Line-of-sight-attenuation chemical species tomography through the level set method

•Infer gas species concentration from line-of-sight-attenuation (LOSA) data.•Underling matrix problem is rank-deficient.•Additional information must be added based on presumed solution attributes.•Level set method promotes smooth, contiguous solution with distinct phase boundary.•Superior performance compared to simple Tikhonov smoothing/non-negativity.

Chemical species tomography based on line-of-sight attenuation (LOSA-CST) is an emerging diagnostic for mapping the concentration of a gaseous species. Since laser absorption measurements alone are insufficient to specify a unique species concentration distribution, reconstruction algorithms must incorporate additional information that promotes presumed physical attributes of the distribution. This paper pioneers the application of the level set method to LOSA-CST. The species concentration distribution is initially represented by a signed distance function, which is progressively deformed by forces that scale with the difference between the measured and simulated absorption data, as well as deviation from spatial smoothness. The final distribution explains the LOSA data and is also qualitatively consistent with mixed advection/diffusion transport physics. The algorithm is demonstrated by solving a simulated laser tomography experiment on a turbulent methane plume.