Validation Study of Active Microwave Soil Moisture Products in Korea and Brazil

Abstract

Soil moisture is a key component of the hydrology meteorology, climatology, and agriculture management in terms of interaction between land surface and atmosphere. Understanding energy and water cycles processes is needed to accurately monitor spatial and temporal variability of soil moisture. In this study, we conducted validation study of active microwave satellite soil moisture data by comparing and evaluating with in-situ soil moisture measured from South Korea and Brazil. The satellite data are derived from the advanced Scatterometer (ASCAT) on board the Metop (VV polarization C-band to 5.255 GHz) satellite, called as Soil Water Index (SWI). We will focus on growing season from May through September in 2012, to avoid any effect on soil moisture data quality due to the severe wintry weather. The comparison results of this validation task were expressed in three statistical values: Correlation coefficient (R), Bias and Root Mean Square Error (RMSE). The results showed that the ASCAT SWI products have reliable agreements with ground measurements in Korea and Brazil. Thus, the lack of data on soil moisture for the Brazilian territory, with the level of accuracy and the geographic extent necessary for studies on a regional scale, limited understanding of the interaction between soil moisture and the atmosphere. On the other hand, even South Korea is a country of smaller dimensions they have a range of 50 sampling stations of in-situ measurements. Therefore, it is possible to do the validation of remote sensing data with an unquestionable quality, even if this study we will only be 5 stations with the highest values of correlation coefficient. In this paper, the main purpose is to assess the accuracy of soil moisture estimates from the ASCAT sensor comparing them with in-situ data for two different regions. Therefore, a recursive exponential filter formulation which allows to estimate the SWI (Soil Water Index) from intermittent SSM measurements (8) is used to compare the quality of the data between Brazil and South Korea.