Scattering induced ultrasonic attenuation offers a simple way to characterize material inhomogeneities. This method has a wide range of applications from tissue characterization [1,2] to ultrasonic NDE, such as grain size measurement in polycrystalline materials [3,4], structural diagnostics in ceramics [5,6], porosity assessment in cast metals [7,8] and composites [9], etc. The scattering induced attenuation of a through transmitted coherent ultrasonic wave can be readily related to certain characteristics of the average inhomogeneity via its total scattering cross-section. In many cases however, ultrasonic attenuation measurement is not feasible except from the backscattered signal. For want of better approximation, the scattering induced attenuation is presumed to have the same relation to the average inhomogeneity as if it were measured by the simpler transmission technique. It was recently reported [10] that this approximation breaks down in porosity assessment, and it probably does not work in many other NDE applications either.