Concepts and solutions to overcome the refraction problem in terrestrial precision measurement

Refraction is a detrimental problem in terrestrial optical measurements and can be regarded as major source of systematic errors in the precise determination of distances and directions. In general, refraction is a function of the density inhomogeneities of the propagation medium. As the “classical” method of temperature-gradient determination, it does not meet the requirement of a representative integral determination of the refractive index gradient fi eld. At the Institute of Geodesy and Photogrammetry of the ETH Zurich, two methods to determine and correct the refraction infl uence have been developed further during the last few years. One approach focuses on determining the refractive index gradient in measuring the turbulence of the air by scintillometry or CDD-based image processing, which is presently the key technology in tracking tacheometers and digital levels. Turbulence is a measure of the energy in the heat exchanging process and can be converted by the Monin-Obukov-Similarity into temperature gradients. Th e advantage of optical scintillation measurements is to derive line-averaged-turbulence parameters of the atmospheric surface layer. Another challenging approach was the successful development of a compact laser-dispersometer at the ETH, which could be a component of actual geodetic instruments in the future. A dispersometer theodolite, based on the dual-wavelength method for dispersive air, is capable of refraction-free direction measurements. Th e results of both technologies, turbulence determination and dispersometry, will be presented and discussed in this paper. Article in English Refrakcijos mažinimo preciziniuose žemės paviršiaus matavimuose sprendimai bei koncepcijos Refrakcija – esminė problema optiniuose žemės paviršiaus matavimuose ir yra laikoma pagrindine sistemingųjų paklaidų priežastimi nustatant atstumą bei kryptį. Bendrąja prasme refrakcija yra tankio nevienalytiškumo šviesos sklidimo terpėje funkcija. Kadangi „klasikinis“ temperatūrinio gradiento nustatymo metodas neatitinka reikalavimų, keliamų nustatant tipinį integralųjį atspindžio indekso gradiento lauką, pastaraisiais metais Ciuricho ETH Geodezijos ir fotogrametrijos institute buvo sukurti du refrakcijos įtakos tyrimo bei koregavimo būdai. Vienu būdu atspindžio indekso gradientas randamas matuojant oro turbulenciją scintilometriškai ar apdorojant CCD (Charge Coupled Device) vaizdą. Tai dabar pagrindinė tacheometrų bei skaitmeninių nivelyrų stebėjimo technologija.Turbulencija yra energijos šilumos mainuose matas. Monino ir Obuchovo panašumo metodu iš turbulencijos gali būti apskaičiuotas temperatūrinis gradientas. Optinės scintiliacijos matavimų pranašumas yra vidutinių turbulencijos parametrų radimas tiriant atmosferinio paviršiaus sluoksnį. Kitas įdomus būdas tapo prieinamas sukūrus lazerinį dispersometrą ETH. Jis ateityje galėtų tapti serijinių geodezinių prietaisų dalimi. Dispersometrinis teodolitas, kurio veikimo principas grindžiamas dvigubojo bangos ilgio sklindančiame ore metodu, matuojant padeda išvengti refrakcijos. Straipsnyje aptarti abiejų minėtųjų technologijų – turbulencijos nustatymo bei dispersometrijos rezultatai

A tool to model 3D coarse-root development with annual resolution

Dynamic root-development models are indispensable for biomechanical and biomass allocation studies, and also play an important role in understanding slope stability. There are few root-development models in the literature, and there is a specific lack of dynamic models. Therefore, the aim of this study is to develop a 3D growth-development model for coarse roots, which is species independent, as long as annual rings are formed. In order to implement this model, the objectives are (I) to interpolate annual growth layers, and (II) to evaluate the interpolations and annual volume computations. The model developed is a combination of 3D laser scans and 2D tree-ring data. A FARO laser ScanArm is used to acquire the coarse-root structure. A MATLAB program then integrates the ring-width measurements into the 3D model. A weighted interpolation algorithm is used to compute cross sections at any point within the model to obtain growth layers. The algorithm considers both the root structure and the ring-width data. The model reconstructed ring profiles with a mean absolute error for mean ring chronologies of <9% and for single radii of <20%. The interpolation accuracy was dependent on the number of input sections and root curvature. Total volume computations deviated by 3.5-6.6% from the reference model. A new robust root-modelling tool was developed which allows for annual volume computations and sophisticated root-development analyse

