Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://ip.rsu.ru/~zabotin/p1/diagn.htm
Дата изменения: Fri Feb 2 12:02:01 2007 Дата индексирования: Mon Oct 1 20:46:43 2012 Кодировка: Поисковые слова: р р р р р р п п р р р р р р |
Reference: Abstr. for the 8th Scientific Assembly of IAGA with ICMA and STP Symposia (Sveden, Uppsala, August 1997). Editors: Rolf Bostrom, Tobia Carozzi, Inger Arlefjard, Ann-Sofi Wahlberg, P O Dovner. P. 178.
DIAGNOSTICS OF IONOSPHERIC IRREGULARITY SPECTRUM USING MEASUREMENTS OF RADIO WAVE ANOMALOUS ATTENUATION UNDER VERTICAL SOUNDING
(poster paper #28 full text)
A G Bronin, N A Zabotin, G A Zhbankov
(Rostov State University, Rostov-on-Don, 344090, Russia)
I B Egorov, A L Karpenko, V V Koltsov, E V Kuznetsov
(IZMIRAN, Troitsk, Moscow Reg., 142092, Russia)
Under radio wave ionospheric propagation the multiple
scattering on small-scale (500 m - 5 km) field-aligned irregularities
takes place. The shape of irregularities is the reason for the
ionospheric scattering strong anisotropy. Both under oblique and
vertical sounding the basic energy flow in a reflected signal
may not coincide with a direction determined by geometrical optics
laws.
One of the multiple scattering effects consists in
anomalous attenuation of a wave reflected from the ionosphere
which is registered on the Earth' surface in a vicinity of sounding
station and in its site. Attenuation of a vertical sounding signal
depends on frequency what allows one to solve an inverse problem
- to find parameters of irregularities from the measured wave
attenuation. In this report the results of the first experimental
realization of this approach are stated.
The measurements were carried out at Troitsk on the
digital ionosond "Parus". The selected experimental
data are characterized by a high average level of attenuation
of a signal of vertical sounding (10 dB and above), which cannot
be caused by collisional absorption of radio waves (practically
absent in a dark time of day) and, hence, being a consequence
of scattering on random irregularities. The algorithm of solving
of the inverse problem was based on the Levenberg-Marquardt nonlinear
optimization method. The attenuation dependencies for ordinary
and extraordinary waves at the same frequency bands are close.
It is necessary to note the good qualitative and quantitative
agreement between altitude dependencies of the irregularity level
obtained from the data on attenuation of ordinary and extraordinary
waves. In some sessions the change of irregularity level altitude
dependence character at heights about 200 km is observed. It can
be caused by distinction of mechanisms of formation of irregular
structure at different heights in ionosphere.
The basic model of ionospheric irregularities spectrum is
or
The sectrum is normed with respect to value of irregularities
structural function in given scale R.
Poeverlein's construction
It is convenient to display graphically the electromagnetic
wave propagation in a plane-stratified plasma layer with the aid
of the Poeverlein construction (see fig. 1). Convenience of this
construction (in fact, this is an example of coordinate system
in space of wave vectors ) is become evident
when drawing the wave trajectory: it is represented by a straight
line, parallel to the axis
. This is a
consequence of the generalized Snell law, which also requires
of equality of the incident angle and outgoing angle from a layer
(
), and constantness of the wave vector
azimuth angle (
). The crossing point of
a wave trajectory with the refractive index surface under given
value of
determines current direction
of the wave vector in a layer (it is anti-parallel to a radius-vector)
and current direction of the group speed vector (it coincides
with the normal to the refractive index surface). The projection
of a wave trajectory onto the plane
is
a point which radius-vector has module
and its angle with relation to axis
equals
to
. Thus, the coordinates
define completely the whole ray path shape in a plane layer and
outside of it and are, in this sense, invariant on this ray path.
Radiation of an arbitrary point source of electromagnetic
waves within the solid angle ;
corresponds to the energy flux in the
-space
inside of a cylindrical ray tube parallel to axis
with cross section
.
In case of regular (without random irregularities) plasma layer
this energy flux is conserved and completely determined by the
source directivity diagram:
(1)
where P is energy flux density in the direction determined
by angles through the point
on some base plane situated outside of the layer parallel to it
(in the ionosphere case it is convenient to choose the Earth'
surface as the base plane),
is distance
from the base plane (height in the ionosphere case).
