Research On Modeling Of IR FPA Imaging System & TOD Performance Characterization Method

As infrared focal plane array (FPA) detectors continue to mature, FPA based IR imaging systems become a main trend in infrared imaging field compared to scanning imaging system. How to effectively characterize the performance of infrared imaging system based on FPA become more and more important. Traditional performance characterization methods or models become insufficient for this type of imaging systems. Hence, it is necessary to improve traditional performance evaluation method or propose completely new performance model to satisfy the performance evaluation of the novel IR FPA imaging system. In this paper, the following works are studied.(1) According to signal transfer mechanism of IR FPA imaging system, the Continuous/Discrete/Continuous model is introduced to analyze various effects of infrared imaging system. Based on the modeling of the linear effect, nonlinear effects: geometric distortion, vignetting, sampling artifacts, nonlinear response character, noise, reconstruction algorithm, et al are modeled and simulated utilizing the pixel processing method in spatial domain. Further, the model of imaging system is validated by minimum resolvable temperature difference(MRTD) experiment simulation.(2) Pixel transfer function(PTF) used to describe micro-scanning imaging process is derived for the staring detector array. Further, this model is utilized to calculate the amount of the improvement of micro-scanning to the imaging resolution for the detector array of different fill factors. Analytical results show that micro-scanning can significantly improve the resolution and quality of the reconstructed image, and the amount of improvement of different micro-scanning modes to the imaging resolution is different, which is closely associated with the fill factor. It will be helpful to choose the optimum micros-canning mode according to the fill factor of the detector array. On the other hand, an application-oriented analytical method of micro-scanning imager is proposed. The modified model of MRTD is achieved by considering the micro-scanning. The field performance of infrared imaging system based on micro-scanning is predicted and discussed with the target acquisition model. The simulated results show whether micro-scanning improve infrared imaging system performance depends on the other imaging system parameters, and working conditions.(3) Based on the idea of Triangle Orientation Discrimination Threshold(TOD) measurement method, several triangle patterns with different sizes are designed, accurate TOD measure is studied. Uncertainty of the TOD measure curve is firstanalyzed quantitatively by considering the components of the experimental instrument and the measure method, and the stability of the TOD measure results is validated.(4) A method for predicting TOD curve is proposed based on the triangle pattern simulation image. Specifically, the standard equilateral triangle patterns with different spatial frequency and different radiometric temperature are first generated, and discriminated by triangle orientation classification algorithm. The correct discrimination probability of the triangle pattern orientation is obtained utilizing the statistical method. The psychometric function-Weibull function is used to fit the probability data, and the TOD prediction curve is achieved. Comparisons with the experimental results indicate that the TOD prediction curve is reasonable.(5) Equation-based TOD performance model was first developed focusing on staring and scanning thermal imagers. Specifically, the spatial distribution of the non-periodic triangle standard pattern is determined quantitatively. Various effects of overall components of system on the triangle standard pattern are analyzed and modeled. The matched filter idea is adopted to quantitatively characterize the spatial-temporal integration of the human visual system to signal, aliasing and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio of thermal imager is derived. Experimental results show that this model can give reasonable prediction of the TOD performance curve for the scanning and staring imaging system.(6) According to the idea of TOD measure method, TOD criteria is determined utilizing the Weibull psychological function based on the field experimental data. A novel target acquisition (TA) performance prediction method based on the triangle orientation discrimination (TOD) threshold curve is proposed by considering thermal structure of the target. Comparisons with the experimental results show that this improved TA approach indeed leads to more accurate prediction of the field performance over the TA model based on the MRTD curve.