vts improvements – introduction of wave monitoring ...

ISEP 2012

VTS IMPROVEMENTS – INTRODUCTION OF WAVE MONITORING SYSTEM AS A NAVIGATIONAL SENSOR Serdjo Kos, Renato Ivče, David Brčić University of Rijeka – Faculty of Maritime Studies Studentska 2, 51 000 Rijeka [email protected] [email protected] [email protected] Abstract The possibility of unwanted effects appears whenever the ship experiences significant wave forces, which reflects on ship’s surfaces, causing uncontrolled motion and behaviour. These effects may occur during navigation, port and coastal approaches or especially while the vessel is berthed alongside. If, due to high seas, mooring of the vessel fails, there appears a risk of ship’s damage, not to mention accidents due to sudden interruption of cargo operations. The paper elaborates the integration of ship’s navigational bridge with systems of wave force monitoring, with the aim to avoid mentioned consequences. Key Words Integrated Navigation Systems, Wave monitoring System, Wave forces

1 INTRODUCTION Radar has become both obligatory and inevitable navigational tool for collision avoidance, as well as for navigation in coastal waters. Radar’s emitted electromagnetic pulse bounces off the objects in the surrounding of the ship (more specifically radar’s antenna) and returns showing the presence of detected objects on a specific point. By knowing the position of desired object and calculating the further, the navigator has a competent insight in the dynamical situation which takes place. However, not all of the received signals are favourable. The signal which travels back through the antenna, the receiver and finally displayed on the radar screen, is composed both of useful information regarding ship targets, coast and/or other objects, and unwanted echoes with their origin in the state of sea and wind, precipitation, interferences and other numerous accidental or deliberate effects. In heavy rain, for example, the radar image will be masked with scatters representing rain drops all over the corresponding area in which the precipitation occurs. As for the nuisances regarding sea state, the result on the screen will be similar, indicating from which direction the waves are coming, and from where wind blows, respectively. Mentioned effects are nowadays effectively suppressed with various controls, and certainly with the skills of the navigator. One of the nuisances, the Sea Clutter, will be mentioned in the further text in a complete opposite context; the unwanted echoes from waves can be used to measure the actual state of the sea, which represents essential information regarding wave forces and their impact on the berthed or approaching ships. Acting as a sensor, this system provides accurate real-time information regarding wave forces and their load on the surface of the

vessels. Beside ships, this information is also important to the Vessel Traffic System (VTS) and the Pilot Office, as well as to shore facilities, in order to prevent bursts of the mooring lines or the abruption of cargo operations due to excessive forces. The following text gives an insight to the importance of data regarding wave loads, and also elaborates the possibility of integration of such a system on the Integrated Bridge. In this way the vessel gives an insight of her surrounding to all concerned parties providing timely response. 2 WAVE LOADS AFFECTED ON BERTHED VESSEL Ports and terminals around the world have various berthing layouts and mooring facilities that are exposed to different wind, wave, tidal and swell conditions1. Ship's master must take into consideration the critical value of mentioned meteorological and oceanographic phenomena which are acting on berthed vessel in order to ensure that the vessel is adequately moored to withstand the anticipated forces. It is important that the ship's master promptly takes extra precautions to keep the vessel alongside in adverse weather and that is ready and able to vacate the berth safely when conditions make it difficult for mooring. Moorings are provided to prevent vessels from drifting away from a berth or from colliding with adjacent moored vessels. Movement should be restrained by means of an adequate number of mooring lines, which can be readily handled by the operating personnel, compatible with the meteorological and oceanographic conditions during the period the vessel is berthed. The mooring equipment is dependent on the ship size and type and its position at port, spacing and strength of the mooring lines. In case that forces which are acting on ship's mooring lines exceed its breaking load, the mooring system will be disabled. The consequences of these incidents range from personal injury, significant contact damage to the vessel including grounding damage, damage to adjacent vessels, shore/terminal structures, and pollution damage to the environment. Wave loads on a vessel can vary depending on the vessel’s response to waves of varying periods and heights. When the wave energy in the berthing area is sufficient to cause significant movement of moored ships, several 1

This is especially important at berths that are not situated in port basins or bays, but off the shore, where the moorings (jetty's) are extracted out of the coastline.

