Accurate infrared ship signature codes are needed by the Navy in order to predict signatures of existing ships, test algorithms used for detection, classification and homing, study signature reduction techniques, and reduce the IR detectability of future vessels. Currently, the signature codes being used by the Navy do not include contributions from radiation undergoing one or more reflections off surfaces between the ship and sensor. In most instances, reflected infrared radiation can be neglected since the absorptance of most reflecting surfaces (e.g. water, painted surfaces, etc.) is high in the infrared. However, for the case of grazing or near-grazing incidence on a water surface, the IR reflectivity becomes very large. Hence, low angle observations of the sea near a ship tends to show a warmer region in front of the ship; in rough seas the IR image of the ship's reflection is blurred into an infrared 'halo'. Recent infrared field measurements performed by NRL on the USS Ticonderoga clearly show the halo effect. In this report we determine the mean temperature difference between the halo and background for a Ticonderoga image, and then propose a simple one-dimensional model for the angular dependence of the halo's apparent temperature.


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