The invention is a process for determining the resistivity of a layered structure
including a layer of resistive material hidden under a topcoat and a tile layer,
the process comprises the steps of; 1) directing electromagnetic radiation over
a selected frequency range to the outer surface of the layered structure; 2) measuring
the reflection of the electromagnetic radiation from the layered structure surface;
3) converting the signal into the time domain; 4) analyzing the first echo to obtain
the topcoat thickness; 5) obtaining the tile thickness from the time delay between
the first and second echoes; 6) compensating the second echo with electromagnetic
power loss due to the topcoat and tile; and 7) determining the resistance of the
resistive layer from the compensated second echo.