The resonant transition radiation from an electron charge that moves along the concentration gradient of a cold isotropic plasma is calculated. The possibility of using this radio-emission for inhomogeneous plasma diagnostics is discussed. Measurements of this kind of radiation in a planar-stratified cold isotropic plasma give the possibility of finding out the profile function of the plasma concentration profile (parts of the plasma density profile where the density is increased over its previous maximum value along the direction of the plasma bunch velocity).