Comparison of forest attributes derived from two terrestrial lidar systems.

Abstract Terrestrial lidar (TLS) is an emerging technology for deriving forest attributes, including conventional inventory and canopy characterizations. However, little is known about the influence of scanner specifications on derived forest parameters. We compared two TLS systems at two sites in British Columbia. Common scanning benchmarks and identical algorithms were used to obtain estimates of tree diameter, position, and canopy characteristics. Visualization of range images and point clouds showed clear differences, even though both scanners were relatively high-resolution instruments. These translated into quantifiable differences in impulse penetration, characterization of stems and crowns far from the scan location, and gap fraction. Differences between scanners in estimates of effective plant area index were greater than differences between sites. Both scanners provided a detailed digital model of forest structure, and gross structural characterizations (including crown dimensions and position) were relatively robust; but comparison of canopy density metrics may require consideration of scanner attributes

Terrestrial laser scanning in forest inventories

AbstractDecision making on forest resources relies on the precise information that is collected using inventory. There are many different kinds of forest inventory techniques that can be applied depending on the goal, scale, resources and the required accuracy. Most of the forest inventories are based on field sample. Therefore, the accuracy of the forest inventories depends on the quality and quantity of the field sample. Conventionally, field sample has been measured using simple tools. When map is required, remote sensing materials are needed. Terrestrial laser scanning (TLS) provides a measurement technique that can acquire millimeter-level of detail from the surrounding area, which allows rapid, automatic and periodical estimates of many important forest inventory attributes. It is expected that TLS will be operationally used in forest inventories as soon as the appropriate software becomes available, best practices become known and general knowledge of these findings becomes more wide spread. Meanwhile, mobile laser scanning, personal laser scanning, and image-based point clouds became capable of capturing similar terrestrial point cloud data as TLS. This paper reviews the advances of applying TLS in forest inventories, discusses its properties with reference to other related techniques and discusses the future prospects of this technique

Laserbasert oppmåling av bygningsobjekter og bygninger

Building information models (BIMs) for facility management is gaining interest. Different technologies for collecting the raw material to extract such model are in rapid development. The most common technologies are based on images, structure light, laser or a combination of these. The new technologies have the potential to provide efficient data collection, but not necessarily at the same accuracy compared to the traditional methods. This thesis has explored how to rapidly establish a BIM for an existing building. This was done by investigating two different aspects related to this task. The first aspect was related to product specification and provide a framework for ordering and controlling a laser-based survey of a building. The second aspect explores how a laser-based system could be used to rapidly survey an existing building. Through the thesis and the first aspect, it is shown that the Norwegian survey community is lacking an unambiguous product specification for building surveys performed for BIM extraction and that the survey seldomly is adequately controlled. Based on these findings a product specification has been developed in cooperation with building owners. This cooperation made it possible to test the product specification in real projects. The product specification was developed through three different versions. The zero version was presented at the World Building Congress in 2016 and was tested in a renovation project at the Norwegian University of Life Sciences. The evaluation of the project led to the first version that was used in a framework competition arranged by Ullensaker municipality in the south-east of Norway. The result led to the second and final version of the product specification. The proposed product specification follows a simplified transaction pattern between the customer and the producer. The focus has been on the customer's request for a building survey suitable for BIM extraction and the customer's acceptance actions when the building survey is delivered. The acceptance actions are based on well–known standards created by the Norwegian Mapping Authority. The customer request is based on the acceptance actions. This ensures that every requirements can be verified in the accepting stage. The main purposes of the product specification were to ensure reliable results and to minimize the difference between the customer request and the producer’s delivery. Additionally, an unambiguous product specification can ensure a fair competition situation between the producers and give the producers the possibility to select the best-suited technology. The second aspect is related to how a building can be efficiently surveyed and explores how this could be done with a laser-based system. A human carried survey system was developed through three stages. The first and second stages focused on circle shaped objects and were realized in cooperation with the Faculty of Environmental Sciences and Natural Resource Management at the Norwegian University of Life Sciences. The system surveyed tree diameter at breast height within sample plots in size 250-500 m2. The system was able to detect 87.5% of the trees with a mean difference of 0.1 cm, and a root mean square of 2.2 cm. The novel aspect is related to how the trees are segmented and how the diameters are estimated without losing precision due to degraded pose solution. The result can be used in forestry inventory projects together with airborne laser surveys. The third stage was made for indoor measurements. The main focus was on how to aid the navigation solution in the absence of Global Navigation Satellite System signals. The method divides the laser point measurements into small time frames. For each time frame, the laser points were automatically classified into column, walls, floor, and ceiling. This information was used to support a scan matching method called semantic-assisted normal distributions transform. The result from the scan matching was used to create a trajectory of the walking path followed during data capture. This result was fed back into the inertial navigation processing to aid the solution when the system was located inside the building. This gives the inertial navigation process the ability to reject scan matching failures. The novel method was able to improve the survey accuracy from a maximum deviation of 12.6 m to 1.1 m. The third stage had two different Inertial Measurement Units (IMU) installed. The most accurate system was a tactical graded IMU, and the lowest accurate system was an automotive graded IMU. With the proposed method, the automotive graded system was able to perform at a higher level than a standalone tactical graded solution.Interessen for å bruke BygningsInformasjonsModeller (BIMer) i forvaltning, drift og vedlikehold av bygninger er økende. Ulike teknologier for innsamling av data for å etablere slike modeller er i rask utvikling. De vanligste teknologiene er basert på bilder, strukturert lys, laser eller en kombinasjon av disse. Ny teknologi utfører målingene veldig effektivt, men ikke med samme nøyaktighet som tradisjoneller metoder. Denne studien har undersøkt hvordan en raskt kan etablere en BIM i et eksisterende bygg. Dette ble gjort ved å utforske to ulike aspekter av problemstillingen. Det første aspektet ser på produktspesifikasjon og foreslår et rammeverk til bruk ved bestilling og kontroll av laser-basert innmåling av eksisterende bygning. Det andre aspektet utforsker hvordan et laser-basert system raskt kan måle opp eksisterende bygg.The Norwegian Building Authority, Cautus Geo AS and Geomatikk survey have kindly founded parts of the studies

