96 research outputs found

    Lidar and true-orthorectification of infrared aerial imagery of high Pinus sylvestris forest in mountainous relief

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    Combination of various data sources has been demonstrated more effective than using them separately. Information retrieval is significantly improved by synergies between laser scanner and optical imagery. Digital photography relies on traditional methods for orthorectification in order to accomplish an accurate correspondence with Lidar. We investigated combinatorial techniques in a high pine forest situated in mountainous relief in the Guadarrama Range (Spain). Results have shown critical inaccuracies in the integration of these data, even when obtained simultaneously. We propose the use of Lidar-derived Digital Surface Model in the process of orthorectification of aerial imagery. We hypothesised that the use of true-orthophoto techniques for improving the planimetric accuracy of VHR can be reliable for forestry applications. The methodology slightly improved the geometrical results obtained, though radiometric results might be meaningless. Consequently, other possible solutions are also discussed

    Panorama Generation for Stereoscopic Visualization of Large-Scale Scenes

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    In this thesis, we address the problem of modeling and stereoscopically visualizing large-scale scenes captured with a single moving camera. In many applications that image large-scale scenes the critical information desired is the 3D spatial information of stationary objects and movers within the scene. Stereo panoramas, like regular panoramas, provide a wide field-of-view that can represent the entire scene, with the stereo panoramas additionally representing the motion parallax and allowing for 3D visualization and reconstruction of the scene. The primary issue with stereo panorama construction methods is that they are constrained for a particular camera motion model; typically the camera is constrained to move along a linear or circular path. Here we present a method for constructing stereo panoramas for general camera motion, and we develop a (1) Unified Stereo Mosaic Framework that handles general camera motion models. To construct stereo panoramas for general motion we created a new (2) Stereo Mosaic Layering algorithm that speeds up panorama construction enabling real-time applications. In large-scale scene applications it is often the case that the scene will be imaged persistently by passing over the same path multiple times or two or more sensors of different modalities will pass over the the same scene. To address these issues we developed methods for (3) Multi-Run and Multi-Modal Mosaic Alignment. Finally, we developed an (4) Intelligent Stereo Visualization that allows a viewer to interact and stereoscopically view the stereo panoramas developed from general motion

    Hyperspectral Imaging for Fine to Medium Scale Applications in Environmental Sciences

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    The aim of the Special Issue “Hyperspectral Imaging for Fine to Medium Scale Applications in Environmental Sciences” was to present a selection of innovative studies using hyperspectral imaging (HSI) in different thematic fields. This intention reflects the technical developments in the last three decades, which have brought the capacity of HSI to provide spectrally, spatially and temporally detailed data, favoured by e.g., hyperspectral snapshot technologies, miniaturized hyperspectral sensors and hyperspectral microscopy imaging. The present book comprises a suite of papers in various fields of environmental sciences—geology/mineral exploration, digital soil mapping, mapping and characterization of vegetation, and sensing of water bodies (including under-ice and underwater applications). In addition, there are two rather methodically/technically-oriented contributions dealing with the optimized processing of UAV data and on the design and test of a multi-channel optical receiver for ground-based applications. All in all, this compilation documents that HSI is a multi-faceted research topic and will remain so in the future

    Enhancing Remote Sensing for Agriculture Using Small Unmanned Aerial Systems: San Diego, CA, as a Test Case

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    The development of small Global Positioning System (GPS) antennas and microprocessors has propelled the advancement of affordable Small Unmanned Aerial Systems (SUASs), which will dramatically expand the remote sensing field, making timely, high-resolution imagery readily available. The low cost and simple operation of SUASs makes them an attractive option for agriculture. Flying a SUAS 400 ft above ground level (AGL) in a flight path that allows for significant image overlap can yield sub- 5cm resolution imagery, which in turn can be mosaicked and used for multispectral imagery analysis. With results rivaling the most advanced commercial imaging sensors, SUASs can be used to identify stressed vegetation and aid in decision making that ultimately leads to more efficient farming practices and consistent yields. Furthermore, minimal operating costs promote reduced revisit times and enable persistent collection to monitor changes over time

