I claim:
1. A method for determining a subsurface property value gradient of a body having a surface comprising the steps of:
generating a Rayleigh wave in the body by passing a current through a first meander coil having predetermined spaced wires determining a wavelength of the generated Rayleigh wave;
spacing a second meander coil identical to the first meander coil at a predetermined distance from the first meander coil;
detecting the Rayleigh wave with the second meander coil;
determining the velocity of the Rayleigh wave;
determining a property value at a depth determined by the wavelength of the Rayleigh wave which property value is a function of the determined velocity;
repeating the above steps with at least one other pair of first and second meander coils having different predetermined spaced wires than the first-mentioned pair of first and second meander coils such that at least one second property value at a second depth is determined; and
determining a subsurface property value gradient from the first-mentioned property value and the at least one second property value.
2. A method for determining a subsurface property value gradient as claimed in claim 1 and further including the steps of mounting each pair of first and second coils to respective identical bases such that the distance between respective pairs of first and second coils is the same for all the pairs of first and second coils.
3. A method for determining a subsurface property value gradient as claimed in claim 1 wherein the property values determined are temperatures, and further including the step of initially determining a modulus versus temperature profile for a material of the body.