Investigating the Feasibility of Multi-Scan Terrestrial Laser Scanning to Characterize Tree Communities in Southern Boreal Forests

Terrestrial laser scanning (TLS) has proven to accurately represent individual trees, while the use of TLS for plot-level forest characterization has been studied less. We used 91 sample plots to assess the feasibility of TLS in estimating plot-level forest inventory attributes, namely the stem number (N), basal area (G), and volume (V) as well as the basal area weighed mean diameter (Dg) and height (Hg). The effect of the sample plot size was investigated by using different-sized sample plots with a fixed scan set-up to also observe possible differences in the quality of point clouds. The Gini coefficient was used to measure the variation in tree size distribution at the plot-level to investigate the relationship between stand heterogeneity and the performance of the TLS-based method. Higher performances in tree detection and forest attribute estimation were recorded for sample plots with a low degree of tree size variation. The TLS-based approach captured 95% of the variation in Hg and V, 85% of the variation in Dg and G, and 67% of the variation in N. By increasing the sample plot size, the tree detection rate was decreased, and the accuracy of the estimates, especially G and N, decreased. This study emphasizes the feasibility of TLS-based approaches in plot-level forest inventories in varying southern boreal forest conditions

Puiden paikannus ja lajitunnistaminen maalaserkeilausaineistosta

The requirements for more accurate and up-to-date spatial data increases constantly due to changes occurring in the environment. In addition, there is a technical and economical need to map trees, tree ages and sizes, as well in wide forest areas as park areas in cities by modern scanning techniques. The aim of this thesis was to investigate different positioning methods for terrestrial laser scanned trees. The second aim was to examine different techniques to identify the species of the positioned trees. Laser scans from two separate relatively small woodlands were acquired for the thesis. These scans were utilised for tree locating and species identification. Tree positioning was based on the cylinder fitting method performed for tree stems provided by the scans. The results achieved by the positioning were analyzed based on the comparison to the manually measured reference values. To identify the tree species, the tree intensities and structure parameters extracted from the point clouds were used. According to the study results, the classification of some tree species was relatively well succeeded. However, the identification of some other species did not succeed as expected. The best classification correctness of 80 percent was achieved using the combination of tree intensities and the structure parameters, as well as by the structure parameters only. Classification using the intensities only provided considerably more unreliable results. Instead of that, one tree species (spruce) identification succeeded perfectly in each case. However, tree positioning succeeded obviously well, so the tree locations deviated slightly from the reference values. This examination indicated that a reliable evaluation of the tree classification results did not fully succeed with the relatively small tree sample size used in this thesis. To obtain more reliable