John Gamon
University of Alberta, Earth and Atmospheric Sciences, Faculty Member
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Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating societal responses. The Group on Earth Observations Biodiversity Observation Network (GEO BON) was created in 2008 to develop a global... more
Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating societal responses. The Group on Earth Observations Biodiversity Observation Network (GEO BON) was created in 2008 to develop a global monitoring network, but that is a huge task with much remaining work. Fortunately, satellite remote sensing can help by providing periodic, global data that is not otherwise available. Continued advances – many of which are discussed in this book’s 19 chapters – in science as well as sensor and computational technology have an increasingly important role. However, taking advantage of these requires bringing together a variety of elements and disciplines, and it is with this in mind that a conceptual system architecture is here suggested. Key elements of this cloud-based architecture include: explicit support for collaboration, particularly across disciplines, to facilitate development of new algorithms; access to a wide variety of data, including satelli...
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Research Interests: Environmental Science, Remote Sensing, Near Infrared, Los Angeles, Canopy, and 15 moreGeomatic Engineering, Multiple Regression, Water Absorption, Infrared, Reflectance, Moisture Content, Plant Community, Infrared imaging, Normalized Difference Water Index, Spectral Imaging, Vegetation Structure, scrublands, Relative Water Content, Canopy cover, and Canopy structure
Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primary productivity across space and time. Terrestrial productivity, however, has many facets (e.g., spatial and temporal variability, including... more
Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primary productivity across space and time. Terrestrial productivity, however, has many facets (e.g., spatial and temporal variability, including seasonality, interannual variability, and trends), and different vegetation indices may not be equally good at predicting them. Their accuracy in monitoring productivity has been mostly tested in single-ecosystem studies, but their performance in different ecosystems distributed over large areas still needs to be fully explored. To fill this gap, we identified the facets of terrestrial gross primary production (GPP) that could be monitored using RSVIs. We compared the temporal and spatial patterns of four vegetation indices (NDVI, EVI, NIRV, and CCI), derived from the MODIS MAIAC data set and of GPP derived from data from 58 eddy-flux towers in eight ecosystems with different plant functional types (evergreen needle-leaved forest, evergreen broad-lea...
Research Interests: Earth Sciences, Environmental Science, Computer Science, Economics, Remote Sensing, and 15 moreBiology, Environmental Monitoring, Natural Resource Economics, Seasonality, Environmental Sciences, Forests, Shrubland, Primary Production, Deciduous, Ecosystem, Evergreen, Terrestrial Ecosystem, Interannual Variability, GPP, and Normalized Difference Vegetation Index
Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global... more
Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global change, novel approaches that are rapid, repeatable and scalable are critical, especially in ecosystems for which information about species identity and the number of species is difficult to acquire. Here, we present 'spectral diversity'-a spectroscopic index of the variability of electromagnetic radiation reflected from plants measured in the visible, near-infrared and short-wave infrared regions (400-2,400 nm). Using data collected from the Cedar Creek biodiversity experiment (Minnesota, USA), we provide evidence that the dissimilarity of species' leaf spectra increases with functional dissimilarity and evolutionary divergence time. Spectral diversity at the leaf level explains 51% of total variation in productivity-a proportion compara...
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Research Interests: Environmental Science, Computer Science, Remote Sensing, Environment and natural resources conservation, Environmental Sciences, and 9 moreAtmospheric sciences, Eddy Covariance, Ndvi, Grassland, Primary Production, Optical Remote Sensing, Gap Filling, Photosynthetically active radiation (PAR), and Normalized Difference Vegetation Index
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Research Interests: Environmental Science, Geology, Computer Science, Economics, Remote Sensing, and 13 moreEnvironment and natural resources conservation, Drought, Environmental Sciences, MODIS, Temperate deciduous forest, Photochemical Reflectance Index, Isoprene, Reducing Power, PRI, Photorespiration, GPP, Substrate Availability, and megan
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Most photosynthesis measurements involve remote determinations. In gas-exchange systems, including those based on chambers, atmospheric gradients, and eddy correlation, photosynthesis determinations are remote in the sense that the... more
Most photosynthesis measurements involve remote determinations. In gas-exchange systems, including those based on chambers, atmospheric gradients, and eddy correlation, photosynthesis determinations are remote in the sense that the measurements are based on effects of leaves, plants, or canopies on the gaseous environment. In radiation-based remote sensing, the subject of this chapter, photosynthesis determinations are based on interactions between leaves, plants, or canopies and the radiation environment. The wavelength bands potentially useful for measurements related to photosynthesis range from the visible through the thermal and microwave regions. While remote sensing generally connotes large-scale satellite measurements, radiation-based remote sensing can be effectively utilized to address questions in photosynthesis research ranging in spatial scale from the chloroplast to the globe.
