Browsing by Subject "laserkeilaus"

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  • Hovi, Aarne (Helsingfors universitet, 2011)
    Understory trees often emerging beneath dominant tree layer in even-aged stands have significance for timber harvesting operations, forest regeneration, landscape and visibility analysis, biodiversity and carbon balance. Airborne laser scanning (ALS) has proven to be an efficient remote sensing method in inventory of mature forest stands. Recent introduction of ALS to operational forest inventory systems could potentially enable cost-efficient acquisition of information on understory tree layer. In this study, accurate field reference and discrete return LiDAR data (1–2 km flying altitude, 0.9–9.7 pulses m-2) were used. The LiDAR data were obtained with Optech ALTM3100 and Leica ALS50-II sensors. The field reference plots represented typical commercially managed, even-aged pine stands in different developmental stages. Aims of the study were 1) to study the LiDAR signal from understory trees at pulse level and the factors affecting the signal, and 2) to explore what is the explanatory power of area-based LiDAR features in predicting the properties of understory tree layer. Special attention was paid in studying the effect of transmission losses to upper canopy layers on the obtained signal and possibilities to make compensations for transmission losses to the LiDAR return intensity. Differences in intensity between understory tree species were small and varied between data sets. Thus, intensity is of little use in tree species classification. Transmission losses increased noise in intensity observations from understory tree layer. Compensations for transmission losses were made to the 2nd and 3rd return data. The compensations decreased intensity variation within targets and improved classification accuracy between targets. In classification between ground and most abundant understory tree species using 2nd return data, overall classification accuracies were 49.2–54.9 % and 57.3–62.0 %, and kappa values 0.03–0.13 and 0.10–0.22, before and after compensations, respectively. The classification accuracy improved also in 3rd return data. The most important variable explaining the transmission losses was the intensity from previous echoes and pulse intersection geometry with upper canopy layer had a minor effect. The probability of getting an echo from an understory tree was studied, and differences between tree species were observed. Spruce produced an echo with a greater probability than broadleaved trees. If the pulse was subject to transmission losses, the differences were increased. The results imply that area-based LiDAR height distribution metrics could depend on tree species. There were differences in intensity data between sensors, which are a problem if multiple LiDAR data sets are used in inventory systems. Also the echo probabilities differed between sensors, which caused minor changes in LiDAR height distribution metrics. Area-based predictors for stem number and mean height of understory trees were detected if trees with height < 1 m were not included. In general, predictions for stem number were more accurate than for mean height. Explanatory power of the studied features did not markedly decrease with decreasing pulse density, which is important for practical applications. Proportion of broadleaved trees could not be predicted. As a conclusion, discrete return LiDAR data could be utilized e.g. in detecting the need for initial clearings before harvesting operations. However, accurate characterization of understory trees (e.g. detection of tree species) or detection of the smallest seedlings seems to be out of reach. Additional research is needed to generalize the results to different forests.
  • Junttila, Samuli (Helsingin yliopisto, 2014)
    The effect of forest health and structure to the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Canopy surface temperature has long been recognized useful in monitoring vegetation water status. Recent studies have shown also its potential in monitoring vegetation health. Airborne thermal imagery, Airborne Light Detection and Ranging (LiDAR) and field measurements were acquired from the area of interest (AOI). The relative surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and logarithm of basal area at resolution of 254m2 (9-m radius). In other words, taller and older stands had colder surface temperatures. In addition, LiDAR metrics, such as height percentiles and canopy cover percentage, were compared with surface temperature. Standard deviation of canopy height model, height features (H90, CHM_max) and canopy cover percentage were most strongly negatively correlated with the surface temperature. On average, higher surface temperatures were detected in defoliated canopies indicating that thermal images may provide some additional information for classifying forests health status. However, the surface temperature of defoliated plots varied considerably. It was also found that surface temperature differences between canopy and ground responses were higher in defoliated plots. Based on the results, forest health and structure affect to the surface temperature captured by airborne thermal imagery and these effects should be taken into account when developing forest health mapping applications using thermal imagery.
