The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
T.f. Eck - One of the best experts on this subject based on the ideXlab platform.
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Absorbed Photosynthetically Active Radiation and sun‐view geometry effects on remote sensing relationships∗
Remote Sensing Reviews, 1998Co-Authors: Elizabeth A. Walter-shea, Blaine L. Blad, Mark A. Mesarch, Cynthia J. Hays, D.w. Deering, T.f. EckAbstract:Quantifying the amount of Photosynthetically Active Radiation (PAR) absorbed by vegetation is an essential consideration for determining useful vegetative photosynthetic capacity and surface conductance values for regional and global carbon cycle studies. This study was conducted to compare absorbed Photosynthetically Active Radiation at the FIFE‐89 Konza prairie sites to that of the KUREX‐91 steppe grassland sites and to investigate variations in relationships between absorbed PAR and spectral vegetation indices derived from bidirectional reflectance factors. Incoming, reflected and transmitted PAR were measured from which fractions of reflected, transmitted and absorbed PAR were computed at selected FIFE prairie and KUREX steppe sites. Fractions of direct and diffuse PAR transmitted through canopies were estimated. Fractions of absorbed PAR were much lower at the FIFE sites (ranging from 0.35 to 0.65) than those at KUREX (ranging from 0.75 to 0.95) which can be explained by differences between leaf area...
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satellite estimation of incident Photosynthetically Active Radiation using ultraviolet reflectance
Remote Sensing of Environment, 1991Co-Authors: T.f. Eck, Dennis G. DyeAbstract:Abstract A new satellite remote sensing method for estimating the amount of Photosynthetically Active Radiation (PAR, 400–700 nm) incident at the earth's surface is described and tested. Potential incident PAR for clear sky conditions is computed from an existing spectral model. Actual incident PAR is estimated by accounting for the attenuation of PAR due to reflectance by clouds. PAR reflectance from clouds is inferred from ultraviolet (UV) reflectance at 370 nm, based on the evidently constant reflectivity of clouds across UV and PAR wavebands. A major advantage of the UV approach over existing visible band approaches to estimating insolation is the improved ability to discriminate clouds from high-albedo background surfaces. UV spectral reflectance data from the Total Ozone Mapping Spectrometer (TOMS) were used to test the approach for three climatically distinct, midlatitude locations. Estimates of monthly total incident PAR from the satellite technique differed from values computed from ground-based pyranometer measurements by less than 6 %. This UV remote sensing method can be applied to estimate PAR insolation over ocean and land surfaces which are free of ice and snow.
Yunhua Zhoub - One of the best experts on this subject based on the ideXlab platform.
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measuring and modelling Photosynthetically Active Radiation in tibet plateau during april october
Agricultural and Forest Meteorology, 2000Co-Authors: Xianzhou Zhang, Yiguang Zhang, Yunhua ZhoubAbstract:Abstract Based on the measured data of spectral solar Radiation in Lhasa, Tibet from 15 April to 15 October 1994, the ratio of Photosynthetically Active Radiation (PAR) to solar global Radiation was presented, i.e. ηPAR=0.439±0.014, and 1 J energy of PAR is equivalent to 4.43 μmol quantum. In the climatological estimation of Tibet Plateau, following equations can be used to estimate the daily total PAR energy flux density QPAR (MJ m−2 per day) and daily total PAR photo flux density UPAR(mol photon m−2 per day): Q PAR =(0.3914+0.0190 ln E ∗ ) Q U PAR =(1.7339+0.0842 ln E ∗ ) Q Here, Q (MJ m−2 per day) is the daily global Radiation. E*=E P0/P, E (hpa) is the water vapor pressure at site, P0(hpa) is the standard atmosphere pressure at sea level, P (hpa) is the atmosphere pressure at site.
Dennis G. Dye - One of the best experts on this subject based on the ideXlab platform.
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Photosynthetically Active Radiation absorbed by global land vegetation in August 1984
International Journal of Remote Sensing, 1993Co-Authors: Dennis G. Dye, Samuel N. GowardAbstract:Solar Radiation in the wavelength interval between approximately 400 and 700 nm provides the energy that powers photosynthesis and primary production. The capture and utilization of this Photosynthetically Active Radiation (PAR) represents the energetic foundation for the origin, evolution and sustained existence of the biosphere (Budyko 1980). Information on the amount of PAR absorbed by phototrophic biota is important in efforts to model and monitor primary production and related biospheric processes (Monteith 1977, Goward and Dye 1987, Prince 1991, Field 1991, Sellers 1991). Contemporary satellite remote sensing techniques provide an effective means with which to estimate absorbed PAR (APAR) on a global basis (...)
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satellite estimation of incident Photosynthetically Active Radiation using ultraviolet reflectance
Remote Sensing of Environment, 1991Co-Authors: T.f. Eck, Dennis G. DyeAbstract:Abstract A new satellite remote sensing method for estimating the amount of Photosynthetically Active Radiation (PAR, 400–700 nm) incident at the earth's surface is described and tested. Potential incident PAR for clear sky conditions is computed from an existing spectral model. Actual incident PAR is estimated by accounting for the attenuation of PAR due to reflectance by clouds. PAR reflectance from clouds is inferred from ultraviolet (UV) reflectance at 370 nm, based on the evidently constant reflectivity of clouds across UV and PAR wavebands. A major advantage of the UV approach over existing visible band approaches to estimating insolation is the improved ability to discriminate clouds from high-albedo background surfaces. UV spectral reflectance data from the Total Ozone Mapping Spectrometer (TOMS) were used to test the approach for three climatically distinct, midlatitude locations. Estimates of monthly total incident PAR from the satellite technique differed from values computed from ground-based pyranometer measurements by less than 6 %. This UV remote sensing method can be applied to estimate PAR insolation over ocean and land surfaces which are free of ice and snow.
