Transcript THE GROUND-BASED RADIO INSTRUMENT NETWORK FOR …

Comparison of the electron density
profiles measured with the
Incoherent Scatter Radar, Digisonde
DPS-4 and Chirp-Ionosonde
Ratovsky K.G., Shpynev* B.G., Kim A.G.,
Potekhin A.P., Medvedev A.V. and Petko P.V
Institute of Solar-Terrestrial Physics,
664033, P.O.Box 4026, Irkutsk, Russia
E-mail: [email protected]
Irkutsk ground-based radio instrument network includes :
The Irkutsk incoherent scatter (IS) radar (53°N, 103.3°E) used to
measure electron densities, electron and ion temperatures, and
plasma drift velocities.
The multi-position chirp-ionosonde (FMCW sounder) for
investigating the ionosphere using the methods of vertical,
oblique-incidence and backscatter sounding includes 1 receiving
station at Tory (51.7°, 103.8°) and 3 transmitting stations located
at Norilsk (69°N, 88°E), Magadan (60°N, 150.7°E), and near the
IS radar.
Continuous observations of the ionosphere are made with the
Digisonde (DPS-4 sounder) at Irkutsk (52°N, 104°E).
Irkutsk Incoherent Scatter Radar (ISR)
Chirp-sounder or FMCW ionosonde
( ionosonde with linear frequency modulation )
chirp signal
Digisonde ( DPS-4 sounder )
53.0
IS Radar & FMCW sounder
98
km
h=200km
latitude
52.5
h=300km
Irkutsk
DPS-4
76km
h=400km
km
95
52.0
Tory
h=600km
BAIKAL
FMCW receiver
51.5
101.0
101.5
102.0
102.5
103.0
103.5
104.0
104.5
longitude
The locations of the instruments
FMCW radio path
Ground projections of ISR beam at various heights
ISR beam inclination is 16 from a vertical
105.0
INTRODUCTION
 The electron density measurements with the three closely spaced radio technical
instruments enable us both to perform mutual calibration of the instruments and to
explore the capabilities which cannot be realized with each of the instruments by
itself.
 The distinctive property of the Irkutsk ISR implies that the electron density profile is
measured by the Faraday rotation method and hence ISR has no need of calibration by
ionosonde.
 The comparison technique consisted in separate comparison of slow Ne(z,t) and fast
Ne(z,t) electron density variations. The separation of variations into slow and fast
ones was carried out by the filtering. The filter band was chosen so that the slow
variations represented fluctuations with the periods T > 4h., and fast variations were
fluctuations in a range of the periods 1h. < T < 4h. The comparison of slow variations
has been performed for revealing the discrepancies in diurnal variations of the
electron density. The comparison of fast variations has been conducted in an effort to
extract an additional information about traveling ionospheric disturbances. Further we
shall assume that function Ne describes regular variations of the electron density and
Ne corresponds to disturbances.
 All ionogram data have been manually scaled with the interactive ionogram scaling
technology SAO-Explorer. The profiles were reconstructed using the Reinisch and
Huang (1983) method with the extrapolation above a peak height by the Reinisch and
Huang (2001) method .
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4
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0
 The comparisons of regular electron
density variations have revealed two main
z=320 km
types of discrepancies.
 With the strong Ne gradients in the
morning hours the DPS-4 overestimate the
ISR density. The strong spatial electron
density gradients deflect the HF radiowave
Ne 10 -5 (cm -3 )
path from the vertical in the direction of
increasing density, as a result the ionosonde
z=280 km
receives echoes from the east regions and
gives the overestimated Ne values.
 In the daytime the ISR overestimate the
DPS-4 density at heights below and above
Ne 10 -5 (cm -3 )

the peak height, i.e. ISR produces thicker
profile. The distinction may be connected
z=240 km
with several reasons. Because of he finite
pulse duration and large horizontal beam
size along with a beam inclination the ISR
produces the height-averaged profile. On the
Ne 10 -5 (cm -3 )
other hand the absence of ionogram traces at
low frequencies because of absorption or
z=200 km
blanketing by Es-layer may cause the
ionosonde profile thickness to decrease.
 At the moment it is not clear what
0 1 2 3 4 5 6 7 8 9 10 11 12 UT instrument distorts the profile to a greater
Regular Ne variations measured by I SR and DPS-4
extent.
+
November 12, 2004. LT=UT+7. Kp=33
Ne 10 -5 (cm -3 )
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0
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0
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12
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0
Ne 10 -5 (cm -3 )
z=280 km
Ne 10 -5 (cm -3 )
z=260 km
Ne 10 -5 (cm -3 )
z=240 km
The regular electron density
variations observable by the
Chirp-Ionosonde are closer
to the DPS-4 than to the ISR
data. Chirp-ionosonde – ISR
discrepancies replicate the
main features of DPS-4 –
ISR discrepancies:
• the ionosondes
overestimate the ISR density
in the morning hours.