  • Järnstedt, Janne (Helsingfors universitet, 2010)
    The objective of this study was to develop a method for estimation of forest stand variables and updating the forest resource data, based on a well known and widely used method among forest sector, aerial photography. The second objective was to produce information of cost-effectiveness and accuracy of digital surface model (DSM) generated from very high resolution aerial images in comparison of methods based on aerial laser scanning (ALS). The study area covering circa 2000 hectares is located in state owned forest in Hämeenlinna, Southern Finland. The study material consisted of 85 digitised and orthorectified colour-infrared (CIR) aerial photographs, LiDAR measurements of the corresponding area and field measurements of 402 concentric circular plots. Both the remote sensing data and the field measurements were acquired in 2009. In this study, the accuracy of DSM generated from very high resolution CIR - aerial images was examined in the estimation of forest stand variables. Estimation of forest stand variables was made using non-parametric k-nearest neighbour method. Sequential forward selection was used for selecting features from remote sensing data and the examination of accuracy was done with cross validation. The variables examined were mean diameter, basal area, mean height, dominant height and mean volume. Relative RMSE -values of DMS estimation were at the best with mean diameter, basal area, mean height, dominant height and mean volume 33,67 %, 36,23 %, 25,33 %, 23,53 % and 40,39 %. For the reference ALS-data, relative RMSE-values were 25,26 %, 27,89 %, 19,94 %, 16,76 % ja 31,26 %. Photogrammetric DSM was best suited for estimating dominant and mean height and produced estimates slightly more inaccurate than those of reference ALS-data. When estimating mean diameter, photogrammetric DSM was slightly better, but at mean volume estimation, ALS-data proved again to be a little more a accurate than photogrammetric DSM. At basal area estimation, ALS-data gave considerably better results than photogrammetric DSM. This research showed that the photogrammetric DSM suits well for updating the forest resource data, and also satisfies the requirements in a more economic way.
  • Nykänen, Mikko (Helsingfors universitet, 2011)
    In Finland collation of data needed in forest planning is changing from traditional standwise field inventory to area-based airborne laser scanning and aerial photography inventorying. The aim of this study was to compare prediction accuracy of stand total volume and diameter distribution using following methods: MSN, PRM, ML, FMM and Weibull-distribution. Results were calculated separately for pine, spruce, birch and other tree species. In addition need of calculation time and storage space was established. Sampling plot and stand information used in this study were collected in the vicinity of Evo, Finland. Total of 249 sampling plots were measured. 12 clear-cutting areas measured by logging machine were used as reference data. In addition area-based laser scanning and aerial photographbased features were used in estimation of variables of interest. Results were calculated in all 12 stands and stands which area was over 0,5 hectares (8 pcs). Number of grid neighbours differed between 1 and 10. Depending on method and number of neighbours the relative RMSE and bias of stand total volume varied between 20,76 – 52,86 % and -12,04 – 46,54 % respectively in all stands and between 6,74 – 59,41 % and -8,04 – 49,59 % respectively in stands which area was over 0,5 hectares. Calculation time varied strongly depending on method and number of neighbours. With more developed programming and programs calculation times could decrease substantially. Storage space needed in saving information is not an issue in tested methods even in large-scale applications. According to diameter distribution PRM-method predicts narrow distribution if sampling plot consists of only few trees nearly same size. This affected results especially in PRM2.
  • Järvinen, Vesa (Helsingin yliopisto, 2015)
    The purpose of this Master’s thesis is to find out what kind of views Finnish forest professionals have concerning forest data that’s based on laser scanning. Lately there have been a lot of changes in forest organizations and in the forest professional’s work environment. One of these big changes is that forest data based on laser scanning is becoming a part of operative forest planning. Extensive mapping of forest areas is more often done with airplane or satellite remote sensing. This way it is possible to cut down costs and make mapping more efficient by reducing sample plots and using more remote sensing data. This study focuses on this change from the perspective of an employee of a forest planning or advisory organization. The theoretical frame is action theory. The aim is to find out how this new forest data suits forest planning and is the quality of the data good enough to make forest plans. This research is a very topical subject because forest data that is based on laser scanning is going to bring significant changes to the forest planning field practices. The strengths of laser scanning are that it is objective and it gives at least as accurate tree data measures as other methods. Forest data based on laser scanning is also quite inexpensive, it can be acquired very quickly and it is easy to update. There is very little previous research about this subject. It is likely that new researched information is going to improve the usability of forest data that is based on laser scanning at forest planners’ everyday work. This research was implemented with web-based questionnaire and both quantitative and qualitative methods where used. The sample was taken from three forest organizations (The Finnish Forest Centre, OTSO Forest Services and The Forest Management Associations). The aim was to select forest professionals that use laser scanning based forest information at their work. The whole sample size was 929 respondents and the response rate was 37 percent. The research methods used were statistical description, cross tables and qualitative thematic analysis. When we look at the results it is clear that there are differences on how regularly forest data based on laser scanning is used in these three organizations. The Finnish Forest Centre and OTSO Forest services are using forest data based on laser scanning more often than The Forest Management Associations, but in all of these organizations there was a desire to use it more. The results of this study clearly show that a main part of forest professionals think that this new method is suitable for forest planning at least as an aid to making forest plans. The forest professionals also thought that there is still room for improvement in this new forest data collection method. There are too many errors at reliability especially in young and untreated forest. There is also a difficulty to determine the ratio of tree species. Generally it can be said that forest data based on laser scanning is liked among the forest professionals and they would like to use it more in the future.
