Browsing by Subject "terrestrial laser scanning"

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  • Hu, Man; Pitkanen, Timo P.; Minunno, Francesco; Tian, Xianglin; Lehtonen, Aleksi; Makela, Annikki (2021)
    Background and Aims Branch biomass and other attributes are important for estimating the carbon budget of forest stands and characterizing crown structure. As destructive measuring is time-consuming and labour-intensive, terrestrial laser scanning (TLS) as a solution has been used to estimate branch biomass quickly and non-destructively. However, branch information extraction from TLS data alone is challenging due to occlusion and other defects, especially for estimating individual branch attributes in coniferous trees. Methods This study presents a method, entitled TSMtls, to estimate individual branch biomass non-destructively and accurately by combining tree structure models and TLS data. The TSMtls method constructs the stem-taper curve from TLS data, then uses tree structure models to determine the number, basal area and biomass of individual branches at whorl level. We estimated the tree structural model parameters from 122 destructively measured Scots pine (Pinus sylvestris) trees and tested the method on six Scots pine trees that were first TLS-scanned and later destructively measured. Additionally, we estimated the branch biomass using other TLS-based approaches for comparison. Key Results Tree-level branch biomass estimates derived from TSMtls showed the best agreement with the destructive measurements [coefficient of variation of root mean square error (CV-RMSE) = 9.66 % and concordance correlation coefficient (CCC) = 0.99], outperforming the other TLS-based approaches (CV-RMSE 12.97-57.45 % and CCC 0.43-0.98 ). Whorl-level individual branch attributes estimates produced from TSMtls showed more accurate results than those produced from TLS data directly. Conclusions The results showed that the TSMtls method proposed in this study holds promise for extension to more species and larger areas.
  • Saarinen, Ninni; Kankare, Ville; Pyorala, Jiri; Yrttimaa, Tuomas; Liang, Xinlian; Wulder, Michael A.; Holopainen, Markus; Hyyppa, Juha; Vastaranta, Mikko (2019)
    Large and comprehensive datasets, traditionally based on destructive stem analysis or other labor-intensive approaches, are commonly considered as a necessity in developing stem-volume equations. The aim here was to investigate how a decreasing number of sample trees affects parametrizing an existing taper curve equation and resultant stem-volume estimates. Furthermore, the potential of terrestrial laser scanning (TLS) in producing taper curves was examined. A TLS-based taper curve was derived for 246 Scots pines (Pinus sylvestris L.) from southern Finland to parametrize an existing taper curve equation. To assess sensitivity of the parametrization regarding sample size, the number of Scots pines included in the parametrization varied between full census and 1 Scots pine at a time. Root mean square error of stem-volume estimates remained = 46 Scots pines. Thus, it can be concluded that, with a rather small sample size, a taper curve equation can be re-parametrized for local conditions using point clouds from TLS to produce consistent stem-volume estimates.
  • Junttila, Samuli; Sugano, Junko; Vastaranta, Mikko; Linnakoski, Riikka; Kaartinen, Harri; Kukko, Antero; Holopainen, Markus; Hyyppa, Hannu; Hyyppa, Juha (2018)
    Changing climate is increasing the amount and intensity of forest stress agents, such as drought, pest insects, and pathogens. Leaf water content, measured here in terms of equivalent water thickness (EWT), is an early indicator of tree stress that provides timely information about the health status of forests. Multispectral terrestrial laser scanning (MS-TLS) measures target geometry and reflectance simultaneously, providing spatially explicit reflectance information at several wavelengths. EWT and leaf internal structure affect leaf reflectance in the shortwave infrared region that can be used to predict EWT with MS-TLS. A second wavelength that is sensitive to leaf internal structure but not affected by EWT can be used to normalize leaf internal effects on the shortwave infrared region and improve the prediction of EWT. Here we investigated the relationship between EWT and laser intensity features using multisensor MS-TLS at 690, 905, and 1,550 nm wavelengths with both drought-treated and Endoconidiophora polonica inoculated Norway spruce seedlings to better understand how MS-TLS measurements can explain variation in EWT. In our study, a normalized ratio of two wavelengths at 905 and 1,550 nm and length of seedling explained 91% of the variation (R-2) in EWT as the respective prediction accuracy for EWT was 0.003 g/cm(2) in greenhouse conditions. The relation between EWT and the normalized ratio of 905 and 1,550 nm wavelengths did not seem sensitive to a decreased point density of the MS-TLS data. Based on our results, different EWTs in Norway spruce seedlings show different spectral responses when measured using MS-TLS. These results can be further used when developing EWT monitoring for improving forest health assessments.