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ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen.... more
ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient-stress (N-stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen-limited. Water-stress (H2O-stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient-stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen-use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O-stress treatments. In addition, N-stress reduced photosynthetic water-use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O-stress. In addition, sunflower plants responded to H2O-stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O-stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field-grown sunflower manages a trade-off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.
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summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm... more
summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance ('PRI', Photochemical ...
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Research Interests: Environmental Science, Photosynthesis, Plant Biology, Aquatic botany, Aquatic Plant, and 9 morePhotochemical Reflectance Index, Aquatic Vegetation, Xanthophyll Cycle, Spectral Reflectance, Reflectivity, Spectral Resolution, Chlorophyll a, Radiation Use Efficiency, and ENVIRONMENTAL SCIENCE AND MANAGEMENT
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In advance of the FLEX mission, experimental studies are needed to better understand the factors driving Solar-Induced Fluorescence (SIF) emission from vegetation across different temporal and spatial scales. Here, we present findings... more
In advance of the FLEX mission, experimental studies are needed to better understand the factors driving Solar-Induced Fluorescence (SIF) emission from vegetation across different temporal and spatial scales. Here, we present findings from boreal (evergreen and deciduous) forest trees and Midwestern (annual) crops, illustrating effects of seasonal downregulation and drought on the fluorescence signals. Further work is needed to develop defensible, quantitative fluorescence measurements, and to partition the drivers of the fluorescence signals into effects of structure and physiology.
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Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a more integrated approach to optical sampling that includes SIF along with reflectance-based indices and other approaches. The influence of both... more
Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a more integrated approach to optical sampling that includes SIF along with reflectance-based indices and other approaches. The influence of both APAR and downregulation on fluorescence signals have been mentioned, and additional references on SIF have been added. However, given the length of the review, a full discussion of all the SIF literature seemed beyond the scope of the current paper, particularly since most of that literature has not yet been fully integrated with reflectance-based approaches. Also, there remain practical and theoretical challenges to doing so (given the parallel history of the approaches and the ongoing need for more robust instrumentation). I leave integrated SIF-reflectance studies as a recommendation for future work, particularly in the context of radiative transfer modeling, with the flux tower network as an ideal testbed for advancing our understanding of the ...
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Here we investigate relationships between NDVI, Biomass, and Leaf Area Index (LAI) for six key plant species near Barrow, Alaska. We explore how key plant species differ in biomass, leaf area index (LAI) and how can vegetation spectral... more
Here we investigate relationships between NDVI, Biomass, and Leaf Area Index (LAI) for six key plant species near Barrow, Alaska. We explore how key plant species differ in biomass, leaf area index (LAI) and how can vegetation spectral indices be used to estimate biomass and LAI for key plant species. A vegetation index (VI) or a spectral vegetation index (SVI) is a quantitative predictor of plant biomass or vegetative vigor, usually formed from combinations of several spectral bands, whose values are added, divided, or multiplied in order to yield a single value that indicates the amount or vigor of vegetation. For six key plant species, NDVI was strongly correlated with biomass (R2 = 0.83) and LAI (R2 = 0.70) but showed evidence of saturation above a biomass of 100 g/m2 and an LAI of 2 m2/m2. Extrapolation of a biomass-plant cover model to a multi-decadal time series of plant cover observations suggested that Carex aquatilis and Eriophorum angustifolium decreased in biomass while ...