Tilden P Meyers - One of the best experts on this subject based on the ideXlab platform.
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determining vegetation indices from solar and Photosynthetically Active Radiation fluxes
Agricultural and Forest Meteorology, 2007Co-Authors: Tim Wilson, Tilden P MeyersAbstract:Abstract The objective of this study was to quantify the seasonal variability of vegetation spectral indices to deduce leaf area index (LAI) for use in soil–vegetation–atmosphere exchange models using near-real-time and archived flux tower Radiation data. The 30-min data from 11 flux tower locations in 5 vegetation types (desert grassland, temperate grasslands, crops, deciduous forests, and pine forest) were collected across the United States. Vegetation indices were derived using solar Radiation and Photosynthetically Active Radiation (PAR) measured above the vegetation canopy throughout the year. The normalized-difference vegetation index (NDVI) estimated using the 30-min data was then used to quantify the LAI of the vegetation types at the various sites. The exponential function between LAI and NDVI indicated a non-linear relationship with the maximum tower-derived NDVI/LAI about 0.82/4.5 for corn, 0.85/6 for soybean, 0.6/2–0.8/4 for grasslands, and 0.81/7 for forest. Each vegetation type and environment exhibited unique seasonal and annual signatures of NDVI/LAI. The NDVI/LAI from the flux towers compared well with the Moderate Resolution Imaging Spectroradiometer (MODIS) data derived at 1-km resolution and derived LAI showed excellent agreement with measurements in corn/soybean crops. These results encourage the use of real-time single point measurements of vegetation spectral indices in characterizing vegetation for routine plant-environment models.
Liangyun Liu - One of the best experts on this subject based on the ideXlab platform.
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Assessing spectral indices to estimate the fraction of Photosynthetically Active Radiation absorbed by the vegetation canopy
International Journal of Remote Sensing, 2018Co-Authors: Dailiang Peng, Helin Zhang, Fumin Wang, Wenjiang Huang, Liangyun Liu, Rui Sun, Dacheng WangAbstract:ABSTRACTThe fraction of absorbed Photosynthetically Active Radiation (FPAR) by the vegetation canopy (FPARcanopy) is an important parameter for vegetation productivity estimation using remote-sensi...
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response of canopy solar induced chlorophyll fluorescence to the absorbed Photosynthetically Active Radiation absorbed by chlorophyll
Remote Sensing, 2017Co-Authors: Liangyun Liu, Xinjie LiuAbstract:Solar-induced chlorophyll fluorescence (SIF), which can be used as a novel proxy for estimating gross primary production (GPP), can be effectively retrieved using ground-based, airborne and satellite measurements. Absorbed Photosynthetically Active Radiation (APAR) is the key bridge linking SIF and GPP. Remotely sensed SIF at the canopy level ( S I F c a n o p y ) is only a part of the total SIF emission at the photosystem level. An SIF-based model for GPP estimation would be strongly influenced by the fraction of SIF photons escaping from the canopy ( f e s c ). Understanding the response of S I F c a n o p y to the absorbed Photosynthetically Active Radiation absorbed by chlorophyll ( A P A R c h l ) is a key step in estimating GPP but, as yet, this has not been well explored. In this study, we aim to investigate the relationship between remotely sensed S I F c a n o p y and A P A R c h l based on simulations made by the Soil Canopy Observation Photosynthesis Energy fluxes (SCOPE) model and field measurements. First, the ratio of the fraction of the absorbed Photosynthetically Active Radiation absorbed by chlorophyll ( fPAR c h l ) to the fraction of absorbed Photosynthetically Active Radiation absorbed by green leaves ( fPAR g r e e n ) is investigated using a dataset simulated by the SCOPE model. The results give a mean value of 0.722 for Cab at 5 μg cm−2, 0.761 for Cab at 10 μg cm−2 and 0.795 for other Cab content (ranging from 0.71 to 0.81). The response of S I F c a n o p y to A P A R c h l is then explored using simulations corresponding to different biochemical and biophysical conditions and it is found that S I F c a n o p y is well correlated with A P A R c h l . At the O2-A band, for a given plant type, the relationship between S I F c a n o p y and A P A R c h l can be approximately expressed by a linear statistical model even for different values of the leaf area index (LAI) and chlorophyll content, whereas the relationship varies with the LAI and chlorophyll content at the O2-B band. Finally, the response of S I F c a n o p y to A P A R c h l for different leaf angle distribution (LAD) functions is investigated using field observations and simulations; the results show that f e s c is larger for a planophile canopy structure. The values of the ratio of S I F c a n o p y to A P A R c h l are 0.0092 ± 0.0020 , 0.0076 ± 0.0036 and 0.0052 ± 0.0004 μm−1 sr−1 for planophile vegetables/crops, planophile grass and spherical winter wheat, respectively, at the O2-A band. At the O2-B band, the ratios are 0.0063 ± 0.0014 , 0.0049 ± 0.0030 and 0.0033 ± 0.0004 μm−1 sr−1, respectively. The values of this ratio derived from observations agree with simulations, giving values of 0.0055 ± 0.0002 and 0.0068 ± 0.0001 μm−1 sr−1 at the O2-A band and 0.0032 ± 0.0002 and 0.0047 ± 0.0001 μm−1 sr−1 at the O2-B band for spherical and planophile canopies, respectively. Therefore, both the simulations and observations confirm that the relationship between S I F c a n o p y and APAR c h l is species-specific and affected by biochemical components and canopy structure, especially at the O2-B band. It is also very important to correct for reabsorption and scattering of the SIF radiative transfer from the photosystem to the canopy level before the remotely sensed S I F c a n o p y is linked to the GPP.
