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Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Cosoli S.,National Institute of Oceanography and Applied Geophysics - OGS | Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Ivankovi D.,Croatian Institute Of Oceanography And Fisheries | And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2011

A network of high-frequency (HF) radars was installed in the northern Adriatic in the second half of 2007, aimed to measure surface currents in the framework of the North Adriatic Surface Current Mapping (NASCUM) project. This study includes a detailed analysis of current measurements from February to August 2008, a period in which three radars were simultaneously operational. Current patterns and temporal evolutions of different physical processes were extracted by using self-organizing map (SOM) analysis. The analysis focused on subtidal frequency band and extracted 12 different circulation patterns on a 4 × 3 rectangular SOM grid. The SOM was also applied on a joint data set that included contemporaneous surface wind data obtained from the operational hydrostatic mesoscale meteorological model ALADIN/HR. The strongest currents were recorded during energetic bora episodes, being recognized by several current patterns and having the characteristic downwind flow with magnitudes exceeding 35 cm/s at some grid points. Another characteristic wind, the sirocco, was represented by three current patterns, while the remaining current structures were attributed to weak winds and the residual thermohaline circulation. A strong resemblance has been found between SOM patterns extracted from HF radar data only and from combined HF radar and wind data sets, revealing the predominant wind influence to the surface circulation structures and their temporal changes in the northern Adriatic. These results show the SOM analysis being a valuable tool for extracting characteristic surface current patterns and forcing functions. Copyright © 2011 by the American Geophysical Union.

Rako N.,Marine Conservation Institute | Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Mihanovic H.,Hydrographic Institute of the Republic of Croatia
Journal of the Acoustical Society of America | Year: 2013

This study aims to provide an objective mapping of the underwater noise and its sources over an Adriatic coastal marine habitat by applying the self-organizing maps (SOM) method. Systematic sampling of sea ambient noise (SAN) was carried out at ten predefined acoustic stations between 2007 and 2009. Analyses of noise levels were performed for 1/3 octave band standard centered frequencies in terms of instantaneous sound pressure levels averaged over 300 s to calculate the equivalent continuous sound pressure levels. Data on vessels' presence, type, and distance from the monitoring stations were also collected at each acoustic station during the acoustic sampling. Altogether 69 noise surveys were introduced to the SOM predefined 2 × 2 array. The overall results of the analysis distinguished two dominant underwater soundscapes, associating them mainly to the seasonal changes in the nautical tourism and fishing activities within the study area and to the wind and wave action. The analysis identified recreational vessels as the dominant anthropogenic source of underwater noise, particularly during the tourist season. The method demonstrated to be an efficient tool in predicting the SAN levels based on the vessel distribution, indicating also the possibility of its wider implication for marine conservation. © 2013 Acoustical Society of America.

Sikora M.,University of Split | Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Vilibic I.,Croatian Institute Of Oceanography And Fisheries
Acta Adriatica | Year: 2014

The paper documents the use of a Digital Elevation Model (DEM) method to reconstruct paleo-channels and the paleo-coastline during the Last Glacial Maximum (LGM) in the Central Eastern Adriatic area. We focused on the paleo-coastline and paleo-channels of the Neretva and the Cetina rivers, which were estimated from the 15’’ bathymetry available for the Adriatic Sea. While being aware of the limitations of the method and the resolution of the bathymetry grid, we successfully reproduced the paleo-channels of both rivers. Results for the Cetina River indicate the presence of depressions that were filled with water along its flow. The configurations of existing seabeds in the vicinity of the Cetina and Neretva River mouths indicate morphologies, similar to river mouths. The vertical profiles suggest that during the LGM the sea level was about 115 m lower than today. The total length of the Neretva riverbed was longer for about 136 km than today, and the Cetina River was approximately 154 km longer. © 2014, Institute of Oceanography and Fisheries. All rights reserved.

Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Charrayre F.,Institute of Engineering science of Toulon and Var
Natural Hazards | Year: 2013

High-resolution air pressure series collected from a triangle of middle Adriatic microbarograph stations between April 2009 and March 2011 have been analysed to extract the rapid pressure changes normally found during meteotsunamis. Five-minute air pressure tendencies were used to detect an event. Wavelet and cross-wavelet analysis showed that the energies of high-frequency pressure changes that occurred during the warm part of the year were an order of magnitude higher than those that occurred during the cold part of the year. Coherence between stations was normally found at periods longer than 1 h, while air pressure disturbances were dispersive and not coherent at shorter periods. This implies that the disturbances had little to no potential to generate meteotsunamis in the middle Adriatic area, as the eigenoscillations in bays and harbours of the region are over timescales of minutes up to a few tens of minutes. © 2013, Springer Science+Business Media Dordrecht.

Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Mihanovic H.,Croatian Institute Of Oceanography And Fisheries | Beg Paklar G.,Croatian Institute Of Oceanography And Fisheries | Orlic M.,University of Zagreb
Continental Shelf Research | Year: 2014

Analysis of oceanographic data collected during 2006 in the eastern Adriatic Sea indicated the presence of large internal waves (with a maximum range of about 30. m) at the diurnal frequency around the island of Lastovo. The amplitude ratio and phase difference between diurnal surface tides and diurnal isotherm fluctuations changed considerably between pronounced internal wave episodes, depending on stratification properties, thus suggesting possible resonant excitation of internal oscillations. On the contrary, no significant diurnal thermocline fluctuations were observed at two other islands (Biševo and Sušac). Theoretical analysis presented here focused on the trapping of long-period internal waves around a circular island corresponding to Lastovo and confirmed that stratification properties during the summer of 2006 around the island were close to resonant ones. The analysis also showed that Biševo and Sušac are too small to support diurnal near-resonant excitation. Application of a numerical model for the current flow around equivalent circular and elliptical islands in the stratified sea provided more details on resonant excitation. Theoretical and numerical modeling results particularly emphasized the importance of island dimensions, stratification properties (pyconocline depth and density defect) and the periodicity of the forcing. Furthermore, idealized numerical simulations demonstrated that the waves trapped at Lastovo behave as the gravest azimuthal mode of internal Kelvin-like waves, revolving in a clockwise direction around the island, and that the eccentricity of the island has almost no effect on the resonant period. © 2014 Elsevier Ltd.

Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Sepic J.,Croatian Institute Of Oceanography And Fisheries | Matijevic S.,Croatian Institute Of Oceanography And Fisheries
Continental Shelf Research | Year: 2011

The paper attempts to document long-term changes in deep Adriatic water patterns by applying the Self-Organising Maps (SOM) method to temperature, salinity, dissolved-oxygen content, orthophosphate and total inorganic nitrogen profiles sampled at a single deep station in the South Adriatic Pit (SAP) over a half century (1957-2009). Seasonality observed in upper layers has been removed by the least-squares fitting of the annual and semi-annual sinusoidal functions. The sensitivity of the SOM to various parameter combinations reveals the importance of temperature, salinity and dissolved oxygen for mapping different water patterns, while nutrients have less influence on quality and applicability of SOM solutions to the extraction of characteristic SAP water profiles. The quality of fit obtained for different combination of the measured parameters introduced to a SOM suggests that the incomplete combinations of input parameters increase an imperfection in the applicability of SOMs to the dataset. Two modes of long-term changes in the SAP obtained by the SOM analyses are discussed with respect to the processes that drive the variability in the area, e.g., the Adriatic-Ionian Bimodal Oscillation: where the first mode is characterised by rapid changes in the transition of SAP water masses, observed before 1980s (less adoptable by the SOMs), and the second mode is characterised by steady transitions (better adoptable by the SOMs), observed in the 1990s and the 2000s. The SOM method is found to have certain advantages when compared to other methods that have previously been used to distinguish the Adriatic water masses, as it does not depend on predefinition of water mass sources and allows for gaps in series. © 2011 Elsevier Ltd.

Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Mihanovic H.,Hydrographic Institute of the Republic of Croatia
Geophysical Research Letters | Year: 2013

Pressure, temperature, and salinity data collected during the winter of 2011/2012 by an Argo profiling float over the Adriatic shelf were used to document the dense water formation and subsequent bottom density current (BDC) normally occurring along the shelf slope. The float was advected to the Jabuka Pit and neighboring shallow area (<275 m) after October 2010. The parking depth was set to approximately 150 m, enabling the float to mostly follow the firstOnlineseabed between December 2011 and July 2012. The profiler measured strong spatial-temporal changes in the BDC thickness (from a few to about 50 m) and the bottom density (between 29.46 and 29.88 kg/m3). These observations show that an Argo float has the capability to observe a bottom density current and suggest that it would be possible to systematically use such floats to investigate these processes on coastal shelves. © 2013. American Geophysical Union. All Rights Reserved.

