by Valery DYADYUCHENKO, Cand. Sc. (Tech.), Adviser to the Head of Rosgidromet, Deputy Director of Planeta Research Center; Yuri PAVLYUKOV, Head of the Radiometeorological Department of Rosgidromet Central Aerological Observatory; Ivan VYLEGZHANIN, Cand. Sc. (Phys. & Math.), Chief Designer of Meteorological Radars of OAO Lianozovo Electromechanical Plant

Meteorological radar sets united into an observation network provide for round-the-clock monitoring of cloudy atmosphere, precipitation and associated dangerous weather phenomena such as heavy showers, thunderstorms, hails, squalls and tornadoes. Today Russia is making up for lost time and is creating a modern automated network based on a national innovative work, i.e. the meteorological Doppler polarization radar set DMRL-S.

The number of dangerous significant weather phenomena increased substantially for the last decades (annual growth by ~6-7 percent) in conditions of a varying climate and intense urbanization. So, it is very important to have available advanced means of efficient weather observations. The modern meteorological radar set has unique properties such as efficiency, ability to control vast territories and provision of detailed information on the inner structure of zones of cloudiness and precipitation.

Radiometeorology as a field of applied science emerged more than 60 years ago. At the turn of 1940-1941 military radars recorded for the first time reflections from clouds and precipitation considered by observers as annoying interference, which complicated search for enemy aircraft and ships. But specialists were quick to realize what practical benefit they could get for weather forecasts by such equipment.

Over a period of the 1940s-1960s a theoretical basis of radiometeorology was being laid down in the world. The national scientists and engineers also made a substantial contribution to solution of this problem. The noticeable landmarks were results obtained in the course of substantiation of a radar method used for atmospheric precipita-

tion measuring, large-scale radar experiments on testing grounds of Ukraine, Moldavia, Caucasia and Valdai, as well as studies of relations between radar characteristics of clouds and precipitation and their microstructure including those carried out from board of aircraft-meteolaboratories.

In the 1970s the principle of polarization measurements in meteorological radiolocation of the atmosphere was suggested in the USSR. At that time meteorological radars of the MRL family were developed, including MRL-5, the only in the world serial two-wave radar set of X- and S-wave bands. By the Olympic Games-80 the first meteorological radar network was put in operation in Moscow, and by the mid-1980s the first national automated complex AKSOPRI, which provided continuous day and night monitoring of cloud and precipitation conditions. Based on this complex the first national automated radar network was constructed in the Moscow Region.

Today radar meteorological information is widely used for very short-range forecasts (nowcasting), including warning about dangerous phenomena: heavy showers, thunder storms, hails, squalls and tornadoes; in numerical models of weather forecast; for preparation of hydrological forecasts and flood warning; for meteorological support to aviation and land transport; for efficient information on cloud and precipitation conditions for bodies of state and municipal administration, enterprises of different branches of economy (power engineering, construction, transport); for exerting influence on weather conditions, antihail works and assessment of their efficiency.

The meteorological radar employs, as a rule, a pulse method: radar set radiates a periodic sequence of sounding pulses to the atmosphere and receives a return signal during intervals between them. The distance to the reflector is determined by the value of time delay between radiated and received signals, and characteristics of the reflecting medium are assessed by the change of their parameters.

To obtain a three-dimensional model of the cloudy atmosphere the radar set performs circular scanning of the upper semisphere at several incline angles of a parabolic antenna which forms a narrow directional beam. As a result of the cycle of observations we get a set of inserted conic sections covering an area of up to 250 km in distance and up to 20 km in height. The cycle duration is from 5 to 15 min depending on the observation mode.

The modern meteorological radar set has three measuring channels. Measurements in the first channel of reflected signal power from hydrometeors (cloud and precipitation particles of typical sizes from hundreds of microns to several millimeters and, in case of hail, even to several centimeters) provide information on the so-called "radar scanning capacity".

The second channel furnishes information on the radial rate and width of the Doppler spectrum by measurements of a frequency shift of the reflected echo-signal, i.e. it allows to analyze movements of hydrometeors and to diagnose atmospheric vortexes, gusts, squalls and tornadoes.

Polarization measurements are an advanced trend in world radiometeorology. The radar set with complete polarization processing (third channel) radiates and receives reflected signals simultaneously on two orthogonal polarizations--horizontal and vertical. This makes it possible to assess the phase composition (rain, snow), check up precipitation intensity calculations and identification of meteorological phenomena, and carry out correction of attenuation of radio radiation in precipitation.

The new national meteorological radar set DMRL-S was developed under a technical assignment of Rosgidromet by Almaz-Antey AAD concern in the shortest period of time--two years from the moment of receiving the technical assignment to the start of mass production in 2011. This became possible, first of all, due to the use of work already done in aeronautical and military radiolocation. In contradistinction to analogous predecessors, the modern complex with digital processing of signals allows to carry on in automated mode round-the-clock continuous observations and get information on location and characteristics of cloudiness, precipitation and associated dangerous weather phenomena. Equipped with two new measuring channels--Doppler and polarization--DMRL-S with its technical potentialities becomes one of the best world meteorological radar sets. Thus, the method of polarization radiolocation of the atmosphere suggested in the USSR returned to Russia in 40 years, embodied in a completed engineering solution.