  • Junttila, Samuli; Sugano, Junko; Vastaranta, Mikko; Linnakoski, Riikka; Kaartinen, Harri; Kukko, Antero; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha (Frontiers Reseach Foundation, 2018)
    Frontiers in Plant Science
    Changing climate is increasing the amount and intensity of forest stress agents, such as drought, pest insects, and pathogens. Leaf water content, measured here in terms of equivalent water thickness (EWT), is an early indicator of tree stress that provides timely information about the health status of forests. Multispectral terrestrial laser scanning (MS-TLS) measures target geometry and reflectance simultaneously, providing spatially explicit reflectance information at several wavelengths. EWT and leaf internal structure affect leaf reflectance in the shortwave infrared region that can be used to predict EWT with MS-TLS. A second wavelength that is sensitive to leaf internal structure but not affected by EWT can be used to normalize leaf internal effects on the shortwave infrared region and improve the prediction of EWT. Here we investigated the relationship between EWT and laser intensity features using multisensor MS-TLS at 690, 905, and 1,550 nm wavelengths with both drought-treated and Endoconidiophora polonica inoculated Norway spruce seedlings to better understand how MS-TLS measurements can explain variation in EWT. In our study, a normalized ratio of two wavelengths at 905 and 1,550 nm and length of seedling explained 91% of the variation (R2) in EWT as the respective prediction accuracy for EWT was 0.003 g/cm2 in greenhouse conditions. The relation between EWT and the normalized ratio of 905 and 1,550 nm wavelengths did not seem sensitive to a decreased point density of the MS-TLS data. Based on our results, different EWTs in Norway spruce seedlings show different spectral responses when measured using MS-TLS. These results can be further used when developing EWT monitoring for improving forest health assessments.
  • Saarinen, Ninni; Kankare, Ville; Huuskonen, Saija; Hynynen, Jari; Bianchi, Simone; Yrttimaa, Tuomas; Luoma, Ville; Junttila, Samuli; Holopainen, Markus; Hyyppae, Juha; Vastaranta, Mikko (2022)
    Trees adapt to their growing conditions by regulating the sizes of their parts and their relationships. For example, removal or death of adjacent trees increases the growing space and the amount of light received by the remaining trees enabling their crowns to expand. Knowledge about the effects of silvicultural practices on crown size and shape and also about the quality of branches affecting the shape of a crown is, however, still limited. Thus, the aim was to study the crown structure of individual Scots pine trees in forest stands with varying stem densities due to past forest management practices. Furthermore, we wanted to understand how crown and stem attributes and also tree growth affect stem area at the height of maximum crown diameter (SAHMC), which could be used as a proxy for tree growth potential. We used terrestrial laser scanning (TLS) to generate attributes characterizing crown size and shape. The results showed that increasing stem density decreased Scots pine crown size. TLS provided more detailed attributes for crown characterization compared with traditional field measurements. Furthermore, decreasing stem density increased SAHMC, and strong relationships (Spearman's correlations > 0.5) were found between SAHMC and crown and stem size and also stem growth. Thus, this study provided quantitative and more comprehensive characterization of Scots pine crowns and their growth potential. The combination of a traditional growth and yield study design and 3D characterization of crown architecture and growth potential can open up new research possibilities.
  • Kankare, Ville; Joensuu, Marianna; Vauhkonen, Jari; Holopainen, Markus; Tanhuanpaa, Topi; Vastaranta, Mikko; Hyyppa, Juha; Hyyppa, Hannu; Alho, Petteri; Rikala, Juha; Sipi, Marketta (2014)
  • Luoma, Ville; Saarinen, Ninni; Kankare, Ville; Tanhuanpaa, Topi; Kaartinen, Harri; Kukko, Antero; Holopainen, Markus; Hyyppa, Juha; Vastaranta, Mikko (2019)
    Exact knowledge over tree growth is valuable information for decision makers when considering the purposes of sustainable forest management and planning or optimizing the use of timber, for example. Terrestrial laser scanning (TLS) can be used for measuring tree and forest attributes in very high detail. The study aims at characterizing changes in individual tree attributes (e.g., stem volume growth and taper) during a nine year-long study period in boreal forest conditions. TLS-based three-dimensional (3D) point cloud data were used for identifying and quantifying these changes. The results showed that observing changes in stem volume was possible from TLS point cloud data collected at two different time points. The average volume growth of sample trees was 0.226 m(3) during the study period, and the mean relative change in stem volume was 65.0%. In addition, the results of a pairwise Student's t-test gave strong support (p-value 0.0001) that the used method was able to detect tree growth within the nine-year period between 2008-2017. The findings of this study allow the further development of enhanced methods for TLS-based single tree and forest growth modeling and estimation, which can thus improve the accuracy of forest inventories and offer better tools for future decision-making processes.
