- Conference date: 3–8 August 2008
- Location: Foz do Iguaçu (Brazil)
Estimating the aerosol optical depth (AOD) in the vicinity of clouds is a long‐standing problem. A few recent studies have provided important demonstration of how three‐dimensional (3D) effects can increase substantially the clear sky reflectance and, therefore, lead to significant overestimation (up to 140%) of AOD. We first assess the importance of the 3D cloud effects on the reflectance ratios for pixels located far away from clouds and their shadows (clear pixels) and show that for clear pixels the reflectance ratios for two pairs of wavelengths (660, 470 nm and 870, 470 nm) are less sensitive to the 3D cloud effects than the reflectances themselves. We also propose an approach for converting reflectance ratios to the AOD for the clear pixels. Finally, we use Monte Carlo radiative transfer calculations and 3D fields of cumulus clouds and aerosol generated by a large eddy simulation (LES) model to illustrate the performance of the retrieval with the model‐output inverse problem. Results of the model‐inverse problem suggest that the ratio method has capability to (i) detect clear pixels outside of cloud shadows and (ii) estimate AOD for the majority of them quite accurately
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