Assessment of SMAP and AMSR2 freeze/thaw products over Russia using in situ measurements

Abstract

ABSTRACT Recently, many freeze/thaw (FT) products have been developed using spaceborne microwave measurements. In this letter, we compared the newest FT products, SMAP36 (36 km resolution) and SMAP09 (9 km resolution) provided by the Soil Moisture Active Passive (SMAP) mission and one product, AMSR2 FT, generated by the Advanced Microwave Scanning Radiometer 2 (AMSR2) against surface soil temperature measurements across Russia using a total of 494 stations. The results indicate that AMSR2 FT has a better performance in Russia than the SMAP products, which is more pronounced in the AM (descending orbit) value of overall accuracy (OA) than in the PM (ascending orbit). It is challenging to distinguish FT states in the transition periods between warm and cold seasons, but AMSR2 FT performs better than SMAP products. AMSR2 FT has a high OA in inland areas but a low OA along coastal zones because pixels may contain a water body or lake ice. The poorest SMAP results are mainly distributed in mixed forest areas, indicating that the algorithm should be improved to solve the wet snow problem in these areas. The results of this study could help improve FT products in Russia and provide application instructions for FT product users.