  • Tienaho, Noora (Helsingin yliopisto, 2021)
    Structural complexity of trees is related to various ecological processes and ecosystem services. It can also improve the forests’ ability to adapt to environmental changes. In order to implement the management for complexity and to estimate its functionality, the level of structural complexity must be defined. The fractal-based box dimension (Db) provides an objective and holistic way to define the structural complexity for individual trees. The aim of this study was to compare structural complexity of Scots pine (Pinus sylvestris) trees measured by two remote sensing techniques, namely, terrestrial laser scanning (TLS) and aerial imagery acquired with unmanned aerial vehicle (UAV). Structural complexity for each Scots pine tree (n=2065) was defined by Db-values derived from the TLS and UAV measured point clouds. TLS produced the point clouds directly whereas UAV imagery was converted into point clouds with structure from motion (SfM) technology. The premise was that TLS provides the best available information on Db-values as the point density is higher in TLS than in UAV, and be-cause TLS is able to penetrate vegetation. TLS and UAV measured Db-values were found to significantly differ from each other and, thus, the techniques did not provide comparable information on structural complexity of individual Scots pine trees. On average, UAV measured Db-values were 5% bigger than TLS measured. The divergence between the TLS and UAV measured Db-values was found to be explained by the differences in the number and distribution of the points in the point clouds and by the differences in the estimated tree heights and number of boxes in the box dimension method. Forest structure (two thinning intensities, three thinning types and a control group) significantly affected the variation of both TLS and UAV measured Db-values. However, the divergence between TLS and UAV measured Db-values remained in all the treatments. In terms of the individual tree detection, the number of obtained points in the point cloud, and the distribution of these points, UAV measurements were better when the forest structure was sparser. In conclusion, while aerial imaging is a continuously developing study area and provides many advantageous attributes, at the moment, the TLS methods still dominate in accuracy when measuring the structural complexity at the tree-level. In the future, it should be studied whether TLS and UAV could be used as complementary techniques to provide more accurate and holistic view of the structural complexity in the perspective of both tree- and stand-level.
  • Liang, Xinlian (Finnish Geodetic Institute, 2013)
    Publications of the Finnish Geodetic Institute No 149
    Detailed, up-to-date forest information is increasingly important in quantitative forest inventories. The accuracy of the information retrieval is highly dependent on the quality and quantity of the reference data collected on field sample plots. In practice, the plotwise forest data are used as a reference for the calibration of large-area inventory data measured by aerial and space-borne remote sensing techniques. Field reference data are conventionally collected at the sample plot level by manual measurements. Because of the high costs and labor intensity of manual measurements, the number of tree attributes collected is limited. Some of the most important tree attributes are not even measured or sampled. Terrestrial laser scanning (TLS) has been recently shown to be a promising technique for forest-related studies. Many tree attributes have been correlated with measurements from TLS data. Numerous TLS methods have been proposed. 6However, the feasibility of applying TLS in plotwise forest inventories is still unclear. The major missing factor is automation of data processing. Other factors hampering the acceptance of the technology include the relatively high cost of the TLS instrument, the low measurement accuracy achieved using the automated data processing currently available, and the shortage of experimental results related to the retrieval of advanced stem attributes (e.g., stem curve) and to different forest conditions. In this study, a series of methods to map sample plots were developed, and their applicability in plotwise forest inventories was analyzed. The accuracy of stem mapping, the efficiency of data collection, and the limitations of the techniques were discussed. The results indicate that TLS is capable of documenting a forest sample plot in detail and that automated mapping methods yield accurate measurements of the most important tree attributes, such as diameter at breast height and stem curve. The fully-automated TLS data processing that was developed in this study resulted in measurement accuracy similar to that of manual measurements using conventional tools or models and of manual measurements from point cloud data. The results of this study support the feasibility of TLS for practical forest field inventories. Further research is needed to explore new protocols for the application of TLS in field