  • Tanhuanpää, Topi (Helsingfors universitet, 2011)
    There is an ever growing interest in coarse woody debris (CWD). This is because of its role in maintaining biodiversity and storing atmospheric carbon. The aim of this study was to create an ALS-data utilizing model for mapping CWD and estimating its volume. The effect of grid cell size change to the model's performance was also considered. The study area is located in Sonkajärvi in eastern Finland and it consisted mostly of young commercially managed forests. The study utilized low-frequency ALS-data and precise strip-wise field inventory of CWD. The data was divided into two parts: one fourth of the data was used for modeling and the remaining three fourths for validating the models that were constructed. Both parametric and non-parametric modelling practices were used for modelling the area's CWD. Logistic regression was used to predict the probability of encountering CWD in grid cells of different sizes (0.04, 0.20, 0.32, 0.52 and 1.00 ha). The explanatory variables were chosen among 80 ALS-based variables and their conversions in three stages. Firstly, the variables were plotted against CWD volumes. Secondly, the best variables plotted in the first stage were examined in single-variable variable models. Thirdly, variables to the final multivariable model were chosen using 95 % level of significance. The 0.20 ha model was parametrized to other grid cell sizes. In addition to parametric model constructed with logistic regression, 0.04 ha and 1.0 ha grid cells were also classified with CART-modelling (Classification and Regression Trees). With CARTmodelling, non-linear dependecies were sought between ALS-variables and CWD. CART-models were constructed for both CWD existence and volume. When the existence of CWD in the study grid cells was considered, CART-modelling resulted in better classification than logistic regression. With logistic model the goodness of classification was improved as the grid cell size grew from 0.04 ha (kappa 0.19) to 0.32 ha (kappa 0.38). On 0.52 ha cell size, kappa value of the classification started to diminish (kappa 0.32) and was futhermore diminished to 1.0 ha cell size (kappa 0.26). The CART classification improved as the cell size grew larger. The results of CART-modelling were better than those of the logistic model in both 0.04 ha (kappa 0.24) and 1.0 ha (kappa 0.52) cell sizes. The relative RMSE of the cellwise CWD volume predicted with CART-models diminished as the cell size was enlarged. On 0.04 ha grid cell size the RMSE of the total CWD volume of the study area was 197.1 % and it diminished to 120.3 % as the grid cell size was enlarged to 1.0 ha. On the grounds of the results of this study it can be stated that the link between CWD and ALS-variables is weak but becomes slightly stronger when cell size increases. However, when cell size increases, small-scale variation of CWD becomes more difficult to spot. In this study, the existence of CWD could be estimated somewhat accurately, but the mapping of small-scale patterns was not successful with the methods that were used. Accurate locating of small-scale CWD variation requires further research, particularly on the use of high density ALS-data in CWD inventories.
