  A method is given for evaluating electromagnetic scattering by an irregular
surface with spatially-varying impedance. This uses an operator expansion with
respect to impedance variation and allows examination of its effects and the
resulting modification of the field scattered by the rough surface. For a fixed
rough surface and randomly varying impedance, expressions are derived for the
scattered field itself, and for the coherent field with respect to impedance
variation for both flat and rough surfaces in the form of effective impedance
conditions.
