Evaluation of surface albedo from GEWEX-SRB and ISCCP-FD data against validated MODIS product over the Tibetan Plateau

摘要

This paper presents a scheme to examine the accuracy of albedos used in two operational satellite-based radiation data sets over the Tibetan Plateau (TP): the Global Energy and Water Cycle Experiment-Surface Radiation Budget (GEWEX-SRB) and the International Satellite Cloud Climatology Project-Flux Data (ISCCP-FD). First, albedo observations at six sites are used to validate the Moderate Resolution Imaging Spectroradiometer (MODIS) 16 day albedo product with a 500 m spatial resolution. It is shown that both the MODIS black-sky and white-sky albedo products are comparable to the in situ measurements made during snow-free periods. Then, the MODIS 500 m albedos are taken as the ground truth, aggregated to the coarse-resolution grid cells, and compared with the GEWEX-SRB and ISCCP-FD albedo values. The results indicate that both data sets have negative biases in the central and western TP and large positive biases in the southeastern glaciated region. It is recommended that the MODIS albedo product be applied as the input in producing the GEWEX-SRB and ISCCP-FD data sets, at least when processing summer data over the TP. However, the MODIS albedo algorithm needs to be improved to take the effect of snow into consideration when the snow duration is much shorter than the MODIS 16 day inversion window.