Mobile coastal monitoring system IGG-ISMAR
In recent past decades, anthropogenic pressure has contributed to a sharp change in the coastal system; wetlands have been replaced by agricultural fields, by roads, by urbanized areas and by industries. The loss of naturalness of our coasts is mainly produced by coastal erosion (more than 60%) and by the expansion of the houses, infrastructures and productive areas. In this context, it is important to understand the relationships between variations in the shoreline and anthropic changes, as essential tools for a better management of the coastal area. Coastline changes are an environmental indicator that can identify: a) areas exposed to erosion; b) goods exposed to risk; c) priorities to mitigate the risk.
The activity described below aims to obtain advanced knowledge on the dynamics and/or variations over time of coastal ecosystems in relation to the physical processes that characterize them. This is developed through the experimentation of new monitoring methods in relation to the specific characteristics of the coastal area adjacent to the outlet of the rivers. Since the depth of the bottom, the hydrodynamic characteristics of the sea surface state, the anthropic impact and the discharges of material carried to the river mouths strongly affect the environmental state of the coastal system, the monitoring activity concerns the study of the variations of the shoreline and the shallow bathymetry in such a way as to fit into the Integrated Management Plan of the Coastal Zone.
X-band radars, in recent years, are establishing among the monitoring systems for the great advantage of having broad distribution and low costs. In addition to receiving echoes from possible obstacles on the water, they also receive the echo reflected from the surface. It is such data, generally rejected, as it is considered a noise for the detection of targets, that is the most useful to know the surface state. In particular, data processing makes it possible to obtain essential information, such as wavelength, direction and period of dominant waves, surface currents and bathymetry of the seabed. They also offer advanced work flexibility due to their small size, low weight and ease of installation.
The peculiarities and potential of an innovative technology, the 'Wave Radar', has recently received an increasing interest in the field of coastal monitoring thanks to its uses for coastal surveillance and emergency situations. In particular, the model in use is named 'Mobile' because it has the characteristic of being placed on a pneumatic column mounted on board of a towed platform. The nautical radar in question, used for scientific research purposes, works exclusively with short pulses, the transmission is inhibited to land and has a narrow angle of emission directed only to the sea, irradiating it at intervals of non-continuous time of a few minutes and only in correspondence of high swells, so as to enable the acquisition of sufficient data to perform an analysis of the characteristics of wave motion and surface currents in the area of the sea in front of the chosen site of installation, up to a distance of 3 nautical miles.
The ability to know in real time and with good accuracy the sea surface state allows to deploy a series of applications and tools. The X-band radar system, mounted on fixed stations, near ports or other strategic sites, can be used, for example, to monitor the evolution of the shoreline, generating maps of surface current and the wave field that breaks in generating erosion, and can be a system for the tuning of models for the transport and dissemination of suspended material and the monitoring of river outlets.
INSTRUMENTS AND PERSONNEL
A "wave radar" system consists of:
- 6ft radar antenna for transceiving in the 9300 ÷ 9500 MHz frequency band;
- Acquisition and data conversion system;
- PC for radar control and data processing;
- Software modules devoted to the control and management of the radar unit, of the acquisition interface and for the physical parameters determination that contribute to the definition of the sea state in an area of range up to 1.5 nautical miles from the radar and its storage in a database;
- Software modules dedicated to the generation of surface current maps with high spatial resolution, to the transmission of detected information to database/remote system on TCP/IP protocol with automatic selection of the better transmission channel, to the management and remote control of the system (including the GUI for the visualization of results). The interface for the acquisition and processing of radar signals for the generation of images of the sea surface complies with IEC60945. The Processing Unit is dedicated to post-processing and data storage.
In particular, the model in question is called Mobile because it has the characteristic of being placed on a pneumatic column mounted on board of a platform that can be towed by RSA ITALIA Srl. The pneumatic column can be driven by a single-cylinder 4-stroke gasoline engine generator HONDA GX160 with dimensions (W x D x H) 312 x 362 x 346 mm and dry weight 15.1 kg, displacement 163 cm³, net power 3.6 kW (4.8 HP)/3600 rpm, continuous nominal power 2.5 kW (3.4 HP)/3000 rpm. The fuel tank capacity is 3.1 litres and the estimated fuel consumption at continuous power is 1.4 L/O - 3600 rpm.
