|Kustas, William - Bill|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2009
Publication Date: 3/16/2009
Citation: Agam, N., Ben-Gal, A., Kustas, W.P., Cohen, Y., Anderson, M.C., Elchanatis, V., Dag, A., Yermiyahu, U. 2009. Thermal remote sensing of crop water status: pros and cons of two different approaches [abstract]. The Dahli Greidinger International Symposium-2009 Crop Production in the 21st Century: Global Climate Change, Environmental Risks and Water Scarcity. 2009 CDROM. Interpretive Summary:
Technical Abstract: Recent climate change has lead, in many places around the world, to a decrease in the availability of water resources. This limited water availability is decreasing the cost-effectiveness of irrigated agricultural crops, and practices reducing the required amount of water without decreasing the quantity and/or quality of the yield are desirable. Routine monitoring of crop water status may provide useful information allowing growers to irrigate only when and where needed and conserve water. Continuously growing availability of airborne and spaceborne data has led to development of various methods utilizing thermal remote sensing to detecting and monitoring water status in agricultural crops. In large, these methods can be divided into two main approaches. The first approach, being used since the 1960s, is based on the understanding that canopy temperature is indicative of crop water status. Generally, the canopy temperature is normalized to upper and lower bounds, representing non-transpiring and fully transpiring leaves, respectively, forming the crop water stress index (CWSI). The normalization allows comparing the CWSI under different environmental conditions. This approach is simple to apply and requires fewer inputs, but necessitates thermal images at high spatial resolution, since the remotely sensed temperature must represent the canopy only, extracted from the surrounding soil. Such high resolution thermal images are not routinely available to date. The second approach is based on more complex physical models, of which the prime input is thermal images. Numerous models have been developed, which can be further divided into two main categories. The first is based on the "big leaf" theory, according to which the land surface is assumed homogeneous and is treated as a whole. In the second category are the Two-Source models, which relate to the vegetation and the soil separately. The physical models in general and the Two-Source models particularly require more inputs than the CWSI approach, but can utilize thermal images at a coarser spatial resolution. Such imagery is regularly available from several satellite systems.A discussion of the pros and cons of each of the two approaches will follow a brief description of their principles and utility.