ISEP 2012 problems can result. Motions which exceed safe limits can lead to difficulty or stoppage of passengers transfer or loading and unloading cargo. Moorings in relatively shallow waters and in low tide/high wave conditions are matter of special concern. These conditions can lead to violent vessel behaviour at the moorings (breaking waves, excessive motions, snatch loads etc.), and in extreme cases they can result in loss of under-keel clearance in wave troughs, especially expressed for larger, deeper draft vessels. A berthed vessel's response in harbour is affected by wind waves and swells characteristics including wave energy, frequencies and directional distribution. The wave climate within a harbour is primarily influenced by the wave condition at the sea area in front of harbour and its entrance. Waves are then transformed during its propagation to the berth location by the diffraction, refraction and shoaling. For this reason harbours are often exposed to waves with periods longer than wind and swell wave periods. These waves behave very different compared with ordinary waves. They have strong velocities which often results in resonant oscillation and they can lead to unfavourable motions of the ship. Determination of the forces exerted by various wave types is complex and there appears to be no simple and universally agreed method of evaluating the magnitude of these loads. Usually, the visual observation performed by the VTS duty person is not enough, and there appears a need for faster detection, in order to reduce or avoid possibility for damaging of the berthed ship. On the other hand, it is difficult to assess the magnitude of waves at a specific position, e.g. the pilot station, where the pilot embarks onboard ship and takes her to the anticipated berth. Numerous researches, models and programs have been carried out to determine the physical nature of wave characteristics and its impact on ships. One possibility for obtaining required wave characteristics and its impact on ships is the utilisation of the standard navigational X-Band radar in a manner that the part of backscatter which is normally rendered as a nuisance, once distinguished, provides useful information regarding waves and wave forces.

increased unwanted echoes with their origin in sea and precipitations. For this reasons, according to the SOLAS Convention [1] every vessel must be equipped with S-Band (3 GHz/10 cm) and X-Band (9Ghz/3 cm) frequency radar. 3.2 Sea Clutter Scattering and reflection are variations of the same physical process [2]. In marine navigation means, sea roughness will cause unwanted echoes on the radar screen in form of scattered image. In the context of the marine radar, nuisances from the sea (Sea Clutter, Sea Echoes) represent emitted pulse reflected energy from the rough surface of the sea. The amount of reflected energy directed to the radar antenna depends of signal's angle of incidence, his polarization, wavelength and, naturally, the state of the sea and the wind. The surface of the sea can be considered as a series of elementary reflectors - these surfaces are independent of each other, and they lead to electromagnetic wave scattering [2]. These nuisances have to be mitigated to the extent that does not represent interference, while maintaining echoes which matter2. The following figure shows radar images with and without suppressed echoes from the surface of the sea.

Figure 1: Radar image with (left) and without Anti Clutter Sea Control activated and adjuste Source: www.navnet.com

3 WAVE MONITORING RADAR SYSTEM 3.1 Navigational radar

3.3 Wave Monitoring System Radar uses radio waves propagation for determination of distances and bearings of the objects in the ships' vicinity. Measuring the time required for the signal to travel in the surrounding and, once reflected, back in the receiver, distance to the object/s is determined. The signal is displayed on plan position indicator (PPI), which rotates at the same angular velocity as the antenna, indicating the pointing direction of the antenna and therefore bearings of objects. It is preferable that navigational radar operates on smaller wavelengths. Higher frequency (9 GHz) compared to smaller one (3 GHz) has better radar beam direction, it provides better resolution – more detailed image, and the dimensions of the antenna are smaller. However, there are drawbacks of X-Band with regards to the wavelength which are manifested in smaller operational range, greater losses of the signal due to poor atmospheric conditions and

Real-time information about the sea state, such as wave height, direction and period have great importance for safety of the shipping traffic, coastal protection, as well as offshore operation management. Naturally, it is valuable information regarding port efficiency, whether used for pilot berth-to-berth sailing or management at the pier. Routine sea state measurements are carried out mainly using moored wave buoys, altimeters and pressure cells. Moored wave buoys are providing reliable measurements. However, they

2

The sea is highly conductive as an electrolyte. It has the reflection coefficient of 0.8. Fortunately, electromagnetic waves are reflecting by the radar antenna, otherwise radar would be useless for marine purposes.