  • Niemi, Pietari (Helsingin yliopisto, 2018)
    Suomen metsätalous on jo pitkään ollut kestävällä tasolla, sillä metsien vuotuiset hakkuut ovat pienemmät kuin vuotuinen metsänkasvu. Tulevaisuudessa puun tarve kuitenkin tulee kasvamaan, mikä tulee lisäämään hakkuiden määrää. Hakkuiden määrän lisääntyessä hyvälaatuisen puun kysyntä kasvaa, jolloin Suomen metsätalouden yksi suurimmista ongelmista – metsänhoitorästit, nostaa päätään. Metsänhoitorästit ovat Suomessa yleisimpiä taimikoissa ja nuorissa kasvatusmetsissä, jolloin ne vaikuttavat pitkällä tähtäimellä hakattavan puun laatuun. Rästien määrä taimikoissa ja nuorissa kasvatusmetsissä on lähes kaksinkertaistunut viimeisen kymmenen vuoden aikana. Maa- ja metsätalousministeriö onkin käynnistänyt Kansallinen metsästrategia 2025 -hankkeen, jonka yhtenä tavoitteena on keksiä ratkaisu metsänhoitorästien vähentämiseksi. Tämän tutkimuksen tarkoituksena oli selvittää laserkeilatun metsävaratiedon hyödyntämisen vaikutuksia metsänhoidon toimenpiteiden toteutumiseen eri alueilla ja eri omistajaryhmissä. Aineistona käytettiin yhdeksän maakunnan alueelta vuosina 2009–2016 mitattuja Valtakunnan metsien inventointi (VMI) 11 ja 12 maastokoealoja, joista osa oli Suomen Metsäkeskuksen 2010–2012 laserkeilaamalla alueella ja osa ei. Laserkeilatun metsävaratiedon hyödyntämisen erojen tarkastelun avuksi luotiin neljä logistista regressiomallia mallintamaan taimikonhoito- ja ensiharvennusrästien syntymisen todennäköisyyttä: 1) eri alueilla, 2) eri omistajaryhmissä, sekä taimikonhoidon ja ensiharvennuksen toteutumisen todennäköisyyttä 3) eri omistajaryhmissä, ja 4) ilman erottelua omistajien suhteen. Tulosten perusteella laserkeilattu metsävaratieto laskee taimikonhoito ja ensiharvennusrästien syntymisen todennäköisyyttä alueellisesti taimikoissa keskimäärin 0,8 % ja nuorissa kasvatusmetsissä 1,2 %. Omistajaryhmien välillä laserkeilattu metsävaratieto laski taimikonhoito- ja ensiharvennusrästien syntymisen todennäköisyyttä molemmissa omistajaryhmissä. Yksityisomistuksessa olevissa taimikoissa keskimäärin 1,5 % ja muut-ryhmän omistamissa 1 %. Ensiharvennusrästien syntymisen todennäköisyyttä keilaus laski yksityismetsissä keskimäärin 2,4 % ja muut-ryhmän omistamissa metsissä 1,8 %. Taimikonhoitojen ja ensiharvennusten toteutumisen todennäköisyyteen laserkeilatulla metsävaratiedolla oli alentava vaikutus. Keilaus laski taimikonhoidon todennäköisyyttä yksityismailla 1,3 % ja muut-ryhmän omistamilla mailla 1,2 %. Ilman omistajaryhmien huomioimista keilatulla alueella oli 1,1 % pienempi todennäköisyys taimikonhoidolle. Vastaavat luvut ensiharvennukselle olivat yksityismailla 1,5 %, muut-ryhmän mailla 1,3 % ja ilman omistajaryhmiä 1,2 %. Vaikka tutkimuksen mukaan laserkeilattu metsävaratieto laski taimikonhoito- ja ensiharvennusrästien syntymisen todennäköisyyttä, niin johtopäätösten kanssa täytyy olla varovainen, sillä metsänhoidon aktiivisuuteen vaikuttaa myös muita tekijöitä kuten metsänomistajien tavoitteet, alueen metsänhoitoyhdistyksen toiminta ja puun hinta. Laserkeilatun metsävaratiedon laskevaa vaikutusta taimikonhoidon ja ensiharvennuksen toteutumisen todennäköisyyteen ei voida perustella tämän tutkimuksen aineiston avulla. Tutkimus osoitti, että laserkeilatulla metsävaratiedolla on mahdollisesti metsänhoitoa aktivoiva vaikutus, mutta aihe vaatii vielä lisätutkimuksia.