DMRL-S is the first in the world production meteorological radar set for efficient observations based on the technology of digital forming and compression of complex signals. Its advantage is considered to be lack of losses during weighing in case of digital processing of signals, which reach in foreign samples 25-40 percent of pulse energy. To confirm the theoretical results the specialists of OAO Lianozovo Electromechanical Plant (Moscow) and Rosgidromet carried out field tests which proved well-grounded application of complex signals in meteorological radiolocation.

DMRL-S employs complex sounding signals of 25 and 60 mcs duration, "compressed" to 1 mcs at the stage of digital processing. Specially for DMRL-S a new microwave amplifier (electronic tube) in the form of multibeam klystron KIU-222 was developed at NPO Faza (Rostov-on-Don), which secures high stability of the radiated signal (above 55 dB), which is imperative during noise filtering. This invention allowed to borrow transmitter high-voltage units from navigation radars, which substantially reduced time of DMRL-S creation. Foreign producers dealing with transmitters for big manufacturers of meteorological radars in the USA, Europe and Canada have already got interested in it.

The software support of the secondary (meteorological) processing of information GIMET-2010, developed specially for DMRL-S radar set, allows to get important characteristics of cloudiness and precipitation: radar reflectivity at different altitude levels, height of upper boundary of cloudiness, accumulated precipitation intensity, integral water content in a column, and also to identify types of weather phenomena: upper and middle layers of clouds, strati and cloud packs, precipitation, heavy showers, thunder-storms, squalls, hail and tornadoes. Besides, GIMET-2010 allows to calculate horizontal wind fields at different altitudes, a vertical wind profile basing on measurements of the radial Doppler velocity, to process polarization characteristics of cloudiness and precipitation, determine the displacement vector of cloud systems in the observation zone, etc.

In 2011-2012, the following seven DMRL-S were put into operation: Valdai, Mineralniye Vody, Bryansk, Izhevsk, Smolensk, Volgograd and Kazan. In 2013 the following radars were tested and are ready for operation: Stavropol, Sheremetyevo, Moscow, Arkhangelsk, Petrozavodsk, Orenburg, Ufa, Vladivostok, Barabinsk and Vologda.

By the mid-2013 above 30 sets of DMRL-S for Rosgidromet observation network were already produced at the Lianozovo Electromechanical Plant. Orders for such radar sets have been made from the CIS countries, South-East Asia and Latin America. All in all 34 DMRL-S radars shall be installed on Rosgidromet network by the end of 2013.

The efficiency of information increases many times when processing data received from radars united into a single observation network. Similar networks were created over the past 20 years in the USA, Canada, the European Union, Japan, South Korea, China, Australia and other countries. Since 2004 Rosgidromet radars transmit observation data to a private network of the automated data-transmission system in the meteorological notation FM-94 BUFR, which allows construction of integrated radar maps with 4x4 km resolution.

DEVELOPMENT PERSPECTIVES OF THE RADAR NETWORK IN THE RF

By 2020 it is planned to create in Russia an advanced automated network on the basis of around 140 DMRL-S radars to be installed under two federal target programs "Modernization of the Unified System of Air Traffic Management in the Russian Federation (2009-2020)" and "Creation and Development of a Monitoring System of Geophysical Conditions over the Territory of the Russian Federation in 2008-2015". The planned zone of radar scanning will cover the European part of the country and also the habitable areas of Siberia and the Far East.

Creation of a radar network will secure computer-based synchronous observations under a single schedule and solution of problems unavailable before in case of data processing of individual MRL or small networks.

To implement this program the Scientific and Technical Center for Development and Operation of DMRL Network has been established at the Central Aerological Observatory, one of the main research centers of Rosgidromet. Its duties include collection, processing and archiving of radar information, preparation and distribution of secondary radar products, including for access via Internet, scientific-methodological guidance of DMRL network, conducting of studies in radiometeorology and physics of the atmosphere. Processing of primary data (the so-called "large-volume files") of DMRL-S network allows to get secondary radar products both in a high (1x1 km) and low (4x4 km) resolution.

Having created a computer-based network of Doppler radars Russia alongside with countries of the European Union, the USA, Japan and China will join the club of developed countries, implementing a computer-based radar monitoring in their territory in the interests of different branches of economy such as the Ministry of Emergencies, aviation and ground transport, power engineering, public utilities, road service, etc. The successive implementation of this program supported by the RF government will enable Rosgidromet to improve essentially the system of forecasting of rapidly developing dangerous meteorological processes, connected with cloudiness and precipitation, inflicting material damage to the economy and presenting a danger to human life and safety.