We compare theory and microwave intensity measurements (5-mm wavelength) on a dynamical model of a compressible gas. The model consists of a slab-region styrofoam container (25 cm × 50 cm × 60 cm) whose top and bottom are grids which allow for the passage of turbulent air streams, but serve to confine light-weight randomly moving spheres (3.45-cm diam, relative index of refraction of 1.016 at 5-mm wavelength). We varied the number (N) of scatterers in the container (fractional volume w in the central region ranging from about 0.03 to 0.3), and made measurements in the forward direction (θ = 0), as well as at off-forward angles in the range θ=0° to 15°, and θ=30° to 80°. The essential limitations on the general utility of our data are set by difficulties in relating w to N, and by the supplementary statistical procedures used to reduce our chart records of instantaneous total intensity data into coherent and incoherent components. For most parts of the program, the accord between numerical computations based on theory and our specific measurements is adequate, and the general predictions of theory are satisfactorily substantiated, e.g., that for gaslike distributions of lossless large scatterers the incoherent intensity divided by the departure of the coherent intensity from the forward intensity in the absence of scatterers is practically independent of concentration.
C. I. Beard, T. H. Kays, and V. Twersky, "Scattered Intensities for Random Distributions—Microwave Data and Optical Applications," Appl. Opt. 4, 1299-1315 (1965)