In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
Q 26 50 100 150 200 
Figure 1. Study region 
2.2 AMSR-E 
The AMSR-E instrument provides global microwave 
measurements using different bands (56 km for the C band, 38 
km for the X band, and 12 km for the Ka band) over two passes: 
ascending (1:30 pm) and descending (1:30 am). The Vrije 
Universiteit Amsterdam (VUA) AMSR-E soil moisture 
products are retrieved from the Land Surface Parameter Model 
(LPRM) (Owe et al., 2008). The model is based on a three- 
parameter forward retrieval procedure which uses one dual 
polarized channel (e.g., C or X band) to optimize soil moisture 
and Vegetation Water Content (VWC) (Owe et al., 2008). Land 
surface temperature is derived from the vertical polarized Ka 
band (e.g., 36.5 GHz). The LPRM parameterizes vegetation 
optical depth using Polarization ratios, Microwave Polarization 
Difference Index (MPDI) described as 
MPDI = (T br -T bH )l(J br +T iH ) (1) 
where Tbv and T bH are the brightness temperature at vertical and 
horizontal polarizations, respectively. 
2.3 MODIS-NDVI 
Terrestrial vegetation greatly influences on the energy balance, 
hydrologic and biogeochemical cycle on earth. Vegetation can 
also serve as an indicator of anthropogenic influences on the 
environment (Huete et al., 1999). Vegetation Index (VI) was 
developed to understand the roles of vegetation as a contributor 
to maintain biophysical systems and as an indicator of global 
environmental change (Huete et al., 1999). Many Vis have been 
developed, and most of them are expressed as the relationship 
between light reflection in the red and near infrared (NIR) 
section of the spectrum to separate the landscape into water, 
soil, and vegetation (Glenn et al., 2008). Normalized Difference 
Vegetation Index (NDVI), one of the most common among 
those Vis, was developed by Rouse et al. (1974). There is a 
global record of NDVI data since 1981 from Advance Very 
High Resolution Radiometer (AVHRR) mounted on the 
National Oceanic and Atmospheric Administration (NOAA) 
satellites. This AVHRR-NDVI is currently inter-calibrated with 
NDVI data from the Moderate Resolution Imaging 
Spectroradiometer (MODIS) on the terra and aqua satellites 
(Glenn et al., 2008). NDVI can be described as (Glenn et al., 
2008): 
NDVI = (pNIR- pRed) / ( pNIR+ pRed) 
where pNIR and pRed are reflectance values of Near Infrared 
and Red light received at the sensors. Recently, Several 
researchsers investigated the potential use of MODIS-driven 
NDVI to estimate soil moisture with some success (i.e., Schnur 
et al., 2010). Based on their suggestions, we tested this 
possibility of MODIS-NDVI for estimating soil moisture at the 
eight selected sites in Korea. MYD13A2 product from Aqua 
satellite with 1km-16 day of spatio-temporal scale was used in 
this study. 
3. EVALUATION 
In this study, we validated the AMSR-E products from land 
parameter retrieval model products by National Aeronautics and 
Space Administration (NASA) and Vrije Universiteit 
Amsterdam (VUA), the Netherlands for ground measurements 
from selected Korean monitoring network sites during 2004 
study period. The relationship between AMSR-E and MODIS 
NDVI was also tested.The ground based measurements were 
extracted at Aqua overpass time: 1:30 pm EST to match the 
time of the AMSR-E soil moisture products. Figure 2 shows 
that there were reasonable temporal patterns respond with 
precipitation events (not shown here). 
Overall, VUA AMSR-E soil moisture and MODIS NDVI 
showed the reasonable agreement with ground based 
measurements (RMSE = 8-26% and BIAS = 0-24%) (Table 1). 
However, we found that AMSR-E soil moisture products 
showed relatively higher temporal variability. These patterns 
may likely due to vegetation transmissivity as a function of the 
vegetation optical depth. The vegetation tramsmissivity was 
very uncertain in densely vegetated areas because microwave 
polarization difference indices became very small (Owe et al., 
2001). 
y: AMSR-E soil moisture, x: ground based soil moisture 
Equation 
R 2 
BIAS 
RMSE 
Chuncheon 
y= 1.1523X+10.092 
0.2031 
-22 
26 
Pyeongchang 
y=0.4145x+37.016 
0.0436 
-24 
26 
Bonghwa 
y=-0.1505x+42.148 
0.0032 
-16 
20 
Sangju 
y=0.1059x+31.446 
0.0215 
12 
17 
Andong 
y=0.5569x+22.383 
0.0869 
-8 
11 
Cheongsong 
y=0.7131x+19.841 
0.1195 
-14 
16 
Nonsan 
y=0.0473x+36.457 
0.0019 
0 
8 
Cheongju 
y=0.326x+25.816 
0.0996 
2 
10 
Table 1. A comparison of the ground based soil moisture with 
AMSR-E soil moisture