491
1 INTRODUCTION
The peculiarity of tracking objects with a ship’s radar
in the presence of precipitation of varying intensity,
which complicates the process of navigation, is the
need to take into account their radar characteristics,
which are especially important when they are used
while the ship is moving through the precipitation
zone. The value of such information is greatly
increased when the echo is recognized in the
background of the precipitation echo on the display
screen of a ship's radar. Methods for processing radar
data on precipitation, taking into account their radar
characteristics, allow the operator of a ship's radar to
make the right decision about the presence or absence
of an echo signal of an object, which generally
increases the safety of navigation in difficult
atmospheric conditions.
2 ANALYSIS OF RECENT RESULTS AND
PUBLICATIONS IN WHICH THE SOLUTION TO
THIS PROBLEM HAS BEEN STARTED AND THE
ALLOCATION OF PREVIOUSLY UNSOLVED
PARTS OF THE GENERAL PROBLEM
A method for researching the radar characteristics of
clouds and precipitation was proposed in [1], and in
[2], as well as the influence of meteorological factors
and the underlying surface on the operation of the
radar were also considered.
Radar Characteristics of Precipitation Affecting the
Tracking of Ship’s Radar Objects
V.Yu. Revenko
National University «Odessa Maritime Academy», Odessa, Ukraine
ABSTRACT: In this paper, we consider the possibility of using the radar characteristics of precipitation in order
to reduce the negative impact of the echo signal generated by them on the radar tracking of objects performed
by the ship’s radar. In the formation of an echo signal by precipitation, both the precipitation particles
themselves: their size, state (solid or liquid phase), shape, and the factors that determine their combined action
(concentration, relative position, preferred orientation), are important. The size of rain particles when compared
to the wavelength emitted by the ship's radar antenna contributes to the creation of a larger or smaller noise
echo on the display of the ship's radar, the power of which in the Rayleigh scattering region toward the radar is
characterized by the effective scattering area. Falling raindrops are a collection of randomly located reflectors
and their scattering properties depend on the spatial distribution and regularity of movement. At the same
time, the radar characteristics of clouds with precipitation generated by them can be used in ship radars to
determine the intensity of the atmospheric process along the ship’s route, and the uncertainty in determining
the attenuation of the power of an electromagnetic wave emitted by a ship’s radar antenna and passing through
the precipitation zone can be reduced by simultaneous use of two wavelengths on which ship’s radars operate.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 16
Number 3
September 2022
DOI: 10.12716/1001.16.03.10
492
In [3], an electrodynamic model of interference
from hydrometeors is considered. In [4], models of
interfering reflections from the earth's surface are
considered for the analysis and design of radars.
3 PURPOSE STATEMENT
The purpose of the paper is to analyze some features
of the precipitation radar characteristics that affect the
tracking objects by the ship’s radar.
4 PRESENTATION OF THE MATERIAL OF THE
RESEARCH WITH THE SUBSTANTIATION OF
THE RESULTS OBTAINED
The weakening of the electromagnetic wave of the 3-
cm range emitted by the ship's radar antenna
significantly affects the radar tracking of the ship's
radar objects. The weakening of electromagnetic
energy is a function of the intensity of precipitation,
which depends on radar characteristics and is
determined by the content of water in the liquid phase
in a unit of the radar space. The vertical distribution
of rain intensity is determined by its structure. Thus,
in long continuous rains, this distribution is described
by an exponential dependence, rains of conventional
origin are characterized by a diverse structure with
the presence of separate bands raised above the water
surface, due to the focal nature of shower clouds.
A thunderstorm area consists of one or more storm
zones centered at a height of one kilometer from the
water surface. Powerful thunderstorm formations are
associated with high-intensity precipitation, which
degrades the radar surveillance of objects on the
ship's path by illuminating large sections of the ship's
radar indicator and completely masks the echo signals
of an oncoming ship.
Even the use of circular polarized waves does not
solve the problem of radio visibility of objects during
precipitation with an intensity of one hundred to two
hundred mm / h, because each particle of such
precipitation is significantly different from the sphere
and the decrease in the echo signal from precipitation
is negligible.
When analyzing the echo signals of an object (Fig.
1, 2), there are still unsolved issues related to the
systematization of the assessment of the attenuation
of electromagnetic radio waves of three and ten-
centimeter ranges in rain in various climatic regions of
the globe, where the trajectories of sea vessels pass.
Since 1960 and up to the present time, the quantitative
interpretation of radar echoes and the search for their
dependence on the intensity of the falling rain, the
size of its drops, and the speed of their fall, has not
been completed. This is largely due to the fact that the
laboratory for research is the troposphere, in which
laboratory conditions are beyond the possibility of
recording them.
