Abstract: Correlation thermography permits high resolution passive remote thermal radiation sensing for non-invasive temperature measurement of the interior of a body. At least two directional transducers are coupled to the surface of the body at different locations about the body in such a manner that their directional receiving patterns intersect. These transducers may be acoustic or electromagnetic transducers, but in any case are capable of receiving thermally-generated energy from inside the body and generating corresponding electrical signals. The intersection of the receiving patterns of the transducers defines a common volume which is relatively small, and the signals at each transducer originating from this common volume within the body exhibit a high degree of correlation. A multiplier receives the electrical signals produced by the transducers. A fixed or variable delay is interposed between at least one of the transducers and the multiplier.