Shoreline changes are an environmental indicator capable of identifying: a) areas exposed to erosion; b) public assets at risk; c) priorities for risk mitigation. The ability to accurately and in real time measure the state of the sea surface enables the use of a range of applications and tools. X-band radar systems, mounted on fixed stations near ports or other strategic sites, can be used, up to a distance of 3 nautical miles, to monitor shoreline evolution, generating maps of surface currents and wave fields that intrude and cause erosion. They can also be used to develop models of suspended material transport and diffusion and monitor river mouths.
The Laboratory
The use of X-band radar has attracted growing interest due to its potential as a wave radar, allowing for highly precise, real-time measurement of wave spectra and surface current fields within a range of up to 5 km. The unique features and potential of this innovative technology, wave radar, have recently attracted growing interest in the field of coastal monitoring due to its applications in coastal surveillance and emergency situations. Among monitoring systems, wave radars are gaining popularity due to their significant advantages in terms of flexibility of use, thanks to their small size, low weight, and ease of installation. Specifically, the model currently in use is called "mobile" because it is positioned on a pneumatic column mounted aboard a towed platform. The nautical radar in question, used for scientific research purposes, operates exclusively with short pulses. Transmission is inhibited on land and it has a narrow emission angle directed only towards the sea. It radiates at non-continuous intervals of a few minutes and only in correspondence with strong seas, so as to allow the acquisition of sufficient data to carry out an analysis of the characteristics of the wave motion and surface currents in the sea area in front of the chosen installation site.
The work described below focuses on coastal applications of X-band radar, in particular on their ability to provide accurate, real-time wavefield measurements, with much lower costs and greater precision than wave buoys and, therefore, on the likelihood of real-time and remote detection of coastal siltation and erosion phenomena.
Instruments
A “wave radar” system consists of:
- 6-foot radar antenna for transceiver operation in the 9300 to 9500 MHz frequency band;
- Data acquisition and conversion system;
- PC for radar control and data processing;
- Software modules dedicated to the control and management of the radar unit, the acquisition interface and for the determination of the physical parameters that contribute to the definition of the sea state in an area with a radius of up to 1.5 nautical miles from the radar and related database archiving;
- Software modules dedicated to generating high-resolution surface current maps, transmitting the detected information to a database/remote system via TCP/IP protocol with automatic selection of the best transmission channel, and remote system management and control (including a graphical user interface for displaying results). The radar signal acquisition and processing interface for generating sea surface images complies with the IEC60945 standard. The processing unit is dedicated to post-processing and data archiving.
In particular, the model in question is called Mobile as it has the characteristic of being placed on a pneumatic column mounted on board a trailer-mounted platform from RSA ITALIA Srl. The pneumatic column can be operated via a HONDA GX160 single-cylinder 4-stroke petrol engine generator with dimensions (L x W 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 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, including a detail of the electric generator installed inside the structure. The photo on the left shows the system with the radar antenna mounted on the pneumatic column, which is in a vertical position; the photo on the right shows the system with the column at rest and taking up minimal space.
The flexibility and mobility of the Mobile Radar system make it unique in its kind as it offers the advantage of being able to carry out coastal monitoring extremely simply and quickly from any position without the need for a fixed installation, as long as there is a view of the sea.
Staff and Contacts
Dr. Francesco Raffa (CNR Technologist – Radar System Manager)
Dr. Fabrizio Lirer (CNR Researcher)
Carlo Sardo (CNR Technician)
Contacts
Phones
+39 347 1803641 (Francesco Raffa)
+39 050 6212387 (Serena Botteghi)
E-mail:
Methods and Applications
Monitoring is essential for understanding coastal phenomena and verifying the effects of implemented interventions. Marine radar has always been used to aid navigation, enabling the identification of targets at sea. For improved target visualization, the device uses an anti-clutter filter to reduce the return of electromagnetic radiation, known as clutter, from the sea surface. Only in the last decade have radar devices been used for another application: monitoring parameters characterizing sea state. By analyzing the clutter signal received by a common X-band radar, it is possible to obtain significant information on sea state, such as wavelength, direction, and period of the dominant waves, surface currents, and seabed bathymetry. Under specific conditions, it is also possible to reconstruct the spatiotemporal evolution of wave motion and thus monitor the height and propagation of individual sea surface waves. Knowledge of this information is useful for developing a range of applications and services, such as coastal protection and safeguarding. X-band wave radar allows for scanning the sea surface with high spatial and temporal resolution. This is possible because backscatter from the sea surface, the intensity of which can be comparable to that of normal targets, is captured by the radar antenna. The interaction between the radar's electromagnetic waves and the free sea surface can be divided into two very different phenomena:
- the reflection of electromagnetic fields according to the laws of geometric optics.
- the dispersion of electromagnetic waves or backscattering, which is the most significant effect when measuring
The wave field through common X-band nautical radars in grazing angle mode, i.e., acquisition geometry with a viewing angle nearly 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 capillary waves formed by the local wind and other phenomena such as the presence of foam on the sea surface. Therefore, wave measurement by radar is dependent on the presence of wind in the area illuminated by the radar. Experimental results show that a wind of at least 2.5 m/s is required for ripples to form on the sea surface, sufficient to provide a sufficiently strong return on the radar video signal.
For this reason, in the absence of wind, the system is unable to provide images of the sea surface because the transmitted signal is reflected in a specular fashion with respect to the position of the transmitting antenna and is not scattered in all directions.