Silovic T.,Ruder Boskovic Institute | Ljubesic Z.,University of Zagreb | Mihanovic H.,Hydrographic Institute of the Republic of Croatia | Olujic G.,Hydrographic Institute of the Republic of Croatia | And 3 more authors.
Estuarine, Coastal and Shelf Science | Year: 2011

Picoplankton distribution at the boundary zone of the southern Adriatic in May 2009 on a 75km long shelf-continental slope transect was assessed by combining epifluorescence microscopy, flow cytometry and high-performance liquid chromatography data with hydrographic observations. The picoplankton distribution was greatly influenced by the hydrographic conditions prevailing in the southern Adriatic because of the influence of the Levantine Intermediate Water (LIW) and East Adriatic Current (EAC) forcing. Heterotrophic bacteria numerically dominated the picoplankton community through the entire transect with no significant accumulation. By contrast, picophytoplankton accumulated in the 50-75m layer, forming a pronounced deep chlorophyll maximum. Synechococcus dominated the photosynthetic picoplankton, whereas picoeukaryotes were the least abundant. The intrusion of warm LIW observed in the layer between 100 and 350m was followed by Prochlorococcus and Synechococcus peaks (10×10 3cellsmL -1 and 90×10 3cellsmL -1, respectively), as well as by the appearance of two Synechococcus ecotypes. Most picoeukaryotes were observed at the offshore stations, where geostrophic current calculation revealed the strongest EAC influence. A strong EAC spread over the central and eastern basin created a barrier for Prochlorococcus, whereas the picoeukaryote maxima coincided with the core of the EAC, suggesting its persistence to hydrological instabilities. © 2010 Elsevier Ltd.

Loncar G.,University of Zagreb | Leder N.,Hydrographic Institute of the Republic of Croatia | Paladin M.,University of Zagreb
Oceanologia | Year: 2012

Hypothetical cases of oil spills, caused by ship failure in the northern Adriatic, are analysed with the aim of producing three-dimensional models of sea circulation and oil contaminant transport. Sea surface elevations, sea temperature and salinity fields are applied as a forcing argument on the model's open boundaries. The Aladin-HR model with a spatial resolution of 8 km and a time interval of 3 hours is used for atmospheric forcing. River discharges along the coastline in question are introduced as point source terms and are assumed to have zero salinity at their respective locations. The results of the numerical modelling of physical oceanography parameters are validated by measurements carried out in the 'Adriatic Sea monitoring programme' in a series of current meter and CTD stations in the period from 1 January 2008 to 15 November 2008. The oil spill model uses the current field obtained from a circulation model. Besides the convective dispersive transport of oil pollution (Lagrangian model of discrete particles), the model takes into account a number of reactive processes such as emulsification, dissolution, evaporation and heat balance between the oil, sea and atmosphere. An actual event took place on 6 February 2008, when the ship 'Und Adriyatik' caught fire in the vicinity of the town of Rovinj (Croatia) en route from Istanbul (Turkey) to Trieste (Italy). At the time the fire broke out, the ship was carrying around 800 tons of oil. Thanks to the rapid intervention of the fire department, the fire was extinguished during the following 12 hours, preventing possible catastrophic environmental consequences. Based on this occurrence, five hypothetical scenarios of ship failure with a consequent spill of 800 tons of oil over 12 hours were analysed. The main distinction between the simulated scenarios is the time of the start of the oil spill, corresponding to the times when stronger winds were blowing (>7 m s-1) with a minimum duration of 24 h within the timeframe. Each scenario includes a simulation of oil transport for a period of two months after the beginning of the oil spill. The results show that the coastal belt between the towns of Poreč and Rovinj is seriously exposed to an oil pollution load, especially a few days after a strong and persistent bora (NE wind). © Polish Academy of Sciences, Institute of Oceanology, 2012.

Lovrincevic D.,Hydrographic Institute of the Republic of Croatia
Cartographic Journal | Year: 2016

A good seabed representation is one of the important characteristics of any navigational chart. Along with depth contours and coloured depth areas, soundings are used for this task. All the soundings on a navigational chart are selected for a reason. Soundings contribute to the navigational chart safety aspect by alerting to all the threats and dangers. They also show all the attributes of a seabed relief without overcrowding it, thus maintaining the overall chart quality. Soundings are selected from a hydrographic survey and since it consists of a vast number of data, the process of sounding selection is a challenging and demanding task. It requires experience and knowledge from the nautical cartographer and is mostly done manually. Some types of software nowadays provide an automatic selection feature. This paper analyses a process of automatic sounding selection in the dKart Editor software. On the Croatian side of the Adriatic Sea, Šibenski Kanal (Šibenik channel) and Kanal Sv. Ante (St. Ante’s channel) are used as the study area. A hydrographic survey of the area represents the input data. The official navigational chart of the surveyed area is used as the basis for determining three different sets of parameters for the selection process. After the selection, obtained results are assessed based on geometrical accuracy and on the conservation level of navigational safety. For geometrical accuracy, the best results were produced by the third set that was divided in two subsets for each channel. It was determined that the nature of the seabed relief had an impact on the selection process. The same set had the best result for navigational safety assessment but it was concluded that all the sets undermined the aspect. Because of these crucial shortcomings noticed in all the tested sets of parameters, the feature is considered inadequate for serious usage as a completely automatic tool for the process of sounding selection on navigational charts. © The British Cartographic Society 2016

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