The Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX): a multidisciplinary project to develop a robust remote sensing-based ET modeling tool for vineyards

Authors: Kustas, William - Bill

Submitted to: International Conference on Dryland Development
Publication Type: Abstract Only
Publication Acceptance Date: 3/26/2018
Publication Date: 11/6/2017
Citation: Kustas, W.P. 2017. The Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX): a multidisciplinary project to develop a robust remote sensing-based ET modeling tool for vineyards. International Conference on Dryland Development. P.84

Interpretive Summary:

Technical Abstract: The recent drought in much of California, particularly in the Central Valley region, has caused severe reduction in water reservoir levels and a major depletion of ground water by agriculture. Dramatic improvements in water and irrigation management practices are critical for agriculture to remain sustainable in this semi-arid region. This necessitates the development of tools and technologies for monitoring water use and plant stress at both the field and regional scale. California growers devote significant acreage to the cultivation of orchard crops and vineyards, at over 3 million acres, with much of it irrigated. These crop types share a unique canopy structure and row spacing. The architecture of wine-grape vineyards is characterized by widely spaced rows (~3 m) and tall plants (~2 m) with most of the biomass concentrated in the upper one-third to one-half of the plant. This wide row spacing and canopy architecture facilitates sunlight interception, air flow, and field operations and results in two distinct management zones: the vines and the interrow. Often, the treatment of these two management zones is further complicated by a cover crop grown in the inter-row. To reliably estimate evapotranspiration (ET) from the vine and interrow systems, a better understanding of the micro and macro-scale exchanges between the vine, interrow and atmospheric boundary layer is needed. Moreover, to monitor ET and plant stress of vineyards (and orchards) at field to regional scales operationally will require a remote-sensing-based modeling system having the capabilities to separate ET contributions from the row and interrow zones. Such a remote sensing-based modeling system exists and is called the Atmospheric Land EXchange Inverse (ALEXI) model along with a Disaggregation module (DisALEXI) allowing multiscale assessments of ET and plant stress. The ALEXI/DisALEXI land surface scheme is based on the Two-Source Energy Balance (TSEB) formulation that addresses the key factors affecting the convective and radiative exchange within the soil/substrate–plant canopy–atmosphere system. The GRAPEX project conducted at vineyard sites in California since 2013 has involved the collection of ground validation data centered on Landsat overpasses under a full range of environmental conditions and vine phenological stages. These data include in-situ measurements of the water and energy fluxes, meteorological conditions, soil moisture, and biophysical properties along with high resolution airborne imagery for determining inter-row and vine cover fractions and thermal temperatures. A description of the measurements during the field campaigns and some initial results of modeling vine plant and interrow ET and energy fluxes applying both the TSEB with local/airborne remote sensing data and ALEXI/DisALEXI with satellite observations will be presented. Issues in both in the measurement and modeling of fluxes caused by the unique vineyard architecture will also be discussed.