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Development of a portable instrument for measuring the photon irradiance response (PIR) of UV missile warning sensors

A large number of military aircraft are equipped with the AN/AAR-47 missile approach warning system (MAWS). The AN/AAR-47 comprises four ultraviolet (UV) sensors, a computer processor (CP) and a control indicator (CI). In-band photon irradiance from incoming missiles produces sensor outputs that are analyzed by the CP to produce threat declaration. The output signal level produced by each sensor for a given photon irradiance level depends on its sensitivity, expressed in terms of photon irradiance response (PIR). All new sensors are tested in manufacture for a minimum PIR before delivery. However, years of operation in harsh military environment may cause sensitivity degradation that makes a sensor unserviceable. A new instrument, the PIR Meter, developed by the Defence Research Establishment Valcartier (DREV), allows for accurately measuring the PIR of AAR-47 sensors, making it possible to identify those sensors whose sensitivity has dropped below the serviceable level. This paper describes the PIR Meter, its components, its interconnections with installed or uninstalled AAR-47 sensors and the PIR measurement procedure. It also covers the signal processing algorithms that were developed to obtain accurate PIR measurements in the operational environment.