A scene dependent sensitivity analysis of top of the atmosphere near infrared radiances and polarized radiances to aerosol optical depth was performed. The analysis was performed for the hemisphere of viewing angles. The analysis includes a comprehensive examination of errors resulting from both the assumed aerosol size distribution and optical properties, as well as radiative transfer model assumptions. Three parameters are introduced. These parameters are the signal, the noise and the signal to noise ratio. The angular structure, as well as the angular averages of these parameters, are examined. It was found that, on the average, the top of the atmosphere signal to noise ratio is roughly three times larger for the radiances than for the polarized radiances. As a result, it was concluded that the majority of the information in the retrieval of optical depth is contained in the intensity measurements. The error analysis was used in the development of a two-channel optimal estimation retrieval of aerosol optical depth which utilizes the intensities only. Noise free and noisy synthetic radiances created from radiative transfer simulations are used to analyze the performance of the retrieval. Biases due to a priori constraints, viewing geometry, and forward model noise are analyzed.