A multiple sensor payload for a multi-rotor based UAV platform was developed and tested for measu... more A multiple sensor payload for a multi-rotor based UAV platform was developed and tested for measuring land surface albedo and spectral measurements at user-defined spatial, temporal, and spectral resolutions. The system includes a Matrice 600 UAV with an RGB camera and a set of four downward pointing radiation sensors including a pyranometer, quantum sensor, and VIS and NIR spectrometers, measuring surface reflected radiation. A companion ground unit consisting of a second set of identical sensors simultaneously measure downwelling radiation. The reflected and downwelling radiation measured by the four sensors are used for calculating albedo for the total shortwave broadband, visible band and any narrowband at a 1.5 nm spectral resolution within the range of 350–1100 nm. The UAV-derived albedo was compared with those derived from Landsat 8 and Sentinel-2 satellite observations. Results show the agreement between total shortwave albedo from UAV pyranometer and Landsat 8 (R2 = 0.73) a...
The exact extend and change of Canada forests are of great importance in climate change and susta... more The exact extend and change of Canada forests are of great importance in climate change and sustainable development as forests provide wildlife habitat and ecosystem mechanisms to clean air and water, and sequester carbon. Measuring the area of forested land in Canada on a regular basis provides an indicator of the availability of these important ecosystem services. A methodology was developed to quantify forest cover based on crown closure estimates. Field data, spectral and directional remote sensing imageries, and a canopy radiative transfer model (Five-Scale) are used for mapping crown closure at 1-km resolution. The main challenge of the research is in the transition zone between boreal forest and the tundra, where few inventory data are available and the trees are found in clusters. The results will be used in a Canada-wide forest indicator that aimed at monitoring yearly changes in the forest extend due in part to forest fires, insect defoliation, regrowth and changes due to climate change. Initial results using SPOT-VGT data and foliage clumping information from ADEOS-POLDER are presented.
Development of forest modeling framework.Simulation of hemispherical photographs (HPs).Assessment... more Development of forest modeling framework.Simulation of hemispherical photographs (HPs).Assessment of HPs canopy retrieval methods.Estimation of forest structural attributes.Three-dimensional simulations of forest scenes rendered with the freeware POV-Ray (www.povray.org) were used to assess retrievals of plant and leaf area index (PAI and LAI) from hemispherical photography (HP). Ten HPs were simulated in 75 scenes with random, erectophile and planophile leaf angle distributions. PAI retrieved using Beer's law near 57.3° (55–60°) and with the truncated Miller integration over zenith angles from 10° to 65° gave similar results. The importance of clumping was also shown to obtain accurate PAI. Foliage density inside the crown was a major factor causing underestimates of the PAI because the clumping effect was underestimated. Moreover, best PAI retrievals were found with the clumping index method using the Chen and Cihlar method combined with the Lang and Xiang method (relative RMSE of 23–24% and relative median absolute error of 12–14%) and was slightly less affected by the averaging length when compared with only using the Lang and Xiang. Previous error measurements of 29% were reduced to 16–23% for a black spruce stand using updated input variables and the method presented here, and they were shown to fall within the errors of the simulation framework.
This paper presents results of model parameter testing required for the global application of a m... more This paper presents results of model parameter testing required for the global application of a methodology that proven applicable in the Canadian environment. The Four-Scale model represents a four kernel model to simulate the anisotropy of forested environments. Its accuracy in simulating the maximum (Hotspot) and the minimum (Darkspot) of reflectance in the backscattering and forward scattering along the principal plane has allowed the formulation of the Normalised Difference of Hotspot and Darkspot (NDHD). This angular index has been shown to correlate with the vegetation clumping index, that describes the deviation of foliage distribution from a Poisson based random distribution. The clumping of vegetation significantly affects carbon budget models because it allows the correction of effective LAI observed from single angle measurements. Additional tree crown shapes have been included, and vegetation density variations within and between ecosystems are investigated. The results are evaluated in terms of model applicability to global derivation of the clumping index using POLDER data from ADEOS-1.
