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.
As we all know, the temperature distributions reflected in the thermal images are the basis for detecting the information of subsurface defect in thermographic NDT. In the actual work of thermographic nondestructive inspection of the inner surface geometry of a plate-shaped structure, the cave defect in the inner heated surface usually results in a temperature rise of the outer inspection surface. However, on some specific conditions, an extension on the inner surface will also result in the same temperature rise of the inspection surface. Because the extension has no negative effect on the reliability of the plate or this extension is an originally designed functional structure, we may call this extension of the inner surface “fake defect”. In this paper, we will take a three-dimensional plate with a cylindrical extension as an example to discuss how this fake-defect phenomenon forms and when this phenomenon appears. This study is of meaning to both the inspection and quantitative identification of the inner-surface defect based on infrared thermographic temperature measurements of the outer plate surface.