    Guidelines for Best Practice and Quality Checking of Ortho Imagery

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    For almost 10 years JRC's ¿Guidelines for Best Practice and Quality Control of Ortho Imagery¿ has served as a reference document for the production of orthoimagery not only for the purposes of CAP but also for many medium-to-large scale photogrammetric applications. The aim is to provide the European Commission and the remote sensing user community with a general framework of the best approaches for quality checking of orthorectified remotely sensed imagery, and the expected best practice, required to achieve good results. Since the last major revision (2003) the document was regularly updated in order to include state-of-the-art technologies. The major revision of the document was initiated last year in order to consolidate the information that was introduced to the document in the last five years. Following the internal discussion and the outcomes of the meeting with an expert panel it was decided to adopt as possible a process-based structure instead of a more sensor-based used before and also to keep the document as much generic as possible by focusing on the core aspects of the photogrammetric process. Additionally to any structural changes in the document new information was introduced mainly concerned with image resolution and radiometry, digital airborne sensors, data fusion, mosaicking and data compression. The Guidelines of best practice is used as the base for our work on the definition of technical specifications for the orthoimagery. The scope is to establish a core set of measures to ensure sufficient image quality for the purposes of CAP and particularly for the Land Parcel Identification System (PLIS), and also to define the set of metadata necessary for data documentation and overall job tracking.JRC.G.3-Agricultur

    Small Unmanned Aerial Systems (sUAS) for environmental remote sensing: challenges and opportunities revisited

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    Hardin and Jensen (2011) presented six challenges to using small Unmanned Aerial Systems (sUAS) for environmental remote sensing: challenge of the hostile flying environment, challenge of power, challenge of available sensors, challenge of payload weight, challenge of data analysis, and challenge of regulation. Eight years later we revisit each of the challenges in the context of the current sUAS environment. We conclude that technological advances made in the interim (as applied to environmental remote sensing) have either (1) improved practitioner ability to respond to a challenge or (2) decreased the magnitude of the challenge itself. However, relatively short flight time remains a primary challenge to using sUAS in environmental remote sensing

    USING HYPERSPECTRAL IMAGERY TO ASSIST FEDERAL FOREST MONITORING AND RESTORATION PROJECTS IN THE SOUTHERN ROCKY MOUNTAINS, COLORADO

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    Hyperspectral imagery and the corresponding ability to conduct analysis below the pixel level have tremendous potential to aid in landcover monitoring. During large ecosystem restoration projects, being able to monitor specific aspects of the recovery over large and often inaccessible areas under constrained finances are major challenges. The Civil Air Patrol's Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance (ARCHER) can provide hyperspectral data in most parts of the United States at relatively low cost. Although designed specifically for use in locating downed aircraft, the imagery holds the potential to identify specific aspects of landcover at far greater fidelity than traditional multispectral means. The goals of this research were to improve the use of ARCHER hyperspectral imagery to classify sub-canopy and open-area vegetation in coniferous forests located in the Southern Rockies and to determine how much fidelity might be lost from a baseline of 1 meter spatial resolution resampled to 2 and 5 meter pixel size to simulate higher altitude collection. Based on analysis comparing linear spectral unmixing with a traditional supervised classification, the linear spectral unmixing proved to be statistically superior. More importantly, however, linear spectral unmixing provided additional sub-pixel information that was unavailable using other techniques. The second goal of determining fidelity loss based on spatial resolution was more difficult to determine due to how the data are represented. Furthermore,the 2 and 5 meter imagery were obtained by resampling the 1 meter imagery and therefore may not be representative of the quality of actual 2 or 5 meter imagery. Ultimately, the information derived from this research may be useful in better utilizing hyperspectral imagery to conduct forest monitoring and assessment

    Earth observations from space: Outlook for the geological sciences

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    Remote sensing from space platforms is discussed as another tool available to geologists. The results of Nimbus observations, the ERTS program, and Skylab EREP are reviewed, and a multidisciplinary approach is recommended for meeting the challenges of remote sensing