  • Kokkoniemi, Samuli (Helsingfors universitet, 2012)
    Site index and site type are methods for describing a habitat’s highest annual production of tree (m3/ha/a). Site index is based on the growth of trees’ dominant height, and site type on the existence of plant communities in a habitat. This research examined whether site type can be estimated with site index derived by airborne laser scanning (ALS). ALS is a remote sensing method by which trees’ characteristics are predicted based on the height distribution and density values of laser pulses. Data were gathered from Syöte, Northern Ostrobothnia. Arbonaut Oy provided the ALS-data, and Metsähallitus provided age and habitat data of microstands. Site type, trees’ ages and dominant heights were also measured by field surveying. Experimental data from plots were generalized to microstand data. There were 208 experimental plots that were generalized to 39 microstands. Site indexes for experimental plots and microstands were calculated to index age 100 years with Vuokila and Väliaho’s (1980) growth models for dominant height and with Schumacher’s (1939) guide curve. Site indexes were converted to site types with Vuokila and Väliaho’s (1980) conversion diagram and then compared to site types of the field surveys. The accuracy of the site indexes was evaluated with an error matrix. Accuracy of age and dominant height was evaluated with a paired t-test. Variation of index aged dominant height inside a site type was examined with root mean square error (RMSE). The effect of the proportions of tree species on the site index was analyzed with a correlation coefficient. The percentage of properly classified site types was 57 % at best when using Schumacher’s (1939) guide curve and two site types (rich and poor). With Vuokila and Väliaho’s (1980) growth models for dominant height the best percentage of correctly classified site types was 46 %. The variation (RMSE) of index aged dominant height as an average in all site types was 3,2 m. The maximum variation of index aged dominant height in one site type was 6 m. This indicated that the dependency between site index and site type was poor with this data. The proportions of tree species did not have a significant effect on site index. Based on this study, predicting site types with ALS does not work. One problem is the absence of very rich site types. There are also many sources of error: SutiGIS’ (position knowledge system) age data, prescribed burning, possible fertilization of stands, and the problems of fitting site index and site type. Vuokila and Väliaho’s (1980) growth models for dominant height were made in the 1980s, so they do not acknowledge the increased growth of present-day trees. Site index cannot reliably predict the site type, but site index gives valuable extra information about the trees for example when evaluating the value of forest estates.
  • Kananen, Eero (Helsingfors universitet, 2017)
    Metsistä tarvitaan tarkkaa, ajantasaista ja harhatonta tietoa strategiseen suunnitteluun sekä operatiivisen metsä- ja leimikkosuunnittelun tarpeisiin. Perinteisesti tietoa on kerätty kuvioittaisella arvioinnilla, mutta tiedon tarpeen lisääntyessä ja kustannuksia karsittaessa on tullut tarvetta yhä tehokkaammille menetelmille. Tämän hetken tutkimusten valossa lupaavimmalle menetelmälle vaikuttaa lentolaserkeilaukseen (ALS) perustuva metsieninventointi ja monet suomalaiset metsäorganisaatiot ovatkin ottaneet sen käyttöön operatiivisessa metsävaratiedon tuottamisessa. Jotta menetelmän avulla saadulla tiedoilla voidaan luotettavasti tehdä päätöksiä, on sen laadusta pystyttävä varmistumaan. Tässä tutkimuksessa testattiin ja analysoitiin Tornator Oy:n laserkeilauspohjaisen metsävaratiedon laatua sekä laadun valvontamenetelmää. Tutkimusalueena oli noin 16 000 hehtaaria Tornatorin maita Etelä-Savossa. Alue oli laserkeilattu ja ilmakuvattu Blom Kartta Oy:n toimesta kesällä 2011 ja Blom Kartan tekemän tulkinnan tukena käytettiin Metsäkeskus Etelä-Savon mittaamia maastokoealoja (700 kpl). Tulosten laadun tarkastamiseksi suoritettiin kontrolli-inventoiniti kesällä 2012. Kontrolli-inventoinnissa suoritettiin alueen metsäkuviolle ositettu otanta, jolla valittiin 60 kuviota mitattaviksi. Kullekin kuviolle sijoitettiin 4-6 koealaa, joilta puustotiedot mitattiin. Tutkimuksen tavoitteena oli selvittää kuinka tarkkaa saavutettiinko inventoinnin suorittajalle asetetut laatuvaatimukset sekä kuinka inventoinnin laatua voidaan valvoa luotettavasti, kustannustehokkaasti ja riippumattomasti. Lisäksi tarkasteltiin kuinka inventointiaineistossa ilmenneet virheet vaikuttavat metsänhoitotoimenpiteiden määritykseen ja ajoitukseen. Tuloksia tarkasteltiin usealla eri tavalla kattavan käsityksen saamiseksi. 1) Tunnuksille laskettiin RMSE ja harha. 2) Tunnuksia tarkasteltiin visuaalisten kuvaajien avulla. 3) Muodostettiin pistekuviot 95 % luottamusväleillä ja tarkastettiin suhde 1:1 viivaan. 4) Muodostettiin Bland-Altman kuvat laskemalla kontrollimittauksen ja laserkeilauksen attribuuttien erotuksen keskiarvot ja kuvaamalla nämä vastaavien attribuuttien keskiarvoja vasten. 5) Yhdistämällä toleranssirajat Bland-Altman kuviin. Bland-Altman kuvia käytettäessä kumpaakaan menetelmää ei oleteta täysin tarkaksi ja siten ne tarjoavat oikeudenmukaista tulkintaa laadunvalvonnan tuloksille. Tulosten perusteella inventoinnin suorittajalle asetetut vaatimukset täyttyivät hyvin. Yksittäisillä kuvioilla ilmeni kuitenkin poikkeamia, joiden vaikutukset metsänhoitotoimenpiteiden ajoitukseen ovat merkittäviä. Laserkeilauspohjainen metsävaratieto toimii hyvin mestsäsuunnittelun tukena, mutta sen laadun varmistamiseksi on oltava käytössä menetelmä, jolla mahdolliset poikkeamat pystytään löytämään.
