High-Resolution Enhanced Product based on SMAP Active-Passive Approach and Sentinel 1A Radar Data

The SMAP active-passive soil moisture product (L2SMAP) was discontinued on July 7th, 2015 due to malfunction in the SMAP radar. The active-passive algorithm developed for the SMAP mission is also capable of working with different combinations of coarse resolution passive microwave (L-/C-band radiometer) and high-resolution active microwave (L-/C-band SAR) observations, provided they meet certain criteria. This feature of the microwave active-passive algorithm enables us to work on an Enhanced SMAP-Sentinel high-resolution soil moisture product. We used 2.5 months (April 20th, 2015 to July 7th, 2015) of SMAP L2SMAP product and compared with the SMAP-Sentinel combined product, the initial results show promise. To further investigate and develop the methodology and algorithm parameters, more Sentinel-1A data at a regular time series is desired. Such long time-series of Sentinel data at regular interval is only available on the European continent because unlike other parts of the world the Sentinel C-band SAR consistently observes most of the European countries. For further investigation, we selected a region of Spain to implement the SMAP-Sentinel active-passive algorithm for couple of reasons: 1) The vegetation of the regions is optimum (not very dense) to evaluate the algorithm performance; 2) A core calibration and validation (cal/val) site that contributed to the SMAP mission is also located in this region. From the study over this region in Spain, we will present the methodology to determine snapshot algorithm parameters and compare them with the parameters derived through statistical means, and characterization of errors propagation through the algorithm. Finally, we present the SMAP-Sentinel algorithm outputs and retrieved high-resolution (1 km and 3 km) soil moisture data validated against the core cal/val site in situ observations. This study helps to establish the Enhanced SMAP-Sentinel high-resolution soil moisture product and prepare for the operational implementation that will facilitate product release in the month of March, 2017.