It has long been recognized that standard radiative transfer formulations for continuous media ar... more It has long been recognized that standard radiative transfer formulations for continuous media are not appropriate for characterizing the radiance field within and above natural vegetation. This problem is often manifested in the "hotspot effect" where the probability of an incident and exitant direction of a photon interacting with a canopy volume is correlated. The most common approach to deal with this effect is to adjust the scattering phase function. However, there are two problems with this solution: 1. Gaps exists over a range of scales so the adjustment must take into account correlations between directions due to gaps at all scales and not just the leaf scale. 2. Vegetation elements are in general non-randomly dispersed at a given scale so the parameterization of the location of vegetation elements must include clumping at potentially all scales. We present a vegetation radiative transfer model based on a multi-scale statistical parameterization of vegetation structure. The concept of the conditional gap probability function is introduced to deal with the hotspot effect. The model is compared to both measurements of below canopy gap size distributions and above canopy BRDF over BOREAS tower
Leaf area index is a fundamental land surface parameter. Moderate (1km) resolution sensors curren... more Leaf area index is a fundamental land surface parameter. Moderate (1km) resolution sensors currently offer sufficient repeat frequency to provide large area estimates of LAI within the growing season. Recently, a number of LAI products have been produced and distributed for use in ecosystem and climate models. We describe an approach to validet these products using a sampling of consistent in-situ LAI measurements scaled up with Landsat data. This reference data set is used to quantify both the contribution of scaling versus retrieval algorithm uncertainties in the MODIS, CCRS, ESA and IGBP LAI products. An additional intensively sampled site near Ottawa, Canada and within the VALERI international validation network is used to compare our reference approach to other international reference standards. The LAI uncertainties are propoagated into a land surface process model to quantify expected downstream uncertainties in modelled fluxes.
IEEE International Geoscience and Remote Sensing Symposium, 2000
ABSTRACT A method for calculating the diurnal distribution of direct and diffuse solar radiation ... more ABSTRACT A method for calculating the diurnal distribution of direct and diffuse solar radiation was developed. Based on this method, we analysed the changing patterns of the two radiation components under different weather conditions. The results were then used to investigate the effect of underlying snow of a forest on the surface albedo. It shows that the albedo contribution from the underlying snow is stable on overcast days when the radiation is dominated by the diffuse component. However, on clear days when the radiation is dominated by the direct component, the diurnal change of albedo contributed from the snow is significant and it exhibits a "w" shape. It was also found that under any weather conditions, the vegetation masking effect is very significant. As a result, the albedo contribution from the underlying snow in the high latitude is much less than that obtained by the fractional average method commonly used in land surface schemes of climate models.
... For example, there was no statistical difference in LAI based on a sample of six plots ... Th... more ... For example, there was no statistical difference in LAI based on a sample of six plots ... The scene-selection procedure was an important process toward defining a statistical relationship between field ... The total error budget for LAI retrieval based on the ISR was documented at the ...
Forests cover nearly half of Canada's landmass. While forested lands are often viewed as area... more Forests cover nearly half of Canada's landmass. While forested lands are often viewed as areas of wood production, forests also provide wildlife habitat and ecosystem mechanisms to clean air and water, and sequester carbon. Measuring the area of forested land in Canada on a regular basis provides an indicator of the availability of these important ecosystem services. This study examines the capability of coarse spatial resolution satellite data to quantify forest cover based on crown closure estimates. Field data, high and medium resolution remote sensing imageries, and a canopy radiative transfer model (Five-Scale) are used to assess the mapping potential of 1-km data, such as AVHRR, VGT and MODIS. The main challenge of the research is in the transition zone between boreal forest and the tundra, where few inventory data are available and the trees are found in clusters. The results will be used in a Canada-wide forest indicator that aimed at monitoring yearly changes in the for...
