This chapter describes the optical properties of leaves at the epidermis and how, to a large exte... more This chapter describes the optical properties of leaves at the epidermis and how, to a large extent, the anatomical and morphological structure of the epidermis moderates, controls, and influences the optical properties of the leaf mesophyll and its functioning. We start with the properties of waxes, hairs, and the three-dimensional surface structures and explain many optical phenomena related to scattering of light away from the leaf such as iridescence and specular reflectance, and how surface roughness interacts with water. We discuss how light is focused into the leaf by the epidermal cells, illustrating how this is critical to leaf functions like exchanges of energy and gases.
Plant leaves collectively represent the largest above-ground surface area of plant material in vi... more Plant leaves collectively represent the largest above-ground surface area of plant material in virtually all environments. Their optical properties determine where and how energy and gas exchange occurs, which in turn drives the energy budget of the planet, and defines its ecology and habitability. This book reviews the state-of-the-art research on leaf optics. Topics covered include leaf traits, the anatomy and structure of leaves, leaf colour, biophysics and spectroscopy, radiometry, radiative transfer models, and remote and proximal sensing. A physical approach is emphasised throughout, providing the necessary foundations in physics, chemistry and biology to make the context accessible to readers from various subject backgrounds. It is a valuable resource for advanced students, researchers and government agency practitioners in remote sensing, plant physiology, ecology, resource management and conservation.
Applications of leaf spectroscopy have many different end uses. Leaf level information is crucial... more Applications of leaf spectroscopy have many different end uses. Leaf level information is crucial to quantify the state of physiological processes, for example the energy budget and transpiration. It is used to monitor photosynthetic rates and respiration rates. It provides a basis to scale environmental processes from the molecule to the planet. Leaf spectroscopy is also used in remote sensing studies to calibrate processes and provide ground truth data for interpretation, and in agriculture to indirectly calibrate foliar nutrients like nitrogen concentration.
The need to protect forests and enhance the capacity of mountain ecosystems is highlighted in the... more The need to protect forests and enhance the capacity of mountain ecosystems is highlighted in the U.N.'s Sustainable Development Goal (SDG) 15. The worst-hit areas of the 2008 Wenchuan Earthquake in southwest China were mountainous regions with high biodiversity and the impacted area is typical of other montane regions, with the need for detecting vegetation changes following the impacts of catastrophes. While the widely used remotely sensed vegetation indicator NDVI is available from various satellite data sources, these satellites are available for different monitoring periods and durations. Combining these datasets proved challenging to make a continuous characterization of vegetation change over an extended time period. In this study, compared with linear regression, multiple linear regression, and random forest, Convolutional Neural Networks (CNNs) performed best with an average R 2 of 0.819 (leave-one-out cross-validation). Thus, the CNNs model was selected to establish the map of the overlapping periods of two remote-sensing products: SPOT-VGT NDVI and PROBA-V NDVI, to reconstruct a SPOT-VGT NDVI for the period from June 2014 to December 2018 in the worst-hit areas of the Wenchuan earthquake. We analyzed the original and reconstructed SPOT-VGT NDVI in the hard-hit areas of the Wenchuan earthquake from 1999 to 2018, and we concluded that NDVI showed an overall upward trend throughout the study period, but experienced a sharp decline in 2008 and reached its lowest value a year later (2009). Vegetation recovery was rapid from 2009 until 2011 after which, it returned to a pattern of slower natural growth (2012)(2013)(2014)(2015)(2016)(2017)(2018). The Longmenshan fault zone experienced the greatest vegetation damage and initiation of recovery there has caused the overall regional average recovery to lag by 1-2 years. In areas where the land was denuded of vegetation (i.e., effectively all vegetation was stripped from the surface) after the earthquake, the damage exceeded what was experienced anywhere else in the entire study area, and by 2018 it remained unrestored. In the 15 years since the earthquake, the areas that were denuded were expected to recover to the level of restoration equivalent with the NDVI of 2007, as was the case in other earthquake-damaged regions. In addition to the earthquake and the immediate loss of vegetation, the Chinese government's Grain for Green Policy, the elevation ranges within the region, the forest's phenological conditions, and human activities all had an impact on vegetation recovery and restoration. The reconstructed NDVI provides a long-term continuous record, which contributes to the identifying changes that are improving predictive forest recovery models and to better vegetation management following catastrophic disturbances, such as earthquakes.
