Clifford and Wang, 1977;Clifford et al, 1978;Kon, 1984a]. In the presence of winds, however, the turbulence-induced broadening of the focal spot serves to increase the received power, as discussed by Kon [1984b].…”

“…The behavior of the backscattered power under a variety of conditions can be best discussed in terms of the RASS focal spot caused by the focusing of the incident electromagnetic radiation by the spherical perturbations in the refractive index induced by the acoustic wave [Clifford et al, 1978]. (Here we have assumed that the scattering volume lies in the far field of both the radar and acoustic source and that the radar beam is narrower than the acoustic beam.)…”

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

“…It is obvious that the horizontal wind field plays a crucial role but that not simply geometric relationships can solve this kink. In addition, though some of inves-tigators [e.g., Clifford et al, 1978;Masuda et al, 1990] believe that there are less influences by turbulence on the RASS echo, the atmospheric inhomogeneities still seem to be a strong candidate for a role in FM CW RASS. Without considering turbulence, the intrepretation is difficult to be make completely.…”

Effect of atmospheric turbulence on the spot size of a radio‐acoustic sounding system: A calculation revisited

“…Two of the earliest studies examining the role of atmospheric turbulence on the performance of a radio acoustic sounding system (RASS) were conducted by Clifford and Wang [1977] and Clifford et al [1978]. Clifford et al developed a theoretical expression for the average intensity profile of the spot produced when electromagnetic radiation scattered from a Bragg-matched, spherical acoustic wave is focused back onto the ground.…”