The thermal wake would be formed owing to the cooling water or exhaust heat discharged by ship, and the cold wake could be formed by the cool water in the lower part of sea stirred up by the ship propeller or vortexes. Owing to the difference of surface temperature and emissivity between the ship wake and the surrounding ocean the ship wake will be easily detected by the infrared detecting system. The wave of wake also could be detected by the difference of reflected radiance between the background and the Kelvin wake of ship. In this paper the simulating models of infrared imaging of ship wake are developed based on the selfradiation of wake, the reflected radiance of the sky and sun and the transmitted radiance of atmosphere, and the infrared imaging signatures of ship wake are investigated. The results show that the infrared imaging signatures of ship wake can be really simulated by the models proposed in this paper. The effects of the detecting height, the angle of view, the NETD of detector and the temperature of wake on the infrared imaging signatures of ship wake are studied. The temperature difference between the ship wake and surrounding ocean is a main fact which effects on the detecting distance. The infrared imaging signatures of ship wake in 8-14μm wave band is stronger than that in 2-5μm wave band whenever the temperature of ship wake is warmer or cooler than the surrounding ocean. Further, the infrared imaging of thermal wake is investigated in the homogenous water and temperature stratified water at different speed of a ship and different flow rate and depth of the discharged water in a water tank. The spreading and decaying laws of infrared signature of ship wake are obtained experimentally. The results obtained in this paper have an important application in the infrared remote sensing of ship wake.
Based on the theory of infrared radiation and of the infrared thermography, the mathematical correction model of the infrared radiation temperature measurement of semitransparent object is developed taking account by the effects of the atmosphere, surroundings, radiation of transmissivity and many other factors. The effects of the emissivity, transmissivity and measurement error are analysed on temperature measurement error of the infrared thermography. The measurement error of semitransparent object are compared with that of opaque object. The countermeasures to reduce the measurement error are also discussed.
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