Plant leaves collectively represent the largest above-ground surface area of plant material in vi... more Plant leaves collectively represent the largest above-ground surface area of plant material in virtually all environments. Their optical properties determine where and how energy and gas exchange occurs, which in turn drives the energy budget of the planet, and defines its ecology and habitability. This book reviews the state-of-the-art research on leaf optics. Topics covered include leaf traits, the anatomy and structure of leaves, leaf colour, biophysics and spectroscopy, radiometry, radiative transfer models, and remote and proximal sensing. A physical approach is emphasised throughout, providing the necessary foundations in physics, chemistry and biology to make the context accessible to readers from various subject backgrounds. It is a valuable resource for advanced students, researchers and government agency practitioners in remote sensing, plant physiology, ecology, resource management and conservation.
Hyperspectral water retrievals from AVIRIS data, equivalent water thickness (EWT), were compared ... more Hyperspectral water retrievals from AVIRIS data, equivalent water thickness (EWT), were compared to in situ leaf water content and LAI measurements at a semiarid site in southeastern Arizona. Retrievals of EWT showed good correlation with field canopy water content measurements. Statistical analysis suggested that EWT was significantly different among seven community types, from savanna to agriculture. Four band-ratio indexes (NDVI, EVI, NDWI, and NDII) were derived from MODIS showing strong spatial agreement between maps of AVIRIS EWT and MODIS indexes, and good statistical agreement for the range of habitats at the site. Temporal patterns of these four indexes in all vegetation communities except creosote bush and agriculture showed distinct seasonal patterns that responded to the timing and amount of precipitation. Moreover, these time series captured different ecological responses among the different vegetation communities.
The geospatial distribution pattern in traditional Chinese settlements (TCSs) reflects the tradit... more The geospatial distribution pattern in traditional Chinese settlements (TCSs) reflects the traditional harmony between humans and nature, which has been learned over centuries. However, TCSs have experienced serious disturbances by urbanization and migration. It is crucial to explore the local wisdom of geospatial patterns and dominant factors for TCSs at the national scale in China. This study sought to determine the geospatial wisdom of traditional settlements to enrich our future settlement development with the aim of establishing Chinese settlement values for modern living. Herein, a dataset of 4000 TCSs were analyzed and clustered for environmental factors that affect their geospatial patterns by machine learning algorithms. We concluded that (1) five geospatial patterns of TCSs were clustered on a national scale, and the threshold of environmental factors of TCS groups was detected. (2) Environmental conditions and settlement concepts interacted and determined the similarities and differences among TCS groups. (3) The key boundary for TCSs and the dominant factors for each zone were determined, and topographical conditions and hydrologic resources played significant roles in all five TCS zones. This study provides a better understanding of the adaptability of the environment in relation to the TCSs and aids in planning TCS conservation and rural revitalization.
Submerged aquatic vegetation (SAV) has welldocumented effects on water clarity. SAV beds can slow... more Submerged aquatic vegetation (SAV) has welldocumented effects on water clarity. SAV beds can slow water movement and reduce bed shear stress, promoting sedimentation and reducing suspension. However, estuaries have multiple controls on turbidity that make it difficult to determine the effect of SAV on water clarity. In this study, we investigated the effect of primarily invasive SAV expansion on a concomitant decline in turbidity in the Sacramento-San Joaquin River Delta. The objective of this study was to separate the effects of decreasing sediment supply from the watershed from increasing SAV cover to determine the effect of SAVon the declining turbidity trend. SAV cover was determined by airborne hyperspectral remote sensing and turbidity data from longterm monitoring records. The turbidity trends were corrected for the declining sediment supply using suspended-sediment concentration data from a station immediately upstream of the Delta. We found a significant negative trend in turbidity from 1975 to 2008, and when we removed the sediment supply signal from the trend it was still significant and negative, indicating that a factor other than sediment supply was responsible for part of the turbidity decline. Turbidity monitoring stations with high rates of SAV expansion had steeper and more significant turbidity trends than those with low SAV cover. Our findings suggest that SAV is an important (but not sole) factor in the turbidity decline, and we estimate that 21-70 % of the total declining turbidity trend is due to SAV expansion.
