A concise band selection method employing multispectral signatures of stealth aircraft whose infrared radiation was remarkably reduced was proposed for precise target detection. The key step was to select two or more optimal bands which could clearly signify the radiation difference between the target and its background. The principle of preliminary selection was based on the differences of radiation characteristics for the two main constituents of the aircraft’s plume gas, i.e., CO2 and H2O. Two narrow bands of 2.86 to 3.3 and 4.17 to 4.55 μm were finally selected after detailed analyses on contrast characteristics between the target and background. Also, the stability of the selected bands was tested under varying environments. Further simulations and calculations demonstrated that the multispectral detection method utilizing the two selected narrow bands could markedly improve the essential performances of target detection systems and increase their achievable detection distance. The stability of the aircraft’s multispectral signatures enabled this target detection method to achieve excellent results.
To acquire high-resolution IR polarization images, a pixel-level image reconstruction method was introduced. It was aimed at IR polarization imaging systems employing multi-aperture principle. The geometric mapping relation between images was firstly studied and was basis of this method. Parameters of the mapping relation were calculated, and then pixels of each image obtained were mapped to a virtual digital plane at which precise and resolution enhanced polarization images could be obtained by taking advantage of the pixel deviation and rearranging the pixels. Experimental results demonstrated that the algorithm could assist the multi-aperture imaging system in rendering easily precise and high-resolution polarization images.
A novel IR polarization staring imaging system employing a four-camera-array is designed for target detection and recognition, especially man-made targets hidden in complex battle field. The design bases on the existence of the difference in infrared radiation’s polarization characteristics, which is particularly remarkable between artificial objects and the natural environment. The system designed employs four cameras simultaneously to capture the00 polarization difference to replace the commonly used systems engaging only one camera. Since both types of systems have to obtain intensity images in four different directions (I0 , I45 , I90 , I-45 ), the four-camera design allows better real-time capability and lower error without the mechanical rotating parts which is essential to one-camera systems. Information extraction and detailed analysis demonstrate that the caught polarization images include valuable polarization information which can effectively increase the images’ contrast and make it easier to segment the target even the hidden target from various scenes.
Proc. SPIE. 8871, Satellite Data Compression, Communications, and Processing IX
KEYWORDS: Signal to noise ratio, Optical filters, Laser applications, Interference (communication), Signal processing, Electronic filtering, Detection theory, Signal detection, Laser countermeasures, Laser systems engineering
It is very important to extract the useful information from weak laser signal which is obtained in complex battlefield environment as laser warning taking an increasingly important role in laser countermeasures. The weak signal merging in noise becomes difficult to detect since the signal to noise ratio (SNR) of the signal received by the laser warning system is very low in real battlefield. Traditional signal detection methods, in which only mean filter or wiener filter are used; perform poorly in improving the SNR of the signals. A modified matrix of Hadamard Transform based on the Weighting Theory, overcame the disadvantages of matrices that are commonly used to cope with the low SNR signal. The modified matrix generating method of Hadamard Transform is introduced in detail, and then theory analysis, calculations and simulations on the modified matrix Hadamard Transform are presented. The results showed that this kind of Hadamard Transform performs excellently in increasing detection probability and decreasing False Alarm Ratio (FAR) of the laser warning system.
An improved optical structure of a laser warning system based on microlens array is proposed aiming at the high precision imaging warning system with a smaller size. Microlens array owning the advantage of high efficiency of energy use, motion sensitivity, etc. as a multi-aperture optical element, is applied in many optical systems. It is a tough task to obtain satisfied images with a curved base microlens array because the widely used plane detectors are not fit for these kinds of microlens array with poor imaging quality though it achieves the goal of wide field of view (FOV). We address to design a model by combining the curved base microlens array with the aspheric converging lens to solve the poor imaging quality caused by cured base microlens array. This method will make it possible to enlarge the FOV with better image quality. The ray tracing results show that the image quality acquired from plane detectors is improved using curved base microlens array, but with more simple fabricated structure than that of fisheye lens, which is widely used to get a wider FOV.