• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 462
  • 137
  • 95
  • 60
  • 49
  • 30
  • 25
  • 15
  • 12
  • 11
  • 6
  • 4
  • 3
  • 3
  • 3
  • Tagged with
  • 1086
  • 166
  • 161
  • 156
  • 116
  • 111
  • 107
  • 95
  • 90
  • 87
  • 79
  • 77
  • 71
  • 71
  • 66
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Single Chip LIDAR with Discrete Beam Steering by Digital Micromirror Device

Smith, Braden James, Smith, Braden James January 2017 (has links)
A novel method of beam steering that utilizes a mass-produced Digital Micromirror Device (DMD) enables a large field of view and reliable single chip Light Detection and Ranging (LIDAR). Using a short pulsed laser, the micromirrors' rotation is frozen mid-transition which forms a programmable blazed grating which efficiently redistributes the light to a single diffraction order, among several. With a nanosecond 905nm laser and Si avalanche photo diode, measurement accuracy of < 1 cm for 3340 points/sec is demonstrated over a 1 m distance range and with a 48° full field of view.
12

3D Reconstruction Using Lidar and Visual Images

Duraisamy, Prakash 12 1900 (has links)
In this research, multi-perspective image registration using LiDAR and visual images was considered. 2D-3D image registration is a difficult task because it requires the extraction of different semantic features from each modality. This problem is solved in three parts. The first step involves detection and extraction of common features from each of the data sets. The second step consists of associating the common features between two different modalities. Traditional methods use lines or orthogonal corners as common features. The third step consists of building the projection matrix. Many existing methods use global positing system (GPS) or inertial navigation system (INS) for an initial estimate of the camera pose. However, the approach discussed herein does not use GPS, INS, or any such devices for initial estimate; hence the model can be used in places like the lunar surface or Mars where GPS or INS are not available. A variation of the method is also described, which does not require strong features from both images but rather uses intensity gradients in the image. This can be useful when one image does not have strong features (such as lines) or there are too many extraneous features.
13

Estudo das propriedades ópticas dos aerossóis no Estado de São Paulo com a técnica de LIDAR  Raman / Study of the optical properties of aerosols in the State of São Paulo with the Raman LIDAR technique

Costa, Renata Facundes da 15 October 2010 (has links)
O estudo desenvolvido nessa dissertação foi dividido em dois momentos. Na primeira parte foi apresentado a realização de uma calibração independente do sistema LIDAR Raman de vapor d\'água instalado no CLA seguindo uma metodologia desenvolvida na Howard University, baseada em uma análise cuidadosa da eficiência óptica dos componentes do sistema tendo como objetivo determinar essa eficiência e apresentar a resposta espectral do sistema. Após esse estudo, que permitiu obter um melhor entendimento da área instrumental do sistema, é apresentado, na segunda parte, uma análise preliminar das propriedades ópticas dos aerossóis na troposfera por meio da avaliação de alguns parâmetros como, por exemplo, os perfis verticais de extinção desses aerossóis, a LR e a SR, utilizando um sistema LIDAR Raman móvel desenvolvido pela Raymetrics Lidar Systems durante campanhas realizadas em alguns institutos de pesquisa no Estado de São Paulo. / The investigation reported in this dissertation has been divided in two parts. The first part was made to carry out an independent calibration of a Raman lidar system for water vapor in the CLA installed using a methodology that was developed at Howard University, based on a careful analysis of the efficiency of the optical system components aimed at determining the efficiency and displaying the spectral response of the system. After this study, which led to a better understanding of the field of instrumental system, the second part, presents a preliminary study of the optical properties of aerosols in the troposphere by evaluating parameters such as, for example, the vertical proles of aerosol extinction, SR and LR, using a mobile Raman LIDAR system developed by Raymetrics Lidar Systems, during campaigns conducted in some research institutes in the State of São Paulo.
14

Estudo das propriedades ópticas dos aerossóis no Estado de São Paulo com a técnica de LIDAR  Raman / Study of the optical properties of aerosols in the State of São Paulo with the Raman LIDAR technique