estimate of success rate for the results provided by terrestrial laser scanning data, a larger sample size may be required. Furthermore, the laser scans for this work were performed in autumn when there were no leaves in the trees. This, of course, affected the intensity-based tree classification. However, modern tree positioning and classification methods appear quite promising. The future use of these techniques require further development and examination work.Yhä tarkemman ja ajantasaisen paikkatiedon tarve kasvaa jatkuvasti ympäristössä tapahtuvien nopeiden muutosten myötä. Tämä näkyy myös teknistaloudellisena tarpeena kartoittaa puulajeja, niiden ikää ja kokoa mm. erilaisilla nykyajan keilausmenetelmillä, niin laajoilla metsäalueilla kuin kaupunkien puistoalueilla. Tämän työn tavoitteena oli tutkia maastolaserkeilattujen puiden erilaisia paikannusmenetelmiä. Toisena tavoitteena oli tarkastella paikannettujen puiden lajitunnistusmenetelmiä. Työn toteuttamiseksi suoritettiin laserkeilauksia kahdella erillisellä pienehköllä metsäalueella. Näitä keilausaineistoja käytettiin puiden paikantamiseen ja lajitunnistukseen. Paikannus perustui keilausten tuloksena saaduille puun rungoille tehtyyn sylinterisovitusmenetelmään. Laskennalla saatuja tuloksia analysoitiin vertaamalla niitä referenssiarvoihin, jotka saatiin pistepilvistä manuaalisesti mittaamalla. Lajitunnistuksessa käytettiin puista saatujen pistepilvien intensiteettejä ja rakenneparametreja. Suoritetun tarkastelun perusteella joidenkin puulajien tunnistaminen onnistui melko hyvin. Kaikkien puiden tunnistaminen ei kuitenkaan onnistunut odotetulla tavalla. Käyttäen pistepilvien intensiteettien ja pistepilvistä saatujen puiden rakenneparametrien yhdistelmää, sekä pelkkiä rakenneparametreja, tulkittiin parhaimmillaankin noin 80 prosenttia tuloksista oikein. Pelkkiä intensiteettejä käyttäen saatiin huomattavasti epäluotettavampi tulos. Sen sijaan yhden puulajin (kuusen) tunnistaminen onnistui kaikissa tapauksissa täydellisesti. Toisaalta, suoritetussa tarkastelussa puiden paikantaminen onnistui kokonaisuudessaan hyvin, sillä laskennalla puille saadut sijainnit poikkesivat referenssiarvoista kauttaaltaan varsin vähän. Tarkastelu osoitti, että maalaserkeilattujen puiden tunnistaminen tässä työssä käytetyllä suhteellisen pienellä otoskoolla ei täysin onnistunut. Tarkempi arvio maalaserkeilausaineistosta saatujen tulosten onnistumisprosentista olisi edellyttänyt suurempaa otoskokoa. Lisäksi puiden laserkeilaukset tehtiin syksyllä, jolloin puissa ei ollut lehtiä. Tämä tietenkin vaikutti puiden tunnistamiseen intensiteettien avulla. Nykyiset puiden tunnistusmenetelmät vaikuttavat kuitenkin kokonaisuudessaan varsin lupaavilta. Menetelmien hyödyntäminen edellyttää yhä tutkimus- ja kehitystyötä

Carisma workshop: from 21 to 23 August 2017 in Helsinki, Finland

Abstraktit201

White paper – On the use of LiDAR data at AmeriFlux sites

Our aim is to inform the AmeriFlux community on existing and upcoming LiDAR technologies (atmospheric Doppler or Raman LiDAR often deployed at flux sites are not considered here), how it is currently used at flux sites, and how we believe it could, in the future, further contribute to the AmeriFlux vision. Heterogeneity in vegetation and ground properties at various spatial scales is omnipresent at flux sites, and 3D mapping of canopy, understory, and ground surface can help move the science forward