PHASE-ARRAY RADAR AT RUSSIAN UPPER-AIR NETWORK
Ivanov Alexei A., Kochin Alexander V.
Central Aerological Observatory, Roshydromet
Pervomayskaya Str.,3, Dolgoprudny, Moscow Region, 141700, Russia
Tel.: (+7) (095) 408-6148, Fax.: (+7) (095) 576-3327
E-mail:cao@mecom.ru
INTRODUCTION
About 10 years ago the development of perspective upper-air system was begun which should
come on change of the basic system for air sounding in Russia AVK-1. At a choice a new system we
proceeded from the following principles:
- Opportunity of independent work and independence of external navigating systems;
- Preservation high tracking characteristics;
- Low cost of a system including a radiosonde.
To the greatest degree to these requirements the radar-tracking system satisfies. The basic
problems of the existing radar-tracking system AVK-1 are: the complex and precision mechanics of
the antenna rotation, difficulty of auto-tracking of a sonde at pass through zeniths, powerful pulse
radiation, high cost, weight, dimensions and power supplement of radar.
NEW RADIOSOUNDING SYSTEM
In new development all advantages of the radar-tracking system were kept and the disadvantages
inherent traditional radar are appreciably overcome.
The new system MARL - A is constructed on the basis of the active phased array with 64
receiving-transmitting modules, which phase controls independently by 4-bit code. The total pulse
power is 100 Watts. The control of a direction of a beam - electronic in an elevation -10…+100
degrees, in azimuth +40… - 40 degrees. At achievement of the set boundary value of azimuth angle
the phased array is rotated automatically by mechanics.
With the purpose of increase of reliability of the
automatic capture and the tracking of a sonde at a
short distance is used a mode of a "wide" beam, when
8 elements are switched on only. The zone of
automatic capture of a radiosonde in this mode makes
+ -25 degrees on an azimuth and + -15 degrees on an
elevation. At a distance after 1.5…2.0 km all
elements of a phased array are included in the work.
General weight of MARL-A is 250 kg (without
wind-protection radom), power supply less 500 Wt
from a single-phase network 220V*50Hz. The phased
array incorporates to the personal computer through
the device of interface by two cables of length up to
30 m. All control of radar is made with this computer
with help specially developed software.
The screen of the managing computer in a mode of
launch of a radiopsonde is shown on a fig.2. During
flight of a sonde the operator has an opportunity to
see a vertical profiles of calculated temperature,
humidity and wind (fig.3). After achievement of
geopotential height of 100 hPa and after the end of a
flight all necessary telegrams are automatically formed which also automatically are transmitted in
channels of communication.
Fig.2. The screen of the managing computer
Fig.3.The current profile of humidity
In the software the algorithms of allocation of the telemetry signals are realized at the small ratio
signal - noise and also correlation method of allocation of a back-answer signal at the reduced in 100
times transmitting power. The used algorithms allow to accompany with radiosonde and to process
signals of telemetry from the distance more than 200 km.
The software can be adjusted on various types of radiosonde on frequency 1680 MHz, and also (at
installation in a radiosonde of the pressure sensor) to provide a radiotheodolite mode.
TEST RESULTS
During tests and skilled operation of the first copies MARL-A the basic attention was given to
study of the following characteristics:
- Diagram of an orientation of the antenna and accuracy of angular tracking;
- Estimation of influence of a surface of the Earth on angular errors at small elevation;
- Energy potential and sensitivity of the radar-tracking system;
- Research distance measuring channel at reduced in two order transmitted pulse power;
- Reliability of control elevation near to 90 degrees.
Fig.4
Fig.5
The antenna beam pattern (in horizontal and vertical cross-section) is submitted in a fig. 4. The
diagram is received at electronic scanning of a beam and practically does not differ for modes of
receiving and transmitting. A level of a side lobes and width of the main beam correspond to
calculated meanings and provide the necessary characteristics on accuracy. In a fig. 5 are submitted
angular-voltage curves in modes of a narrow and wide beam. The quality of these curves substantially
defines reliability and accuracy of angular tracking, and also area of capture of a radiosonde.
