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  • 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.
1

Advancing next generation adaptive optics in astronomy: from the lab to the sky

Turri, Paolo 31 August 2017 (has links)
High resolution imaging of wide fields has been a prerogative of space telescopes for decades. Multi-conjugate adaptive optics (MCAO) is a key technology for the future of ground-based astronomy, especially as we approach the era of ELTs, where the large apertures will provide diffraction limits that will significantly surpass even the James Webb Space Telescope. NFIRAOS will be the first light MCAO system for the Thirty Meter Telescope and to support its development I have worked on HeNOS, its test bench integrated in Victoria at NRC Herzberg. I have aligned the optics, tested the electronic hardware, calibrated the subsystems (cameras, deformable mirrors, light sources, etc.) and characterized the system parameters. Development and support for future MCAO instruments also involves data analysis, a critical process in delivering the expected performance of any scientific instrument. To develop a strategy for optimal stellar photometry with MCAO, I have observed the Galactic globular cluster NGC 1851 with GeMS, the MCAO system on the 8-meter Gemini South telescope. From near-infrared images of this target in two bands, I have found the optimal parameters to employ in the profile-fitting photometry and calibration. As testimony to the precision of the results, I have obtained the deepest near-infrared photometry of a crowded field from the ground and used it to determine the age of the cluster with a method recently proposed that exploits the bend in the lower main sequence. The precise color-magnitude diagram also allows us to clearly observe the double subgiant branch for the first time from the ground, caused by the multiple stellar populations in the cluster. As the only facility MCAO system, GeMS is an important instrument that serves to illuminate the challenges of obtaining accurate photometry using such a system. By coupling the knowledge acquired from an instrument already on-sky with experiments in the lab on a prototype of a future system, I have addressed new challenges in photometry and astrometry, like the promising technique of point spread function reconstruction. This thesis informs the development of appropriate data processing techniques and observing strategies to ensure the ELTs deliver their full scientific promise over extended fields of view. / Graduate
2

Performance Evaluation of Stereo Reconstruction Algorithms on NIR Images / Utvärdering av algoritmer för stereorekonstruktion av NIR-bilder

Vidas, Dario January 2016 (has links)
Stereo vision is one of the most active research areas in computer vision. While hundreds of stereo reconstruction algorithms have been developed, little work has been done on the evaluation of such algorithms and almost none on evaluation on Near-Infrared (NIR) images. Of almost a hundred examined, we selected a set of 15 stereo algorithms, mostly with real-time performance, which were then categorized and evaluated on several NIR image datasets, including single stereo pair and stream datasets. The accuracy and run time of each algorithm are measured and compared, giving an insight into which categories of algorithms perform best on NIR images and which algorithms may be candidates for real-time applications. Our comparison indicates that adaptive support-weight and belief propagation algorithms have the highest accuracy of all fast methods, but also longer run times (2-3 seconds). On the other hand, faster algorithms (that achieve 30 or more fps on a single thread) usually perform an order of magnitude worse when measuring the per-centage of incorrectly computed pixels.
3

利用近紅外光影像之近景攝影測量建立數值表面模型之研究 / Construction of digital surface model using Near-IR close range photogrammetry

廖振廷, Liao, Chen Ting Unknown Date (has links)
點雲(point cloud)為以大量三維坐標描述地表實際情形的資料形式,其中包含其三維坐標及相關屬性。通常點雲資料取得方式為光達測量,其以單一波段雷射光束掃描獲取資料,以光達獲取點雲,常面臨掃描時間差、缺乏多波段資訊、可靠邊緣線及角點資訊、大量離散點雲又缺乏語意資訊(semantic information)難以直接判讀及缺乏多餘觀測量等問題。 攝影測量藉由感測反射自太陽光或地物本身放射之能量,可記錄為二維多光譜影像,透過地物在不同光譜範圍表現之特性,可輔助分類,改善分類成果。若匹配多張高重疊率的多波段影像,可以獲取包含多波段資訊且位於明顯特徵點上的點雲,提供光達以外的點雲資料來源。 傳統空中三角測量平差解算地物點坐標及產製數值表面模型(Digital Surface Model, DSM)時,多採用可見光影像為主;而目前常見之高空間解析度數值航照影像,除了記錄可見光波段之外,亦可蒐集近紅外光波段影像。但較少採用近紅外光波段影像,以求解地物點坐標及建立DSM。 因此本研究利用多波段影像所蘊含的豐富光譜資訊,以取像方式簡易及低限制條件的近景攝影測量方式,匹配多張可見光、近紅外光及紅外彩色影像,分別建立可見光、近紅外光及紅外彩色之DSM,其目的在於探討加入近紅外光波段後,所產生的近紅外光及紅外彩色DSM,和可見光DSM之異同;並比較該DSM是否更能突顯植被區。 研究顯示,以可見光點雲為檢核資料,計算近紅外光與紅外彩色點雲的均方根誤差為其距離門檻值之相對檢核方法,可獲得約21%的點雲增加率;然而使用近紅外光或紅外彩色影像,即使能增加點雲資料量,但對於增加可見光影像未能匹配的資料方面,其效果仍屬有限。 / Point cloud represents the surface as mass 3D coordinates and attributes. Generally, these data are usually collected by LIDAR (LIght Detection And Ranging), which acquires data through single band laser scanning. But the data collected by LIDAR could face problems, such as scanning process is not instantaneous, lack of multispectral information, breaklines, corners, semantic information and redundancies. However, photogrammetry record the electromagnetic energy reflected or emitted from the surface as 2D multispectral images, via ground features with different characteristics differ in spectrum, it can be classified more efficiently and precisely. By matching multiple high overlapping multispectral images, point cloud including multispectral information and locating on obvious feature points can be acquired. This provides another point cloud source aparting from LIDAR. In most studies, visible light (VIS) images are used primarily, while calculating ground point coordinates and generating digital surface models (DSM) through aerotriangulation. Although nowadays, high spatial resolution digital aerial images can acquire not only VIS channel, but also near infrared (NIR) channel as well. But there is lack of research doing the former procedures by using NIR images. Therefore, this research focuses on the rich spectral information in multispectral images, by using easy image collection and low restriction close range photogrammetry method. It matches several VIS, NIR and color infrared (CIR) images, and generate DSMs respectively. The purpose is to analyze the difference between VIS, NIR and CIR data sets, and whether it can emphasize the vegetation area, after adding NIR channel in DSM generation. The result shows that by using relative check points between NIR, CIR data with VIS one. First, VIS point cloud was set as check point data, then, the RMSE (Root Mean Square Error) of NIR and CIR point cloud was calculated as distance threshold. Its data increment is 21% ca. However, the point cloud data amount can be increased, by matching NIR and CIR images. But the effect of increasing data, which was not being matched from VIS images are limited.

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