Infrared imaging spectrometer for measurement of temperature in high-speed events

Abstract

Munition development has always been driven by the necessity of delivering enough explosives to a targeted object to destroy it. Targets that are protected by steel reinforced concrete housings have become increasingly more difficult to destroy. Improvements must be made in munitions engineering design to either deliver more payload to the target or to make the weapon more potent. In most cases, due to aircraft weight limitations, the delivery of more payload is not an option. Therefore, improving the destructive power of a weapon of a given payload requires the use of more powerful explosives. However, when the potency of an explosive is increased, its sensitivity to premature detonation also increases. The characteristics of the metal casing containing the explosive contribute significantly to the weapon's detonation sensitivity. Casing experience significant heating during weapon penetration. This heating can cause the weapon to detonate before it reaches its target location. In the past, computer codes used to model detonating weapons have not taken heating into account in their performance predictions. Consequently, the theoretical models and the actual field tests are not in agreement. New models, that include temperature information, are currently being developed which are based on work done in the area of computational fluid dynamics. In this research, a remotely located, high-speed, infrared (IR) camera is used to obtain detailed measurements of the passive radiation from an object in an energetic environment. This radiation information is used to determine both the emissivity and the temperature of the surface of an object. However, before the temperature or emissivity was determined, the functional form of the emissivity was calculated to be an Mth degree polynomial with respect to wavelength dependence. With the advent of large, high-speed, IR detector arrays, it has now become possible to realize IR imaging spectrometers that have very high spatial resolution. The IR spectrometer system developed in this research utilized a large detector array to allow multiple spectral images to be formed simultaneously on the image plane. In conjunction with the correct emissivity model, this imaging IR spectrometer can determine temperature to within ±5 degrees Celsius. These experimentally verified temperature maps were then integrated into the newly developed computer models. This additional information will result in more accurate computer codes for modeling the energetic environment. In turn, this will allow the weapon designer to accurately optimize weapon performance with respect to different materials, geometries and kinetics.