Renata Facundes da Costa 15 October 2010 (has links)
O estudo desenvolvido nessa dissertação foi dividido em dois momentos. Na primeira parte foi apresentado a realização de uma calibração independente do sistema LIDAR Raman de vapor d\'água instalado no CLA seguindo uma metodologia desenvolvida na Howard University, baseada em uma análise cuidadosa da eficiência óptica dos componentes do sistema tendo como objetivo determinar essa eficiência e apresentar a resposta espectral do sistema. Após esse estudo, que permitiu obter um melhor entendimento da área instrumental do sistema, é apresentado, na segunda parte, uma análise preliminar das propriedades ópticas dos aerossóis na troposfera por meio da avaliação de alguns parâmetros como, por exemplo, os perfis verticais de extinção desses aerossóis, a LR e a SR, utilizando um sistema LIDAR Raman móvel desenvolvido pela Raymetrics Lidar Systems durante campanhas realizadas em alguns institutos de pesquisa no Estado de São Paulo. / The investigation reported in this dissertation has been divided in two parts. The first part was made to carry out an independent calibration of a Raman lidar system for water vapor in the CLA installed using a methodology that was developed at Howard University, based on a careful analysis of the efficiency of the optical system components aimed at determining the efficiency and displaying the spectral response of the system. After this study, which led to a better understanding of the field of instrumental system, the second part, presents a preliminary study of the optical properties of aerosols in the troposphere by evaluating parameters such as, for example, the vertical proles of aerosol extinction, SR and LR, using a mobile Raman LIDAR system developed by Raymetrics Lidar Systems, during campaigns conducted in some research institutes in the State of São Paulo.
15

Undersökning av algoritmer och programvaror för markklassning av punktmoln från flygburen laserskanning

Viklander, Mikael January 2011 (has links)
Lantmäteriet har sedan 2009 arbetat på projektet Ny Nationell Höjdmodell som ska täcka hela Sverige. Denna gång används flygburen laserskanning för data insamling. För att skapa terrängmodeller av dessa laserdata behöver bearbetning först göras, där markpunkter skiljs från andra typer av objekt som laserpulsen registrerar. Det är detta som är ett av de största problemen för att uppnå en bra kvalité för slutprodukten (terrängmodeller). Eftersom Sveriges yta är så stor måste punktmolnet klassificeras med programvaror där en algoritm försöker filtrera ut markpunkterna. Manuell bearbetning kan endast göras i form av kvalitets kontroll i efterhand, eftersom det annars skulle ta för lång tid. Idag använder Lantmäteriet en programvara som heter TerraScan, men de är intresserade av vad marknaden har att erbjuda förutom TerraScan och vad dessa andra programvaror kan åstadkomma i kvalité och användbarhet. Därför har fyra programvaror för markklassning av laserdata valts ut för att genomgå en test. Information om hur varje programvara fungerar och dess möjlighet till inställning redovisas. De laserdata som används är utvalda för att se hur programvarorna klarar olika miljöer och kända svårigheter för markklassning har från tidigare litteraturer om ämnet har använts för att hitta dessa. En kvalitativ samt kvantitativ undersökning görs sedan av de klassificerade områdena för att hitta likheter och skillnader. Resultatet ger en klar bild över hur programvarorna presterar. Ingen programvara är felfri, några har större problem än andra men om man ser till olika aspekter och det totala paketet de erbjuder finns det klara fördelar för vissa för olika ändamål. Men i slutändan finns det egentligen endast en programvara kvar som i dagsläget är tillräckligt bra för Lantmäteriets projekt som de just nu utför, och det är den programvaran som redan används, nämligen TerraScan. / The Swedish National Land Survey has since 2009 worked on the project “New National Elevation model”, that is a terrain model that will cover the whole area of Sweden, this time using airborne laser scanning for data collection instead of photogrammetry. In order to create terrain models from the laser data, the data need to be processed to separate the ground from other types of objects that the laser scanners laser pulse register. This is one of the main problems for achieving a good quality of the final product (terrain models). Because the country's area is so large, the classification is done by a software, where an algorithm tries to filter out the ground points. Manual process can only be done in the form of quality control after the software has done the classification, because it would otherwise take too long time. Today, the Swedish National Land Survey uses a software called TerraScan, but they are interested in what the market has to offer besides TerraScan and what these other softwares can bring in quality and usability. Therefore, four softwares were chosen to evaluate their ground filtering ability of laser data. Information on how each software works and its ability to change settings is presented. The laser data used is selected to see how the software can handle different environments, and the known difficulties of “bare ground filtration” from the previous literature on the subject have been used to find these difficult parts. A qualitative and quantitative study is then made of the classified areas to find similarities and differences. The results give a clear picture of how the software performs. No software is flawless, where some have more problems than others but if you look at different factors and the overall package they offer, there are clear advantages for each of the software depending on the purpose of use. In the end there is really only one of the softwares that remain that is good enough for the Swedish National Land Survey, for the project that is currently being carried out, and it is the software already in use, namely TerraScan.
16