Radiation energy balance equation:
When scattering is present the radiation energy redistributes
over angular variables and in space what
is described by variable
. The value of
satisfies in this case to the equation
of radiation energy balance:
where ,
,
is cosine of a ray trajectory
inclination angle corresponding to the invariant angles
and
;
is Jacobean
of transition from angular coordinates
to the wave vector polar and azimuth angles
and
in the "magnetic" coordinate
system (which axis
is parallel to the
magnetic field);
is scattering differential
cross section describing intensity of the scattered wave with
wave vector coordinates
,
in magnetic coordinate system (corresponding invariant coordinates
are
and
) which
arises at interaction of the wave with wave vector coordinates
,
(invariant
coordinates
and
)
with irregularities. Vector function
represents the displacement of the point of arrival onto the base
plane of a ray which has angular coordinates
and
after scattering at level
with relation to the point of arrival of an incident ray with
angular coordinates
.
Let us suppose that scattering causes a small change
in invariant angles a ray path: (it also
means that
). Note that in this approximation
the angle of scattering may be large. For example, near the turning
point small change in inariant angles correspond to large chage
of wave vector direction.
We search for the solution of a kind:
,
and
.
For basic energetic term we obtain:
where .
Numerical estimation of the solution for reflection
from the isotropic plasma layer:
The solution describes three basic observable effects:
- Attenuation of a vertical sounding signal (up to 1020 dB in the location and in vicinities of the sounding station)
- Change of angles of arrival
- Angular spectrum broadening (~1 2 )
Fig. 2 represents the results of numeric calculations of effect of attenuation of vertical sounding signal in the vicinity of sounding station (in dB) for the following parameters of irregularities spectrum:
The frequency dependance of attenuation is represented
on Fig. 3. The frequency dependance is different for spectra with
different parameters what gives the principle opportunity to determine
this parameters from attenuation measurements data.
The sequence of the solution of an inverse problem:
Ю) division of initial data into similar frequency intervals;
c) realization of leasts quares algorithm on the base of repeated solution of a direct problem;
d) determination of the best set of parameters of high-altitude dependence of a irregularities level for each interval;
The results of solution of inverse problem are reprsented
at Fig.5 and Fig. 6.
Results
of account of frequent dependence of absorption for optimum parameters
of high-altitude dependence of a irregularities
level
Electron Density Random Irregularities and
Decameter Radio Wave Anomalous Attenuation
at the Mid-Latitude Ionosphere
A G Bronin, P F Denisenko, N A Zabotin,
G A Zhbankov, V I Vodolazkin
(Rostov State University, Rostov-on-Don, 344090,
Russia)
It has been stated lately that natural random electron density irregularities of the ionospheric plasma play an essential role in energy redistribution of decameter radio waves radiated from a point source located on the Earth surface. In particular, under vertical sounding the multiple scattering takes place that results in the collisionless attenuation of waves. The attenuation in the
ionospheric F region, being measured by the A1 method,
reaches of 10 - 15 dB. The attenuation value depends on the irregularity
spatial spectrum and, therefore, it can be used for determination
of their parameters.
The present paper describes the results of irregularity
diagnostics in the mid-latitude ionospheric F region. Frequency
dependencies of o- and x-wave attenuation obtained by the A1 method
were used as initial data. The measurements were carried out at
point Rostov in the 1989 winter season (high solar activity period)
at night time. Estimation of the irregularity spectrum parameters
was obtained by means of the inverse problem solution based on
the Levenberg-Markvardt nonlinear optimization numerical algorithm.
The method of calculations is described in poster # 28 "Diagnostics
of ionospheric irregularity spectrum using measurements of radio
wave anomalous attenuation under vertical sounding"(A G Bronin,
N A Zabotin, G A Zhbankov I B Egorov, A L Karpenko, V V Koltsov,
E V Kuznetsov). For calculations there were chosen experimental
data from 4 sounding sessions carried out at January 23, 25 and
28 and February 2. The results of calculations are represented
on Fig.1 - Fig.8. On Fig.1 - Fig. 4 are shown the the best fits
to experimental data for each session. On each figure plot "a"
corresponds to ordinary wave and plot "b" corresponds
to extraordinary wave. The obtained high-altitude profiles of
irregularities level for each session are show on Fig.5 - Fig.8.
It was assumed in calculations that the irregularity spectrum
has power-law shape with index 2.5. For the irregularity level
in a scale length of 1 km values in the range
were obtained. This value has the tendency to decrease with growth
of height in the ionospheric layer both for ordinary wave data
and for extraordinary wave data.
a) b)
Fig. 1
a) b)
a) b)
Results
of synthesis of high-altitude dependence of irregularities level:
Fig. 5 Fig.6
Fig. 7 Fig.8