  • Junttila, Samuli; Vastaranta, Mikko; Liang, Xinlian; Kaartinen, Harri; Kukko, Antero; Kaasalainen, Sanna; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha (2017)
    Decreased leaf moisture content, typically measured as equivalent water thickness (EWT), is an early signal of tree stress caused by drought, disease, or pest insects. We investigated the use of two terrestrial laser scanners (TLSs) employing different wavelengths for improving the understanding how EWT can be retrieved in a laboratory setting. Two wavelengths were examined for normalizing the effects of varying leaf structure and geometry on the measured intensity. The relationship between laser intensity features, using red (690 nm) and shortwave infrared (1550 nm) wavelengths, and the EWT of individual leaves or groups of needles were determined with and without intensity corrections. To account for wrinkles and curvatures of the leaves and needles, a model describing the relationship between incidence angle and backscattered intensity was applied. Additionally, a reflectance model describing both diffuse and specular reflectance was employed to remove the fraction of specular reflectance from backscattered intensity. A strong correlation (R-2 = 0.93, RMSE = 0.004 g/cm(2)) was found between a normalized ratio of the two wavelengths and the measured EWT of samples. The applied intensity correction methods did not significantly improve the results of the study. The backscattered intensity responded to changes in EWT but more investigations are needed to test the suitability of TLSs to retrieve EWT in a forest environment.
  • Niemi, Mikko (Helsingfors universitet, 2013)
    Accurate and economical remote sensing method with good temporal resolution is required for mapping up-to-date information about the forest resources. Detecting forests by optical satellite images is an inaccurate procedure with the saturation problem. Airborne laser scanning (ALS) is a precise application, but the inventory process is slow and expensive. Recently the new synthetic aperture radar (SAR) satellites with a high spatial resolution have caused a renaissance of radar-based remote sensing. The purpose of the master’s thesis was to investigate the accuracy of forest mapping by radargrammetric processing of TerraSAR-X satellite images. The radargrammetry is based on stereoscopic measurement, which calculates 3D coordinates for corresponding points of the SAR image pair. In the research an area-based approach (ABA) was utilized to estimate forest attributes from the 3D points, and digital terrain model (DTM) produced by ALS was used to calculate height of the corresponding points. In plot-level the relative RMSEs for stem volume, biomass, basal area and mean height were 40.3 %, 39.9 %, 34.0 % and 15.9 %. In stands larger than 2 hectares the corresponding RMSEs were 20.2 %, 20.4 %, 36.1 % and 6.9 %. It’s notable that the estimation of basal area didn’t improve in stand-level at all. According to the research SAR radargrammetry is a precise technology to estimate forest canopy height, but the mapping of forest density is very unclear. Nevertheless the results about the estimation accuracy of forest stem volume and biomass by SAR radargrammetry were clearly better than the comparable estimation accuracy of optical satellite images.
