Patent ID: 6803577
Filing Date: 2004-10-12
Classification: G01M,G01N

Abstract:
A method for imaging of gas distributions utilizing optical techniques, comprising: the use of gas correlation techniques for spectral identification of substances and cancellation of spatially varying background temperatures and emissivities;the utilization of absorption of natural thermal background radiation or self-emission spectrum due to a selected gas (passive recording technique); and wherein two images, A and B are stored using a dual-image infrared camera device adapted to a selected wavelength region where the gas absorption or emission spectrum is present; Aâ€”is the infrared scene recorded in one of the images (direct image); Bâ€”is the same scene recorded with the infrared light passing a gas correlation cell; characterized by a calibration procedure as follows: the background temperature is recorded using the information contained in image A; the relevant zero images A0 and B0, consisting of self-radiation from the dual-image camera device including the gas correlation cell and electronic offset, are subtracted from A and B, respectively, wherein the individual zero level in each pixel of the images has been determined before the gas measurement by recording a black body radiator at different temperatures and plotting the pixel intensity obtained versus a theoretically calculated intensity, and the axis intercept of a straight line, which is fitted to the data, provides the zero level; the images are digitally overlapped within a field of interest containing the gas release, and the continuing image processing is constrained to this field; a gas correlation image, G=(Aâˆ’A0)/(Bâˆ’Bo), is calculated; the concentration level in each pixel of image G is calculated using a diagram showing the integrated transmission within the chosen spectral profile as a function of the integrated concentration of the gas expressed in ppmÃ—meter for the particular gas, temperature difference between the background temperature and the gas emission temperature, and absolute temperatures; and finally, the resulting gas concentration image is superimposed on a visible image C of the scene and the result is displayed.