Scaling Vegetation Water Content from Thematic Mapper to MODIS During SMEX04

Vegetation water content (VWC) is important for accurate retrievals of soil moisture using microwave sensors and may be important for determining water stress and forest fire potential. The MODerate resolution Imaging Spectroradiometer (MODIS) and future operational sensors have bands in the shortwave infrared region which can be used for monitoring VWC. The Soil Moisture Experiments 2004 (SMEX04) were conducted during the summer-monsoon season in Arizona, USA, and Sonora, Mexico, as part of the North American Monsoon Experiment. Plots from different vegetation types were sampled for leaf area index and leaf equivalent water thickness. Landsat 5 Thematic Mapper (TM) and MODIS imagery were acquired for three dates, before, during and after the SMEX04 experiment. The Normalized Difference Infrared Index [NDII = (R₈₅₀ - R₁₆₅₀)/(R₈₅₀ + R₁₆₅₀)] was linearly related to canopy equivalent water thickness for the Landsat 5 TM data. The TM-estimated canopy equivalent water thickness were aggregated and linearly related to canopy equivalent water thickness from MODIS, showing that MODIS and future sensors would be useful in estimating vegetation water content.