  • Puolakka, Paula (Helsingfors universitet, 2010)
    Leaf and needle biomasses are key factors in forest health. Insects that feed on needles cause growth losses and tree mortality. Insect outbreaks in Finnish forests have increased rapidly during the last decade and due to climate change the damages are expected to become more serious. There is a need for cost-efficient methods for inventorying these outbreaks. Remote sensing is a promising means for estimating forests and damages. The purpose of this study is to investigate the usability of airborne laser scanning in estimating Scots pine defoliation caused by the common pine sawfly (Diprion pini L.). The study area is situated in Ilomantsi district, eastern Finland. Study materials included high-pulse airborne laser scannings from July and October 2008. Reference data consisted of 90 circular field plots measured in May-June 2009. Defoliation percentage on these field plots was estimated visually. The study was made on plot-level and methods used were linear regression, unsupervised classification, Maximum likelihood method, and stepwise linear regression. Field plots were divided in defoliation classes in two different ways: When divided in two classes the defoliation percentages used were 0–20 % and 20–100 % and when divided in four classes 0–10 %, 10–20 %, 20–30 % and 30–100 %. The results varied depending on method and laser scanning. In the first laser scanning the best results were obtained with stepwise linear regression. The kappa value was 0,47 when using two classes and 0,37 when divided in four classes. In the second laser scanning the best results were obtained with Maximum likelihood. The kappa values were 0,42 and 0,37, correspondingly. The feature that explained defoliation best was vegetation index (pulses reflected from height > 2m / all pulses). There was no significant difference in the results between the two laser scannings so the seasonal change in defoliation could not be detected in this study.
  • Imponen, Joni (Helsingfors universitet, 2015)
    Metsäkanalintujen elinympäristövaatimukset tunnetaan Suomessa hyvin ja elinympäristöihin kiinnitetään yhä enemmän huomiota osana metsän- ja luonnonhoidon toimia. Metso (Tetrao urogallus) ja pyy (Tetrastes bonasia) ovat elinympäris-töjen valinnassaan melko tarkkoja ja lajien välillä on selkeitä eroja. Elinympäristöjen ennakkotarkasteluun ei tällä hetkellä ole olemassa monipuolisia metsäsuunnittelun työkaluja ja lentolaserkeilauksella kerättyä aineistoa ei ole käytetty metsä-kanalintujen elinympäristötutkimuksiin Suomessa. Tässä kvalitatiivisessa tutkimuksessa selvitettiin Maanmittauslaitoksen vuonna 2012 keräämän lentolaserkeilausai-neiston soveltuvuutta potentiaalisten metso- ja pyyelinympäristöjen ohjaamattomaan luokitukseen. Aineiston pulssitiheys oli 0,74–0,8 / m2. Tutkimusalueena oli noin 1 200 hehtaaria Metsähallituksen omistamaa metsätalousmetsää Hämeenlinnan Evolla. Tutkimusalue jaettiin 16 x 16 metrin soluihin. Laserkeilausaineistosta laskettiin viisi elinympäristöä kuvaavaa lisäpiirrettä: latvuspeitto CC, alikasvostunnus US, puuston korkeusosuuden tiheystunnus k60_den, korkeusosuuden keski-hajonta H60_stdv sekä pituustunnus H_max. Menetelmänä käytettiin solukohtaista ohjaamatonta luokitusta (K-means), joka jakoi solut 43 luokkaan. Edelleen kohdennettuun maasto-otantaan valittiin 16 luokkaa. Säteeltään kiinteitä 9 metrin ympyräkoealoja mitattiin alueelta kaikkiaan 168 kpl, joista selkeitä pyykohteita ja vähintään arvosanalla 8 arvioituja metsokohteita oli molempia 12 kpl. Ohjaamaton luokitus ei nostanut esiin yhtä tai useampaa potentiaalisia kohteita kuvaavaa luokkaa, vaan potentiaalisten kohteiden lisäksi luokissa oli paljon ei-potentiaalisia soluja. Vähintään arvosanalla 8 arvioitujen metsokohteiden lisäpiirteet täyttäviä kohteita oli suhteellisesti eniten luokissa 3, 7 ja 8 osuuksilla 40,4 %, 35,6 % ja 31,8 %. Vastaavasti pyylle osuudet luokissa 4, 18 ja 20 olivat 38,4 %, 28,5 % ja 23,8 % minimiarvosanalla 6. Tutkimusalue sisältää arvioitujen kohteiden lisäpiirteiden perusteella hyviä elinympäristöjä metsolle (Arvosana ≥ 8) 15,0 % ja pyylle (Arvosana ≥ 6) 9,2 % sen pinta-alasta. Korkeimman arvosanan kohteiden lisäpiirteiden arvojen herkkyysanalyysissä alueet olivat vastaavasti 8,5 % ja 14,4 % kunkin lisäpiirteen ± 30 % marginaaleilla. Arvosanarajoite toimi loogisesti eli lisäpiirteiden vaihteluväli kapeni arvosanan kasvaessa. Tuloksena saadut poten-tiaaliset solut olivat toisiinsa erittäin kytkeytyneitä molemmissa analyyseissä vaikka käytetty menetelmä oli täysin riip-pumaton solujen sijainnista toistensa suhteen. Pyyhavainnot olivat potentiaalisuutta kuvaavalla solulla neljässä ja hyvin lähellä potentiaalisuutta kuvaavaa solua kahdessa havainnossa kuudesta, kun lisäpiirteiltään potentiaaliset solut valittiin arvosanoihin perustuen. Käytetyn aineiston kyky kuvata tässä tutkimuksessa määritettyjä potentiaalisia kohteita on siis lupaava. Aineiston kykyä tulee kuitenkin edelleen testata ennen kuin luotettavia metsäsuunnittelun työkaluja voidaan soveltaa operatiiviseen käyttöön.
