Reconstruction of Infrared Absorption and Scattering Coefficient Distributions of Semitransparent Medium Using Adam Algorithm Combined with Adjoint Model

Precise reconstruction of infrared optical coefficient distributions within semitransparent medium holds great significance in engineering field. This study introduces the Adam algorithm to reconstruct the infrared absorption and scattering coefficient distributions of a 2D semitransparent slab. The discrete ordinate method (DOM) is utilized to solve the time-domain radiative transfer equation (TD-RTE), and the radiative intensity at boundary is employed as input signal. The gradient calculation of the objective function employs the adjoint equation method (AEM). Results demonstrate that the adaptive moment estimation (Adam) algorithm can simultaneously estimate the infrared absorption and scattering coefficient distributions with high accuracy. Compared to traditional optimization methods, the Adam algorithm demonstrates significant superiority in terms of reconstruction accuracy, computational efficiency, and tolerance to measurement errors. Furthermore, it is also appropriate for determining the infrared optical parameters of different internal structures. Balancing both calculation accuracy and computation time, a recommended learning rate of eta = 50 is suggested for the reconstruction task. The Adam algorithm presents limitations for reconstructing the distributions in scattering-dominant medium. The normalized root-mean-square errors of the absorption and scattering coefficients respectively increase to 0.2311 and 0.0655 when the standard measurement error is increased to 20 %.