Journal Of Geophysical Research: Biogeosciences, Sep 1, 2022
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
This chapter describes the optical properties of leaves at the epidermis and how, to a large exte... more This chapter describes the optical properties of leaves at the epidermis and how, to a large extent, the anatomical and morphological structure of the epidermis moderates, controls, and influences the optical properties of the leaf mesophyll and its functioning. We start with the properties of waxes, hairs, and the three-dimensional surface structures and explain many optical phenomena related to scattering of light away from the leaf such as iridescence and specular reflectance, and how surface roughness interacts with water. We discuss how light is focused into the leaf by the epidermal cells, illustrating how this is critical to leaf functions like exchanges of energy and gases.
Plant leaves collectively represent the largest above-ground surface area of plant material in vi... more Plant leaves collectively represent the largest above-ground surface area of plant material in virtually all environments. Their optical properties determine where and how energy and gas exchange occurs, which in turn drives the energy budget of the planet, and defines its ecology and habitability. This book reviews the state-of-the-art research on leaf optics. Topics covered include leaf traits, the anatomy and structure of leaves, leaf colour, biophysics and spectroscopy, radiometry, radiative transfer models, and remote and proximal sensing. A physical approach is emphasised throughout, providing the necessary foundations in physics, chemistry and biology to make the context accessible to readers from various subject backgrounds. It is a valuable resource for advanced students, researchers and government agency practitioners in remote sensing, plant physiology, ecology, resource management and conservation.
Applications of leaf spectroscopy have many different end uses. Leaf level information is crucial... more Applications of leaf spectroscopy have many different end uses. Leaf level information is crucial to quantify the state of physiological processes, for example the energy budget and transpiration. It is used to monitor photosynthetic rates and respiration rates. It provides a basis to scale environmental processes from the molecule to the planet. Leaf spectroscopy is also used in remote sensing studies to calibrate processes and provide ground truth data for interpretation, and in agriculture to indirectly calibrate foliar nutrients like nitrogen concentration.
The need to protect forests and enhance the capacity of mountain ecosystems is highlighted in the... more The need to protect forests and enhance the capacity of mountain ecosystems is highlighted in the U.N.'s Sustainable Development Goal (SDG) 15. The worst-hit areas of the 2008 Wenchuan Earthquake in southwest China were mountainous regions with high biodiversity and the impacted area is typical of other montane regions, with the need for detecting vegetation changes following the impacts of catastrophes. While the widely used remotely sensed vegetation indicator NDVI is available from various satellite data sources, these satellites are available for different monitoring periods and durations. Combining these datasets proved challenging to make a continuous characterization of vegetation change over an extended time period. In this study, compared with linear regression, multiple linear regression, and random forest, Convolutional Neural Networks (CNNs) performed best with an average R 2 of 0.819 (leave-one-out cross-validation). Thus, the CNNs model was selected to establish the map of the overlapping periods of two remote-sensing products: SPOT-VGT NDVI and PROBA-V NDVI, to reconstruct a SPOT-VGT NDVI for the period from June 2014 to December 2018 in the worst-hit areas of the Wenchuan earthquake. We analyzed the original and reconstructed SPOT-VGT NDVI in the hard-hit areas of the Wenchuan earthquake from 1999 to 2018, and we concluded that NDVI showed an overall upward trend throughout the study period, but experienced a sharp decline in 2008 and reached its lowest value a year later (2009). Vegetation recovery was rapid from 2009 until 2011 after which, it returned to a pattern of slower natural growth (2012)(2013)(2014)(2015)(2016)(2017)(2018). The Longmenshan fault zone experienced the greatest vegetation damage and initiation of recovery there has caused the overall regional average recovery to lag by 1-2 years. In areas where the land was denuded of vegetation (i.e., effectively all vegetation was stripped from the surface) after the earthquake, the damage exceeded what was experienced anywhere else in the entire study area, and by 2018 it remained unrestored. In the 15 years since the earthquake, the areas that were denuded were expected to recover to the level of restoration equivalent with the NDVI of 2007, as was the case in other earthquake-damaged regions. In addition to the earthquake and the immediate loss of vegetation, the Chinese government's Grain for Green Policy, the elevation ranges within the region, the forest's phenological conditions, and human activities all had an impact on vegetation recovery and restoration. The reconstructed NDVI provides a long-term continuous record, which contributes to the identifying changes that are improving predictive forest recovery models and to better vegetation management following catastrophic disturbances, such as earthquakes.
