Lianjun Sun

Two-point nonuniformity correction based on LMS

In real-time system, the Infrared Focal Plane Array (IRFPA) should be compensated in traditional method of two-point temperature non-uniformity correction (NUC) before system was used every time, which make the system complex. Based on discussion of traditional two-point temperature NUC algorithm, Two-point temperature NUC based on least mean square (LMS) algorithm was proposed in the paper. In the view of the LMS algorithm theory, the correction gain and offset coefficients were iterated one by one during image processing, so that the expected correction result were obtained in little time. At the same time, the correction and coefficients iteration processes were completed in FPGA and DSP respectively, and make the arithmetic structure simple. The simplified structure, low cost and out-door suitable operation-systems are the merits of the system.

Infrared target tracking in real-time video and its implementation

An infrared target tracking system has been introduced in details for unmanned monitor application and its corresponding method for extracting and tracking moving targets from real-time infrared video has also been described. To ensure its real-time implementation on the tracking system, mature motion estimation techniques such as the time-domain statistics method and the DT method are adopted in the tracking method which includes three stages: target extracting, target classification and target tracking. A two-strategy classification method is adopted to improve classification accuracy. The tracking process involves correlation matching between a template and the current motion regions. The motion region with the best correlation is tracked and is used to update the template for subsequent tracking. The infrared target tracking system is based on a high-speed DSP chip with an internet interface, which may transmit the doubtful targets information to monitor center in time. To illustrate the effectivity of the infrared target tracking system, experimental results has been given in the end of this paper.

Performance analysis and improvement of microbolometer imaging system

Microbolometer focal plane array (FPA), as a popular kind of uncooled infrared detector, has a wide range of low cost thermal imaging applications due to its high sensitivity and simple micro-fabrication process. The performance of microbolometer imaging system is determined by many factors such as the property of the FPA, the effect of nonuniformity correction, the condition of operation and so on. In this paper, the micro-structure and heat transfer mechanism of microbolometer FPA are analysed to find out the substrate temperature characteristic. The response nonuniformity of the FPA and corresponding two-point correction method are discussed to find out the calibration temperature characteristic. And the power dissipation property of the thermal-electrical cooler (TEC) integrated under the FPA is described to find out the ambient temperature characteristic. According to the simulation and experiment results obtained from a 320×240 amorphous silicon microbolometer imaging system, it is concluded that all these temperature parameters have a great influence on the system performance and should be well considered for different working conditions to gain high system performance and imaging quality.

Study of uncooled thermal imaging system with multiple working temperatures

An uncooled thermal imaging system with multiple working temperatures will be presented. Transient response performance of α-si microbolometer detectors is simulated firstly when the working temperature varies in the range from -40deg. to +60deg. Simulating results show that α-si microbolometer detectors have coherent response performance in a large range of working temperature, which lay basis for designing uncooled thermal imaging system with multiple working temperatures. Different from traditional thermal imaging systems, this thermal imaging system has three working temperature with an accuracy range of less than ±0.01deg. When working, the temperature control circuit will switch between the working temperatures according to the variety of the environmental temperature. To evaluate this thermal imaging system, we measure its power consumption and NETD in the environmental temperature range from -40deg. to +60deg. The measurement results are that the total power is less than 2500mW and the NETD is less than 120mk. This indicates that the thermal imaging system has nearly the same imaging quality and obviously lower power, compared with traditional thermal imaging systems.

Signal processing of microbolometer infrared focal-plane arrays

A 320×240-uncooled-microbolometer-based signal processing circuit for infrared focal-plane arrays is presented, and the software designs of this circuit system are also discussed in details. This signal processing circuit comprises such devices as FPGA, D/A, A/D, SRAM, Flash, DSP, etc., among which, FPGA is the crucial part, which realizing the generation of drive signals for infrared focal-plane, nonuniformity correction, image enhancement and video composition. The device of DSP, mainly offering auxiliary functions, carries out communication with PC and loads data when power-up. The phase locked loops (PLL) is used to generate high-quality clocks with low phase dithering and multiple clocks are to used satisfy the demands of focal-plane arrays, A/D, D/A and FPGA. The alternate structure is used to read or write SRAM in order to avoid the contradiction between different modules. FIFO embedded in FPGA not only makes full use of the resources of FPGA but acts as the channel between different modules which have different-speed clocks. Whats more, working conditions, working process, physical design and management of the circuit are discussed. In software designing, all the function modules realized by FPGA and DSP devices, which are mentioned in the previous part, are discussed explicitly. Particularly to the nonuniformity correction module, the pipeline structure is designed to improve the working frequency and the ability to realize more complex algorithm.

