scholarly journals Contribution of woody elements to tree level reflectance in boreal forests

Silva Fennica ◽  
2021 ◽  
Vol 55 (5) ◽  
Author(s):  
Nea Kuusinen ◽  
Aarne Hovi ◽  
Miina Rautiainen
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Forest Floor ◽  
Laser Scanning ◽  
Remote Sensing Data ◽  
Hyperspectral Data ◽  
Tree Level ◽  
Area Index ◽  
Reflectance Model ◽  
Physically Based

Spectral mixture analysis was used to estimate the contribution of woody elements to tree level reflectance from airborne hyperspectral data in boreal forest stands in Finland. Knowledge of the contribution of woody elements to tree or forest reflectance is important in the context of lea area index (LAI) estimation and, e.g., in the estimation of defoliation due to insect outbreaks, from remote sensing data. Field measurements from four Scots pine ( L.), five Norway spruce ( (L.) Karst.) and four birch ( Roth and Ehrh.) dominated plots, spectral measurements of needles, leaves, bark, and forest floor, airborne hyperspectral as well as airborne laser scanning data were used together with a physically-based forest reflectance model. We compared the results based on simple linear combinations of measured bark and needle/leaf spectra to those obtained by accounting for multiple scattering of radiation within the canopy using a physically-based forest reflectance model. The contribution of forest floor to reflectance was additionally considered. The resulted mean woody element contribution estimates varied from 0.140 to 0.186 for Scots pine, from 0.116 to 0.196 for birches and from 0.090 to 0.095 for Norway spruce, depending on the model used. The contribution of woody elements to tree reflectance had a weak connection to plot level forest variables.Pinus sylvestrisPicea abiesBetula pendulaBetula pubescens

scholarly journals Using Remote Sensing Based Metrics to Quantify the Hydrological Response in a City

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1763 ◽  
Author(s):  
Charlotte Wirion ◽  
Willy Bauwens ◽  
Boud Verbeiren
Keyword(s):  
Remote Sensing ◽  
Potential Evapotranspiration ◽  
Remote Sensing Data ◽  
Hyperspectral Data ◽  
Hydrological Response ◽  
Area Index ◽  
Impervious Area ◽  
Urban Catchments ◽  
The City ◽  
Total Impervious Area

We propose a remote-sensing based metric approach to evaluate the hydrological response of highly urbanized areas and apply it to the city of Brussels. The model is set-up using 2 m resolution hyperspectral data. Next, it is upscaled to the city level, using multi-spectral Sentinel-2 data with 20 m resolution. We identify the total impervious area, the vegetation cover and the leaf area index as important metrics to derive a timeseries of spatially distributed net rainfall, runoff and infiltration from rainfall data. For the estimation of the actual evapotranspiration we use the potential evapotranspiration and the available water storage based on the interception, the depression storage and the infiltration. Additionally, we route the runoff to the outlet of selected sub-catchments. An important metric for the routing is the timing to the outlet which is approximated using the total impervious area and the hydrological distance to the outlet. We compare our approach to WetSpa model simulations and reach R 2 values of 98% for net rainfall, 95% for surface runoff, 99% for infiltration and 97% for cumulative evapotranspiration. The routing in the Watermaelbeek catchment is evaluated with discharge observations and reaches NSE values of 0.89 at a 2 m resolution and 0.88 at a 20 m resolution using an hourly timestep. At the timestep of 10 min and a 20 m resolution the NSE is reduced to 0.76. For the Roodebeek catchment we reach an NSE of 0.73 at a spatial resolution of 20 m and an hourly timestep. The results presented in this paper are optimistic for using spatial and temporal metrics retrieved from remote sensing data to quantify the water balance of urban catchments.

scholarly journals Large-area inventory of species composition using airborne laser scanning and hyperspectral data

Silva Fennica ◽  
2021 ◽  
Vol 55 (4) ◽  
Author(s):  
Hans Ørka ◽  
Endre Hansen ◽  
Michele Dalponte ◽  
Terje Gobakken ◽  
Erik Næsset
Keyword(s):  
Forest Management ◽  
Species Composition ◽  
Laser Scanning ◽  
Hyperspectral Data ◽  
Airborne Laser Scanning ◽  
Tree Level ◽  
Small Scale ◽  
Large Area ◽  
Airborne Laser ◽  
Species Specific

