Abstract: An apparatus and method for remotely measuring emissivity and hence temperature of a surface of an object. The apparatus includes a detector having a radiation receptor for measuring infra-red radiation, an integrating cavity surrounding the receptor for receiving radiation from a surface facing the cavity and delivering the radiation to the receptor, at least two sources of infra-red containing radiation (e.g. light from an incandescent lamp) within the integrating cavity positioned to produce separate beams of the radiation which strike the surface at different angles suitable for reflection to the receptor, and a processor for determining the temperature of the surface from the radiation measured by the detecting means. The use of at least two mutually angled radiation beams compensates for surface anisotropy of the surface whose temperature is to be measured.