Method and apparatus for processing the output signals of an optical earth-horizon sensor operating in the infrared range of an orbiting earth satellite

Claim 1

Method for processing the output signals of an optical earth-horizon sensor operating in the infrared range of an orbiting earth satellite with respect to variously warm oppositely located earth rims (earth anomaly) for forming an off-course signal which is a measurement of the off-course angle of a line of sight of said earth horizon sensor in relation to a satellite/earth central point connecting line, wherein said earth-horizon sensor comprises a periodically reciprocated chopper disk located in the focal plane of an input lens, said chopper disk having a diameter corresponding to the image of the earth, and a detector collecting the periodically interrupted radiation falling in said input lens, wherein the output signals of said detector are amplified and demodulated with the chopper frequency in order to form said off-course signal, characterized in that in order to reduce error of said sensor off-course signals produced by differently warm earth rims (anomaly), said method comprises operating said earth-horizon sensor with different chopper amplitudes, comparing the respective off-course signals for the chopper amplitudes with the values of the standard sensor off-course signals for chopper amplitudes without said anomaly in a common off-course angle, when the corresponding values for a common off-course angle do not coincide, determining the difference between the measured values and said standard off-course signal values, and selectively amplifying or attenuating said detector output signals, in dependence on said difference, by the same factor in each instance in such a way that the amplitude changes caused by said earth anomaly are cancelled.