Anatomy of a Plume Measurement

In this Plume of the Week we dissect a plume image. The QLM LiDAR gas camera builds up a point cloud: the LiDAR’s laser scatters from hard objects in the distance (like the tree and car in this example), and the camera measures the backscattered light intensity, range and spectroscopic absorption of methane (concentration path length in ppm*m) for every point in the point cloud. The laser passes through a methane gas cell and the background methane in the air, and registers an absorption signal for both. To reveal the enhanced absorption of a plume, this background level (cell + ambient CH4) is subtracted, in this case revealing a plume that happens to be shaped like a manatee. For context, the background-subtracted methane density image is superimposed on the signal intensity image.