Determining Stomatal Conductance and Transpiration from Remotely-Sensed Plant Parameters.

Remote sensing of plant canopy temperature has tremendous potential for estimating water and carbon fluxes in plants.  Data from continual plant monitoring, whether ground-based or aerial, can be used for estimations of plant water use and stress status.  Such data, thus, can allow for plant-based irrigation scheduling (timing and amount required), and yield estimations.  Currently, indirect determinations of plant water requirements from soil moisture content involve complex equipment and many steps.  We explored similar determinations from crop water stress index (CWSI) and its applicability under cloudy and windy conditions.  Calculating plant water needs from simple and direct plant monitoring methods of canopy temperature and ground cover may provide an effective additional alternative.  Here, we calculate canopy stomatal conductance (g_c) and transpiration with the Penman-Monteith (PM) procedure using weather and oblique-angled infrared thermometer (IRTs) data, and compare against g_c and transpiration determined from heat-balance type sap flow gages installed on field plants.  We also calculate plant canopy temperature using PM and weather data, and compare against IRT data.  Efforts verify ET calculations determined from PM against ET determined from plant measurements of sap flow.