Systems and methods construct a 2 dimensional (2D) gas concentration map (image) from data from one or more laser based absorption projection paths. Embodiments use a Bayesian approach to construct a 2D gas concentration map of a combustion region cross section plane by modeling the 2D map as a Gaussian Process (GP). The GP models the global correlation among all pixels in the 2D map. Data from one or more projection paths is propagated to all pixels in the map instead of just local pixels. The correlation among map pixels is used to propagate projection path data from map pixels traversed by a projection path to other map pixels.