KEYWORDS: Cameras, Infrared cameras, Signal to noise ratio, Signal processing, Infrared radiation, Sensors, Infrared imaging, Signal detection, Long wavelength infrared
When a space infrared camera has a higher temperature sensitivity , the more tiny temperature information it can record in the imaging data. High sensitive infrared camera takes an important role in observation of urban and sea targets and so on. A new space infrared camera system is designed based on pixel-level digital accumulation technology. The new infrared camera based on this technology realize the analog-to-digital convert of detecting signals into single detector pixel, which can reduce the noise caused by readout of analog signal markedly. This infrared system processes input signal by little capacitor packet digital-counting method,the integral capacitor plays the part of “voltage-to-frequency conversion”, which vary far from the traditional detector. The signal quantization process realized by the capacitor packet digitalcounting, every single charge packet is small, a capacitor of several fF in new system has the equal effect of a capacitor of thousands pF in traditional system, that makes the new infrared system can break the limit of integral capacitor’s physical restriction. So the new camera has the ability of achieving 1mK(0.001K) temperature sensitivity by theory without saturation electrons restriction. This ultra-high temperature sensitivity infrared camera system will break the temperature sensitivity limits of all infrared cameras on hand, and improve infrared system’s ability of distinguishing the tiny temperature a lot. The prototype camera has been manufactured and it has a 5mK NETD (Noise Equivalent Temperature Difference), the engineering feasibility of this camera system is valid. The pixel-level digital accumulation infrared camera will be an important development direction of future high-sensitivity space infrared camera technique.
This paper gives the preprocessing technique research which includes odd-even calibration, bad pixels compensation and non-uniformity calibration for the high sensitivity push-broom long wave infrared camera. The noise equivalent temperature difference (NETD) of the infrared camera has achieved less than 10 mK. The paper analyzes high sensitive imaging effects by using different preprocessing standards according to the test data, also analyzes the effects on imaging quality when using different preprocessing methods. At last the paper gives the suitable image preprocessing methods for the high sensitive infrared camera: the odd-even calibration method considering velocity to height ratio, the bad pixels compensation methods which are unique for temporal and spatial bad pixels and the non-uniformity calibration methods which combines the calibration based on black body testing data and the calibration based on real scene imaging data. It is validated that the residual nonuniformity of the infrared image can be reduced to 0.03% by using the preprocessing methods, which is satisfied for the requirement of high sensitive imaging.
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