Abstract: A method in accordance with the invention is implemented via a computer program to determine the density and water (or other fluid) content of the various layers within a multilayer system. For convenience, the program is referred to as SIDARS. A conventional ground penetrating radar (GPR) system is used to obtain digitized images of a reflected radar signal from a multilayer pavement system. From these images standard mathematical techniques are applied to determine the number of layers, the thickness of each layer, and the dielectric constant for each layer within the multilayer system. SIDARS takes advantage of the fact that each layer is itself composed of three distinct types of material: solids, fluids, and gases. Thus, the dielectric constant obtained for a layer is in fact a composite value, namely a combination of the layer's solid, fluid, and gas dielectric constants. SIDARS employs a wave propagation model of the pavement system to generate a synthetic reflected radar signal.