Below are some photos of the 'Wave Radar Mobile' system with the detail of the electric generator plugged into the structure. The photo on the left shows the system with the radar antenna mounted on the pneumatic column that is in a vertical position, while the photo on the right shows the system with the column at rest and with minimum space requirement.
The characteristics of flexibility and mobility of the Radar Mobile system make it unique in the sense that it offers the advantage of allowing coastal monitoring to be carried out ease and fast from any position without the need for a permanent installation, given that the system has a sea view.
Francesco Raffa (CNR Technologist - Responsible for the Laboratory)
Serena Botteghi (CNR Researcher)
Carlo Sardo (CNR Technician)
+39 347 1803641 (Francesco Raffa)
+39 050 6212387 (Serena Botteghi)
The monitoring activity plays a key role in understanding the ongoing phenomena on the shoreline and in evaluating the effects of the actions carried out. Marine radar has always been used to support navigation, allowing the identification of targets at sea. For a better visualization of the targets, the device allows to reduce, through the use of an anti-clutter filter, the return of electromagnetic radiation, called clutter, coming from the sea surface. Only in the last decade the radar devices are used for another application: the monitoring of parameters that characterize the state of the sea. Through the analysis of the clutter signal received by a common X-band radar, it is possible to obtain relevant information on the sea state such as the wavelength, the direction, the period of the dominant waves, the surface currents and the bathymetry of the bottom. Under specific conditions it is also possible to determine the spatial-temporal evolution of the wave motion and monitor, therefore, the height and propagation of the individual waves of the sea surface. This information is useful for the implementation of a range of applications and tools, such as coastal protection and safeguard. Wave Radar in X-band allows to scan the sea surface with high spatial and temporal resolution; this is possible because backscattering from the sea surface, whose intensity may be comparable to that of normal targets, is detected by the radar antenna. The interaction between the electromagnetic waves of the radar and the free surface of the sea can be split into two very different phenomena:
- the reflection of electromagnetic fields according to the laws of optical geometry;
- the dispersion of electromagnetic waves or backscattering, which is the most significant effect whenmeasuring the wave field through common nautical radars in X-band in grazing angle mode, i.e. geometry of acquisition with an angle of view almost parallel to the sea surface. The backscattering effect is caused by the interference of the waves transmitted by the radar with the roughness of the sea surface. This roughness is mainly due to the capillary waves formed by the local wind and other phenomena such as the presence of foam on the sea surface. Therefore, the detection of waves by radar is related to the presence of wind in the area covered by the radar. Experimental results show that a wind of at least 2.5m/s is needed to form ripples on the sea surface, which can give a relatively strong return on the radar video signal.
For this reason, in the wind absence, the system is not able to provide images of the sea surface because the transmitted signal is reflected in a mirror image to the position of the transmitting antenna and not scattered in all directions.
The application aims to support the acquisition of advanced knowledge on the dynamics and/or variations over time of coastal ecosystems in connection with the physical processes that characterize them, to be developed through the experimentation of new monitoring methods in relation to the specific characteristics of the coastal area. With remote detection through the Wave Radar, to be combined with more traditional systems for detailed surveys, important datasets will be provided to test the software, calibrate the systems and compare the results. Changes in the shoreline of the order of magnitude of a few meters can be identified. Data at this spatial-temporal scale are not easily obtained by other remote sensing methods. The use of Wave Radar as a tool to quantify coastal variation at seasonal and event scales in complex hydrodynamic systems is a unique application to monitor areas with dynamic morphology or vulnerable to erosion caused by storm events.
Within the framework of the agreement signed in 2018 with the CNR-ISMAR Naples secondary site, owner of the Wave Radar Mobile, to study and monitor common activities for scientific research purposes, the CNR-IGG is currently using this innovative tool for the first time in Italy to collect monitoring data for the coastal areas of Tuscany. A periodical monitoring activity has been started up on a local scale, in order to identify the areas characterized by the most evident phenomena to be monitored in more detail, such as the San Rossore Park area, between Gombo and Marina di Pisa, Versilia, between Marina di Carrara and Lido di Camaiore, Mazzanta, between Vada and Cecina and the Calafuria area. Since the depth of the bottom, the hydrodynamic characteristics of the sea surface state, the anthropic impact and the spills of material at the river mouths strongly affect the environmental state of the coastal system, the proposed monitoring activity concerns the study of the variations of the coastline and the bathymetry of the shallow waters.