    Mass balance of Icelandic glaciers in variable climate

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    The mass balance of a glacier is strongly connected to climate. At high latitudes, mass balance is typically controlled by snow accumulation during the winter and the glacier ablation during the summer. In Iceland, direct mass balance observations have been mostly focused on the three largest ice caps (~600 to ~8000 km2), measured in situ for the last 25 years. There are, however, glaciers and ice caps distributed over all quarters of the country that lack mass balance observations. Remote sensing data with the capability to retrieve the glacier surface geometry through Digital Elevation Models (DEMs) are valuable tools to measure mass balance using the geodetic method. For a typical Icelandic glacier (with an area between 1 km2 and hundreds of km2), this can be optimally achieved from optical stereoscopic imagery, emplaced in airborne or spaceborne sensors, and from airborne lidar. This thesis focuses on remote sensing techniques to accurately measure geodetic mass balance from seasonal to decadal time spans and the relationship of mass balance to climate. As an example of seasonal mass balance, the winter mass balance of Drangajökull was measured from satellite sub-meter stereo images at the beginning, middle and end of the 2014–2015 winter using data from the Pléiades and WorldView-2 satellites. The results were complemented with in situ snow density measurements and validated with snow thickness measurements. The study concludes that images from the sensors mentioned above may often be used to monitor seasonal mass balance without tedious field logistics. A vast archive of aerial photographs exists for Iceland extending back to 1945. Since then, most glaciers were surveyed every 5 to 20 years. In addition, a wealth of modern satellite stereo images is available since the early 2000s as well as airborne lidar data in 2008–2013. This creates a unique dataset to construct a 70-year time series of geodetic mass balances. Eyjafjallajökull (~70 km2) was used to develop semi-automated processing chains based on open-source software. The result is a detailed record of glacier changes resulting from climatic and volcanic forcing. Simple linear regression of the annual mass balance of Eyjafjallajökull indicates that most mass balance variations can be related to changes in summer temperature and winter precipitation. It also allows to infer the sensitivities of mass balance to these two climatic variables. The processing chain was then applied to 14 glaciers and ice caps spatially distributed in all quarters of Iceland, resulting in a dense mass-balance record for the last 70 years. The mean and standard deviation (±SD) of mass balances of the target glaciers were –0.44±0.16 m w.e. a–1 in 1945–1960, 0.00±0.21 m w.e. a–1 in 1960–1980, 0.11±0.25 m w.e. a–1 in 1980–1994, –1.01±0.50 m w.e. a–1 in 1994–2004, –1.27±0.56 m w.e. a–1 in 2004–2010 and –0.14±0.51 m w.e. a–1 in 2010–2015. The glaciers located at the south and west coasts revealed the highest decadal variability, in contrast to glaciers located in the north. This study improves the knowledge of Icelandic glaciers prior to the warm 1990s. The obtained glacier DEMs reveals in some cases elevation changes caused by irregularities in ice motion and opens for opportunities of modelling the ice dynamics of some of these glaciers coupled with their mass balance.Afkoma jökla ræðst af veðurfari. Augljós eru tengslin við snjósöfnun vetrar, en einnig hitastig sumars sem vísbending um orku til leysingar. Hefðbundnar reglulegar afkomumælingar með mælingu þykktar vetrarsjós að hausti og sumarleysingu að hausti, á völdum mælistöðvum, hófust á þremur stærstu jöklum Íslands á níunda og tíunda áratug síðustu aldar og hefur verið haldið úti síðan. Á öðrum jöklum Íslands