Developing Daily Cloud-Free Snow Composite Products From MODIS Terra–Aqua and IMS for the Tibetan Plateau

Daily snow cover mapping is difficult when Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products are cloud obscured. The daily cloud-free snow cover product provides an essential parameter for hydrological modeling, climate system studies, and snow-caused disaster monitoring on the Tibetan Plateau (TP). In this paper, we present an algorithm, Terra-Aqua-IMS (TAI), which combines MODIS Terra and Aqua (500 m) and the Interactive Multisensor Snow and Ice Mapping System (IMS; 4 km) to produce a daily cloud-free snow cover product (500 m). The overall accuracy of the new TAI over the TP is 94% as compared with ground stations in all-sky conditions; this value is significantly higher than the 64% of the blended MODIS Terra-Aqua product and the 55% and 50% of the original MODIS Terra and Aqua products, respectively. Without the IMS, the daily combination of MODIS Terra-Aqua can only remove limited cloud contamination: 37.3% of the annual mean cloud coverage compared with 46.6% (MODIS Terra) and 55.1% (MODIS Aqua). The resulting annual mean snow cover over the TP from the daily TAI data is 19.1%, which is much larger than the 4.7%-8.1% from the daily original MODIS Terra/Aqua and the blended Terra-Aqua snow product due to cloud blockage.