Radiative modeling and characterization of aerosol plumes in hyperspectral imagery

A semianalytical model, named APOM (aerosol plume optical model) and predicting the radiative effects of aerosol plumes in the spectral range [0.4,2.5 mum], is presented in the case of nadir viewing. The scene is represented by an atmospheric layer (molecules and natural aerosols) located above the plume layer. The estimated at-sensor reflectance depends on the solar zenith angle, the plume optical properties (optical depth, single-scattering albedo and asymmetry parameter), the ground reflectance and the wavelength. Its numerical coefficients are derived from COMANCHE radiative transfer simulations. Model accuracy is assessed by using a set of simulations performed in the case of biomass burning and industrial plumes. APOM proves to be accurate and robust for solar zenith angles between 0deg and 60deg whatever the sensor altitude, the standard atmosphere and for plume phase functions defined from urban and rural models. The modeling errors in the at-sensor reflectance are on average below 0.002. They can reach values as high as 0.01 for wavelengths close to 0.4 mum but mainly correspond in such cases to low relative errors (below 5% and 3% on average). This model can be used for forward modeling (quick simulations of multi/hyperspectral images, help in sensor design...) as well as for the retrieval of the plume optical properties. For this purpose, we propose a model for the optical properties involving a few parameters and we show that even in this case the problem is still ill-constrained and that constraints have to be imposed. First retrieval results as well as recommendations for the inversion are presented.