eru beinar afkomumælingar takmarkaðar; á langflestum hafa engar slíkar mælingar verið gerðar. Upplýsingar um afkomu jökla má einnig meta með því að bera saman hæðarkort af yfirborði þeirra á mismunandi tímum. Í þessu skyni eru fjarkönnunargögn eins og loftmyndir, gervihnattaljósmyndir og leysihæðarskönnun (lidar) sem nýtast við gerð hæðarkorta einkar gagnleg. Viðfangsefni ritgerðarinnar er úrvinnsla slíkra gagna og hvernig má nýta þau til að fá sem nákvæmasta mælinga á afkomu jökla á tímabilum sem spanna allt frá árstíð til áratuga, auk þess sem vensl afkomu og veðurfars eru greind. Til að kanna notagildi fjarkönnunargagna við rannsóknir á árstíðabundinni afkomu jökla voru yfirborðshæðarkort af Drangajökli unnin eftir háupplausnarljósmyndum frá Pléiades og WorldView-2 gervitunglunum við upphaf, miðbik og lok vetursins 2014–2015. Mælingar á eðlismassa vetrarsnjós að vori voru nýttar til að skorða betur vetrarafkomu jökulsins auk þess sem niðurstöðurnar voru bornar saman við mælda snjóþykkt í afkomumælistöðum. Niðurstöður rannsóknarinnar sýna ótvírætt að oft er hægt að nýta myndir frá áðurnefndum gervitunglum við mælingu vetrarákomu jökla í stað þess að leggja í og erfiða mælileiðangra. Gríðarmikið safn loftmynda er til af íslenskum jöklum allt aftur til ársins 1945. Síðan þá hafa þeir flestir verið myndaðir á 5 til 20 ára fresti. Einnig hefur verulegu magni gervihnattaljósmynda sem nýtast til vinnslu hæðarkorta af jöklum verið aflað eftir 2000 auk hæðarkorta eftir leysimælingum úr flugvél af flestum jöklum landsins frá 2008 til 2013. Þessi yfirgripsmiklu gögn gera mögulega vinnslu 70 ára afkomusögu margra jökla. Með slíka vinnslu að markmiði var sett saman hálfsjálfvirk úrvinnslulína (flæðilína úrvinnsluþátta) sem byggist á opnum hugbúnaðarlausnum. Hún var þróuð fyrir og fyrst beitt á öll tiltæk gögn af Eyjafjallajökli (~70 km2 ). Úrvinnslan skilaði ítarlegri sögu um hæðarbreytingar, afkomu og umfang Eyjafjallajökuls sem bæði veðurfar og eldgos hafa stjórnað. Útfrá afkomuröðinni var bestað línulegt fall sem lýsir venslum ársafkomu við sumarhita og vetrarúrkomu auk leiðréttingarliðs vegna breytilegs umfangs jökulsins. Þetta fall sýnir að stór þáttur breytileika afkomu jökulsins má skýra með breytileika í þessum veðurfarsþáttum. Það gerir einnig kleift að meta hversu næm afkoma jökulsins er fyrir breytingum í þeim. Úrvinnslulínan var síðan notuð til að setja saman afkomusögu 14 íslenska jökla á um 70 ára tímabili. Jöklar í öllum landsfjórðungum sem og á miðhálendinu voru rannsakaðir. Meðaltal og staðalfrávik afkomu jöklanna á hverju tímabili fyrir sig var -0.44±0.16 m v.g. ár–1 (metrar vatnsígildis á ári) 1945–1960, 0.00±0.21 m v.g. ár–1 1960–1980, 0.11±0.25 m v.g. ár–1 1980–1994, -1.01±0.50 m v.g. ár–1 1994–2004, -1.27±0.56 m v.g. ár–1 2004–2010 og -0.14±0.51 m v.g. ár–-1 2010–2015. Jöklar við suður og vesturströndina sýna breytilegasta afkomu frá einu tímabili til annars, ólíkt jöklum í norðri þar sem þessi breytileiki er mun minni. Þessi rannsókn eykur mjög við þekkingu okkar á íslenskum jöklum áður en mikil hlýnun varð á tíunda áratug síðustu aldar sem og hvernig afkomu íslenskra jökla breyttist í kjölfarið. Jökla-kortin sem þessi vinna hefur skilað sýna víða hæðarbreytingar sem skýrast af tímabreyti-leika eða óreglu í ísflæði frá afkomu- til leysingasvæðis jöklanna. Þau nýtast einnig sem próf fyrir framtíðarrannsóknir með samtengdum líkönum ísflæðis og afkomu þessara jökla.Le bilan de masse des glaciers est fortement lié au climat. Aux hautes latitudes, l’accumulation de neige pendant l’hiver et la fonte de glace pendant l’été sont les principales composantes du bilan de masse. En Islande, le bilan de masse des trois plus larges calottes glaciaires (~600-~8000 km²) a été suivi régulièrement depuis 25 ans notamment grâce à des mesures in situ. Mais les bilans de masse des autres glaciers et calottes glaciaires