Incorporating 2D tree-ring data in 3D laser scans of coarse-root systems

In times of global change biomass calculations and the carbon cycle is gaining in importance. Forests act as carbon sinks and hence, play a crucial role in worlds and forests carbon budgets. Unfortunately, growth models and biomass calculations existing so far mainly concentrate on the above-ground part of trees. For this reason, the aim of the present study is to develop an annually resolved 3D growth model for tree roots, which allows for reliable biomass calculations and can later be combined with above-ground models. A FARO scan arm was used to measure the surface of a tree-root segment. In addition, ring-width measurements were performed manually on sampled cross sections using WinDENDRO. The main goal of this study is to model root growth on an annual scale by combining these data sets. In particular, a laser scan arm was tested as a device for the realistic reproduction of tree-root architecture, although the first evaluation has been performed for a root segment rather than for an entire root system. Deviations in volume calculations differed between 5% and 7% from the actual volume and varied depending on the used modeling technique. The model with the smallest deviations represented the structure of the root segment in a realistic way and distances and diameter of cross sections were acceptable approximations of the real values. However, the volume calculations varied depending on object complexity, modeling technique and order of modeling steps. In addition, it was possible to merge tree-ring borders as coordinates into the surface model and receive age information in connection with the spatial allocation. The scan arm was evaluated as an innovative and applicable device with high potential for root modeling. Nevertheless, there are still many problems connected with the scanning technique which have an influence on the accuracy of the model but are expected to improve with technical progres

How to Evaluate the Quality of Airborne Laser-Scanning Data

The discussion on the quality of digital elevation models form airborne laser scanner was dominated by the proof of vertical and horizontal accuracy. If the accuracy criteria were verified by ground control points, the evidence of high quality was produced. Based on experiences in projects for the Swiss Federal Office of Topography and according to the lidar requirements formulated by the US American Federal Emergency and Mapping Agency (FEMA) the interpretation of quality must change. Six different quality indicators are described as starting point for enhanced specification of laser data sets. Indicators are worthless if they do not contain a level of acceptance; for each indicator a proposal is discussed. With the help of the more precise requirements and specifications the quality evaluation is simplified. A common understanding of the quality between contractual partners is mandatory for efficient and effective lidar projects.ISSN:1682-1750ISSN:2194-9034ISSN:1682-177

Calibration for increased accuracy of the range imaging camera SwissRanger

Range imaging is a new suitable choice for measurement and modeling in many different applications. But due to the technology’srelatively new appearance on the market with a few different realizations, the knowledge of its capabilities is very low. In most applications, like robotics and measurement systems, the accuracy wanted, lies at some millimeters. The raw data of range imaging cameras do not reach this level. Therefore, the calibration of the sensors output is needed. In this paper some of the parameters which influence the behavior and performance of the range imaging camera SwissRangerTM (provided by the Swiss Center for Electronics and Microtechnology - CSEM) are described. Because of the highly systematic structure and correlations between parameters and output data, a parameter based calibration approach is presented. This includes a photogrammetric camera calibration and a distance system calibration with respect to the reflectivity and the distance itself.ISSN:1682-1750ISSN:2194-9034ISSN:1682-177

Ad-Hoc Wireless Sensor Positioning in Hazardous Areas

This paper investigates the capability of GNSS aided smart sensor network positioning based on Wireless Local Area Network (WLAN) signals incorporating access points, to monitor 3D deformation associated with volcanic activity and other comparable hazardous events. While a small number of GNSS receivers provide the coordinate and time references, low-cost low-power wireless sensor nodes with ranging capabilities create a dense positioning network. The simulations presented in this paper arebased on a novel positioning algorithm that is robust with respect to errors in the inter-node range measurements. Based on a fine digital surface model of the Sakurajima volcano, various scenarios for setting up a monitoring network are assessed. The optimal number and location of nodes is determined for a future deployment of such a wireless sensor network. Results show that 2D positioning accuracy is to be expected in the magnitude of the mean range observation error. However, the crucial height component exhibits twice the error variance compared to the horizontal component. This is due to the poor geometric configuration in relation to height that is intrinsic to a ground based network.ISSN:1682-1750ISSN:2194-9034ISSN:1682-177

Incorporating 2D tree-ring data in 3D laser scans of coarse-root systems

ISSN:0032-079XISSN:1573-503

A tool to model 3D coarse-root development with annual resolution

ISSN:0032-079XISSN:1573-503