Abstract: A radiometer has a concave mirror turnable about its optical axis and photoelectric converters which receive light waves reflected by the mirror and are mechanically coupled with the same. An interrupter disk is arranged in the path of the radiation which falls onto the mirror and has a side facing the mirror which is reflective. The converters are heated and a housing surrounds the mirror, the converters and the heater and is provided with a window located on the optical axis and permitting the admission of light to the mirror. An electronic circuit processes the various signals of the device. According to the invention the light-admitting window is arranged in the center of curvature of the hollow part-spherical mirror, which center of curvature is located behind or inwardly of the interrupter disk as seen in the direction of the incoming light.

Abstract: A scanning radiometer in which at least one curved mirror is integral with a drivable optical system. Thermal radiation is directed onto a detector facing the mirror at a distance. An electronic system performs a weighting evaluation corresponding to the position of the detectors, and a threshold value is indicative of the degree of radiation of the observed object shown on a display unit. The optical system together with the detectors is located about axes containing the center of curvature of the curved mirror and is rotatable in steps or continuously. The mirror is, furthermore, shaped in the form of a hollow sphere or a hollow sphere segment. The latter avoids irradiation of detectors by scatter radiation incident via the aperture with boundaries running parallel to the optical axis or with a boundary expanding funnel-like from the entry window towards the mirror.