Methods and apparatus for remotely measuring temperature of a specular surface. Method takes two measurements of P-polarized radiation emitted at or near Brewster angle from the surface. First measurement (SA) collects and detects first amount of radiation emitted directly from a surface portion using a collection optical system. Second measurement (SB) includes first amount of radiation and adds quantity of radiation collected at or near at/near Brewster angle and reflected from the surface with a retro optical system with a round-trip transmission t2 that retro-reflects a quantity of radiation received from surface portion back to same surface portion where it reflects and combines with first amount of radiation collected by collection optical system. Measurements SA and SB and t2 are used to determine surface emissivity (ξ). Calibration curve is used that relates ratio of the first measurement SA to surface emissivity (SA/ξ), to surface temperature. Surface temperature determined from SA/ξ by calibration curve.