Digital Terrain Models Generation from Airborne LiDAR Point Clouds Using A Multi-scale Terrain Filtering Method

Chen, Hufeng 22 May 2012 (has links)
A Digital Terrain Model (DTM) is an important topographic product, required in many applications. Data needed to create a DTM was traditionally obtained via land surveying, however this method can be costly and time consuming depending on the size of the geographic area. Over time, the land surveying was partially replaced by photogrammetry. Today, airborne Light Detection and Ranging (LiDAR) has become another powerful alternative that collect 3D point clouds for digital surface models (DSM) acquisition. LiDAR is especially useful when dealing with heavily vegetated areas using a canopy penetration feature of laser pulse. Nowadays, LiDAR plays an important role in DTM generation. This thesis presents a hierarchical recovery method to generate DTMs from a cloud of 3D points composed of “single returns” and “multiple returns” from laser pulses using the idea of layering. The proposed method will begin by registering the last return points, then layering them. The layering is done by dividing the points into different height layers and assigning layer numbers to each point. The layer numbers are used as a comparison feature in a later identification process. Then a series of rasterized pyramid levels, which consists of the lowest points in each cell, are generated. After layering, outliers are removed; cells in the top level are assumed as terrain points and used as references for identifying cells in the second level. The identification process will identify the cells of the second level into terrain cells and off-terrain cells, and an interpolation will then occur in the cells which identified as off-terrain. The interpolated level will be used as references for the next level and the same process is then repeated for each level that comes after. Once this process has been completed for the bottom level, the proposed method adjusts the results based on the first return feedback, followed by another interpolation. As a result, the final DTM is produced. The developed method is data driven, and does not assume a prior knowledge about the scene complexity. The proposed method was tested with three airborne LiDAR datasets, covering different terrain types and filtering difficulties. Results illustrated that the proposed method can perform well for areas of flat terrain or gentle slope A comparative study was conducted over existing filters and showed that results of the proposed method has similar accuracy in above mentioned area and faster speed than two comparing algorithms.
17

Systematic Sampling of Scanning Lidar Swaths

Marcell, Wesley Tyler 2009 December 1900 (has links)
Proof of concept lidar research has, to date, examined wall-to-wall models of forest ecosystems. While these studies have been important for verifying lidars efficacy for forest surveys, complete coverage is likely not the most cost effective means of using lidar as auxiliary data for operational surveys; sampling of some sort being the better alternative. This study examines the effectiveness of sampling with high point-density scanning lidar data and shows that systematic sampling is a better alternative to simple random sampling. It examines the bias and mean squared error of various estimators, and concludes that a linear-trend-based and especially an autocorrelation-assisted variance estimator perform better than the commonly used simple random sampling based-estimator when sampling is systematic.
18

Extraction et reconstruction de bâtiments en 3D à partir de relevés lidar aéroportés

Tarsha Kurdi, Fayez Grussenmeyer, Pierre. January 2008 (has links) (PDF)
Thèse de doctorat : Sciences pour l'ingénieur. Topographie, géomatique : Strasbourg 1 : 2008. / Titre provenant de l'écran-titre. Bibliogr. p. 261-270.
19

Development and Progression of Aeolian Blowouts in Padre Island National Seashore