A multiple sensor payload for a multi-rotor based UAV platform was developed and tested for measu... more A multiple sensor payload for a multi-rotor based UAV platform was developed and tested for measuring land surface albedo and spectral measurements at user-defined spatial, temporal, and spectral resolutions. The system includes a Matrice 600 UAV with an RGB camera and a set of four downward pointing radiation sensors including a pyranometer, quantum sensor, and VIS and NIR spectrometers, measuring surface reflected radiation. A companion ground unit consisting of a second set of identical sensors simultaneously measure downwelling radiation. The reflected and downwelling radiation measured by the four sensors are used for calculating albedo for the total shortwave broadband, visible band and any narrowband at a 1.5 nm spectral resolution within the range of 350–1100 nm. The UAV-derived albedo was compared with those derived from Landsat 8 and Sentinel-2 satellite observations. Results show the agreement between total shortwave albedo from UAV pyranometer and Landsat 8 (R2 = 0.73) a...
The exact extend and change of Canada forests are of great importance in climate change and susta... more The exact extend and change of Canada forests are of great importance in climate change and sustainable development as forests provide wildlife habitat and ecosystem mechanisms to clean air and water, and sequester carbon. Measuring the area of forested land in Canada on a regular basis provides an indicator of the availability of these important ecosystem services. A methodology was developed to quantify forest cover based on crown closure estimates. Field data, spectral and directional remote sensing imageries, and a canopy radiative transfer model (Five-Scale) are used for mapping crown closure at 1-km resolution. The main challenge of the research is in the transition zone between boreal forest and the tundra, where few inventory data are available and the trees are found in clusters. The results will be used in a Canada-wide forest indicator that aimed at monitoring yearly changes in the forest extend due in part to forest fires, insect defoliation, regrowth and changes due to climate change. Initial results using SPOT-VGT data and foliage clumping information from ADEOS-POLDER are presented.
Development of forest modeling framework.Simulation of hemispherical photographs (HPs).Assessment... more Development of forest modeling framework.Simulation of hemispherical photographs (HPs).Assessment of HPs canopy retrieval methods.Estimation of forest structural attributes.Three-dimensional simulations of forest scenes rendered with the freeware POV-Ray (www.povray.org) were used to assess retrievals of plant and leaf area index (PAI and LAI) from hemispherical photography (HP). Ten HPs were simulated in 75 scenes with random, erectophile and planophile leaf angle distributions. PAI retrieved using Beer's law near 57.3° (55–60°) and with the truncated Miller integration over zenith angles from 10° to 65° gave similar results. The importance of clumping was also shown to obtain accurate PAI. Foliage density inside the crown was a major factor causing underestimates of the PAI because the clumping effect was underestimated. Moreover, best PAI retrievals were found with the clumping index method using the Chen and Cihlar method combined with the Lang and Xiang method (relative RMSE of 23–24% and relative median absolute error of 12–14%) and was slightly less affected by the averaging length when compared with only using the Lang and Xiang. Previous error measurements of 29% were reduced to 16–23% for a black spruce stand using updated input variables and the method presented here, and they were shown to fall within the errors of the simulation framework.
This paper presents results of model parameter testing required for the global application of a m... more This paper presents results of model parameter testing required for the global application of a methodology that proven applicable in the Canadian environment. The Four-Scale model represents a four kernel model to simulate the anisotropy of forested environments. Its accuracy in simulating the maximum (Hotspot) and the minimum (Darkspot) of reflectance in the backscattering and forward scattering along the principal plane has allowed the formulation of the Normalised Difference of Hotspot and Darkspot (NDHD). This angular index has been shown to correlate with the vegetation clumping index, that describes the deviation of foliage distribution from a Poisson based random distribution. The clumping of vegetation significantly affects carbon budget models because it allows the correction of effective LAI observed from single angle measurements. Additional tree crown shapes have been included, and vegetation density variations within and between ecosystems are investigated. The results are evaluated in terms of model applicability to global derivation of the clumping index using POLDER data from ADEOS-1.
