A reflectance inversion model in presented in which particle backscattering is parameterized by the particle backscattering ratio, attenuation and absorption coefficients rather than a hyperbolic function. This parameterization removes backscattering spectral constraints and yields independent estimates of the magnitude and spectral slope of the particle beam attenuation, which have been found to correlate with the particle concentration and size distribution, respectively. The model yields estimates of component absorption and backscattering consistent with observations and Mie models, particularly for environments dominated by phytoplankton and other strongly absorbing particles.