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Decreasing spring snow cover may amplify Arctic warming through the snow albedo feedback. To examine the impact of snowmelt on increasing temperature we used a 5,000 m elevation gradient in Yukon, Canada, extending from valley-bottom... more
Decreasing spring snow cover may amplify Arctic warming through the snow albedo feedback. To examine the impact of snowmelt on increasing temperature we used a 5,000 m elevation gradient in Yukon, Canada, extending from valley-bottom conifer forests, through middle elevation tundra, to high elevation icefields, to compare validated downscaled reanalysis air temperature patterns across elevational bands characterized by different patterns of spring snowmelt. From 2000 to 2014 we observed surface warming of 0.01 °C/a·1,000 m in May (0.14 °C/a at 1,000 m to 0.19 °C/a at 5,000 m), and uniform cooling of 0.09 °C/a in June at all elevations. May temperature trends across elevationally dependent land cover types were highly correlated with each other despite large variations in albedo and snow cover trends. Furthermore, a clear dependency of infrared skin temperature on snow cover mediated albedo decline was observed in tundra, but this was insufficient to influence average diurnal air tem...
Remote sensing has been used to detect plant biodiversity in a range of ecosystems based on the varying spectral properties of different species or functional groups. However, the most appropriate spatial resolution necessary to detect... more
Remote sensing has been used to detect plant biodiversity in a range of ecosystems based on the varying spectral properties of different species or functional groups. However, the most appropriate spatial resolution necessary to detect diversity remains unclear. At coarse resolution, differences among spectral patterns may be too weak to detect. In contrast, at fine resolution, redundant information may be introduced. To explore the effect of spatial resolution, we studied the scale dependence of spectral diversity in a prairie ecosystem experiment at Cedar Creek Ecosystem Science Reserve, Minnesota, USA. Our study involved a scaling exercise comparing synthetic pixels resampled from high-resolution images within manipulated diversity treatments. Hyperspectral data were collected using several instruments on both ground and airborne platforms. We used the coefficient of variation (CV) of spectral reflectance in space as the indicator of spectral diversity and then compared CV at dif...
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The vegetation indices normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI) provide indicators of pigmentation and photosynthetic activity that can be used to model photosynthesis from remote sensing... more
The vegetation indices normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI) provide indicators of pigmentation and photosynthetic activity that can be used to model photosynthesis from remote sensing with the light-use-efficiency model. To help develop and validate this approach, reliable proximal NDVI and PRI sensors have been needed. We tested new NDVI and PRI sensors, "spectral reflectance sensors" (SRS sensors; recently developed by Decagon Devices, during spring activation of photosynthetic activity in evergreen and deciduous stands. We also evaluated two methods of sensor cross-calibration – one that considered sky conditions (cloud cover) at midday only, and another that also considered diurnal sun angle effects. Cross-calibration clearly affected sensor agreement with independent measurements, with the best method dependent upon the study aim and time frame (seasonal vs. diurnal). The seasonal patterns of NDVI and PRI differed for...
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In evergreen conifers, where the foliage amount changes little with season, accurate detection of the underlying "photosynthetic phenology" from satellite remote sensing has been difficult, presenting challenges for global... more
In evergreen conifers, where the foliage amount changes little with season, accurate detection of the underlying "photosynthetic phenology" from satellite remote sensing has been difficult, presenting challenges for global models of ecosystem carbon uptake. Here, we report a close correspondence between seasonally changing foliar pigment levels, expressed as chlorophyll/carotenoid ratios, and evergreen photosynthetic activity, leading to a "chlorophyll/carotenoid index" (CCI) that tracks evergreen photosynthesis at multiple spatial scales. When calculated from NASA's Moderate Resolution Imaging Spectroradiometer satellite sensor, the CCI closely follows the seasonal patterns of daily gross primary productivity of evergreen conifer stands measured by eddy covariance. This discovery provides a way of monitoring evergreen photosynthetic activity from optical remote sensing, and indicates an important regulatory role for carotenoid pigments in evergreen photosynt...
