We present an embedded imaging approach based on low cost sensors that span a long spectral range in the infrared. A system has been implemented with 12 apertures that combine unique uncooled FPAs in the mid infrared domain -2 to 5 microns wavelength- with very low cost microbolometers in the thermal infrared -7 to 14 microns wavelength-. Both FPA technologies are uncooled and low cost, manufactured as monolithic devices. The system is made of two modules, one LWIR, other MWIR. Each module has a system-on-chip GPU/ARM board that carries out all the image processing required for image reconstruction. This includes the calibration of the system, the registration of the images acquired with the many apertures, and the reconstruction of the super resolved image. Besides, the board performs all the operations and transformations required for noise correction. The output of each of the modules is a video stream at 30 frames per second. Each frame is a super resolved image with a resolution 2.5x compared to the images acquired by the FPAs used. Furthermore, the modules may be integrated and the acquired images combined in a single one in the embedded processing boards. Moreover, the boards may also combine and fuse this output with a visible range video stream. The use of low cost FPAs facilitates the deployment in a broad range of applications that an benefit from imaging in the infrared, particularly in the MWIR range in which existing commercial cameras based on hybrid technology are very expensive. The system is being tested in different applications, including surveillance in variable lighting conditions and monitoring in firefighting scenarios
KEYWORDS: Sensors, Cameras, Mid-IR, Modulation, Temperature metrology, Infrared imaging, Signal to noise ratio, Infrared radiation, Optical filters, Black bodies
Uncooled focal plane arrays have revolutionized the market of infrared technology in the last years, reducing the size, weight, power and cost of thermal detectors, and make them accessible to mass markets. This revolution has been lead by micro-bolometers, considered a mature technology for the long wavelength infrared range. However, there is a lack of uncooled detectors in the mid-wavelength infrared (2-5μm) range, one of the most interesting bands for gas identification and temperature measurements of hot objects. Here, we describe the development of a novel gating imaging system for the mid-wavelength infrared. The system is based on unique low cost uncooled PbSe focal plane arrays with a peak response around 3.6 um. The PbSe detectors present some challenges, such as low sensitivity (which limits their application for imaging objects at temperature above 200°C and low signal-to-noise ratio (mainly due to thermal drifts and electronic noise). On the other hand, the photonic detection technology enables high speed acquisition up to 10000 frames per second depending on the resolution. The proposed system combines a modulated aperture, turning the incident light on and off periodically, and a digital lock-in to demodulate the incoming signal and avoid noise in the unwanted region. Contrary to active lighting approaches, the whole scene is modulated at a high frequency and the signal processing is tailored to reduce the internal noise introduced by the detector, while keeping enough bandwidth to achieve video at 30 frames per second. Two imaging prototypes were built: a camera array with six detectors of resolution 32x32, and a camera array with three detectors with increased resolution (128x128) and sensitivity. The proposed technique significantly improves the SNR and reduces the thermal drifts of the PbSe detectors, enabling the imaging of objects at temperatures below 100°C. The camera array was tested in the field during a firefighting training, showing enhanced capabilities to see through fumes, detect fire hotspots and measure temperature robustly.
We present a novel multispectral imaging system that measures temperature without knowledge of emissivity. It combines support vector machine regression with low cost PbSe imagers, sensitive in the MWIR range and capable to achieve very high speed acquisition rates with a medium resolution. The system is modular and builds on two or more apertures sensitive to different but close spectral bands. Inspired by the approach adopted by ratio and multi wavelength pyrometers, we estimate temperature from the combined response at these bands. However, we adopt a flexible and transparent approach to modeling multiple regression based on machine learning and using synthetic datasets. We demonstrate high accuracy and robustness against variations in the value of emissivity. Besides a working prototype, our contribution renders a simple procedure for the design of cost effective thermographic systems for field applications demanding reliable measurements in unconstrained conditions.
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