Tree species composition is an essential attribute in stand-level forest management inventories and remotely sensed data might be useful for its estimation. Previous studies on this topic have had several operational drawbacks, e.g., performance studied at a small scale and at a single tree-level with large fieldwork costs. The current study presents the results from a large-area inventory providing species composition following an operational area-based approach. The study utilizes a combination of airborne laser scanning and hyperspectral data and 97 field sample plots of 250 m collected over 350 km of productive forest in Norway. The results show that, with the availability of hyperspectral data, species-specific volume proportions can be provided in operational forest management inventories with acceptable results in 90% of the cases at the plot level. Dominant species were classified with an overall accuracy of 91% and a kappa-value of 0.73. Species-specific volumes were estimated with relative root mean square differences of 34%, 87%, and 102% for Norway spruce ( (L.) Karst.), Scots pine ( L.), and deciduous species, respectively. A novel tree-based approach for selecting pixels improved the results compared to a traditional approach based on the normalized difference vegetation index.22Picea abiesPinus sylvestris

The accuracy of estimating individual tree variables with airborne laser scanning in a boreal nature reserve

2004 ◽  
Vol 34 (9) ◽  
pp. 1791-1801 ◽  
Author(s):  
M Maltamo ◽  
K Mustonen ◽  
J Hyyppä ◽  
J Pitkänen ◽  
X Yu
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Laser Scanning ◽  
Stand Structure ◽  
Tree Height ◽  
Heterogeneous Structure ◽  
Mixed Stands ◽  
Individual Tree ◽  
Tree Layer ◽  
Pine Trees

This study examines the ability of high-density laser scanning to produce single-tree estimates in mixed stands of heterogeneous structure. Individual trees were detected from a constructed digital canopy height model by locating local maxima of the height values. The reference material comprised accurately measured field data for 10 mapped sample plots containing Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and different birches. To verify the accuracy of height measurements of single trees in more detail, the height of 29 Scots pine trees and their annual shoots of the last few years was carefully measured with a tacheometer and a glass fibre rod. The considered variables were the proportion of detected trees and tree height. As more than 80% of the dominant trees were detected, the results indicated that laser scanning can accurately describe the trees of the dominant tree layer. Because of the dense understorey tree layer in most of the sample plots, about 40% of all trees were detected. On the plot level, the stand structure affected the accuracy of the results considerably. The scanning-based tree height was most accurate for Norway spruce and least accurate for birches. The height of the separately measured 29 Scots pine trees was obtained with an accuracy of ±50 cm or better.

Variation in understory and canopy reflectance during stand development in Finnish coniferous forests

2015 ◽  
Vol 45 (8) ◽  
pp. 1077-1085 ◽  
Author(s):  
Nea Kuusinen ◽  
Pauline Stenberg ◽  
Erkki Tomppo ◽  
Pierre Bernier ◽  
Frank Berninger
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Boreal Forests ◽  
Near Infrared ◽  
Spectral Band ◽  
Stand Development ◽  
Area Index ◽  
Spectral Bands ◽  
Site Fertility ◽  
Infrared Spectral

Inherent variability in the spectral properties of boreal forests complicates the retrieval of canopy properties such as canopy leaf area index from satellite images. Understanding the drivers of this variability could help provide better estimates of desired canopy cover properties. Field plot data from the Finnish National Forest Inventory and Landsat thematic mapper (TM) images were used to investigate the variation in canopy and understory reflectance during stand development in coniferous boreal forests. Spectral data for each plot were obtained from the Landsat pixel within which the plot center coordinates fell. Nonlinear unmixing was used to estimate the bidirectional reflectance factors (BRFs) of the “sunlit understory” and “canopy and shaded ground” components by site fertility and stand development classes. A forest albedo model was used to estimate the contribution of diffuse radiation reflected downwards from the canopy to the sunlit understory component. The sunlit understory BRF in the near-infrared spectral band decreased as the site fertility decreased and the forest matured, whereas the sunlit understory BRFs in the red and shortwave-infrared spectral bands concurrently increased. The BRFs of the canopy and shaded ground component decreased slightly during stand development, mostly in the near-infrared spectral band. Adding the diffuse contribution to the sunlit understory component changed the estimated component BRFs only a little (0.1%–1.7%) compared with those obtained using a linear mixing assumption. This effect was largest in the near-infrared spectral band and smallest in the red spectral band. For Norway spruce plots, the measured and estimated forest variables were well correlated with the BRFs in all of the studied spectral bands, but for the Scots pine plots, the correlations were notably weaker. Results show a greater importance of the fraction of visible sunlit understory on forest reflectance in Scots pine than in Norway spruce forests.

