Estimation of Root-zone Soil Moisture Using Modis-derived Ndvi in Semiarid and Humid Conditions

In semiarid or arid conditions, the change of root-zone soil moisture can be almost instantaneously reflected by vegetation through biophysical process. This study investigated feasibility of mapping root-zone soil moisture using MODIS-derived NDVI via statistic approach at three sites (New Mexico, Arizona, and Texas) selected from the Soil Climate Analysis Network (SCAN). These three sites represent two types of vegetation (shrub and grass) and two types of climate conditions: semi-arid (New Mexico and Arizona) and humid (Texas). Collocated time series of soil moistures at 5 depths (5, 10, 20, 50, and 100 cm) and NDVI (8-day composite in 250 m resolution) during February 2000 through December 2004 were used. Results show that (1) During the growing season, root-zone soil moisture can be effectively estimated by a bivariate linear regression model using deseasonalized NDVI; (2) In semi-arid region, root-zone soil moisture can be better estimated using NDVI in shrub-vegetated area than in grass-vegetated area; (3) The performance of the estimation of soil moisture using NDVI in grass vegetation at the semiarid site in NM and at the humid site in TX does not display observable difference.