Shallow Water Bathymetry Mapping from UAV Imagery based on Machine Learning

The determination of accurate bathymetric information is a key element for near offshore activities, hydrological studies such as coastal engineering applications, sedimentary processes, hydrographic surveying as well as archaeological mapping and biological research. UAV imagery processed with Structure from Motion (SfM) and Multi View Stereo (MVS) techniques can provide a low-cost alternative to established shallow seabed mapping techniques offering as well the important visual information. Nevertheless, water refraction poses significant challenges on depth determination. Till now, this problem has been addressed through customized image-based refraction correction algorithms or by modifying the collinearity equation. In this paper, in order to overcome the water refraction errors, we employ machine learning tools that are able to learn the systematic underestimation of the estimated depths. In the proposed approach, based on known depth observations from bathymetric LiDAR surveys, an SVR model was developed able to estimate more accurately the real depths of point clouds derived from SfM-MVS procedures. Experimental results over two test sites along with the performed quantitative validation indicated the high potential of the developed approach.Comment: 8 pages, 9 figure

Hydrology and circulation in the North Aegean (eastern Mediterranean) throughout 1997 and 1998

The combination of two research projects offered us the opportunity to perform a comprehensive study of the seasonal evolution of the hydrological structure and the circulation of the North Aegean Sea, at the northern extremes of the eastern Mediterranean. The combination of brackish water inflow from the Dardanelles and the sea-bottom relief dictate the significant differences between the North and South Aegean water columns. The relatively warm and highly saline South Aegean waters enter the North Aegean through the dominant cyclonic circulation of the basin. In the North Aegean, three layers of distinct water masses of very different properties are observed: The 20-50 m thick surface layer is occupied mainly by Black Sea Water, modified on its way through the Bosphorus, the Sea of Marmara and the Dardanelles. Below the surface layer there is warm and highly saline water originating in the South Aegean and the Levantine, extending down to 350-400 m depth. Below this layer, the deeper-than-400 m basins of the North Aegean contain locally formed, very dense water with different θ /S characteristics at each subbasin. The circulation is characterised by a series of permanent, semi-permanent and transient mesoscale features, overlaid on the general slow cyclonic circulation of the Aegean. The mesoscale activity, while not necessarily important in enhancing isopycnal mixing in the region, in combination with the very high stratification of the upper layers, however, increases the residence time of the water of the upper layers in the general area of the North Aegean. As a result, water having out-flowed from the Black Sea in the winter, forms a separate distinct layer in the region in spring (lying between “younger” BSW and the Levantine origin water), and is still traceable in the water column in late summer

Forecasting Exchange-Rates via Local Approximation Methods and Neural Networks

There has been an increased number of papers in the literature in recent years, applying several methods and techniques for exchange - rate prediction. This paper focuses on the Greek drachma using daily observations of the drachma rates against four major currencies, namely the U.S. Dollar (USD), the Deutsche Mark (DM), the French Franc (FF) and the British Pound (GBP) for a period of 11 years, aiming at forecasting their short-term course by applying local approximation methods based on both chaotic analysis and neural networks.Key Words: Exchange Rates, Forecasting, Neural Networks

Survival characteristics and adjustment of MNE affiliates in the European integrated market

This is one of the first studies which systematically investigate whether specific characteristics of foreign affiliates that reflect their MNE investment motivations prolong or undermine affiliate survivorship when the host country becomes member of a regional economic union. Using a unique database of 162 foreign affiliates established in the era of protectionism (1960-1980) in Greece, we explore the survival evolution of these affiliates within the European integration period (1981-2011). The study poses two research objectives: the exploration of the key characteristics per type of affiliate and the analysis of the impact of the specific characteristics on affiliate survival. We hypothesize and find that when the protected Greek economy enters the European market, closure risk is relatively high for those affiliates which exploit traditional location advantages such as tariffs and unskilled-labor cost, whereas it is relatively low for those units that adjust to the new institutional framework by investing in advertising and human capital intensity. The results have important implications for policy makers and managers

How schlieren affects beam transmissometers and LISST-Deep: an example from the stratified Danube River delta, NW Black Sea

