Monitoring and Surveillance
During the monitoring and surveillance phase, the Central Functional Center collects data from meteorological satellites, the national radar network and the network of ground stations to ensure continuous control of weather and hydrological phenomena and to follow the course of events throughout the territory, together with the decentralized functional centers. At this stage is fundamental to receive information from the territorial units: structures responsible for observing, monitoring and supervising the phenomena and their evolution on the territory. The information and data collected allow the Central Functional Center to keep constantly updated the Situation Room Italy and monitoring of the territory called System.
The main monitoring and surveillance tools are the national radar network and the network of meteo-hydropluviometric stations. The former can estimate the presence and intensity of precipitation in the atmosphere almost in real time, and observe the movement of disturbances, while the latter can measure precipitation falling on the ground and river level variation.
The meteo-hydropluviometric stations are telemetry stations. They consist of instruments that measure weather conditions and send data in real time. The stations feature several sensors, which deliver the measured data to the regional collection and processing centers in real time. As of early 2012, these stations number more than 4,500 and include 2,000 rain gauges (to measure the amount of rain), 1,130 hydrometers (to monitor river levels) and 3,500 sensors like thermometers (to measure temperature), anemometers (to measure wind intensity) and snow gauges (to measure snowfall).
In the last years the regional owned stations have been upgraded thanks to the application of some measures (e.g. law 267/1998, called Sarno law, and law 365/2000, called Soverato law, and subsequent civil protection ordinances) aimed at improving the observation and monitoring capacity of phenomena and at optimizing the use of data, in real time, for civil protection purposes.
Data sampling
The meteo-hydropluviometric stations have a data sampling time (the interval between the recording of one measurement and another) that varies between one minute and one hour and a "latency time" generally of 30 minutes, that is the time between the measurement and the effective availability of data to the operator.
Data transmission and processing
The measurements collected are transmitted via radio, satellite or GSM/GPRS systems to the monitoring center of each functional center that displays and processes them through the Experience Platform, a software that provides information sharing between functional centers. The data elaborated are sent in "packets" to the server of the Department. In order to compare, integrate and synthesize the data necessary for the real-time evaluation of the meteo-hydrological situation, a further dedicated platform has been designed and is continuously improved: the Dewetra system.
The project of the radar network on a national scale, developed and managed by the Department of Civil Protection, aims to ensure a better monitoring capacity of atmospheric phenomena on a national scale by integrating radar observations both with satellite observations, which provide information on cloud, and with rainfall sensors, which record data accurately, usually not highly representative of an entire catchment area. The realization of an operational system of interconnection and fusion of meteorological radar data in real time implies the definition of a mosaic process. The demand to realize this network arises both from the need of a large scale meteorological monitoring and from the need to improve the quality of the measurements of single radars. In fact, the use of a single radar involves a series of problems that limit its effectiveness. These problems are due to technical-instrumental anomalies (e.g. calibration, interference from W-LAN networks), the orographic complexity of the territory and the physical characteristics of the meteorological phenomenon observed.
The network is being completed and includes twenty-six fixed and four mobile radars, a total of thirty weather radars distributed throughout the country. Currently, the National Radar Network consists of twenty-four operational radars of which ten installed and managed directly by the various regions, four owned by the Air Force and two by ENAV, and eight ( six C-Band Radar and two Mobile Radar in X-Band) were installed by the DPC and are operational around the clock to ensure an effective monitoring of various weather phenomena throughout the country.
The architecture of the whole system foresees that at the Central Functional Center are collected the data made available by all agencies and administrations that contribute to the national radar network. The Central Functional Center generates different products in order to guarantee the best possible coverage, then distributes the data in real time to the Decentralized Functional Centers (CFD) and to the national Institutional Bodies with a frequency of fifteen minutes through different platforms. Each CFD, in full autonomy and under its own responsibility, defines the operational use of these products through any necessary procedures.
What is the radar
The weather radar is a monitoring and surveillance tool, designed to assess the presence of precipitation in the atmosphere almost in real time. Therefore, it allows to follow the evolution of phenomena in the very short term. The term radar is an acronym of the English radio detection and ranging and means detection and determination of the position (of an object) through radio waves. The radar was developed for military purposes and for the first time was used in the meteorological domain in the 50'. The radars used today provide information not only on the intensity of the observed disturbance, but also on the nature of the precipitation (rain, snow, hail, etc.) and its speed of movement.
What it is used for. The weather radar is an instrument used to:
• monitor precipitation phenomena in real time, identifying their intensity and physical state (rain, snow, hail), through the study of polarization characteristics;
• estimate the precipitation over large geographical areas, providing information complementary and integrable with those derived from the conventional ground monitoring network, in order to provide a more accurate reconstruction of precipitation;
• to estimate in real time intensity and average direction of movement of a bad weather event;
• follow the evolution of a bad weather event;
• to make precipitation estimates more accurate by integrating radar network data with ground monitoring data and satellite observations.
How it works
An electromagnetic wave, generated by a transmitter, is radiated into the atmosphere through a directional antenna. As the wave propagates (travels) through the atmosphere, it interacts with objects along its path, being partly absorbed and partly reflected, even in the radar direction from which it is received again. The speed at which the wave travels is known (300,000 km per second), so it is possible to calculate how far the object is from the radar if you take into account the return time of the signal. A meteorological radar allows to detect, within a portion of the atmosphere, the presence of hydrometeors, such as water particles (both liquid and frozen).
Therefore, a meteorological radar consists of a transmitter of electromagnetic waves of high power, a receiver, an antenna - which gives the direction to the signal - and a processor.
The return signal is processed in the receiver of the radar and allows to estimate the intensity of the precipitation, while the direction of pointing of the antenna and the time taken by the signal in the round trip path allow to localize the hydrometeoras in terms of direction and distance. Also, small variations in the phase of the return echo allow to estimate the speed of displacement with respect to the radar direction (radial direction) of the bad weather.