It has long been recognized that standard radiative transfer formulations for continuous media ar... more It has long been recognized that standard radiative transfer formulations for continuous media are not appropriate for characterizing the radiance field within and above natural vegetation. This problem is often manifested in the "hotspot effect" where the probability of an incident and exitant direction of a photon interacting with a canopy volume is correlated. The most common approach to deal with this effect is to adjust the scattering phase function. However, there are two problems with this solution: 1. Gaps exists over a range of scales so the adjustment must take into account correlations between directions due to gaps at all scales and not just the leaf scale. 2. Vegetation elements are in general non-randomly dispersed at a given scale so the parameterization of the location of vegetation elements must include clumping at potentially all scales. We present a vegetation radiative transfer model based on a multi-scale statistical parameterization of vegetation structure. The concept of the conditional gap probability function is introduced to deal with the hotspot effect. The model is compared to both measurements of below canopy gap size distributions and above canopy BRDF over BOREAS tower
Leaf area index is a fundamental land surface parameter. Moderate (1km) resolution sensors curren... more Leaf area index is a fundamental land surface parameter. Moderate (1km) resolution sensors currently offer sufficient repeat frequency to provide large area estimates of LAI within the growing season. Recently, a number of LAI products have been produced and distributed for use in ecosystem and climate models. We describe an approach to validet these products using a sampling of consistent in-situ LAI measurements scaled up with Landsat data. This reference data set is used to quantify both the contribution of scaling versus retrieval algorithm uncertainties in the MODIS, CCRS, ESA and IGBP LAI products. An additional intensively sampled site near Ottawa, Canada and within the VALERI international validation network is used to compare our reference approach to other international reference standards. The LAI uncertainties are propoagated into a land surface process model to quantify expected downstream uncertainties in modelled fluxes.
IEEE International Geoscience and Remote Sensing Symposium, 2000
ABSTRACT A method for calculating the diurnal distribution of direct and diffuse solar radiation ... more ABSTRACT A method for calculating the diurnal distribution of direct and diffuse solar radiation was developed. Based on this method, we analysed the changing patterns of the two radiation components under different weather conditions. The results were then used to investigate the effect of underlying snow of a forest on the surface albedo. It shows that the albedo contribution from the underlying snow is stable on overcast days when the radiation is dominated by the diffuse component. However, on clear days when the radiation is dominated by the direct component, the diurnal change of albedo contributed from the snow is significant and it exhibits a "w" shape. It was also found that under any weather conditions, the vegetation masking effect is very significant. As a result, the albedo contribution from the underlying snow in the high latitude is much less than that obtained by the fractional average method commonly used in land surface schemes of climate models.
... For example, there was no statistical difference in LAI based on a sample of six plots ... Th... more ... For example, there was no statistical difference in LAI based on a sample of six plots ... The scene-selection procedure was an important process toward defining a statistical relationship between field ... The total error budget for LAI retrieval based on the ISR was documented at the ...
Forests cover nearly half of Canada's landmass. While forested lands are often viewed as area... more Forests cover nearly half of Canada's landmass. While forested lands are often viewed as areas of wood production, forests also provide wildlife habitat and ecosystem mechanisms to clean air and water, and sequester carbon. Measuring the area of forested land in Canada on a regular basis provides an indicator of the availability of these important ecosystem services. This study examines the capability of coarse spatial resolution satellite data to quantify forest cover based on crown closure estimates. Field data, high and medium resolution remote sensing imageries, and a canopy radiative transfer model (Five-Scale) are used to assess the mapping potential of 1-km data, such as AVHRR, VGT and MODIS. The main challenge of the research is in the transition zone between boreal forest and the tundra, where few inventory data are available and the trees are found in clusters. The results will be used in a Canada-wide forest indicator that aimed at monitoring yearly changes in the for...
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Papers by Sylvain Leblanc