A near-field effect has been discovered experimentally in thermal radio emission of an absorbing dielectric medium. It is related to a specific character of the distribution of a quasistationary field component near a radiating surface. The effect consists of the fact that the effective depth of the received emission formation appears to be less than the skin-layer depth and depends on the size of the receiver antenna and its height above the surface. It can be considered as a new source of information about depth temperature distribution. A theory has been developed that allows for determining the relative contribution of wave and quasistationary components to the Plank emission received near the surface.