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ABSTRACT
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High Arctic landscapes are expansive and changing rapidly. However our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy... more
High Arctic landscapes are expansive and changing rapidly. However our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO2 with polar semidesert and meadow wetland landscapes at the highest-latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near zero sink of atmospheric CO2 (NEE: -0.3±13.5 g C m(-2) ). A nearby meadow wetland accumulated over 300 times more carbon (NEE: -79.3±20.0 g C m(-2) ) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southerly latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO2 emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO2 uptake. Our upscaling assessment found that polar semidesert NDVI measured on site was low (mean: 0.120-0.157) and similar to satellite measurements (mean: 0.155-0.163). However, weak plant growth resulted in poor satellite NDVI-NEE relationships and created challenges for remotely-detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote-sensing, however high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases substantially, climate-related changes of dry high Arctic landscapes may be restricted by poor soil moisture retention, and therefore have some inertia against short-term changes in NEE. This article is protected by copyright. All rights reserved.
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The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over 2 decades of proximal remote sensing at flux... more
The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over 2 decades of proximal remote sensing at flux tower sites are reviewed. The organizing framework used here is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the photochemical reflectance index (PRI) and solar-induced chlorophyll fluorescence (SIF), are discussed within the context of the LUE model. Multi-scale analysis across temporal and spatial axes is a central theme because suc...
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The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over two decades of proximal remote sensing at... more
The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over two decades of proximal remote sensing at flux tower sites are reviewed. An organizing framework is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the Photochemical Reflectance Index (PRI) and Solar-Induced Fluorescence (SIF), are discussed within the context of the LUE model. Multi-scale analysis across temporal and spatial axes is a central theme, because such scaling can provid...
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Abstract We studied the reflectance spectra of the aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer. The three aquatic typessubmerged, floating, and... more
Abstract We studied the reflectance spectra of the aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer. The three aquatic typessubmerged, floating, and emergentexhibited clear differences in ...
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Research Interests: Environmental Science, Remote Sensing, Climate Change, Productivity, Global Warming, and 15 moreSoil moisture, Landforms, Ecosystems, Moisture, Temperature, Ndvi, Geomatic Engineering, SNOW, Solar radiation, Melting, Spectral Reflectance, Snowmelt, Arctic Tundra, Cloud Cover, and Normalized Difference Vegetation Index
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In evergreens, the seasonal down-regulation and reactivation of photosynthesis is largely invisible and difficult to assess with remote sensing. This invisible phenology may be changing as a result of climate change. To better understand... more
In evergreens, the seasonal down-regulation and reactivation of photosynthesis is largely invisible and difficult to assess with remote sensing. This invisible phenology may be changing as a result of climate change. To better understand the mechanism and timing of these hidden physiological transitions, we explored several assays and optical indicators of spring photosynthetic activation in conifers exposed to a boreal climate. The photochemical reflectance index (PRI), chlorophyll fluorescence, and leaf pigments for evergreen conifer seedlings were monitored over 1 yr of a boreal climate with the addition of gas exchange during the spring. PRI, electron transport rate, pigment levels, light-use efficiency and photosynthesis all exhibited striking seasonal changes, with varying kinetics and strengths of correlation, which were used to evaluate the mechanisms and timing of spring activation. PRI and pigment pools were closely timed with photosynthetic reactivation measured by gas exchange. The PRI provided a clear optical indicator of spring photosynthetic activation that was detectable at leaf and stand scales in conifers. We propose that PRI might provide a useful metric of effective growing season length amenable to remote sensing and could improve remote-sensing-driven models of carbon uptake in evergreen ecosystems.