inventories. Three possible new directions are the integration of detailed tree attributes (e.g., stem curve, volume, and biomass) in large-area inventories, the utilization of TLS field plots in national forest inventories, and the mapping of large sample plots, e.g., in operational harvest planning. More studies need to be performed on sample plots under different forest conditions (development class, tree species, and amount of ground vegetation). Tarkka ja ajantasainen metsävaratieto on yhä tärkeämpää metsätaloudessa. Laajojen metsäalueiden inventointi ja seuranta perustuu maastomittauksiin ja kaukokartoitustulkintaan. Maastossa mitattuja koealoja hyödynnetään kaukokartoituksen referenssi- tai kalibrointiaineistoina. Tällöin tulkinnassa käytettävien referenssi- tai kalibrointikoealojen mittaustarkkuus on ratkaisevan tärkeää. Perinteisesti maastoreferenssi on kerätty koealoilta manuaalisilla mittauksilla, mikä on työlästä. Korkeiden työvoimakustannusten vuoksi mitattavien puutunnusten määrä on rajallinen, ja joitakin tärkeitä puutunnuksia ei voida operatiivisesti edes mitata. Maastolaserkeilaus (Terrestrial Laser Scanning, TLS) on viime aikoina antanut lupauksia puiden mittaamiseen. Monet puutunnukset korreloivat hyvin TLS-piirteiden kanssa, ja useita menetelmiä puiden mittaukseen on esitetty. TLS:n soveltuvuus koealoihin perustuvaan metsävarojen inventointiin on kuitenkin edelleen epäselvää. Suurin ongelma on TLS-aineiston automaattinen käsittely ja tulkinta. Muita uuden tekniikan käyttöönottoa rajoittavia tekijöitä ovat TLS-laitteiston suhteellisen korkea hinta, tarjolla olevien automaattisten menetelmien huonot mittaustarkkuudet sekä käytännön testien puuttuminen (esim. runkokäyrän mittaus) erilaisissa puustoissa ja metsiköissä. Tutkimuksessa kehitettiin useita TLS-menetelmiä koealojen kartoitukseen ja mittaukseen. Lisäksi menetelmien soveltuvuutta koealoihin perustuvassa metsävarojen inventoinnissa analysoitiin ottaen huomioon runkojen paikannuksen tarkkuus, aineiston keruun tehokkuus sekä tekniikan rajoitukset. Tulosten mukaan TLS-mittaukset ovat soveltuvia metsikkökoealan tarkkaan kartoitukseen ja automaattiset menetelmät tuottivat tarkkoja mittaustuloksia tärkeimmistä puutunnuksista, kuten puiden rinnankorkeusläpimitasta ja runkokäyrästä. Täysin automaattinen TLS-aineiston käsittelymenetelmä, joka tutkimuksessa kehitettiin, tuotti samantasoista mittaustarkkuutta kuin perinteiset metsässä tehtävät mittausmenetelmät tai TLS-pistepilvestä suoritetut manuaaliset mittaukset. Tulokset osoittavat TLS-mittausten olevan potentiaalinen menetelmä operatiiviseen metsävarojen maastoinventointiin. Jatkotutkimuksia tarvitaan operatiivisen TLS-inventointimenetelmän kehittämiseen. Kolme mahdollista tutkimuslinjaa ovat TLS:llä mitattujen tarkkojen puutunnusten (esim. runkokäyrä, tilavuus ja biomassa) integrointi laajojen alueiden inventointeihin, TLS-koealojen hyödyntäminen operatiivisessa valtakunnan metsien inventoinnissa (VMI) sekä laajojen koealojen mittaaminen TLS:llä, esimerkiksi operatiivisen leimikkosuunnittelun yhteydessä. Lisäksi tarvitaan edelleen jatkotutkimuksia TLS-mittausten tarkkuudesta erilaisissa metsiköissä (kehitysluokka, puulaji, aluskasvillisuuden määrä).
  • Yrttimaa, Tuomas; Saarinen, Ninni; Kankare, Ville; Viljanen, Niko; Hynynen, Jari; Huuskonen, Saija; Holopainen, Markus; Hyyppa, Juha; Honkavaara, Eija; Vastaranta, Mikko (2020)
    Terrestrial laser scanning (TLS) provides a detailed three-dimensional representation of surrounding forest structures. However, due to close-range hemispherical scanning geometry, the ability of TLS technique to comprehensively characterize all trees, and especially upper parts of forest canopy, is often limited. In this study, we investigated how much forest characterization capacity can be improved in managed Scots pine (Pinus sylvestris L.) stands if TLS point clouds are complemented with photogrammetric point clouds acquired from above the canopy using unmanned aerial vehicle (UAV). In this multisensorial (TLS+UAV) close-range sensing approach, the used UAV point cloud data were considered especially suitable for characterizing the vertical forest structure and improvements were obtained in estimation accuracy of tree height as well as plot-level basal-area weighted mean height (H-g) and mean stem volume (V-mean). Most notably, the root-mean-square-error (RMSE) in H-g improved from 0.8 to 0.58 m and the bias improved from -0.75 to -0.45 m with the multisensorial close-range sensing approach. However, in managed Scots pine stands, the mere TLS also captured the upper parts of the forest canopy rather well. Both approaches were capable of deriving stem number, basal area, V-mean, H-g, and basal area-weighted mean diameter with the relative RMSE less than 5.5% for all the sample plots. Although the multisensorial close-range sensing approach mainly enhanced the characterization of the forest vertical structure in single-species, single-layer forest conditions, representation of more complex forest structures may benefit more from point clouds collected with sensors of different measurement geometries.
