The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform
Frederick C Meinzer - One of the best experts on this subject based on the ideXlab platform.
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regulation of transpiration in field grown sugarcane evaluation of the stomatal response to humidity with the bowen ratio technique
Agricultural and Forest Meteorology, 1991Co-Authors: David A Grantz, Frederick C MeinzerAbstract:Abstract Parallel time courses of net radiation, canopy conductance and evapotranspiration in a sugarcane canopy demonstrate the interaction of environmental and physiological factors in regulating water loss. The Bowen ratio-energy balance technique was used to evaluate the stomatal response to humidity in the absence of potential artifacts associated with porometer and leaf chamber measurements. Canopy conductance ( g c ) responded to leaf-air vapor pressure difference ( V ), supporting the validity of available physiological data showing clear stomatal responses to V in Porometers and leaf chambers. Several factors were found to obscure the stomatal response to V under field conditions. The stomatal closing stimulus, V , and the opening stimulus, photon flux density ( I ), were positively correlated. This caused offsetting stomatal responses to V and I , which reduced the net stomatal response when V changed with radiation-driven changes in leaf temperature. Normalization of g c by I revealed the expected hyperbolic decline of g c with increasing V . Low boundary layer conductance attenuated V imposed at the leaf surface relative to V measured with reference to humidity in the bulk atmosphere. This reduced the stimulus for stomatal response to V , below that indicated by agrometeorological measurements. Use of air saturation deficit ( D ) rather than V to express evaporative demand overestimates V , minimizing apparent stomatal sensitivity to evaporative demand, when leaves are cooler than the air. These factors may result in small stomatal responses to V that escape detection by indirect measures of stomatal movement, such as those based on the temperature of exposed leaves.
David A Grantz - One of the best experts on this subject based on the ideXlab platform.
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regulation of transpiration in field grown sugarcane evaluation of the stomatal response to humidity with the bowen ratio technique
Agricultural and Forest Meteorology, 1991Co-Authors: David A Grantz, Frederick C MeinzerAbstract:Abstract Parallel time courses of net radiation, canopy conductance and evapotranspiration in a sugarcane canopy demonstrate the interaction of environmental and physiological factors in regulating water loss. The Bowen ratio-energy balance technique was used to evaluate the stomatal response to humidity in the absence of potential artifacts associated with porometer and leaf chamber measurements. Canopy conductance ( g c ) responded to leaf-air vapor pressure difference ( V ), supporting the validity of available physiological data showing clear stomatal responses to V in Porometers and leaf chambers. Several factors were found to obscure the stomatal response to V under field conditions. The stomatal closing stimulus, V , and the opening stimulus, photon flux density ( I ), were positively correlated. This caused offsetting stomatal responses to V and I , which reduced the net stomatal response when V changed with radiation-driven changes in leaf temperature. Normalization of g c by I revealed the expected hyperbolic decline of g c with increasing V . Low boundary layer conductance attenuated V imposed at the leaf surface relative to V measured with reference to humidity in the bulk atmosphere. This reduced the stimulus for stomatal response to V , below that indicated by agrometeorological measurements. Use of air saturation deficit ( D ) rather than V to express evaporative demand overestimates V , minimizing apparent stomatal sensitivity to evaporative demand, when leaves are cooler than the air. These factors may result in small stomatal responses to V that escape detection by indirect measures of stomatal movement, such as those based on the temperature of exposed leaves.
P.j. Mcgruddy - One of the best experts on this subject based on the ideXlab platform.
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A circuit for a self-timing stomatal diffusion porometer
Agricultural Meteorology, 2003Co-Authors: P. Kenny, P.j. McgruddyAbstract:Abstract Current stomatal diffusion Porometers generally involve the measurement with a stopwatch of the time taken for the cup humidity to increase from one given value to another while the cup is clamped on a leaf. The necessity of closely observing the meter movement while simultaneously holding the porometer head and circuit box, operating the stopwatch and shading the leaf leads to a degree of operator inconvenience. A circuit has been developed which automatically records this time on a digital counter and allows wide adjustment of the humidity range scanned. Facilities for measuring leaf and cup temperature and their difference have also been incorporated. The instrument is battery operated and portable.
Robert J. Reginato - One of the best experts on this subject based on the ideXlab platform.
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Remote estimation of leaf transpiration rate and stomatal resistance based on infrared thermometry
Agricultural and Forest Meteorology, 1990Co-Authors: Yoshio Inoue, Bruce A. Kimball, Ray D. Jackson, Paul J. Pinter, Robert J. ReginatoAbstract:A remote method was developed for monitoring leaf transpiration rate and stomatal resistance on a realtime base. The method utilizes leaf temperatures measured with an infrared radiometer as integral inputs for a model to compute those parameters. The model is based on the energy balance of a plant leaf, accounting for moisture transfer processes in the stomata and boundary layer. Remotely determined transpiration rates and stomatal resistances were compared with those measured with a steady state porometer. The corresponding values obtained from the two methods were linearly related (r=0.79∗∗ and 0.93∗∗ for transpiration and stomatal resistance, respectively); but the porometer transpiration rates were somewhat higher than those obtained by the “remote” method, probably because the air in the porometer cuvette was drier than the ambient air. On the other hand, the stomatal-resistance values from the two methods fell on the 1:1 line with a high correlation coefficient, suggesting that the “remote” method produces excellent estimates of actual stomatal resistance.
Hamza A Cessur - One of the best experts on this subject based on the ideXlab platform.
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Temperature calibration
Materials Today, 2002Co-Authors: Hamza A CessurAbstract:Calibration sources are infrared ra-diators with fixed or adjustable temperatures, which are used for the calibration or verification of the correct temperature indication of pyrometers, thermal imaging sys-tems, heatflux measurement systems or spectrographic analysis systems. Depending on the model of the cali-bration source, single temperature points or temperature curves of an infrared measurement device can be monitored and recorded. LumaSense Technologies, Inc. supplies a unique selection of very precise cali-bration sources that are traceable to national standards. LumaSense black-bodies are superior because of the emissivity values, homogeneous emis-sion areas and a wide range of differ-ent sized apertures to adapt to the desired target area. In addition, fast heat up times and high temperature stability are guaranteed. The quality of our calibration sources is guaranteed by tests, burn-in times, and pyrometric calibrations. If possi-ble, a certificate is provided to docu-ment the traceability to the interna-tional temperature scale ITS90. Highly accurate calibration equipment for pyrometers, thermal imaging cameras, radiometers, heatflux and spectrographic measurement sytems.