Jewell, Mallorie E 16 December 2013 (has links)
This study characterizes the development and migration of blowouts within Padre Island National Seashore (PAIS). A combination of aerial photographs and Light Detection and Ranging (LIDAR) are used to track the migration of eighteen blowouts, while Ground-penetrating Radar (GPR) is used to investigate the subsurface at two smaller sites in the study area. This data, coupled with beach morphology and changing anthropogenic factors, helps understand why the dune blowouts develop and are restricted to a particular section of the National Seashore. Aerial Photographs taken at least twice a decade since 1969 were used to track blowouts. Each blowout was digitized in order to understand its morphometric characteristics by studying its length, width, area, segmentation, perimeter, and the width of the neck, when present, through the foredune. The velocity and direction of movement were also calculated. Cluster analysis was used to analyze the blowouts using these morphological variables. Based on this data, blows appear to group into two morphologically different clusters. Blowouts grouped into Cluster 1 are longer, thinner, have smaller perimeters and areas, smaller throat widths, and are furthest from the beach access road. A lower dune elevation leads to a larger wave runup to crest height ratio. A larger ratio suggests that the dunes are more easily overtopped during large storms, thus scarping, a precursor to blowout development, is increased. Cluster 2 blowouts tend to be longer, wider, and stabilized faster leading to a more undulated perimeter in addition to a smaller wave runup potential due to a higher dune elevation. Historically blowouts covered the entire northern portion of PAIS. In the 1970’s the portion of the beach north of Park Road 22 was designated as non-driving. Since then all blowouts in this section have revegetated, while, blowouts in the driving section are still active. Beach driving pulverizes seaweed leading to less deposition along the dune toe and therefore a lower elevation of the backshore. As a result there is a greater wave runup in storms leading to an increase in susceptibility to scarping, and therefore, blowouts. Despite the fact that storms are the primary mechanism for blow development, anthropogenic effects, such as vehicle traffic, flatten the beach profile allowing for lower areas to become inundated during storms. This, along with decreased sediment budget and increased storm frequency increases the potential for blowouts to form events and leave the island vulnerable to an increased rate of sea level rise. GPR surveys were completed at two sites; an active blowout with a foredune that is not completely reestablished (Site 1) and a blowout that is stabilized by vegetation (Site 2). Six GPR surveys were completed at Site 1 and four surveys were completed at Site 2 that show the preservation of historic phases, surfaces, and facies used to interpret sequences and compare to aerial photography and LiDAR data. Site 1 moves through five phases that begin in 1969 and end at the present location, while Site 2 moves through three active phases and then ends in a fourth phase by becoming completely stabilized with vegetation in 2010.
20

Studying Clouds and Aerosols with Lidar Depolarization Ratio and Backscatter Relationships

Cho, Hyoun-Myoung 2011 December 1900 (has links)
This dissertation consists of three parts, each devoted to a particular issue of significant importance for CALIPSO lidar observation of depolarization ratio (delta) and backscatter (gamma?) to improve current understanding of the microphysical properties of clouds and aerosols. The relationships between depolarization ratio and backscatter allow us to retrieve particle thermodynamic phase and shape and/or orientation of aerosols and clouds. The first part is devoted to the investigation of the relationships between lidar backscatter and the corresponding depolarization ratio for different cloud classifications and aerosol types. For each cloud and aerosol types, layer-averaged backscatter and backscattering depolarization ratio from the CALIPSO measurements are discussed. The present results demonstrate the unique capabilities of the CALIPSO lidar instrument for determining cloud phase and aerosols subtypes. In the second part, we evaluate the MODIS IR cloud phase with the CALIPSO cloud products. The three possible misclassifications of MODIS IR cloud phasealgorithm, which are studied by Nasiri and Kahn (2008) with radiative transfer modeling, are tested by comparing between MODIS IR phase and CALIOP observations. The current results support their hypotheses, which is that the MODIS phase algorithm may tend to classify thin cirrus clouds as water clouds or mixed phase clouds or unknown, and classify midlevel and/or mid-temperature clouds as mixed or unknown phase. In the third part, we present a comparison of mineral dust aerosol retrievals from two instruments, MODIS and CALIPSO lidar. And, we implement and evaluate a new mineral dust detection algorithm based on the analysis of thin dust radiative signature. In comparison, three commonly used visible and IR mineral dust detection algorithms, including BTD procedure, D parameter method, and multi-channel image algorithm, are evaluated with CALIPSO aerosol classification. The comparison reveals that those dust detection algorithms are not effective for optically thin dust layers, but for thick dust storm. The new algorithm using discriminant analysis with CALIPSO observation is much better in detecting thin dust layer of optical thickness between 0.1 and 2.

Page generated in 0.0556 seconds