The application aims to contribute to the acquisition of advanced knowledge on the dynamics and/or changes over time of coastal ecosystems in relation to the physical processes that characterize them, to be developed through the experimentation of new monitoring methodologies tailored to the specific characteristics of the coastal area. Remote sensing using Wave Radar, alongside more traditional systems for detailed surveys, will provide important datasets for software testing, system calibration, and comparison of results. Shoreline variations of the order of a few meters can be identified. Data at this spatial-temporal scale are not easily obtained with other remote sensing techniques. The use of Wave Radar as a tool to quantify coastal variation at seasonal and event-specific scales in complex hydrodynamic systems is a unique application for monitoring areas with dynamic morphology or those vulnerable to erosion caused by storm events.
Scientific Projects and Interests
As part of the agreement signed in 2018 with the CNR-ISMAR Naples branch, which owns the Wave Radar Mobile, for shared study and monitoring activities for scientific research purposes, the CNR-IGG is using this innovative instrumentation for the first time in Italy to collect monitoring data from the coastal areas of Tuscany. A periodic local-scale monitoring activity has been initiated to identify the areas with the most evident phenomena requiring more detailed monitoring, 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 seabed depth, hydrodynamic characteristics of the surface water, human impact, and material discharges at river mouths have a significant impact on the environmental status of the coastal system, the proposed monitoring activity involves studying variations in the coastline and the bathymetry of the shallow waters.
Below is a description of the analysis of data acquired during a storm surge by a Wave Radar in use at the IGG-Pisa Institute: a mobile radar, owned by the CNR of ISMAR-Naples, installed on a mobile platform, in Marina di Pisa (Italy) at the coordinates: Lat: 43°39'23.10 “N and Lon: 10°16'52.56 “E in October 2019.
The following figure shows the areas investigated in detail with the SRT Consilium 25KW X-band Wave Radar model with 9” antenna.
As an example, the following figure shows a radar image acquired at 13:35 UTC from Marina di Pisa. The image shows nearby ships and the radar signature of the sea waves.
The following table shows the operating parameters of the radar system.
| Radar parameters | Values |
| Peak power | 25 kW |
| Antenna length | 2,7 m |
| Radar scale | 1,25 NM |
| Antenna rotation period (Δt) | 2,4 s |
| Image spacing (Δx and Δy) | 4,5 m |
| Antenna height | 15 m |
| Angular sector | 110° N |
Table 1: Radar system operating parameters
The radar data analysis algorithms, developed entirely at the CNR, allow for real-time and highly accurate estimates of sea state parameters (significant wave height, direction, period, and length of dominant waves), surface current flow, and, under appropriate conditions, seabed bathymetry up to a distance of 5 km from the radar. The following images show some examples of the directional spectrum measured during the survey, along with average wave and surface current measurements.
Spectral images and wave measurements reveal the presence of a dominant wave at approximately 250° and 260°. To verify the intensity of the radar measurements obtained during the aforementioned survey, they can be compared with the wave forecasts generated by the model and with the tide gauge measurements corresponding to the same day. The wave forecast models provided by the WWMII model produced by ISMAR-CNR and the measurements taken by the Gombo buoy of the Tuscany Region's meteorological-hydrological monitoring service are consistent with the measurements taken in the study area. Below are the WWMII wave model images of the study area and the time graphs of the wave height, direction, and period measured by the wave gauge.
The Wave Radar system, in addition to providing wave measurements in terms of characteristic parameters, also reconstructs wave elevation in space and time with a spatial resolution of a few meters. The following images show a snapshot of the spatial reconstruction of wave elevation compared to the acquired data. The images, overlaid on a Google map, show the propagation of the dominant wave, coming from the WSW, impacting the coast.
The presence of the coast generates wave reflection and refraction, phenomena associated with the deviation of the wave propagation trajectory when they encounter an obstacle in their path. These phenomena are of fundamental importance for understanding the effects of wave interaction with coastal areas and for monitoring the effects of erosion. A coastal area exposed to greater average wave energy can potentially suffer from more severe natural erosion: a numerical energy calculation model can be used as a preliminary assessment tool to estimate the distribution of natural erosion risk along the coast. However, a necessary condition for correct calculation of this amount of energy through numerical simulations is that the inputs be reliable, in this case, derived from real measurements of significant wave heights.
This information, combined with seabed bathymetry, provides a comprehensive framework for experts to conduct preventive studies for the construction of new infrastructure, as well as for more effective beach nourishment or dredging.
The main scientific interests relate to anthropogenic pressure on the dune and ridge coast, which combines with coastal erosion. Large stretches of sandy coastline are affected by erosion: despite protective structures, in some areas the coastline has retreated by several dozen meters. A regional analysis of the average annual rates of shoreline change indicates that in the period 1984-2005, approximately half of the Tuscan coastline: – 30% showed modest variations (between 0.5 and 1.5 m/year), of which almost 18% was increasing; – 10% saw variations between 1.5 and 3 m/year, evenly distributed between eroding and advancing stretches; – the remaining 6% (4% of the originally sandy coastline is now occupied by an artificial coast) shows greater variations, with a prevalence of erosion phenomena over those of advancement (Source: www.regione.toscana.it/difesasuolo: Operational document for the recovery and rebalancing of the coastal strip, 2016; edited by: Tuscany Region, Land Defence and Civil Protection Directorate, “Civil Engineering Lower Valdarno and Coast” Sector).
Publications
- 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.
- Williams, JJ; Esteves, LS and Atkinson, J. X-band radar system to support coastal management decisions [online]. In: Australasian Coasts & Ports 2017: Working with Nature. Barton, ACT: Engineers Australia, PIANC Australia and Institute of Professional Engineers New Zealand, 2017: 1179-1185.
- 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.