The term ‘schlieren’ describes angular deflection of a light ray when it passes through a fluid region characterized by refractive index inhomogeneities. These inhomogeneities in the marine environment are generally caused by density variations, i.e. salinity and temperature anomalies. The influence of schlieren on transmissometers and the in situ particle sizer LISST-Deep of Sequoia Scientific are examined in the Danube delta during October 2007. A seasonal pycnocline driven mainly by an intense temperature gradient was identified as a major hydrological feature. It was associated with high buoyancy frequency values and minor changes of the refractive index of seawater. Measurements of two 25-cm path-length transmissometers (660 nm and 470 nm) showed distinguishable peaks at the pycnocline. LISST also uses a 5-cm transmissometer (670 nm), which proved to be very sensitive in both cases. This is mainly due to its very small acceptance angle, which enables enhanced light scattering outside the lens, thus increasing beam attenuation. Subsequently, LISST falsely predicts abundance of large particles within the pycnoclines. A buoyancy frequency N of 0.01 s-1 is the new proposed threshold for schlieren occurrence

North-eastern Aegean sea: an effort to estimate steady-state N & P budgets during September 1998

The north-eastern Aegean sea, characterised by a complex topographical structure, is the area where highly saline waters of Levantine and South-Central Aegean origin are diluted by the outflowing through the Dardanelles of less saline waters of Black Sea origin and by river runoff from the Greek and Turkish mainland. Salinity and nutrient data collected during the INTERREG-I project are used to develop budget calculations and empirical models according to the LOICZ biogeochemical modelling guidelines. The results of the study indicate that the dissolved inorganic nitrogen and phosphorus fluxes imported into the NE Aegean through the Dardanelles are less important than it was believed in the past. Overall, the system acts as a net sink of DIN and DIP, as well as being a net producer of organic matter, as primary production exceeds respiration. Moreover, the system appears to fix more nitrogen than is lost through denitrification

HBIM for Documentation, Dissemination and Management of Built Heritage. The Case Study of St. Maria in Scaria d'Intelvi

The research presented here is carried out within the INTERREG EU project framework, which aims to the valorisation and dissemination of the role of the Church of St. Maria di Scaria (Como, Italy). It mainly focuses on the Carloni's intervention (XVIII century), a local family of craftsmen, famous across many European cities and regions contributing to the construction of monuments and their rich decoration apparatus. The laser scanning and photogrammetric surveys have been integrated with the on-site stratigraphic analysis and with the scarcely available historical documents, in an attempt to focus on the reconstruction of the main transformations and chronological phases: BIM approach has been experimented as a way of transmitting a piece of the history of the church life to the local people and for tourist purposes. A Historic Building Information Modeling (HBIM) has been developed while investigating the potential of an object library specially generated to illustrate the structural elements, the construction technologies, and the decorative layers, along with the critical aspects faced by standard BIM in a complex geometry shift from surface approach to object modeling. The research contributes to the explanation of the sequence and construction technologies adopted for the vault system, the first two vaults of the nave, with respect to the vault covering the altar and the apse. The HBIM approach development is analysed to help the generation of a vocabulary and an abacus of elements to be geographically referenced across Europe to disseminate typical construction elements and skills. </jats:p

Ubiquinone-8 Stimulates Phagocytosis in Macrophages by Modulation of the Kinetics of the Fc Receptor

The effect of exogenous ubiquinone-8 (Q8) on IgG- and C3b-mediated phagocytosis of sensitized sheep red blood cells and of opsonized Staphylococcus aureus by macrophages was studied by morphological and quantitative methods. Q8 stimulated the initial events of phagocytosis, that is, attachment and ingestion, in which occupancy of the Fe receptor by IgG was shown to be of critical significance. The kinetics of competitive inhibition of phagocytosis of opsonized bacteria by macrophages by using Fe fragments suggested the intimate role of the kinetics of the Fe receptor in the initial events of phagocytosis and, further, the modulation of the kinetics of the Fe receptor by Q8 as the basis of enhanced phagocytosis by Q