Use of Naturally Available Reference Targets to Calibrate Airborne Laser Scanning Intensity Data

We have studied the possibility of calibrating airborne laser scanning (ALS) intensity data, using land targets typically available in urban areas. For this purpose, a test area around Espoonlahti Harbor, Espoo, Finland, for which a long time series of ALS campaigns is available, was selected. Different target samples (beach sand, concrete, asphalt, different types of gravel) were collected and measured in the laboratory. Using tarps, which have certain backscattering properties, the natural samples were calibrated and studied, taking into account the atmospheric effect, incidence angle and flying height. Using data from different flights and altitudes, a time series for the natural samples was generated. Studying the stability of the samples, we could obtain information on the most ideal types of natural targets for ALS radiometric calibration. Using the selected natural samples as reference, the ALS points of typical land targets were calibrated again and examined. Results showed the need for more accurate ground reference data, before using natural samples in ALS intensity data calibration. Also, the NIR camera-based field system was used for collecting ground reference data. This system proved to be a good means for collecting in situ reference data, especially for targets with inhomogeneous surface reflection properties

Absolute Radiometric Calibration of ALS Intensity Data: Effects on Accuracy and Target Classification

Radiometric calibration of airborne laser scanning (ALS) intensity data aims at retrieving a value related to the target scattering properties, which is independent on the instrument or flight parameters. The aim of a calibration procedure is also to be able to compare results from different flights and instruments, but practical applications are sparsely available, and the performance of calibration methods for this purpose needs to be further assessed. We have studied the radiometric calibration with data from three separate flights and two different instruments using external calibration targets. We find that the intensity data from different flights and instruments can be compared to each other only after a radiometric calibration process using separate calibration targets carefully selected for each flight. The calibration is also necessary for target classification purposes, such as separating vegetation from sand using intensity data from different flights. The classification results are meaningful only for calibrated intensity data

Laserkeilaus puun rakenteen mallinnuksessa

Optimization of wood supply chain and monitoring climate change and human impact on environment creates ever growing need for accurate 3D information of biosphere. Carbon footprint of forests requires information of the size distribution of above ground biomass when logging waste is used as bioenergy. Terrestrial and aerial laser scanning are promising methods to produce dense 3D data from forests and single trees but automation of the data processing is challenge. In this master thesis a novel tree cylinder modelling algorithm developed at Tampere University of Technology is tested with 43 pines growing in the same test plot. Branch size distribution is calculated and divided in classes according to tree height. Hypothesis is that tree height and other ALS derivable tree metrics could be used to make large scale estimations of forest canopy structure when growing conditions are similar. The results point out that connection between tree height and size distribution of branches is present. The method can be further developed by improving data collection methods. Needles on the branches could be detected and classified using laser scanner intensity or spectral information from active hyper spectral LiDAR. Data acquisition could be sped up by use of mobile laser scanning.Metsätalouden tehostamistarve, ilmastonmuutos ja ihmisen toimien vaikutusten seuranta synnyttävät alati kasvavan tarpeen tarkalle kolmiulotteiselle informaatiolle metsistä ja yksittäisistä puista. Yhteiskunnallisesti merkittävässä metsäinventoinnissa arvioidaan myös metsän hiilijalanjälkeä mm. bioenergiatuotannon tarpeisiin, joten tarvitaan muutakin inventointitietoa kuin runkopuun tilavuus. Maa- ja ilmalaserkeilaus on ihanteellinen menetelmä tiheän kolmiulotteisen aineiston tuottamiseen metsistä, mutta aineiston käsittelyn automatisointi on osoittautunut haastavaksi. Diplomityön tarkoituksena on testata Tampereen teknillisessä yliopistossa kehitettyä uutta automaattista puun sylinterimallinnusmenetelmää puun oksiston kokorakenteen mallintamisessa. Aineistona käytetään 43 mäntyä, jotka kasvavat samalla koealalla ja tavoitteena on selvittää, voidaanko kokojakaumatietoa yleistää laajemmille alueille käyttämällä ilmalaserkeilauksella tuotettavaa puutunnusta, kuten puun korkeutta, yhdistävänä tekijänä. Työssä arvioitiin mittausmallinnusmenetelmän toimivuutta ja kehitettiin sen käytännön toteutusta. Työn tuloksena laskettiin oksiston kokojakaumat, jotka luokiteltiin puun korkeuden perusteella neljään luokkaan. Korrelaatio kokojakaumahistogrammin ja korkeuden välillä on olemassa, joten menetelmä vaikuttaa lupaavalta tavalta kerätä maastoferenssiaineistoa aluepohjaisen oksiston kokojakaumaestimoinnin tueksi. Jatkotutkimuksena menetelmän tarkkuutta voidaan parantaa kehittämällä mittausmenetelmää. Havupuiden neulasten havaitseminen aineistosta voidaan tehdä laserkeilauksen intensiteetin avulla tai käyttämällä aktiivisen hyperspektrilaserkeilaimen spektritietoa