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The photochemical reflectance index (PRI) reflects diurnal xanthophyll cycle activity and is also influenced by seasonally changing carotenoid : Chl pigment ratios. Both changing pigment pools and xanthophyll cycle activity contribute to... more
The photochemical reflectance index (PRI) reflects diurnal xanthophyll cycle activity and is also influenced by seasonally changing carotenoid : Chl pigment ratios. Both changing pigment pools and xanthophyll cycle activity contribute to photoprotection in evergreen conifers exposed to boreal winters, but they operate over different timescales, and their relative contribution to the PRI signal has often been unclear. To clarify these responses and their contribution to the PRI signal, leaf PRI, pigment composition, temperature and irradiance were monitored over 2 yr for two evergreen conifers (Pinus contorta and Pinus ponderosa) in a boreal climate. PRI was affected by three distinct processes operating over different timescales and exhibiting contrasting spectral responses. Over the 2 yr study period, the greatest change in PRI resulted from seasonally changing carotenoid : Chl pigment ratios, followed by a previously unreported shifting leaf albedo during periods of deep cold. Remarkably, the smallest change was attributable to the xanthophyll cycle. To properly distinguish these three effects, interpretation of PRI must consider temporal context, physiological responses to evolving environmental conditions, and spectral response. Consideration of the separate mechanisms affecting PRI over different timescales could greatly improve efforts to monitor changing photosynthetic activity using optical remote sensing.
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Unattended optical sensors are increasingly being deployed on eddy covariance flux towers and are often used to complement existing vegetation and micrometeorological measurements to enable assessment of biophysical states and... more
Unattended optical sensors are increasingly being deployed on eddy covariance flux towers and are often used to complement existing vegetation and micrometeorological measurements to enable assessment of biophysical states and biogeochemical processes over a range of spatial scales. Of particular interest are sensors that can measure the photochemical reflectance index (PRI), which can provide information pertaining to leaf pigments and photosynthetic activity. This interest has facilitated the production of a new range of lower-cost multispectral sensors specifically designed to measure temporal changes in the PRI signal. However, little is known about the characteristics (spectral, radiometric and temporal) of many of these PRI sensors, making it difficult to compare data obtained from these sensors across time, geographical locations and instruments. Furthermore, direct testing of the capability of these sensors to actually detect the conversion of the xanthophyll cycle, which is...
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Research Interests: Remote Sensing, Biology, Quantitative analysis, Photochemical Reflectance Index, Geomatic Engineering, and 9 moreRemote Sensing of the Nearshore Environment, Xanthophyll Cycle, Natural Environment, Reflectance, Spectral Reflectance, Quantitative Analysis, Indexation, chlorophyll Content, and Plant Leaf
Our study examined the influence of elevated ozone levels on the growth and mycorrhizal colonization of two populations of Elymus glaucus L. (blue wildrye). We hypothesized that ozone would reduce carbon availability to the plants,... more
Our study examined the influence of elevated ozone levels on the growth and mycorrhizal colonization of two populations of Elymus glaucus L. (blue wildrye). We hypothesized that ozone would reduce carbon availability to the plants, particularly below ground, and would affect mycorrhizal colonization. Because of the wide geographic range of E. glaucus, two populations of plants were selected from areas
Research Interests: Genetics, Adaptation, Biology, Biological Sciences, Environmental Sciences, and 13 moreColonisation, Intraspecific Variation, Ozone, Gramineae, Soil Characteristics, Southern California, Geographic Range, Leaf Area, Perennial Grass, Dry Weight, Perennial Plant, Glomus intraradices, and Arbuscular mycorrhiza
FLUXNET and Remote Sensing Open Workshop: Towards Upscaling Flux Information From Towers to the Globe; Berkeley, California, 7-9 June 2011 About 140 scientists from 15 countries, representing the remote sensing and land-atmosphere flux... more
FLUXNET and Remote Sensing Open Workshop: Towards Upscaling Flux Information From Towers to the Globe; Berkeley, California, 7-9 June 2011 About 140 scientists from 15 countries, representing the remote sensing and land-atmosphere flux measurement and modeling communities, attended a workshop to address the technical, methodological, and scientific challenges to integrating flux and optical measurements across a spectrum of spatial and temporal scales.