Statistical analysis of the uncertainties in cloud optical depth retrievals caused by three-dimensional radiative effects

This paper presents a simple yet general approach to estimate the uncertain ties that arise in satellite retrievals of cloud optical depth when the ret rievals use one-dimensional radiative transfer theory for heterogeneous clo uds that have variations in all three dimensions. For the first time, preli minary error bounds are set to estimate the uncertainty of cloud optical de pth retrievals. These estimates can help us better understand the nature of uncertainties that three-dimensional effects can introduce into retrievals of this important product of the Moderate Resolution Imaging Spectroradiom eter instrument. The probability distribution of resulting retrieval errors is examined through theoretical simulations of shortwave cloud reflection for a set of cloud fields that represent the variability of stratocumulus c louds. The results are used to illustrate how retrieval uncertainties chang e with observable and known parameters, such as solar elevation or cloud br ightness. Furthermore, the results indicate that a tendency observed in an earlier study-clouds appearing thicker for oblique sun-is indeed caused by three-dimensional radiative effects.