Radiometric Calibration of Terrestrial Laser Scanners with External Reference Targets

The intensity data produced by terrestrial laser scanners has become a topic of increasing interest in the remote sensing community. We present a case study of radiometric calibration for two phase-shift continuous wave (CW) terrestrial scanners and discuss some major issues in correcting and applying the intensity data, and a practical calibration scheme based on external reference targets. There are differences in the operation of detectors of different (although similar type) instruments, and the detector effects must be known in order to calibrate the intensity data into values representing the target reflectance. It is, therefore, important that the effects of distance and target reflectance on the recorded intensity are carefully studied before using the intensity data from any terrestrial laser scanner

Monitoring Changes in Rice Cultivated Area from SAR and Optical Satellite Images in Ben Tre and Tra Vinh Provinces in Mekong Delta, Vietnam

The objective of this study was to obtain up-to-date information on land use and to identify long term changes in land use, especially rice, aquaculture and other crops in Ben Tre and Tra Vinh provinces in Vietnam’s Mekong Delta. Long-term changes in land-use of the study area have not been studied using long time series of SAR and optical Earth observation (EO) data before. EO data from 1979–2012 was used: ENVISAT ASAR Wide Swath Mode, SPOT and Landsat imagery. An unsupervised ISODATA classification was performed on multitemporal SAR images. The results were validated using ground truth data. Using the Synthetic Aperture Radar (SAR) imagery maps for 2005, 2009 and 2011 were obtained. Different rice crops, aquaculture and fruit trees could be distinguished with an overall accuracy of 80%. Using available optical imagery the time series was extended from 2005 to 1979. Long-term decrease in the rice acreage and increase in the aquaculture acreage could be detected

Analysis of Incidence Angle and Distance Effects on Terrestrial Laser Scanner Intensity: Search for Correction Methods

The intensity information from terrestrial laser scanners (TLS) has become an important object of study in recent years, and there are an increasing number of applications that would benefit from the addition of calibrated intensity data to the topographic information. In this paper, we study the range and incidence angle effects on the intensity measurements and search for practical correction methods for different TLS instruments and targets. We find that the range (distance) effect is strongly dominated by instrumental factors, whereas the incidence angle effect is mainly caused by the target surface properties. Correction for both effects is possible, but more studies are needed for physical interpretation and more efficient use of intensity data for target characterization

Tree Root System Characterization and Volume Estimation by Terrestrial Laser Scanning and Quantitative Structure Modeling

The accurate characterization of three-dimensional (3D) root architecture, volume, and biomass is important for a wide variety of applications in forest ecology and to better understand tree and soil stability. Technological advancements have led to increasingly more digitized and automated procedures, which have been used to more accurately and quickly describe the 3D structure of root systems. Terrestrial laser scanners (TLS) have successfully been used to describe aboveground structures of individual trees and stand structure, but have only recently been applied to the 3D characterization of whole root systems. In this study, 13 recently harvested Norway spruce root systems were mechanically pulled from the soil, cleaned, and their volumes were measured by displacement. The root systems were suspended, scanned with TLS from three different angles, and the root surfaces from the co-registered point clouds were modeled with the 3D Quantitative Structure Model to determine root architecture and volume. The modeling procedure facilitated the rapid derivation of root volume, diameters, break point diameters, linear root length, cumulative percentages, and root fraction counts. The modeled root systems underestimated root system volume by 4.4%. The modeling procedure is widely applicable and easily adapted to derive other important topological and volumetric root variables