scholarly journals LAI estimation by direct and indirect methods in Scots pine stands in Northern Steppe of Ukraine

2018 ◽  
Vol 64 (No. 12) ◽  
pp. 514-522
Author(s):  
Viktoriia Lovynska ◽  
Petro Lakyda ◽  
Svitlana Sytnyk ◽  
Mykola Kharytonov ◽  
Iryna Piestova
Keyword(s):  
Scots Pine ◽  
Indirect Method ◽  
Direct Method ◽  
Coefficient Of Determination ◽  
Tree Level ◽  
Stand Age ◽  
Area Index ◽  
Crown Diameter ◽  
Pine Stands ◽  
Scots Pine Stands

Leaf area index (LAI) of Scots pine (Pinus sylvestris Linnaeus) in the Northern Steppe of Ukraine was estimated. LAI estimated directly (LAI d, destructive sampling) was compared with LAI determined by digital hemispherical photography (indirect method, LAI id) in Scots pine stands. The studies to determine LAI were performed in pine stands of the age ranging from 57 to 87 years. The high coefficient of determination between needle weight and crown diameter as dependent variables and stand age as an independent variable was found at the tree level. LAI values of the stands estimated by the direct method were higher than those obtained by the indirect method on average by 8.8%. The results obtained by both methods were used for LAI determination from allometric relationships with tree mensuration parameters and stand biometric characteristics. There was a more significant relationship between LAI id values and tree crown diameter, basal area of stands as independent variables.

scholarly journals Physically-Based Retrieval of Canopy Equivalent Water Thickness Using Hyperspectral Data

2018 ◽  
Vol 10 (12) ◽  
pp. 1924 ◽  
Author(s):  
Matthias Wocher ◽  
Katja Berger ◽  
Martin Danner ◽  
Wolfram Mauser ◽  
Tobias Hank
Keyword(s):  
Water Content ◽  
Optical Sensors ◽  
Land Surface ◽  
Hyperspectral Data ◽  
Canopy Reflectance ◽  
Area Index ◽  
Equivalent Water Thickness ◽  
Crop Type ◽  
Physically Based ◽  
Leaf Level

Quantitative equivalent water thickness on canopy level (EWTcanopy) is an important land surface variable and retrieving EWTcanopy from remote sensing has been targeted by many studies. However, the effect of radiative penetration into the canopy has not been fully understood. Therefore, in this study the Beer-Lambert law is applied to inversely determine water content information in the 930 to 1060 nm range of canopy reflectance from measured winter wheat and corn spectra collected in 2015, 2017, and 2018. The spectral model was calibrated using a look-up-table (LUT) of 50,000 PROSPECT spectra. Internal model validation was performed using two leaf optical properties datasets (LOPEX93 and ANGERS). Destructive in-situ measurements of water content were collected separately for leaves, stalks, and fruits. Correlation between measured and modelled water content was most promising for leaves and ears in case of wheat, reaching coefficients of determination (R2) up to 0.72 and relative RMSE (rRMSE) of 26% and in case of corn for the leaf fraction only (R2 = 0.86, rRMSE = 23%). These findings indicate that, depending on the crop type and its structure, different parts of the canopy are observed by optical sensors. The results from the Munich-North-Isar test sites indicated that plant compartment specific EWTcanopy allows us to deduce more information about the physical meaning of model results than from equivalent water thickness on leaf level (EWT) which is upscaled to canopy water content (CWC) by multiplication of the leaf area index (LAI). Therefore, it is suggested to collect EWTcanopy data and corresponding reflectance for different crop types over the entire growing cycle. Nevertheless, the calibrated model proved to be transferable in time and space and thus can be applied for fast and effective retrieval of EWTcanopy in the scope of future hyperspectral satellite missions.

scholarly journals Close-range laser scanning in forests: towards physically based semantics across scales

2018 ◽  
Vol 8 (2) ◽  
pp. 20170046 ◽  
Author(s):  
F. Morsdorf ◽  
D. Kükenbrink ◽  
F. D. Schneider ◽  
M. Abegg ◽  
M. E. Schaepman
Keyword(s):  
Laser Scanning ◽  
Three Dimensional ◽  
Ground Truth ◽  
Vital Role ◽  
Area Index ◽  
Physically Based ◽  
Laser Systems ◽  
Close Range ◽  
Rich Data ◽  
Information Retrieval Methods