Ambient light effect on the uniformity of image intensifier fluorescence screen brightness

When testing the uniformity of Image intensifier fluorescence screen brightness, the million scale CCD brightness meter is used. Due to the distance between the meter and fluorescence screen, the effect of ambient light on the testing result is essential to the design of testing system. Test with super second generation tube, input a constant voltage to insure the fluorescence screen brightness to be constant. Collect the brightness of the same fluorescence screen in different ambient luminance environment of 1×102Lx, 1×101Lx, 1Lx, 1×10-1Lx, 1×10-2Lx, 1×10-3Lx. Study the results with software MATLAB. It is concluded as: In ambient luminance environment of 1×10-1Lx the CCD has the best result. The testing result in ambient luminance environment of above 1×103Lx show untrue image. The testing result in ambient luminance environment of below 1×10-3Lx shows its own noise image and is unbelievable either.

The relationship of image quality of image intensifier and the luminance of its background

Image intensifier is a device to observe in night. To evaluate the quality of Image intensifier, there are two important data which are resolution and SNR. Analyzing the testing principles of resolution and SNR, a test to super second generation image intensifier is designed. Under the luminance of 1Lx,1×10-3Lx and 1×10-5Lx, test with the same resolution card. It was found that image quality of Image intensifier has the best quality when in luminance of background 1×10-1Lx to 1× 10-3Lx. When luminance of its background is above 1×10-1Lx the noise will be high, see fig.2. When luminance of its background is below1×10-3Lx the signal will be weak. It provides a testing foundation for evaluating the quality of an image intensifier.

Area source electron gun uniformity analysis

Fluorescence screen of Image intensifier is the key part to imaging quality of micro light and ultraviolet Image intensifier. To research the performance testing and analysis of Fluorescence screen seems more important in China. The research will help to understand the performance of Fluorescence screen, know where improvement should be made and then a best performance entire tube will be achieved. This article will do the theory analysis to part of testing instrument, area source electron guns uniformity. Electron gun consists of taper tantalum filament, vacuum environment and axial symmetry high pressure static field. The uniformity of hot electron emission of filament has been analyzed. Upon that, this article will specially analyze the uniformity of electron in the effective area after they go through the axial symmetry high pressure static field and get accelerated.

Analysis and measurement of thermal-electrical performance of microbolometer detector

Microbolometer detector is very competent as uncooled infrared detector for a wide range of thermal imaging applications, since it has been found to be more sensitive and has the advantage of using standard Si micro-fabrication process compared with pyroelectric or ferroelectric technology. The heart of microbolometer detector is a two dimensional array of thermal sensitive thin-film layers, which can change their temperatures and resistivities depending on the radiation absorbed. During the entire thermal imaging process, the microbolometer detectors substrate temperature, calibration temperature and ambient temperature are the key parameters which determine the thermal-electrical performance and the ultimate imaging quality of the microbolometer detector. In this work, based on the analysis of the characteristics of these parameters, the experiment has been conducted with the uncooled infrared thermal imaging system based on 320×240 amorphous silicon microbolometer detector working at different substrate temperatures, adopting different calibration temperatures for different ambient temperatures. The corresponding measurement results of the systems NETD, residual nonuniformity and power consumption, as well as the systems imaging results are presented, which all have a great agreement of the theory analysis above.

Thermal and electrical performance of α-Si microbolometer focal plane arrays

Recent advances of microelectromechanical system (MEMS) technology have opened new opportunities for amorphous silicon (α-Si) microbolometer focal plane arrays (FPAs) both for military and civil applications. α-Si membrane is chosen for sensitive material of microbolometer FPAs due to its high temperature coefficient of resistance (TCR), high resistivity and good mechanical properties. However, α-Si membrane also has the disadvantage of high 1/f noise, strict preparation conditions and metastable effect. So nowadays, researches are focused on properties of α-Si membrane to gain high performance of microbolometer FPAs. Since the pulsed bias readout mode of microbolometer FPAs causes a non-steady-state of α-Si membrane during the operation, the transient thermal-electrical response process of the sensing pixel is analyzed detailedly in this paper to predict the thermal and electrical performance of α-Si microbolemeter FPAs such as responsivity, noise equivalent temperature difference (NETD), detectivity and power dissipation. Numerical simulations are presented to investigate the factor which affects the performance of α-Si microbolometer FPAs. The imaging experiment results obtained from a 320×240 α-Si microbolemeter FPA are in good agreement with the theoretical analysis. The way to improve the performance of α-Si microbolemeter FPAs is given in the end of this paper.