: Nowadays, search and tracking of terrestrial, airborne and naval targets is one of the most common applications of infrared waves. Because of advances in the field of elecetronic war and radar, radars don't fulfill the requirements of passive surveillance, are vulnerable against jamming and antiradiation missiles, so the importance of attention to infrared search and tracking (IRST) system is growing everyday. Since the IRST systems are passive, they don't give their location to enemy and use low power too. Because of advances in this field, installation of these systems on a high-altitude airplane at appropriate location can provide detection range close to 100 miles. Nowadays, depending on the operational condition of airplane, these systems are used beside the radar systems or even instead of them. Infrared spectrum is a sub-band of electromagnetic spectrum and ranging from 0.780µm to 1000µm. All objects with any temperature can emit infrared rays. Emitted rays transfer through atmosphere and are attenuated to reach to the detector. Regarding this issue, usually two atmospheric transmission windows means 3-5µm and 8-12µm are used for detecting and tracking purpose because of low attenuation. Target detection is caused by the difference between factors that affected emitted rays from target and background in the scene. But the front scene is composed of background and other false target such as clouds, mountain and etc. So we have to exploit the real target from background and false target in some way. In this thesis for achieving this purpose, different infrared radiation sources in scene are evaluated in the beginning. Under good weather condition and in two cases, with and without attenuation, the amount of infrared radiation emitted from target has been simulated. The recieved radiance and power by the detector have been calculated and compared for different scenarios and distances between target and detector. Then we have proposed an algorithm for detecting real target and applied it for processing two infrared images in this weather condition. In this algorithm, for real target detection, we have used diferent filters and image characteristics such as edge detection filter, morphology filter, object size and etc. Keywords: Infrared, radiance, infrared detection and tarcking, sobel edge detection filter, morphology filter.