资源环境科技发展态势分析平台

Three years of measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on Aqua satellite has been used to develop a new approach to quantify the well-known, yet unresolved zonal bias in MODIS LWP of marine clouds. This new method utilizes two parameters: the solar zenith angle and cloud heterogeneity index, both of which are available for each MODIS pixel. Comparisons with collocated satellite and ground-based microwave measurements in carefully screened clouds shows that this new approach can effectively remove this large first order MODIS LWP bias. Applying this new approach to MODIS pixel level data collocated along the CloudSat footprint suggests annually averaged MODIS LWP overestimation gradually increases at higher latitudes and can reach over 50 g/m² at latitudes greater than around 50⁰. This overestimation can exceed 100 g/m² for seasonal or monthly averages. MODIS LWP measurements were also reprocessed over land and snow/ice regions by eliminating data points with optical depth of 150, which indicates significant 3D bias. This reduces the average LWP by over 100 g/m² in polar regions. The new and improved MODIS LWP dataset can be used to study related cloud processes and to constrain model simulations, especially in polar regions where observational dataset is limited and contain large uncertainties.