Window contamination detector

A contamination detection apparatus (10) is provided for measuring an amount of contamination on an optically transmitting element (14) or pane. The optically transmitting element (14) is capable of transmitting electromagnetic radiation. The contamination detection apparatus (10) includes a contamination detection (CD) radiation source (18) for providing a source intensity (26) of radiation. The source intensity (26) or radiation passes (28,30) through the optically transmitting element (14) at least one time. A reference detector (38) is also provided for detecting the source intensity (26) of radiation, and the reference detector (38) has a reference output level that is representative of the source intensity (26). A measurement detector (36) is further provided for detecting a final pass intensity (30) of the radiation provided by the CD radiation source (18) after the radiation provided by the CD radiation source (18) has passed through the optically transmitting element (4). The measurement detector (36) has a measurement output level that is representative of the final pass intensity (30). A comparator is also provided for comparing the measurement output level with reference output level in order to detect the amount of contamination on the optically transmitting element (14). The comparator can take several forms, such as a microprocessor or other processing device. In one specific embodiment of the present invention, the measurement detector (36) is a target detector (27) for detecting the electromagnetic radiation from a target (11) within an electromagnetic radiation measuring device (16). The electromagnetic radiation measuring device (16) measures the intensity of electromagnetic radiation from the target (11), and the optically transmitting element (14) transmits the electromagnetic radiation from the target (11) to the target detector (27). A sensitivity correction apparatus (70) is also provided for the electromagnetic radiation measuring device (16), and the artificial radiation source creates a path of radiation having a varying intensity, wherein the viewing pane permits radiation from the path of radiation to pass therethrough. The sensitivity correction apparatus (70) includes a correction mask (76) having a plurality of strip spaces and a plurality of transmittance strips (80). Each of the strips reduce the intensity of the beam when the beam passes therethrough, and the strips are placed in the strip spaces according to the distance between the radiation source and each strip space to reduce the intensity of the beam for that strip when the beam passes through the strips within the mask.