Multispectral Monte Carlo radiative transfer simulation by the maximum cross-section method

The maximum cross-section method is useful for efficient Monte Carlo radiative transfer simulation in an inhomogeneous atmosphere that consists of many small volume elements. Here a new method for multispectral radiative transfer calculation is proposed to simultaneously estimate multispectral radiances, irradiances, and flux divergences for atmospheric systems with different absorption coefficients. The maximum cross-section method is used to accelerate the calculation algorithm for atmospheres with spatial and spectral variations of optical properties. An example for a broken cumulus cloud field shows that the proposed method enables acceleration on the computational speed per wavelength by 5, 30, and 70 times faster when simultaneously calculating radiances in 10, 100, and 1000 wavelengths, respectively. The method provides a means for efficiently calculating a high-resolution spectrum in a narrow band for a three-dimensionally inhomogeneous atmosphere.