• the ISR produces thicker
bottomside profile.
Ne 10 -5 (cm -3 )
z=220 km
0
1
2
3
4
5
6
7
8
9 10 11 12 UT
Regular Ne variations measured by I SR, DPS-4 and Chirp-Ionosonde
November 1, 2003. LT=UT+7. Kp=30
DPS-4 produces thicker
profile over the Chirpionosonde. It is concerned
with distinction between
vertical and weakly-oblique
sounding.
-5
-3
2 Ne 10 (cm )
1
0
-1
-2
-5
-3
2 Ne 10 (cm )
1
0
-1
-2
-5
-3
2 Ne 10 (cm )
1
0
-1
-2
-5
-3
2 Ne 10 (cm )
1
0
-1
-2
0 1 2 3 4
z=280 km
z=260 km
z=240 km
z=220 km
UT
5 6 7 8 9 10 11 12
Electron density disturbances measured by I SR and DPS-4.
November 9, 2004. LT=UT+7. Kp=52
The electron density disturbances
obtained by the ISR and DPS we
separated into two types: correlated
and uncorrelated ones. From 0 to 5
UT there is no correlation between
the ISR and DPS-4 disturbances. At
this time the DPS-4 recorded
complex ionograms with oblique or
spread echo traces. The good
correlation between the
disturbances is seen from ~ 6 UT,
when the ISR and DPS-4 data are
about the same fluctuations shifted
in time. At this time the DPS-4
recorded the relatively simple
ionograms.
Here is an example of a complex
ionogram with double o- and xtraces and three versions of Neprofiles:
ISR profile, DPS profile
reconstructed from right trace and
DPS profile reconstructed from
left trace .
None of the DPS profiles is
coincident with ISR version.
z(km )
600
500
ISR
DPS-4 (right trace)
DPS-4 (lef t trace)
400
300
200
100
Ne(cm-3 ) 
0
2
4
6
8
10
November 9, 2004 03:15 UT (10:15 LT) Kp=6
Most likely the uncorrelated
disturbances are due to intensive
ionospheric irregularities of
scales less than or equal to 100
km. The difficulties in measuring
disturbance characteristics are
primarily associated with the
difficulties in interpreting
complex ionograms in the
presence of oblique or spread
echo traces.
Ne 10 -5 (cm -3)
1
z=260 km
More often we observe correlated
disturbances
0
-1
Ne 10 -5 (cm -3)
1
z=240 km
0
-1
Ne 10 -5 (cm -3)
z=220 km
1
0
-1
Ne 10 -5 (cm -3)
1
z=200 km
0
-1
UT
0 1 2 3 4 5 6 7 8 9 10 11 12
Electron density disturbances measured by I SR and DPS-4.
November 12, 2004. LT=UT+7. Kp=33+
Correlated disturbances are due to
ionospheric irregularities of scales
considerably greater then 100 km,
and to the traveling ionospheric
disturbances caused by acousticgravity waves in particular.
Accordingly the observation of
such disturbances by the various
instruments can be used for
measuring disturbance
characteristics, like the velocity and
motion direction.
-5
-3
4 Ne 10 (cm )
During the main phase of the
strong magnetic storm on
2
November 10, 2004 we observed
0
from 6:45 UT the strong positive
electron density disturbance. Both
-2
-5
-3
instruments show some identical
4 Ne 10 (cm )
z=300 km
disturbance properties, such as the
2
duration, the peak time and
increase of disturbance amplitude
0
with height. All this assigns the
-2
disturbance to the correlated type.
-5
-3
4 Ne 10 (cm )
The main discrepancy between the
z=260 km
disturbances consists in higher
2
disturbance amplitude observed by
0
the ISR. Probably this discrepancy
is connected with the fact that the
-2
-5
-3
DPS-4 ionogram height range was
4 Ne 10 (cm )
z=220 km
limited by 730 km. One can see
2
from Fig. 4 that the disturbance
shape noticeably varies with the
0
height, suggesting that there is an
-2
UT interference of two disturbances.
0 1 2 3 4 5 6 7 8 9 10 11 12
Electron density disturbances measured by I SR and DPS-4.
z=340 km
November 10, 2004. LT=UT+7. Kp=56+
Summary
The electron density measurements with the three closely spaced radio
technical instruments allowed us to reveal the listed below types of
discrepancies.
 With the strong electron density gradients in the morning hours the
ionosondes give the overestimated electron density values in comparison
with the ISR.
 The ISR produces thicker profile in comparison with the ionosonde data.
 The electron density disturbances obtained by the different instruments
may have a correlated and uncorrelated nature. The observation of
uncorrelated disturbances is accompanied by recording of complex
ionograms. The difficulties in measuring disturbance characteristics are
primarily associated with the difficulties in interpreting ionograms.
 More often we observe correlated disturbances The observation of the
correlated disturbances by the various instruments can be used for
measuring the disturbance velocity and motion direction.