  • Vastaranta, Mikko; Saarinen, Ninni; Kankare, Ville; Holopainen, Markus; Kaartinen, Harri; Hyyppa, Juha; Hyyppa, Hannu (2014)
  • Holopainen, Markus; Vastaranta, Mikko; Hyyppa, Juha (2014)
  • Junttila, Samuli; Hölttä, Teemu; Puttonen, Eetu; Katoh, Masato; Vastaranta, Mikko; Kaartinen, Harri; Holopainen, Markus; Hyyppä, Hannu (Elsevier, 2021)
    Remote Sensing of Environment
    During the past decades, extreme events have become more prevalent and last longer, and as a result drought-induced plant mortality has increased globally. Timely in-formation on plant water dynamics is essential for under-standing and anticipating drought-induced plant mortality. Leaf water potential (ΨL), which is usually measured de-structively, is the most common metric that has been used for decades for measuring water stress. Remote sensing methods have been developed to obtain information on water dynamics from trees and forested landscapes. However, the spatial and temporal resolutions of the existing methods have limited our understanding of the water dynamics and diurnal variation of ΨL within single trees. Thus, we investi-gated the capability of terrestrial laser scanning (TLS) in-tensity in observing diurnal variation in ΨL during a 50-h monitoring period. We aimed to improve the understanding on how large a part of the diurnal variation in ΨL can be captured using TLS intensity observations. We found that TLS intensity at the 905 nm wavelength measured from a static position was able to explain 77% of the variation in ΨL for three trees of two tree species with a root mean square error of 0.141 MPa. Based on our experiment with three trees, a time series of TLS intensity measurements can be used in detecting changes in ΨL, and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.
  • Junttila, Samuli; Campos, Mariana; Hölttä, Teemu; Lindfors, Lauri; El Issaoui, Aimad; Vastaranta, Mikko; Hyyppä, Hannu; Puttonen, Eetu (MDPI AG, 2022)
    Forests
    Physiological processes cause movements of tree stems and branches that occur in a circadian rhythm and over longer time periods, but there is a lack of quantitative understanding of the cause-and-effect relationships. We investigated the movement of tree branches in a long-term drought experiment and at a circadian time scale using time-series of terrestrial laser scanning measurements coupled with measurements of environmental drivers and tree water status. Our results showed that movement of branches was largely explained by leaf water status measured as leaf water potential in a controlled environment for both measured trees (R2 = 0.86 and R2 = 0.75). Our hypothesis is that changes in leaf and branch water status would cause branch movements was further supported by strong relationship between vapor pressure deficit and overnight branch movement (R2 = [0.57–0.74]). Due to lower atmospheric water demand during the nighttime, tree branches settle down as the amount of water in leaves increases. The results indicate that the quantified movement of tree branches could help us to further monitor and understand the water relations of tree communities.
  • Saarinen, Ninni; Calders, Kim; Kankare, Ville; Yrttimaa, Tuomas; Junttila, Samuli; Luoma, Ville; Huuskonen, Saija; Hynynen, Jari; Verbeeck, Hans (2021)
    Tree functional traits together with processes such as forest regeneration, growth, and mortality affect forest and tree structure. Forest management inherently impacts these processes. Moreover, forest structure, biodiversity, resilience, and carbon uptake can be sustained and enhanced with forest management activities. To assess structural complexity of individual trees, comprehensive and quantitative measures are needed, and they are often lacking for current forest management practices. Here, we utilized 3D information from individual Scots pine (Pinus sylvestris L.) trees obtained with terrestrial laser scanning to, first, assess effects of forest management on structural complexity of individual trees and, second, understand relationship between several tree attributes and structural complexity. We studied structural complexity of individual trees represented by a single scale-independent metric called "box dimension." This study aimed at identifying drivers affecting structural complexity of individual Scots pine trees in boreal forest conditions. The results showed that thinning increased structural complexity of individual Scots pine trees. Furthermore, we found a relationship between structural complexity and stem and crown size and shape as well as tree growth. Thus, it can be concluded that forest management affected structural complexity of individual Scots pine trees in managed boreal forests, and stem, crown, and growth attributes were identified as drivers of it.