The leakage of toxic or hazardous gases not only pollutes the environment, but also threatens people's lives and property safety. Many countries attach great importance to the rapid and effective gas leak detection technology and instrument development. However, the gas leak imaging detection systems currently existing are generally limited to a narrow-band in Medium Wavelength Infrared (MWIR) or Long Wavelength Infrared (LWIR) cooled focal plane imaging, which is difficult to detect the common kinds of the leaking gases. Besides the costly cooled focal plane array is utilized, the application promotion is severely limited. To address this issue, a wide-band gas leak IR imaging detection system using Uncooled Focal Plane Array (UFPA) detector is proposed, which is composed of wide-band IR optical lens, sub-band filters and switching device, wide-band UFPA detector, video processing and system control circuit. A wide-band (3µm~12µm) UFPA detector is obtained by replacing the protection window and optimizing the structural parameters of the detector. A large relative aperture (F#=0.75) wide-band (3μm~12μm) multispectral IR lens is developed by using the focus compensation method, which combining the thickness of the narrow-band filters. The gas leak IR image quality and the detection sensitivity are improved by using the IR image Non-Uniformity Correction (NUC) technology and Digital Detail Enhancement (DDE) technology. The wide-band gas leak IR imaging detection system using UFPA detector takes full advantage of the wide-band (MWIR&LWIR) response characteristic of the UFPA detector and the digital image processing technology to provide the resulting gas leak video easy to be observed for the human eyes. Many kinds of gases, which are not visible to the naked eyes, can be sensitively detected and visualized. The designed system has many commendable advantages, such as scanning a wide range simultaneously, locating the leaking source quickly, visualizing the gas plume intuitively and so on. The simulation experiment shows that the gas IR imaging detection has great advantages and widely promotion space compared with the traditional techniques, such as point-contact or line-contactless detection.
Detector MTF based micro-scanning image reconstruction (dMTF-MSIR) algorithm was presented to reduce image blur due to spatial integration degradation effect (SIDE) of focal plane detector. Firstly, a high-resolution oversampling image was generated from four successive frames in micro-scanning image sequence using inter-frame difference oversampling reconstruction (IFDOR) algorithm, in which case the required inherent inter-frame offsets were obtained by calibration. Secondly, a Wiener filter was built based on the SIDE model characterizing the image blur due to spatial integration of radiation intensity distribution at sensor cell surface. Finally, a high-resolution reconstructed image was generated by processing the oversampling image using the Wiener filter to reduce image blur due to SIDE. Simulation results showed that if spatial sampling frequency of focal plane detector was fixed and micro-scanning images were noise-free, the loss of reconstructed image detail increased with the increase of duty cycle of detector. However the influence of duty cycle of detector was gradually exceeded by that of image noise with the increase in image noise level, and in this case suppressing image noise should be given priority. Furthermore, the performance of the presented method was restricted by aliasing, so imaging light path should introduce an optical low-pass filter with the cutoff frequency that is less than or equal to twice as large as Nyquist sampling frequency of detector. The experiment based on infrared images of actual scene showed that reconstructed images generated by the presented method had a higher image contrast and sharpness than that of IFDOR algorithm.
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