Plant leaves collectively represent the largest above-ground surface area of plant material in vi... more Plant leaves collectively represent the largest above-ground surface area of plant material in virtually all environments. Their optical properties determine where and how energy and gas exchange occurs, which in turn drives the energy budget of the planet, and defines its ecology and habitability. This book reviews the state-of-the-art research on leaf optics. Topics covered include leaf traits, the anatomy and structure of leaves, leaf colour, biophysics and spectroscopy, radiometry, radiative transfer models, and remote and proximal sensing. A physical approach is emphasised throughout, providing the necessary foundations in physics, chemistry and biology to make the context accessible to readers from various subject backgrounds. It is a valuable resource for advanced students, researchers and government agency practitioners in remote sensing, plant physiology, ecology, resource management and conservation.
Hyperspectral water retrievals from AVIRIS data, equivalent water thickness (EWT), were compared ... more Hyperspectral water retrievals from AVIRIS data, equivalent water thickness (EWT), were compared to in situ leaf water content and LAI measurements at a semiarid site in southeastern Arizona. Retrievals of EWT showed good correlation with field canopy water content measurements. Statistical analysis suggested that EWT was significantly different among seven community types, from savanna to agriculture. Four band-ratio indexes (NDVI, EVI, NDWI, and NDII) were derived from MODIS showing strong spatial agreement between maps of AVIRIS EWT and MODIS indexes, and good statistical agreement for the range of habitats at the site. Temporal patterns of these four indexes in all vegetation communities except creosote bush and agriculture showed distinct seasonal patterns that responded to the timing and amount of precipitation. Moreover, these time series captured different ecological responses among the different vegetation communities.
The geospatial distribution pattern in traditional Chinese settlements (TCSs) reflects the tradit... more The geospatial distribution pattern in traditional Chinese settlements (TCSs) reflects the traditional harmony between humans and nature, which has been learned over centuries. However, TCSs have experienced serious disturbances by urbanization and migration. It is crucial to explore the local wisdom of geospatial patterns and dominant factors for TCSs at the national scale in China. This study sought to determine the geospatial wisdom of traditional settlements to enrich our future settlement development with the aim of establishing Chinese settlement values for modern living. Herein, a dataset of 4000 TCSs were analyzed and clustered for environmental factors that affect their geospatial patterns by machine learning algorithms. We concluded that (1) five geospatial patterns of TCSs were clustered on a national scale, and the threshold of environmental factors of TCS groups was detected. (2) Environmental conditions and settlement concepts interacted and determined the similarities and differences among TCS groups. (3) The key boundary for TCSs and the dominant factors for each zone were determined, and topographical conditions and hydrologic resources played significant roles in all five TCS zones. This study provides a better understanding of the adaptability of the environment in relation to the TCSs and aids in planning TCS conservation and rural revitalization.
Submerged aquatic vegetation (SAV) has welldocumented effects on water clarity. SAV beds can slow... more Submerged aquatic vegetation (SAV) has welldocumented effects on water clarity. SAV beds can slow water movement and reduce bed shear stress, promoting sedimentation and reducing suspension. However, estuaries have multiple controls on turbidity that make it difficult to determine the effect of SAV on water clarity. In this study, we investigated the effect of primarily invasive SAV expansion on a concomitant decline in turbidity in the Sacramento-San Joaquin River Delta. The objective of this study was to separate the effects of decreasing sediment supply from the watershed from increasing SAV cover to determine the effect of SAVon the declining turbidity trend. SAV cover was determined by airborne hyperspectral remote sensing and turbidity data from longterm monitoring records. The turbidity trends were corrected for the declining sediment supply using suspended-sediment concentration data from a station immediately upstream of the Delta. We found a significant negative trend in turbidity from 1975 to 2008, and when we removed the sediment supply signal from the trend it was still significant and negative, indicating that a factor other than sediment supply was responsible for part of the turbidity decline. Turbidity monitoring stations with high rates of SAV expansion had steeper and more significant turbidity trends than those with low SAV cover. Our findings suggest that SAV is an important (but not sole) factor in the turbidity decline, and we estimate that 21-70 % of the total declining turbidity trend is due to SAV expansion.
Journal Of Geophysical Research: Biogeosciences, Sep 1, 2022
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
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