Utility of Thermal Remote Sensing for Evapotranspiration Estimation of Vineyards

Given the limited water availability in much of California, particularly the Central Valley where many of the crops are grown, improvements in water management of irrigated croplands is desperately needed. This requires the development of tools and technologies for monitoring water use and improving irrigation efficiency at both the field and regional scale. California growers devote significant acreage to the cultivation of orchard crops, particularly vineyards. Unique to orchards and vineyards is the canopy architecture and row spacing. The architecture of wine-grape vineyards is characterized by tall plants (∼2 m) with most of the biomass in the upper one-half to one-third of the plant and widely spaced rows (∼4 m). This wide row spacing and canopy architecture, facilitating sunlight interception, air flow, and field operations, results in two distinct management zones: the vines and the inter-row. Moreover, the inter-row often has a cover crop which complicates the treatment of these two management zones. Any water management tool/technique for vineyards must consider how these two systems interact and affect water and energy exchange. To develop a multi-scale operational system for monitoring vineyard water use and vine plant and inter-row stress and moisture conditions necessitates the use of remote sensing and a land surface model that captures the micro and macro-scale exchanges between the vine plant, inter-row and atmospheric boundary layer exchange of momentum, water and energy fluxes. Such a remote-sensing-based modeling system has been developed called the Atmospheric Land EXchange Inverse (ALEXI) model together with a Disaggregation module (DisALEXI) for using high resolution thermal remote sensing data. The ALEXI/DisALEXI modeling system has been applied and tested over a wide variety of landscapes and found to be robust. An experiment conducted at vineyard sites in California will be described where ground validation data of water and energy fluxes, soil moisture and biophysical properties were collected during different vine phenological stages along with high resolution aircraft imagery for discriminating inter-row and vine cover and thermal temperatures. A description of the experiment and initial results applying the thermal-based model with satellite and airborne data will be presented. In particular, the capability of the land surface scheme to quantify vine plant and inter-row water and energy fluxes for the unique vineyard architecture will be discussed.