In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
Passive microwave soil moisture evaluations by ground based measurements in Korea 
M. Choi®’*, Y-M. Hur a , H. Kim a T.-W. Kim b , J-H. Ahn c 
a Dept. of Civil and Environmental Engineering, Hanyang University, Seoul, 133-791, Korea - 
(mchoi, youml030, k4ecohydro)@hanyang.ac.kr 
b Dept, of Civil and Environmental Engineering, Hanyang University, Ansan, 426-791, Korea - 
twkim72@hanyang.ac.kr 
c Dept. of Civil Engineering, Seokyeong University, Seoul, 136-704, Korea - 
wrr@skuniv.ac.kr 
Technical Commission VH Symposium 2010 
KEY WORDS: Passive Microwave Sensors, AMSR-E, Soil Moisture, MODIS, NDVI, Korea 
ABSTRACT: 
Passive microwave sensors have many advantages including the ability to directly measured soil moisture at large spatial scales 
regardless of weather conditions or time of day. However, microwave-sensed soil moisture’s inevitable limitation is that it cannot 
describe hydrology at the watershed because its retrieved soil moisture scale is too large. Thus, microwave-sensed soil moisture 
requires validation. Even if there have been great developments for microwave-sensed soil moisture with validation efforts using 
ground based measurements and land surface models, the validations of the remotely sensed soil moisture in Korea are very limited. 
This study validated Advanced Microwave Scanning Radiometer E (AMSR-E) soil moisture productions with ground based 
measurements at eight sites from rural development administration in Korea. The relationship between AMSR-E soil moisture and 
Normalized Difference Vegetation Index (NDVI) retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) for 
estimating soil moisture is also investigated. Overall there was a reasonable agreement between the AMSR-E and ground data, but 
unreliable replication was found in winter season. More intensive validation efforts should be conducted with other AMSR-E soil 
moisture products with vegetation information. This type of estimation provides the utility of the AMSR-E soil moisture products 
and MODIS NDVI as an alternative of the ground based measurements and improves soil moisture retrieval algorithms. 
1. INTRODUCTION 
Fresh water recognized as abundant on our planet is now 
drastically becoming a scarce natural resource (Falkenmark and 
Rockstrom, 2004). The fresh water resources stress may be 
more deteriorated by increasing climate change and population 
growth scenarios in the world including East Asia (Milly et al, 
2005). To better understanding of fresh water availability linked 
between the land surface and the atmosphere, accurate 
estimation of the soil moisture is required even if its amount in 
water resources systems is relatively small. Soil moisture 
determines the partitioning of precipitation into runoff, 
infiltration, and surface storage, as well as the partitioning of 
incoming solar radiation and long wave radiation into outgoing 
long wave radiation, latent heat flux, ground heat flux, and 
sensible heat flux (Pachepsky et al., 2003). 
Recently, larger spatial scaled mean surface soil moisture is 
available from aircraft and satellite instruments comprised of 
various active and passive microwave sensors (Schmugge et al., 
2002). The brightness temperature (T B ) as intensity of natural 
thermal emission on the land surface was measured by these 
passive microwave sensors and surface soil moisture is 
successfully retrieved from the T B observations (Jackson et al., 
1995). Even if there are many advantages of monitoring soil 
moisture at larger scales including the ability to directly 
measurement soil moisture regardless of weather conditions or 
time of day (Jackson, 1993; Jackson and Schmugge, 1995), its 
inevitable limitations are existing. One of the major limitations 
is that it cannot describe hydrology at the watershed or field 
scale because its retrieved soil moisture scale is too large 
(Mohanty and Skaggs, 2001; Jacobs et al., 2004). Thus, 
retrieved soil moisture estimates require validation. 
Validation studies for the AMSR-E soil moisture products have 
been conducted over different continents, Europe (Wagner et al., 
2007), the United States (McCabe et al., 2005; Crow and Zhan, 
2007; Owe et al., 2008; Choi et al., 2008), and Australia (Drape 
et al., 2009). Even if AMSR-E evaluation efforts in many 
regions around the world to estimate the potential of the 
AMSR-E surface soil moisture, there have not been any 
evaluation efforts in Korea. This study was conducted for the 
initial evaluation of the AMSR-E soil moisture products in 
Korea. We used land parameter retrieval model products by 
NASA and Vrije Universiteit Amsterdam (VUA), the 
Netherlands following Owe et al. (2001) using ground based 
measurements at Korean monitoring network sites. 
2. MATERIALS AND METHODS 
2.1 Study Region and Ground Data 
In order to validate AMSR-E retrieved soil moisture, ground 
measured data were obtained from 60 sites with Time Domain 
Reflectometry (TDR) in 10 cm depth from rural development 
administration in Korea (http://weather.rda.go.kr). Data from 
eight sites among the sixty sites were selected (Figure 1). 
Dept, of Civil and Environmental Engineering, Hanyang University, Seoul, 133-791, Korea - mchoi@hanyang.ac.kr