Συμπεριφορά διαφραγμάτων ιστορικών κατασκευών

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Δομοστατικός Σχεδιασμός και Ανάλυση των Κατασκευών

Hyperspectral remote sensing of cyanobacterial pigments as indicators for cell populations and toxins in eutrophic lakes

The growth of mass populations of toxin-producing cyanobacteria is a serious concern for the ecological status of inland waterbodies and for human and animal health. In this study we examined the performance of four semi-analytical algorithms for the retrieval of chlorophyll a (Chl a) and phycocyanin (C-PC) from data acquired by the Compact Airborne Spectrographic Imager-2 (CASI-2) and the Airborne Imaging Spectrometer for Applications (AISA) Eagle sensor. The retrieval accuracies of the semi-analytical models were compared to those returned by optimally calibrated empirical band-ratio algorithms. The best-performing algorithm for the retrieval of Chl a was an empirical band-ratio model based on a quadratic function of the ratio of re!ectance at 710 and 670 nm (R2=0.832; RMSE=29.8%). However, this model only provided a marginally better retrieval than the best semi-analytical algorithm. The best-performing model for the retrieval of C-PC was a semi-analytical nested band-ratio model (R2=0.984; RMSE=3.98 mg m−3). The concentrations of C-PC retrieved using the semi-analytical model were correlated with cyanobacterial cell numbers (R2=0.380) and the particulate and total (particulate plus dissolved) pools of microcystins (R2=0.858 and 0.896 respectively). Importantly, both the empirical and semi-analytical algorithms were able to retrieve the concentration of C-PC at cyanobacterial cell concentrations below current warning thresholds for cyanobacteria in waterbodies. This demonstrates the potential of remote sensing to contribute to early-warning detection and monitoring of cyanobacterial blooms for human health protection at regional and global scales

Optical Remote Sensing of Submerged Aquatic Vegetation: Opportunities for Shallow Clearwater Streams

Remote sensing has rarely been used as a tool to map and monitor submerged aquatic vegetation (SAV) in rivers, due to a combination of insufficient spatial resolution of available image data and strong attenuation of light in water through absorption and scattering. The latter process reduces the possibility to use spectral reflectance information to accurately classify submerged species. However, increasing availability of very high resolution (VHR) image data may enable the use of shape and texture features to help discriminate between species by taking an object based image analysis (OBIA) approach, and overcome some of the present limitations. This study aimed to investigate the possibility of using optical remote sensing for the detection and mapping of SAV. It firstly looked at the possibilities to discriminate submerged macrophyte species based on spectral information only. Reflectance spectra of three macrophyte species were measured in situ across a range of submergence depths. The results showed that water depth will be a limiting factor for the classification of species from remote sensing images. Only Spiked Water Milfoil (Myriophyllum spicatum) was indicated as spectrally distinct through ANOVA analysis, but subsequent Jeffries–Matusita distance analysis did not confirm this. In particular Water Crowfoot (Ranunculus fluitans) and Pondweed (Potamogeton pectinatus) could not be discriminated at 95% significance level. Spectral separability of these two species was also not possible without the effect of an overlying water column. Secondly, the possibility to improve species discrimination, using spatial and textural information was investigated for the same SAV species. VHR image data was acquired with a Near Infrared (NIR) sensitive DSLR camera from four different heights including a telescopic pole and a Helikite UAS. The results show that shape and texture information can improve the detection of the spectrally similar Pondweed and Water Crowfoot from VHR image data. The best performing feature ‘length/width ratio of sub-objects’ was obtained through expert knowledge. All of the shape and texture based features performed better at species differentiation than the spectrally based features. In conclusion this study has shown that there is considerable potential for the combination of VHR data and OBIA to map SAV in shallow stream environments, which can benefit species monitoring and management

High resolution remote sensing of marine reef habitats : towards an integration of satellite and sonar imaging techniques

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Η δομική τρωτότητα της Αθήνας στο σεισμό του 1999

Αν και ως γνωστό η Ελλάδα ανήκει σε μια από τις πιο έντονα σεισμογενείς περιοχές παγκοσμίως, ο σεισμός της 7/9/99 στην Αθήνα ήταν ένα δυσάρεστο ξάφνιασμα για όλους. Από την τραγική εμπειρία αυτού του σεισμού, κατέστη σαφές ότι οι βλάβες και το επίπεδο αντισεισμικής προστασίας του δομικού ιστού της πόλης συνδέεται άμεσα με το χρόνο κατασκευής των κτηρίων αυτής. Είναι φανερό λοιπόν ότι τα κτήρια που είναι κατασκευασμένα πριν το 1959 αλλά και αυτά με τον κανονισμό του 59 (δηλαδή μέχρι το 1985), παρουσιάζουν χαμηλό επίπεδο σεισμικής ασφάλειας . Σκοπός της παρούσας διπλωματικής εργασίας είναι να καταδείξει τις συνήθεις βλάβες που παρατηρήθηκαν μετά τον σεισμό, σε κτήρια κατασκευασμένα πριν το 1985, αλλά και άλλους παράγοντες που επηρέασαν την έκταση των βλαβών στα κτήρια και σε ορισμένες περιπτώσεις οδήγησαν σε ανεπιθύμητους τρόπους αστοχίας. Στη συνέχεια γίνεται προσπάθεια να συσχετιστεί η παλαιότητα κατασκευής των κτιρίων με τις κτηριακές βλάβες που πρόεκυψαν λόγω του σεισμού που έπληξε την Αθήνα το 1999 και να εξαχθούν συμπεράσματα για το σχεδιασμό κατασκευών από Ω.Σ. και τη δομική τρωτότητα του μητροπολιτικού της κέντρου . Σκοπός αυτής της εργασίας είναι να παρουσιάσει μερικές από τις παρατηρήσεις βλαβών του σεισμού της Αθήνας του 1999 και να εξάγει αξιοποιήσιμα συμπεράσματα όσον αφορά τη ενδεχόμενη τρωτότητα της Αθήνας σε έναν μελλοντικό σεισμό αλλά και προτάσεις για την πιθανή βελτίωση της.Although Greece is known to be one of the most seismic areas in the world, the earthquake of 7/9/99 in Athens was an unpleasant surprise for everyone. From the tragic experience of this earthquake, it has become clear that the damage and level of anti-seismic protection of the city's buildings directly related to the time of their construction. It is clear that buildings constructed before 1959, but also those n based on the 1959 anti-seismic building code (ie until 1985), have a low level of seismic safety. The purpose of this thesis is to demonstrate the usual damage observed after the earthquake in buildings constructed before 1985, but also to indicate other factors that have affected the extent of the buildings’ damage and in some cases that led to undesirable ways of failure. An attempt is then made to relate the age of the buildings to the damage that arose due to the 1999 Athens earthquake and to draw conclusions for the design of reinforced concrete structures and for the structural vulnerability of Athens metropolitan center. The aim of this paper is to present some of the observations of 1999 Athens earthquake and to draw useful conclusions regarding the potential vulnerability of Athens to a future earthquake, as well as to make suggestions for its possible improvement