Remote Sensing of Canopy Water Content During SMEX'04 and SMEX'05 Using Shortwave-Infrared Reflectances

The Soil Moisture Experiments in 2004 and 2005 were conducted to validate algorithms for soil moisture retrievals. One of the key parameters for determination of soil moisture from microwave sensors is the vegetation water content of canopy and stems. We tested if canopy water content could be determined from reflectances in the shortwave-infrared and if the amount of canopy water content was related to the total vegetation water content by allometric equations. The normalized difference infrared index (NDII) was linearly related to canopy water content for all plants up to an equivalent water thickness of 1.0 mm. The biggest factor affecting the estimation of canopy water content was the soil background reflectance. For corn and soybean canopy equivalent water thickness were linearly related to total vegetation water content. However, there may be a separate allometric equation required for each vegetation type.