31 luglio 2016

Mosaic on a national scale of radar products

The creation of an operating system for the interconnection and integration of meteorological radar data in real time implies the definition of a mosaic process. The need to create a network of this nature stems from both the need for national weather monitoring and the need to improve the quality of the measurements made by the individual radar. In fact, the use of a single radar entails a series of problems that limit its effectiveness. The main sources of error, which are technical-instrumental, topographical and physical-modelling, can be summarized below:

  • The radar beam is reflected not only by the precipitation along the way, but also by artificial obstacles such as buildings, reliefs and, in certain weather conditions, by the ground itself, generating echoes of not attributable to precipitation that must be properly interpreted and removed (phenomena known as clutter and abnormal propagation of the beam);
  • In the presence of an orographic obstacle, such as a mountain, the radar beam is blocked, completely or partially, at lower altitudes, preventing a correct estimate of the precipitation behind the obstacle (phenomena known as shielding or blocking of the radar beam);
  • When propagating through precipitation zones, the e.m. waves emitted by the radar are subject to a reduction in power caused both by molecular absorption and by reflection in directions other than the useful one (towards the radar). This phenomenon, which depends both on the intensity of precipitation and on its spatial extent, causes the meteorological phenomenon to be detected in a weakened form, reducing the quality of the quantitative estimate of precipitation;
  • The curvature of the earth's surface, associated with the topographical characteristics of the territory, which require observations that are not necessarily horizontal, determines the increase, as the distance from the radar increases, in the altitude of the portion of the observed atmosphere. Due to the considerable vertical variability of the clouds, the observation at altitude may not be representative of what occurs on the ground;
  • The extreme variability in space and time of the physical characteristics of meteorological phenomena make approximate the process of estimation (in jargon "inversion") of the quantities of interest meteo-hydropluviometric from the observable radar

The problems described above can be partially overcome through the use of advanced processing techniques of information from individual radar systems and the combined use of multiple radars, located on the territory in an appropriate manner.

Finally, it should be noted that all radar systems, due to their technical and infrastructural characteristics, require both preventive and extraordinary corrective maintenance interventions, which inevitably compromise their operation; in this sense, the opportunity connected to the combination of the single radar products in a mosaic is evident.

Below are reported the products referring to the national composite and the relative frequency with which they are made available, through the different platforms, to the decentralised Functional Centres and to the national institutional bodies:

  • CAPPI (Costant Altitude Plan Position Indicator) at 2000, 3000 and 5000m - Frequency of 15 min: this is a product referred to a constant altitude. It is obtained through a horizontal section of the volume of data and it is therefore possible to carry it out only at the end of a complete volumetric acquisition. It is one of the most used modes of representations to monitor weather conditions at different altitudes in the atmosphere.
  • VMI [dbz] Vertical Maximum Intensity. - Frequency of 15 min: this is a product in which the maximum values assumed by the variable represented along the vertical are reported.
  • SRI [mm/h] (Surface Rainfall Intensity) - Frequency of 15 min.: is a product already processed, i.e. it does not refer to raw data such as reflectivity, but offers an estimate of the intensity of precipitation on the ground.
  • SRT [mm] (Surface Rainfall Total) - Frequency of 60 min.: From a series of SRI maps it is possible to derive a map called SRT in which the total rain fallen on the ground is represented with reference to the integration period. The cumulated generated are relative to 1h; 3h, 6h, 12h and 24h.

The radars that currently contribute to the National Radar Network:

Operational radar of the Civil Protection Department 
Monte Crocione (LU)
Monte Pettinascura (CS)
Monte Serano (PG)
Monte Il Monte (CH)
Monte Zoufplan (UD)
Monte Lauro (SR)
Aeroporto dello Stretto (RC)
Aeroporto di Fontanarossa (CT)

Regional radar:
Bric della Croce (TO)
Settepani (SV)
Gattatico (RE)
S. Pietro Capofiume (BO)
Monte Grande (PD)
Concordia Sagittaria (VE)
Monte Macaion (BZ)
Fossalon (GO)
Monte Rasu (SS)
Monte Midia (AQ)

Air Force Radar (in extraordinary maintenance)
San Giusto (PI)
Grazzanise (CE)
Decimomannu (CA)

Enav radar
Linate (MI)
Fiumicino (RM)