Schaap, M, Timmermans, RMA, Koelemeijer, RBA, de Leeuw, G, Builtjes, PJH (2008). Evaluation of MODIS aerosol optical thickness over Europe using sun photometer observations. ATMOSPHERIC ENVIRONMENT, 42(9), 2187-2197.
Satellite retrieved aerosol optical thickness (AOT) may be useful to improve the insight in PM distributions in Europe in combination with models and ground-based measurements. To use AOT in mapping or assimilation experiments, it requires well-validated satellite data. We have compared the AOT retrieved by MOMS (collection 4) to sun photometer data from the AERONET network in Europe and found a good temporal correlation between MODIS and AERONET. However, we also found a large positive bias of about 50% in the MODIS AOT data, which is in accordance with earlier findings. We highlight the strong seasonal signature in the overestimation of AOT by MODIS with a maximum during summer. After correction for the bias, the accuracy of MODIS AOT retrievals agrees with reported uncertainties and the residuals show a normal distribution. We have introduced a simple method for the evaluation of the possible extent of cloud contamination and hypothesise that on average, up to one-third of the MODIS retrievals may be cloud contaminated. For some stations in central Europe, this percentage was found to be larger than > 50%. The consequences of a bias between satellite and in situ data for their use in the mapping of aerosol levels are discussed. (c) 2007 Elsevier Ltd. All rights reserved.