Abstract: Method and apparatus for non-contact temperature, emissivity and area estimation for gray and non-gray (uniform and non-uniform surface emissivity) are disclosed. Optical power measurements are obtained for radiation from a surface of interest in multiple wavelength bands. These power measurements are used to generate an expression for surface emissivity as a function of unknown temperature and surface projected area. At each of series of trial temperatures and areas within a predetermined range of physically plausible values, a value for emissivity at each measured wavelength is obtained. A best fit between these emissivity data points and a selected model emissivity function is obtained by least-squares minimization. The trial temperature and area which yield both the smallest minimum sum of squares and an emissivity value within predetermined physical constraints are concluded to be the temperature and projected surface area.