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Search and rescue and general surveillance mission pose a serious challenge to conventional imaging systems used by actual aircraft crews. These systems must often work in low- light and low-visibility conditions to find the identify targets. A new airborne imaging technology has been developed to overcome several deficiencies encountered with common CCD cameras, image intensified system and thermal imaging sensors. The recent developments in laser diode arrays, laser diode beam collimation and gatable micro- channel plate intensifier have made possible the construction of a compact active imagin system, called the Airborne Laser-Based Enhanced Detection and Observation Systems (ALBEDOS). This system proved particularly efficient at night and in degraded weather conditions. In addition, it was demonstrated that range gating, besides eliminating most of the light backscattered by aerosols, provided to some extent immunity to blooming effects specific to highly sensitive cameras. The system was installed on a helicopter and tested in various scenarios in October 1995 to demonstrate its potential. To enhance the surveillance capability over large areas of coverage, to optimize detection of humans and small objects and to improve the effectiveness of the search aircraft, a second-generation payload is presently developed and combines the benefits of two complementary imaging sensors. The Enhanced Low-Light level Visible and IR Surveillance System (ELVISS) consists of an improved range-gated active imager and a high-quality thermal imager, installed in two separate airborne platforms slaved together and controlled by a single user interface. It is expected that such a sensor systems will have a direct impact on improving the response time in finding those in need of assistance or simply in increasing the performance, reliability and efficiency of crews involved in general surveillance operations. This paper explains the concept of range gating, details a preliminary performance model and describes the two generations of Canadian active imagers: ALBEDOS and ELVISS.
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