ISEP 2012 are easily subject to damage and loss. Other traditional instruments used for this purpose have also their advantages and disadvantages. The common feature of all traditional instruments is that they collect wave information at one single point. Therefore, considerable interest has been shown in the use of remote sensing techniques for wave characteristics monitoring. The system for remote sea state determination is based on conventional nautical X-band radar. In contrast to buoy measurements, which are based on the analysis of the buoy motion using accelerometers and tilt sensors, radar measurements of the sea state are based on the analysis of the temporal and spatial evolution of the radar backscatter information, received in the near range of the radar [3]. For traffic monitoring requirements and in standard radar use, these sea clutter signals are recognized as noise and are therefore removed from PPI screen by applying a threshold to the radar echoes [4]. Based on standard marine X-Band radar, the wave monitoring system has proven to be a powerful tool in monitoring the most important parameters of the state of the sea. With respect to the functionality and accuracy of data output, some of these monitoring systems (e.g. WaMoS II[3,4]), have been approved by Classification societies. Wave monitoring system does not affect the navigation performance of the radar unit from which the data stream is taken, and therefore the radar can be used for both wave measurements and navigational purposes. The system was developed for real-time measurements of directional wave spectra to monitor the sea state at deepwater and coastal areas or from moving vessels. Mounted on a ship, oil rig, or on the shore, it is a proven instrument that measures the wave energy, its directions and heights, as well as the speed and direction of surface currents. It can be derived from the shore radar antennas, or the information can be received through different means, but already monitored and analyzed from vessels.3 The wave monitoring system generally consists of navigational, X-Band radar, highspeed video digitizing converter and a standard PC. The analogue radar video signal is read out and transferred through the digitizing device to the PC for storage and further real time processing [5]. The data can then be viewed immediately, transported by removable media, or viewed on-line by modem/telephone or the internet. For example, at port monitoring station, gained data (allowing traffic surveillances) can be displayed directly at site or transferred to remote locations to support weather monitoring services at the port sea area. Figure 2 shows the concept of wave monitoring system. The system is capable of unattended automatic operation. It provides high-resolution wave information based on the backscatter of microwaves from the sea surface that are visible as sea clutter on marine radar. From that observable sea clutter, an analysis is carried out to determine the directional wave spectrum and the surface current direction and speed. Sea state parameters such as wave periods, lengths, directions, and surface current speed and direction are 3

Depending on purpose.

measured. The maximum wave height can be estimated from spatial wave data, and therefore extreme wave events can be observed, studied and elaborated. 4 APPLICATIONS OF WAVE DATA IN THE INTEGRATED SHIP MONITORING SYSTEM Port surveillance radar antennas are usually located on the port control tower. This can create coverage problems depending on the location of the tower and adjacent terminal building facilities. Wave monitoring radar antenna must be located at obstruction-free position, taking the port geometry into account. Received signal will be transferred to the costal VTS using wireless technology. In the coastal VTS center displayed data would provide detailed insight into the state of the sea of surveillance area. Obtained wave characteristics are analyzed together with the data derived from vessels and they are incorporated in the integrated system with software based on the appropriate model. All collected data from the monitoring sites are processed and compared with allowed limits for berthed ship in the processing unit. The processed data are sent back to the ship's master control, where, with addition of other parameters that influences the movement of the ship, master receives suggestions to take certain actions in order to bring the vessel’s safety at satisfying level and within the allowed limit. Figure 3 demonstrates wave radar data integrated in the ship’s monitoring system.

Figure 2: Wave monitoring system Source: Made by the authors Derived information providing wave characteristic data are strongest and most intense in the immediate vicinity of the antenna that is the starting point of the screen. That is why this information is advantageous compared to fixed instruments provided for same purpose; on a VTS operator’s screen moving vessels will appear as sensors giving information regarding sea state in all areas where monitored.

ISEP 2012 SHIP/ INTEGRATED BRIDGE

ADVICES AND SUGGESTIONS

SHIPS DATA

WAVE DATA

WAVE MONITORING RADAR SYSTEM

HARBOUR MASTER OFFICE VTS SHORE FACILITIES PILOT STATION

PROCESSING UNIT

Figure 3: Wave radar data integrated in the ship's monitoring system Source: Made by the authors CONCLUSION Nowadays, the progress in marine navigation, whether it is oceanic or coastal, is achieved in integration. Integrated Bridge has already reached its complex and sophisticated level by means of connecting all navigational instruments and gathering their data at one single device. The integration as such is still evolving in order to gain the highest possible accuracy and reliability. Comprehending this system in a broader context, there is a lot what can be done with regards to safety and safe navigation. The vessel becomes a sensor itself, providing in situ information to all concerned parties, and enriching their ways to decisions. Amongst all relevant data regarding safe handling of vessels, oceanographic parameters are the one of great concern, and the one of the rare which cannot be managed. However, with timely detection and assessment of these indices the risks can be reduced in due time. ACKNOWLEDGMENTS The authors acknowledge the support of research project ''Research into the correlations of maritime-transport elements in marine traffic'' (112-1121722-3066), funded by the Ministry of Science, Education and Sports of the Republic of Croatia. REFERENCES 1. SOLAS Convention, Chapter V.: Safety of Navigation 2. Sušanj, J., Navigacijski radar, Sveučilište u Rijeci, Pomorski fakultet u Rijeci, Rijeka, Hrvatska, 2006. 3. Reichert, K. et al: WaMoS II: A Radar based wave and Current Monitoring System, Proceedings of the Ninth (1999) International Offshore and Polar Engineering Conference, Brest, France, May 30-June 4, 1999. 4. Vogelzang, J. et al: Wave height measurement with navigation radar, International Archives of

Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7, Amsterdam, 2000. 5. Nieto Borge, J.C et al: Use of nautical radar as a wave monitoring instrument, Coastal Engineering, Vol. 39, pp. 331 – 342, Elsevier B.V., 1999.

BIOGRAPHIE Serdjo Kos Dr. sc. Serdjo Kos was born in 1957 in Rijeka. In 1980/89 he was employed as a navigation officer in Croatialine (ex Jugolinija) shipping company, as the Third, Second and Chief officer. In eight effective years of ocean-going service in navigation, Professor Kos sailed on vessels of various types, sizes, technologies and purposes. In 1986 he received B.Sc. degree at The Faculty of Maritime Affairs and Traffic, course Nautical Sciences. Since 1989, he has been fully employed at the Faculty of Maritime Studies, University of Rijeka, where he obtained his M.Sc degree (in 1992) and Ph.D. degree (in 1994). In 2009, professor has been elected as Full Professor at the Faculty of Maritime Studies in Rijeka, Technical Sciences Department, in the field of traffic technology and transport. Today, professor Kos is obtaining the role of the Dean at the Faculty of Maritime Studies. Because his achievement in the domain of Navigation theory – Theory of Loxodromic navigation is internationally recognised, the biography of Professor Kos is included in the 8th edition of Who's Who in Science and Engineering, 2005-2006, by the world's eminent publisher Marquis Who's Who, from the United States of America. Amongst numeruous honourable memberships, Professor Kos is also Fellow of the Royal Institute of Navigation. The Professor's scientific areas of interest are the following domains: Loxodromic and orthodromic navigation theories; Terrestrial, Electronic and Astronomic navigation; Satellite and inertial navigational systems (Positioning errors of the GPS/GLONASS system regarding ionospheric and tropospheric delay, Correction of the Klobuchar model, Positional dilution of precision of the GPS/GLONASS System, Satellite positioning errors related

ISEP 2012 to the extreme space weather/ionospheric effects, GeoRSS systems and technologies, etc.); Ecology and environmental preservation, Multimodal transport networks; Intermodal, Integrated/Multimodal transport systems and Optimization and simulations in maritime transport. Renato Ivče Dr. sc. Renato Ivče is born in Rijeka, Croatia. After he received the B.Sc. degree at Faculty of Maritime Studies, Rijeka, he sailed on the shipping company Lošinjska plovidba – Mali Lošinj, as deck officer and the master for the period 1991/2002. In May 1994, he obtained the highest qualification in Marine profession that is the Master Mariner of ships of 3000 GT or more. Since 2001 he is employed at Faculty of Maritime Studies, University of Rijeka. He obtained the Master of Science degree in 2005 and the Ph.D. degree in 2008 in the field of technical sciences at the University of Rijeka - Faculty of Maritime Studies. He published four books as coauthor and several scientific and technical papers in the field of ships handling, ships maintenance and safety of navigation. He participated as a collaborator in a number of studies/proposals for the maritime economy. He was appointed as a marine expert by Court in investigation in few marine accidents. Dr. Ivče is the member of the Royal Institute of Navigation, the Association of Sea Captains and Officers of North Adriatic, and also of the Croatian Chamber of Engineers Traffic and Transport. He is member of Department of Nautical sciences at the Faculty of Maritime Studies at Rijeka. David Brčić Born in Rijeka in 1979. After he finished Maritime high school in Mali Lošinj, Croatia, he sailed on general cargo ships before he received the Certificate for the Officer of the Navigational Watch of ships of 3000 GT or more. In the period of 1999/2002 he sailed on chemical tankers in the rank of deck officer. Attended and graduated (2008) at the Faculty of Maritime Studies in Rijeka, Croatia. Enrolled at the same Faculty in postgraduate doctoral degree studies, as well as employed as research assistant in the field of Maritime navigation.