The Experts below are selected from a list of 984 Experts worldwide ranked by ideXlab platform
Theresa K Olson - One of the best experts on this subject based on the ideXlab platform.
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estimating variation in surface emissivities of intertidal macroalgae using an infrared thermometer and the effects on temperature measurements
Marine Biology, 2014Co-Authors: Kathryn L Van Alstyne, Theresa K OlsonAbstract:Accurate measurements of surface temperatures with an infrared (IR) thermometer require input of the emissivities of the surfaces being measured; however, few determinations of the emissivities of intertidal organisms’ surfaces have been made. Emissivities of intertidal macroalgae were measured to determine whether algal species, measurement angle, hydration, and layering affected them. Emissivities were similar and averaged 0.94 among 11 of 13 species. The species with lower and more variable emissivities (Chondracanthus exasperatus and Desmarestia viridis) differed in morphology from the other species, which were relatively flat thin blades with little surface texture. Measurement angle caused emissivities to decrease significantly in Mazzaella splendens but not in three other species. Hydration and layering of Ulva lactuca also had no effect. At 22 °C, measured temperatures were within 1 °C of actual temperatures when thermometer emissivity settings ranged from 0.75 to 1.00. When emissivities were set lower than actual values, measured temperatures were lower than actual temperatures at 15 °C and higher than actual temperatures at 60 °C. When the IR thermometer was used to measure surface temperatures of nine species of intertidal algae immediately before they were inundated by the incoming tide, temperatures were higher in mid intertidal than low intertidal individuals and higher on a sunnier Day than an Overcast Day. Temperatures of U. lactuca increased with increasing height on the shore, but temperatures of Ulvaria obscura did not. Temperatures were also higher in Fucus distichus blades than receptacles, and lower in U. lactuca and M. splendens occurring in the lower layers of stacks of algae.
F. Matejka - One of the best experts on this subject based on the ideXlab platform.
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Predicting the effects of soil water content and soil water potential on transpiration of maize
Agricultural Water Management, 2005Co-Authors: V. Novak, T. Hurtalova, F. MatejkaAbstract:Abstract An improved steady-state soil–vegetation–atmosphere transfer model was applied to three types of soils (loess, loamy soil, and sandy soil) and three typical daily meteorological conditions (a sunny Day, a cloudy Day, and an Overcast Day) to calculate the relationships between maize transpiration rates and an average soil water content or soil water potential. The model proposed can simulate the soil–plant–atmosphere continuum allowing to express soil, plant and atmospheric properties in detail, and thus, calculate the relationship between transpiration rate and average soil water content or soil water potential in the root zone. Atmospheric factors strongly affected the ratio between the actual and potential transpiration (relative transpiration) in conditions of the water stress. On the other hand, when the soil water content was sufficiently high, the relative transpiration was practically independent of atmospheric factors. The simulated relationships between transpiration of maize, soil water content and soil water potential were found to be in a good agreement with measured data.
Paul Berbigier - One of the best experts on this subject based on the ideXlab platform.
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Comparison of two methods for estimating the evaporation of a Pinus pinaster (Ait.) stand: sap flow and energy balance with sensible heat flux measurements by an eddy covariance method
Agricultural and Forest Meteorology, 1991Co-Authors: A Diawara, Denis Loustau, Paul BerbigierAbstract:A method combining sensible heat flux measurement based on temperature and vertical wind speed fluctuations, and energy balance, was used to estimate evaporation above the canopy and the understorey of a Pinus pinaster (Ait.) stand in Les Landes forest. The problems of the horizontal homogeneity of net radiation and sensible heat flux under the canopy, and of estimating heat storage, are reviewed. The differences between above- and below-canopy evaporation are compared with sap flow on five experimental Days. Except for one Overcast Day with little tree transpiration, the method fits sap flow within ± 15%.
Kathryn L Van Alstyne - One of the best experts on this subject based on the ideXlab platform.
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estimating variation in surface emissivities of intertidal macroalgae using an infrared thermometer and the effects on temperature measurements
Marine Biology, 2014Co-Authors: Kathryn L Van Alstyne, Theresa K OlsonAbstract:Accurate measurements of surface temperatures with an infrared (IR) thermometer require input of the emissivities of the surfaces being measured; however, few determinations of the emissivities of intertidal organisms’ surfaces have been made. Emissivities of intertidal macroalgae were measured to determine whether algal species, measurement angle, hydration, and layering affected them. Emissivities were similar and averaged 0.94 among 11 of 13 species. The species with lower and more variable emissivities (Chondracanthus exasperatus and Desmarestia viridis) differed in morphology from the other species, which were relatively flat thin blades with little surface texture. Measurement angle caused emissivities to decrease significantly in Mazzaella splendens but not in three other species. Hydration and layering of Ulva lactuca also had no effect. At 22 °C, measured temperatures were within 1 °C of actual temperatures when thermometer emissivity settings ranged from 0.75 to 1.00. When emissivities were set lower than actual values, measured temperatures were lower than actual temperatures at 15 °C and higher than actual temperatures at 60 °C. When the IR thermometer was used to measure surface temperatures of nine species of intertidal algae immediately before they were inundated by the incoming tide, temperatures were higher in mid intertidal than low intertidal individuals and higher on a sunnier Day than an Overcast Day. Temperatures of U. lactuca increased with increasing height on the shore, but temperatures of Ulvaria obscura did not. Temperatures were also higher in Fucus distichus blades than receptacles, and lower in U. lactuca and M. splendens occurring in the lower layers of stacks of algae.
Anthony E. Walsby - One of the best experts on this subject based on the ideXlab platform.
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Numerical integration of phytoplankton photosynthesis through time and depth in a water column
New Phytologist, 1997Co-Authors: Anthony E. WalsbyAbstract:SUMMARY The daily integral of photosynthesis for a population of planktonic cyanobacteria in the Baltic Sea is calculated by numerical analysis based on the photosynthesis-irradiance curve of the organism, the vertical distribution of the population and details of the underwater light field. Variations in the light field are calculated from continuous recordings of surface irradiance and measurements of vertical light attenuation, with corrections for losses by reflection at the water surface that depend on the sun's elevation and roughening by wind. Integrals calculated using models in which simplifying assumptions are made about the surface irradiance overestimate the calculated value by 21% on a cloudless Day and by 75%, or more, on an Overcast Day. Even larger discrepancies (> 100%) result when the population, which is concentrated in near-surface layers, is assumed to be evenly distributed with depth. Errors of up to 5% result from neglect of surface reflection, and up to 12% from neglect of changes in phytoplankton distribution over 24 h. Details are given of the method of numerical analysis, using standard computer spreadsheets. Versions of the spreadsheet are described in which effects of changes in the vertical distribution of the phytoplankton and light attenuation can be calculated and the effects of water temperature and photoinhibition can be modelled. The method will improve estimates of primary productivity in natural waters. It can also be used for calculating values of the euphotic depth integrated over 24 h. The spreadsheets are available on http://www.bio.bris.ac.uk/research/walsby/integral.htm.