An example of the application of Wave Radar in X-band was carried out as part of the "Coastal Monitoring" actions provided by the project SIGIEC PON (Integrated Management System for Coastal Erosion). The project was carried out by the CNR in partnership with universities and companies and studied the causes and effects of erosion phenomena affecting beaches located in Calabria and Puglia. For example, by investigating containment measures as well as developing quantitative methods it allowed the production, evaluation and implementation of a well-adapted coastal management policy.
The site was selected by analysing the quality of the geomorphological and sea-meteorological data: the coastal area of Bagnara Calabra (RC). From 24 to 27 February 2015 more than 1000 images of the sea state within one mile from the coast were acquired and analysed using the Wave Radar system developed at IREA-CNR.
The following images include information about the wave field and its variation over time on a local scale. The energy of the waves trapped by the submerged barriers induces an intense reflection of the waves between the breakwaters and the coastline. In addition, the figure clearly identifies the pier in the port area and two shaded areas, one in a north-easterly direction and the other in a south-westerly direction.
Another interesting aspect is the morphology identified in the area in front of the mouth of the river Assi, at Monasterace Marina (RC).
The radar image (figure above) shows several elements that characterize the coastal area of Monasterace Marina: A) Mouth of the river Assi: comparison between orthophotos and radar images; B) Area of shadow probably caused by the submarine channel located in front of the mouth of the river Assi; C) Reflection of the radar signal at the submerged protuberance of the ancient coast. Some morphological elements, such as the coastal dunes and the main distribution channels of the river delta, are clearly distinguishable (figure A). A less reflective area in front of the Assi river is evident (figure B): it could be related to an underwater channel located in front of the river and therefore due to the greater depth reached in the area. Up to about 800 m from the shoreline, in the area in front of the Museum, there is an intense reflection of the radar signal; this area coincides with the area where the submerged head, similar to a hook, is located and where the ancient shoreline probably was located (figure C).
The main scientific interests are linked to the high rate of urbanization of the Tuscan coastline, with widespread residential housing, development of industrial areas (particularly concentrated along the river sides) and high density of highways (with a significant barrier effect and fragmentation). The anthropogenic pressure on the coast is very heavy, and is combined with coastal erosion. Large parts of the shoreline are affected by erosion: although protection works have been carried out, in some parts the coastline is several tens of metres further back. The regional analysis of the average annual rates of change of the shoreline shows that in the period 1984-2005 about half of the Tuscan coast: - 30% have limited variations (between 0.5 and 1.5 m/year), of which almost 18% have been growing; - 10% have seen variations between 1.5 and 3 m/year, equally distributed between stretches in erosion and advancement; - the remaining 6% (4% of the coast originally of sand is now occupied by artificial coast) has greater variations, with a prevalence of erosion phenomena over those of progress (Source: Hydrological Service Tuscany Region).
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- Michele Punzo, Chiara Lanciano, Daniela Tarallo, Francesco Bianco, Giuseppe Cavuoto, Rosanna De Rosa, Vincenzo Di Fiore, Giuseppe Cianflone, Rocco Dominici, Michele Iavarone, Fabrizio Lirer, Nicola Pelosi, Laura Giordano, Giovanni Ludeno, Antonio Natale, Ennio Marsella, 2016 “Application of X-Band Wave Radar for Coastal Dynamic Analysis: Case Test of Bagnara Calabra (South Tyrrhenian Sea, Italy),” Journal of Sensors, vol. 2016, Article ID 6236925, 9 pages, 2016. https://doi.org/10.1155/2016/6236925.
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- G. Ludeno, F. Raffa, F. Soldovieri, F. Serafino, 2018. Proof of feasibility of the sea state monitoring from data collected in medium pulse mode by a x-band wave radar system. Remote Sensing 10 (3), 459