Laser scanning with its unique measurement concept holds the potential to revolutionize the way we assess and quantify three-dimensional vegetation structure. Modern laser systems used at close range, be it on terrestrial, mobile or unmanned aerial platforms, provide dense and accurate three-dimensional data whose information just waits to be harvested. However, the transformation of such data to information is not as straightforward as for airborne and space-borne approaches, where typically empirical models are built using ground truth of target variables. Simpler variables, such as diameter at breast height, can be readily derived and validated. More complex variables, e.g. leaf area index, need a thorough understanding and consideration of the physical particularities of the measurement process and semantic labelling of the point cloud. Quantified structural models provide a framework for such labelling by deriving stem and branch architecture, a basis for many of the more complex structural variables. The physical information of the laser scanning process is still underused and we show how it could play a vital role in conjunction with three-dimensional radiative transfer models to shape the information retrieval methods of the future. Using such a combined forward and physically based approach will make methods robust and transferable. In addition, it avoids replacing observer bias from field inventories with instrument bias from different laser instruments. Still, an intensive dialogue with the users of the derived information is mandatory to potentially re-design structural concepts and variables so that they profit most of the rich data that close-range laser scanning provides.

scholarly journals Tree stands of Scots pine and Norway spruce state assessment using hemispherical photography by Fish-eye lens and subsequent analysis of the digital images

2020 ◽  
pp. 95-110
Author(s):  
А.С. Алексеев ◽  
И.М. Чернов ◽  
И.В. Никифорчин ◽  
Е.А. Иванова
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Forest Canopy ◽  
The State ◽  
Tree Canopy ◽  
Eye Lens ◽  
Mixed Stands ◽  
Area Index ◽  
Icp Forests ◽  
Fish Eye

На примере чистых и смешанных древостоев хвойных пород с преобладанием сосны обыкновенной и ели европейской было проведено поисковое исследование возможностей определения состояния древостоев на основе цифровой полусферической съемки полога леса снизу вверх объективом типа «Рыбий глаз» и последующей обработки полученных изображений. Исследования были проведены на 25 пробных площадях, заложенных по европейской методике мониторинга состояния лесов ICP-Forest с регулярным их размещением по территории. На пробных площадях традиционным наземным методом были визуально определены такие показатели состояния древостоев как средние дефолиация верхней 1/3 части кроны деревьев, дефолиация всей кроны деревьев и класс повреждения древостоев. На этих же пробных площадях были получены снимки древесного полога объективом для полусферической съемки «Рыбий глаз», которые были обработаны с помощью программы открытого доступа Gap Light Analyzer. Методами регрессионного и дисперсионного анализа были установлены статистически достоверные связи между показателями состояния древостоев и их индексом листовой поверхности, полученным при обработке цифровых изображений. Показатели состояния древостоев и их индекс листовой поверхности связаны обратной зависимостью с коэффициентами детерминации от 79,8 до 87,4%. Полученные результаты позволяют в принципе разработать измерительную методику оценки состояния древостоев, обладающую свойствами объективности, технологичности, экономичности и точности. Основной целью такой методики является удаление из оценок состояния древостоев субъективного подхода, свойственного всем визуальным определениям. On the example of pure and mixed stands of coniferous species with a predominance of Scots pine and Norway spruce, a search study was conducted to determine the state of stands based on digital hemispherical shooting of the forest canopy from bottom to top with a Fish-eye lens and subsequent processing of the images obtained. The research was carried out on 25 test areas laid down according to the European method of monitoring the state of forests ICP-Forests. On the test areas land-based method to identify indicators of the status of the forest as the average defoliationof upper 1/3 part of the trees, defoliation of all trees and the class of damage of forest stands. At the same test areas, images of the tree canopy were obtained with a Fish-eye hemispherical lens, which were processed using the Gap Light Analyzer open access program. Using regression and variance analysis methods, statistically significant relationships were established between indicators of the state of stands and their leaf area index with determination coefficient from 79,8 to 87,4%. The results obtained allow us to develop a methodology for assessing the state of stands, which are usually determined visually with a high degree of subjectivity, by measuring.

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