Abstract
We demonstrate a camera which can image methane gas at video rates, using only a single-pixel detector and structured illumination. The light source is an infrared laser diode operating at 1.651μm tuned to an absorption line of methane gas. The light is structured using an addressable micromirror array to pattern the laser output with a sequence of Hadamard masks. The resulting backscattered light is recorded using a single-pixel InGaAs detector which provides a measure of the correlation between the projected patterns and the gas distribution in the scene. Knowledge of this correlation and the patterns allows an image to be reconstructed of the gas in the scene. For the application of locating gas leaks the frame rate of the camera is of primary importance, which in this case is inversely proportional to the square of the linear resolution. Here we demonstrate gas imaging at ~25 fps while using 256 mask patterns (corresponding to an image resolution of 16×16). To aid the task of locating the source of the gas emission, we overlay an upsampled and smoothed image of the low-resolution gas image onto a high-resolution color image of the scene, recorded using a standard CMOS camera. We demonstrate for an illumination of only 5mW across the field-of-view imaging of a methane gas leak of ~0.2 litres/minute from a distance of ~1 metre.
Highlights
The ability to image invisible gases has applications in industrial and environmental monitoring settings [1, 2], but is technologically challenging to embed in a low-cost device
Video rate gas imaging conveys the direction of dispersal and the location of a leak source, helping users to improve their efficiency of response to hazardous events
Conventional approaches to detecting methane gas leaks have mainly been based upon flame ionization detectors (FIDs) [3] but such technology measures concentration at only a single point, making locating the source of the leak a difficult and slow process
Summary
The ability to image invisible gases has applications in industrial and environmental monitoring settings [1, 2], but is technologically challenging to embed in a low-cost device. DMDs, consisting of hundreds of thousands of individually addressable moving micromirrors, were originally developed for the display industry [16] but have found applications in other areas including wavelength multiplexing [17], real-time infrared imaging [15, 18], multi-object spectroscopy [19] and applied to astronomical observations [20]. They offer a method of modulating light which is fast and works over a broad range of wavelengths. A visible camera is used to provide an image for the operator, upon which the gas data is overlaid
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