The step of discrete control of a beam is about 0.2 degrees, which is defined by the formula:
kN*2^p,
where  -step of the angle discreet,
 -beam width (=7 degrees.),
N - number of elements (=10, in vertical),
p - bit numbers in phase control system (=4),
k - coefficient, depending of algorithm of phase array (=2, for some case).
The angular accuracy in 5 times was realized better at the expense of use for calculation of a direction
of a beam in addition of signal of deviation and averaging of result. The diagram is calculated and
established 30 times per one second. The angular dispersion it is possible to estimate as 0.1 degrees
from the diagrams of tracking of radiosonde in a fig.9, for example.
In a fig.6 the change of an elevation is shown
at tracking of a falling sonde on distance 38-40
km. The velocity of fall was small - about 10-12
Fig.6
m/sec. In the assumption of uniform speed of
incidence it is possible to estimate the errors in
angular measurements and critical elevation,
which has appeared near 7degrees. It is necessary
to note that the measurements were carried out of
an elevation obstructed by 4 degrees.
In this example we also see the result of a
small mistake in the array software which gave a
jump of angle of 1 degree when go through 30
degrees elevation angle – normal direction to array plane- from plus to minus area.
The sensitivity of MARL-A is enough for receiving of microwave radiation of the Sun with a
level +3... 4 dB above a level of own noise. It allows to check and to adjust the characteristics of the
channel of angular support, and also to supervise orientation of station with accuracy not worse than
0.2 degrees.
In the fig.7 the example of angle tracking of
the Sun within 3.2 hours is shown. The angular
dispersion does not exceed 0.1 degrees at
averaging time of 1s, systematic errors are less
than 0.2 degrees. These experiments are very
useful and important for minimization systematic
bias in elevation angle. As a result the standard
monitoring procedure of upper-air data quality
Fig.7. Sun tracking, elevation angle
give the bias OB-FG in geopotential height less
than 20m at 100hpa level.
For regular checking of basic parameters of a
radar such as sensitivity, transmitted power,
antenna pattern and capture curve, efficiency of
every of 64 t/r units and telemetry quality the test
device is supplied and placed at a distance 80-100m.
The theoretical and experimental values of received power of a radiosonde on various distances are
shown in a fig. 8 in logarithmic scale. It is visible, that the reception of signals up to distance of 300
km is possible. While the work MARL-A at range of 150 km is checked up now. Also one can see in
the figure a power levels of noise, Sun radiation and AGC initialization.
At last, in a fig. 9 the example of passage of a radiosonde above radar is given. The MARL-A
works at a narrow beam, as the sonde was already on distance of 10 km. In a wide beam the support of
a sonde is even more reliable.
Skilled operation MARL-A at aerological stations Dolgoprudny, Rostov-na-Donu now will be
carried out, the one set to Hanty-Mansijsk is sent.
There is a plan to install more than ten radar systems MARL-A in 2002-2003 years. The
installation procedure is very simple and inexpensive.
Fig.8
Az
Fig.9
El
CONCLUSIONS
Manufacture of radar MARL-A now is mastered, the perfection program maintenance, both on
increase of accuracy, and on reliability of sonde tracking proceeds. The interactive interface of the
operator develops. It is planned to realize a mode of full automatic search and capture of a radiosonde.
It is necessary to note, that many technical decisions and software MARL-A were used also at
modernization АVК-1, which is necessary for support of serviceability of the out-of-date equipment
before its replacement on MARL-A, as this process can occupy 10 years.
REFERENCES
1. WMO Guide to Meteorological Instruments and Methods of Observation. WMO- No.8,
Sixth edition, 1996, Part I, Chapters 12-13.
2. A.Ivanov, A.Kats, S.Kurnosenko, J.Nash, N.Zaitseva. WMO International Radiosonde
Comparison - Phase III (Dzhambul, USSR, 1989). WMO Report on Instruments and Observing
Methods, No.40, 1991.
3. J.Nash. Upper Wind Observing Systems Used for Meteorological Operations. Annales
Geophysicae. Vol.12, 1994, pp.691-710.
4. D.Call. Comparing the Windfinding Performance of a New Phase Array Radiotheodolite with
GPS Radiosondes. Reports of TECO-98 (Casablanca, Marocco, 1998). WMO Report on Instruments
and Observing Methods, No.70, pp.165-168.