The precipitation zone is characterized by the
following parameters: shape, size, speed of
movement, lifetime, phase of development, and
structure.
Figure 1. Photograph of the radar indicator in the presence
of an echo signal from a powerful thundercloud with high-
intensity heavy rainfall (radius from the center of the image
is 75 km) with the emission and reception of linearly
polarized waves
Figure 2. Photograph of the same indicator under the same
conditions as in Fig. 1 when receiving a circular polarization
echo (at a distance of 75 km from the center of the echo
circle, objects are in the area of the rain shower echoes)
From the point of view of synoptic information,
precipitation is characterized by frontal and air-mass
origin. Air-mass precipitations are subdivided into
thunderstorms, showers, and widespread
precipitation [5, 6]. According to the structure, the
493
precipitation is subdivided into cellular, multicellular,
and striplike [7].
The intensity of precipitation at a given level
depends on the concentration of raindrops, the
spectrum of their sizes, and the rate of fall relative to
the underlying surface and depends on the time and
place of precipitation [8]
max
min
3
( , , ) ( , , , )[ ( ) ( , , , )]
6
d
d
I x y t d N x y t D v d u x y z t dD
=−
(1)
where
()vd
is the rate of balanced fall of drops, m/s;
( , , , )u x y z t
is the vertical speed of air flows, m/s;
max
d
and
min
d
are the maximum and minimum
diameters of droplets in precipitation, mm;
( , , , )N x y t D
is the distribution function of
precipitation particles per unit volume of air by
diameters D.
The amount of precipitation Q is determined from
the condition:
2
1
()
t
t
Q I t dt=
. (2)
Total lifetime
0,22
max
50
tot
tI=
of the precipitation
zone:
0,22
max
50
tot
tI=
. (3)
The sum
of the backscattering cross sections of
all particles in a cloud volume unit is determined by
the equation:
max
min
( ) ( , )
D
D
N D D x dD
=
(4)
where
()ND
is the number of particles with diameter D in
the radar space of precipitation;
( , )Dx
is the effective scattering area of particles
with a diameter D at a wavelength
.
The dependence
of hail precipitation on their
intensity and size on
3,2 cm
=
and
10 cm
=
is
described by the following expressions:
7 2,1
3,2 3
6,7 10 Nd
−
=
, (5)
8 5,4
10 3
3,8 10 Nd
−
=
, (6)
7 0,6
3,2
2,3 10 I
−
=
, (7)
10 1,54
10
6,3 10 I
−
=
. (8)
The precipitation area S is estimated by the
formula:
4
bs
S
ab
=
, (9)
where
b
a
is the major and
s
b
is the minor axis of the precipitation source, km.
Cell parameters for different regions of the globe
have different values. Thus, for the North Atlantic, the
median area for 1141 cells was 22 km
2
; for the eastern
Atlantic off the coast of Africa (Dakar), the maximum
areas were 80 and 200 km
2
.
Radar characteristics of rain cells near Montreal are
given in Table 1.
Table 1. Characteristics of rain cells near Montreal
_______________________________________________
Radar
, mm/hI
charact. 5 10 20 30 60 90 125 175 250
_______________________________________________
cell
N
906 1451 1643 1216 784 504 349 204 38
, km
cell
D
13,6 9,26 — 4,2 3 2 — —
_______________________________________________
Note.
cell
DS
=
,
S
is the area of the radio echo, on the
outer contour of which the threshold
II
=
of
precipitation is set, which is determined by the formula
1,6
200zI=
— radar reflectivity of precipitation.
The dielectric constant
of liquid precipitation
particles is determined by the wavelength
and
temperature and has real and imaginary parts, which
are calculated using the Debye formulas
0
0
2
Re
1 ( )
s
s
−
=+
+
,
0
0
2
()
Im
1 ( )
ss
s
−
=+
+
, (10)
where
0
5,5
=
,
0,0634 2
1,4662 0,000136 0,02729 1,8735
t
s
e t t
−
= + − +
,
2
0,00081 0,4088 88,2
s
tt
= − +
, here t is the
temperature in
C
.
5 CONCLUSIONS AND PROSPECTS FOR
FURTHER WORK IN THIS AREA
The main radar characteristics of precipitation zones,
which may occur along the ship's trajectory, are
considered. Accounting for radar characteristics in the
operation of a ship's radar to track an object, increases
the safety of navigation in a certain region of the
vessel's location.
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494
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