A two-dimensional Monte Carlo model of radiative transfer in sea ice

[1] A two-dimensional, Monte Carlo radiative transfer model was developed for the analysis of optical data from cylindrical samples of sea ice. The backward Monte Carlo method was used to solve the radiative transfer equation in a cylindrical, azimuthally symmetric domain. Horizontal layers between two depths and vertical shells between two radii can be used to simulate spatial gradients in scattering, absorption, and refractive index in the model. The top of the cylinder can be illuminated by either normally incident, collimated radiation or by diffuse radiation. Irradiance and radiance detectors can be located anywhere within or on the cylindrical domain. The model was tested by comparing predicted apparent optical properties with solutions from existing one-dimensional and two-dimensional radiative transfer models. Domains with the largest optical depths and smallest radii were found to be impacted most by the horizontally finite geometry. The model was used to interpret backscattered and transmitted spectral radiance data taken in the laboratory from cylindrical core samples of first-year sea ice at -15degreesC. Use of a similarity parameter facilitated comparison between observations and model predictions by reducing the number of independent variables by one. Concurrent observations of ice microstructure indicated that light scattering due to inclusions of brine, gas, and precipitated salts should result in a scattering coefficient of similar to4.6 cm(-1) in our samples. Combining this value with the inferred similarity parameter yielded an asymmetry parameter of 0.98 for first-year sea ice at -15degreesC. Agreement between observed and predicted spectral radiances demonstrates the viability of this model as a tool for analyzing the optical properties of samples with finite geometry.