  • Lindberg, Aapo (Helsingfors universitet, 2016)
    In recent years objectives to increase fuelwood usage have created a need to develop new re-mote sensing based methods to map fuelwood reserves. Laser scanning (LiDAR) is a remote sensing method which has been used in traditional forest inventories on large forest areas. These inventories have mainly concentrated on the stem volume instead of the total tree bio-mass. Former studies concerning fuelwood inventory accuracy have been made on a sample plot level. The aim of this study was to determine the precision of LiDAR based fuelwood inventory on a forest stand level. Wood stem volume and biomass estimates were produced by using two dif-ferent methods: point cloud and digital terrain model. The estimates were compared with field inventory results and results from the multi-source National Forest Inventory. Of the two compared methods the point cloud method was found to be more accurate than the method based on digital terrain model. When the point cloud was used, the accuracy (RMSE %) of the most important fuelwood estimates were following: waste wood vol-ume 37.4 %, branch biomass 21.8 % and stump biomass 18.6 %. The study indicates that re-sults got by laser scanning are on similar level as results got with traditional standwise inventory. This study concentrated only to predict the amount of fuelwood on the forest stand level. The suitability of the stand for fuelwood harvesting was not estimated. In order to utilize LiDAR-based fuelwood inventory for wood acquisition in forest industry, methods to estimate the suita-bility of the stand for harvesting need to be developed.
  • Wallenius, Tarja (Helsingfors universitet, 2010)
    In this study, a quality assessment method based on sampling of primary laser inventory units (microsegments) was analysed. The accuracy of a laser inventory carried out in Kuhmo was analysed as a case study. Field sample plots were measured on the sampled microsegments in the Kuhmo inventory area. Two main questions were considered. Did the ALS based inventory meet the accuracy requirements set for the provider and how should a reliable, cost-efficient and independent quality assessment be undertaken. The agreement between control measurement and ALS based inventory was analysed in four ways: 1) The root mean squared errors (RMSEs) and bias were calculated. 2) Scatter plots with 95% confidence intervals were plotted and the placing of identity lines was checked. 3) Bland-Altman plots were drawn so that the mean difference of attributes between the control method and ALS-method was calculated and plotted against average value of attributes. 4) The tolerance limits were defined and combined with Bland-Altman plots. The RMSE values were compared to a reference study from which the accuracy requirements had been set to the service provider. The accuracy requirements in Kuhmo were achieved, however comparison of RMSE values proved to be difficult. Field control measurements are costly and time-consuming, but they are considered to be robust. However, control measurements might include errors, which are difficult to take into account. Using the Bland-Altman plots none of the compared methods are considered to be completely exact, so this offers a fair way to interpret results of assessment. The tolerance limits to be set on order combined with Bland-Altman plots were suggested to be taken in practise. In addition, bias should be calculated for total area. Some other approaches for quality control were briefly examined. No method was found to fulfil all the required demands of statistical reliability, cost-efficiency, time efficiency, simplicity and speed of implementation. Some benefits and shortcomings of the studied methods were discussed.