Toward the Generation of 9 km Quasi-Global Microwave Land Surface Emissivity Map Using SMAP Radiometer and CYGNSS Reflectometer

This study introduces a method that combines Soil Moisture Active Passive (SMAP) radiometer and Cyclone Global Navigation Satellite System (CYGNSS) reflectometer to derive a 9 km quasi-global microwave land surface emissivity product. This algorithm aims to utilize CYGNSS reflectivity to capture spatial heterogeneity at 9 km scale, so as to create an emissivity product with a spatial resolution of 9 km and a temporal resolution of 2 days in the area of interest. The global results demonstrate the satisfactory performance of the SMAP/CYGNSS 9 km emissivity, with a median repeat period of 2.5 days for most mid-latitude regions and 4.7 days for all regions. Compared to the SMAP emissivity that has a native 36 km spatial resolution and a revisit time of 2-3 days, the daily SMAP/CYGNSS 9 km emissivity covers approximately 40% of the United States, increasing to 75% for a 3-day average emissivity.