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Based on 183 groups of in situ data measured with a spectroradiometer during 2003-2007 in the Bohai Sea, we calculated the atmospheric direct transmittance T, diffuse transmittance t, Ångstrom exponent α and turbidity coefficient β of aerosol optical thickness, and aerosol multiple forward scattering factor Ba. An empirical formula relating Ba with the two Ångstrom parameters, α and β, is established. The determination coefficient between aerosol multiple forward scattering factors, Ba, estimated by using the above empirical formula and those measured by using an instrument is 0.85. Based on the formula, a new algorithm for the retrieval of atmospheric diffuse transmittance in Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric correction, instead of the MODIS standard algorithm, is proposed. Tests of the algorithms with in situ observations show that the MODIS standard algorithm leads to evident overestimation of diffuse transmittance, while the new algorithm contributes to a notable improvement in accuracy, especially for cases where the value of diffuse transmittance is small. The relative error and rms. error of the new algorithm are merely about a third and a quarter of those obtained by the MODIS standard algorithm, respectively. The new algorithm gives an estimation of t that matches very well with in situ observations in the Bohai Sea. The proposed algorithm can be utilized in MODIS atmospheric correction as an alternative algorithm, which may improve the accuracy of MODIS atmospheric correction in the Bohai Sea and other near-shore areas with large aerosol optical thickness. [ABSTRACT FROM AUTHOR]