Application of hybrid SPSO-SQP algorithm for simultaneous estimation of space-dependent absorption coefficient and scattering coefficient fields in participating media

A hybrid stochastic particle swarm optimization (SPSO) and sequential quadratic programming (SQP) algorithm is proposed to estimate the space-dependent absorption coefficient (κ_a) and scattering coefficient (κ_s) fields simultaneously. The retrieval results of SQP algorithm are highly affected by the initial guess, and thus, SPSO is adopted to obtain the initial value of SQP because of its global search capability and lesser dependence on initial guess. The regularization term based on the generalized Gaussian Markov random field model is employed to overcome the ill-posed characteristic of the inverse problem. The inverse coupled radiation-conduction problem is solved in a one-dimensional participating medium with uniform refractive and graded refractive indices exposed to a pulse laser, respectively. All the results show that the separate space-dependent κ_a and κ_s fields can be estimated simultaneously and accurately from the coupled optical and thermal signals.