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Title: Comparison of vegetation water contents derived from shortwave-infrared and passive-microwave sensors over central Iowa

item Hunt Jr, Earle
item LI, LI - Naval Research Laboratory
item M, TUGRUL - George Mason University
item Jackson, Thomas

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2011
Publication Date: 6/21/2011
Citation: Hunt, E.R., Li, L., M, T.Y., Jackson, T.J. 2011. Comparison of vegetation water contents derived from shortwave-infrared and passive-microwave sensors over central Iowa. Remote Sensing of Environment. 115:2376-2383.

Interpretive Summary: Polar-orbiting environmental satellites obtain daily data with visible, near-infrared and shortwave infrared bands. The shortwave infrared bands are sensitive to the liquid water content in the vegetation canopy. Using relationships between leaf and stem mass, estimates of canopy water content can be used to infer total vegetation water content. Passive microwave satellites are used to determine soil moisture content and are also sensitive to liquid water in the vegetation. We compare vegetation water contents estimated by the MODIS sensor on board the NASA Terra satellite and the microwave sensor on the WindSat satellite over corn and soybean in central Iowa. The two estimates were highly correlated, but the WindSat estimate of vegetation water content was about two times higher than the MODIS estimate. This error biases the WindSat estimates of soil moisture content. Therefore, using MODIS and other polar-orbiting satellite data will improve retrievals of soil moisture content.

Technical Abstract: Retrieval of soil moisture content from microwave sensors also returns an estimate of vegetation water content. Land cover classifications and remotely sensed indices based on liquid water absorption features can be used to estimate canopy water content. The normalized difference infrared index (NDII) was linearly related to canopy water content. During the Soil Moisture Experiments 2002 and 2005 in central Iowa, allometric relationships were found between canopy water content and vegetation water content for corn and soybean. We compared independent estimates of vegetation water content from WindSat retrievals and MODIS NDII over central Iowa from 2003 to 2005. There was a strong linear relationship between the MODIS and WindSat estimates of vegetation water content. These results indicate that soil moisture retrievals from microwave sensors may be more accurate with canopy water content and land cover classifications from optical sensors.