islandaises ont été très peu étudiés. Aujourd’hui, les données de télédétection, notamment via la comparaison des modèles numériques du terrain (MNT), permettent de mesurer le bilan de masse par la méthode géodésique. Pour ces glaciers et calottes de plus petites tailles (de 1 km² et à quelques centaines de km²), les photographies aériennes, l’imagerie satellitaire stéréoscopique sub-métriques, et le lidar aérien sont parfaitement adaptées. Cette thèse se focalise donc sur l’estimation des bilans de masse des « petits » glaciers et calottes islandaises depuis le pas de temps saisonnier jusqu’à pluridécennal et leur relation avec les variations spatiales et temporelles du climat. Le bilan de masse hivernal de la calotte du Drangajökull (NO-Islande) a été mesuré par des images satellitaires stéréoscopiques sub-métriques (données Pléiades et WorldView-2) acquises au début, milieu et à la fin de l’hiver 2014-2015. Les changements de volume ont été convertis en bilan de masse grâce à des mesures in situ de densité de neige, et validés avec des mesures in situ de profondeur de neige. Ce travail permet d’envisager désormais un suivi du bilan de masse saisonnier sans un laborieux travail de terrain. Une importante archive de photographies aériennes est disponible en Islande depuis 1945. Ces données offrent une revisite de 5 à 20 ans pour la majorité des glaciers. De plus, depuis 2000, cette archive est complétée par les données des capteurs satellitaires stéréoscopiques et de lidar aérien acquis entre 2008 et 2013. Cet ensemble de données est exploité pour créer une série temporelle de 70 ans de bilan de masse en Islande. La calotte d’Eyjafjallajökull (~70 km²) sert de zone test pour la création et l’automatisation d’une chaîne de traitement, basée sur des logiciels libres. Le résultat est une série de 70 ans de bilan de masse et changements glaciaires liés au climat et au volcanisme. Les variations décennales du bilan de masse sont mises en relation avec les variations des températures estivales et les précipitations hivernales. Cette relation, quasi linéaire, sert pour le calcul de la sensibilité du bilan de masse au changement de température et précipitation. La chaîne de traitement est alors appliquée à 14 glaciers et calottes glaciaires distribuées aux quatre coins de l’Islande. La moyenne et déviation standard (±DS) du bilan de masse des glaciers sélectionnés est : –0.44±0.16 m w.e. a–1 en 1945–1960, 0.00±0.21 m w.e. a–1 en 1960–1980, 0.11±0.25 m w.e. a–1 en 1980–1994, –1.01±0.50 m w.e. a–1 en 1994–2004, –1.27±0.56 m w.e. a–1 en 2004–2010 et –0.14±0.51 m w.e. a–1 en 2010–2015. Les glaciers maritimes situés près des côtes sud et ouest montrent une plus forte variabilité décennale que les glaciers plus continentaux situés dans le nord et nord-ouest. Notre étude améliore la connaissance des évolutions des glaciers islandais et leur relation avec le climat, en particulier avant les années 1990s et l’augmentation de température. Nos travaux montrent aussi la complexité de la réponse géométrique des glaciers (en lien avec leur dynamique) et offre des données uniques pour la calibration/validation des modèles des glaciers.This work was financially supported by the University of Iceland Research Fund, the Jules Verne Fund and the Katla Kalda project. The lidar mapping of the glaciers in Iceland was funded by the Icelandic Research Fund, the Landsvirkjun research fund, the Icelandic Road Administration, the Reykjavík Energy Environmental and Energy Research Fund, the Klima- og Luftgruppen research fund of the Nordic Council of Ministers, the Vatnajökull National Park, the organization Friends of Vatnajökull, LMÍ, IMO and the UI research fund. Pléiades images were acquired at research price thanks to the CNES ISIS program. WorldView DEMs were obtained through the ArcticDEM project
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