International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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TROPOSPHERIC SCINTILLATION PREDICTION FOR SOME SELECTED
CITIES IN NIGERIA’S TROPICAL CLIMATE
*
Agunlejika O., Raji T.I , Adeleke O.A
Department of Electronic & Electrical Engineering
Ladoke Akintola University of Technology, Ogbomoso, Nigeria
*
E-mail: betlay@yahoo.com
Abstract
This paper reports the prediction of the value of scintillation for six randomly selected
cities in Nigeria – Calabar, Enugu, Kebbi, Abuja, Sokoto and Onitsha, based on the ITUR scintillation prediction model. It was observed that the scintillation is highest in the
coastal site of Calabar and lowest in Sokoto with r.m.s amplitude scintillation value of
0.2 dB and 0.07 dB respectively, and that it varies inversely with the elevation angle. It
was also observed that scintillation is season and frequency dependent.
Keywords: Scintillation, Nigeria, Tropical, Troposphere, Nwet
Introduction
In the field of satellite communications, the lower atmosphere meteorological condition
influences the propagation of radio waves. The atmosphere close to the ground called the
troposphere is constantly in motion because energy from the sun warms the surface of the
earth and the resultant convective activity agitates this layer. This disturbance results in
the turbulent mixture of air mass, which results in variation in the refractive index.
Tropospheric scintillation is caused by small-scale fluctuations of the refractive
index due to turbulence and produces random fades and enhancements of the received
signal amplitude [1]. On satellite-earth links operating at frequencies above 10 GHz, rain
induced attenuation is the dominant signal impairment. Nevertheless, scintillation
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International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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generated on propagation paths at low elevation angles may produce considerable signal
fading in excess of 10 dB [2].
Generally, scintillation occurs continually, regardless of whether the sky is clear
or it is raining [3]. Therefore, scintillation effects must be accounted for in order to
complete the link budget for design of low margin systems especially those at high
frequency and low elevation angles [4]
Methodology
The scintillation values of the chosen cities were computed using the ITU-R P618-8
model. Measurements of atmospheric variables (temperature and relative humidity) taken
over ten-year for each of the chosen cities were used for frequencies of 12.255-GHz and
11.5 GHz. The elevation angles of 40.1o and 30.73o for the earth stations were used.
ITU-R Tropospheric Scintillation Model
The long term tropospheric scintillation prediction model proposed by the ITU-R was
used to calculate the standard deviation of the signal fluctuation due to scintillation. This
model uses the wet term of earth refractivity Ν wet , a function of relative humidity and
temperature, averaged at least over one month, as the input parameter.
The predicted meteorological factor and its relationship with the scintillation
intensity and the earth satellite parameters dependence is given in equation (1) as follows
[5]:
σ = σ ref f 7 / 12 [ g ( x) /(sin θ )1.2 ] dB
where
90810-8383 IJBAS-IJENS @ International Journals of Engineering and Sciences IJENS
(1)
International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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σ = Standard deviation (dB)
σ ref = Normalized or reference standard deviation (dB)
g (x) = Antenna averaging factor
Reference standard deviation is given by
σ ref = 3.6 × 10 −3 + 10 −4 × N wet (dB)
(2)
e
T2
(3)
N wet = 3.732×105
For the temperature range of -20 to 50 ο , the ITU-R P453-9 defined the water vapour
pressure as [6]:
⎛
⎡ 17.502 ⎤ ⎞
λ = 0.01 × H × ⎜⎜ 6.1121exp ⎢
⎟⎟
⎣ t + 240.97 ⎥⎦ ⎠
⎝
(4)
where:
λ : water vapour pressure (hPa)
T: absolute temperature (K)
t : Celsius temperature ( ο C)
H: relative humidity (%)
Results & Discussion
The scintillation intensity comes to a peak in May for all the sites considered except at
Sokoto. The minimum value was observed in February. The highest value, 0.2 dB, of
scintillation was recorded at Calabar in the month of May and the minimum, 0.07 dB, at
Sokoto in the month of February as shown in Figure 1. The result indicates that the
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scintillation is higher in the wet season than in the dry season. In the wet season the
temperature is low and the humidity is high. Consequently, the wet term of the surface
refractivity, N wet becomes high. Since the scintillation intensity strongly depends
on N wet , it automatically increases.
Scintillation is higher around the coastal areas in comparison to the northern
regions. The scintillation intensity decreases as one moves northward in the Country.
Keeping the frequency constant at 12.255 GHz, in the month of February, Calabar has
scintillation value of 0.15 dB while Sokoto has 0.054 dB (Figure 3b). This is as a result of
the fact that the coastal region is highly humid while the northern region is hot, dry and
thus has little moisture content. Calabar is located in the southern region of the country
and Sokoto in the Northern region. Other sites fall between Calabar and Sokoto.
The results show that scintillation is inversely proportional to the elevation angle.
The value increases with reduction in elevation angle as shown in Figure 3a and 3b.
However, the scintillation is directly proportional to the frequency of propagation.
Therefore, as shown in Figure 4, the scintillation becomes significant when using a very
high frequency and a low elevation angle.
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International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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0.25
0.2
0.15
Sigma
Feb
May
Aug
Nov
0.1
0.05
0
Kebbi
Abuja
Sokoto
Calabar
Enugu
Onitsha
Site
Figure 1: Scintillation amplitude deviation at elevation angle of 30.73, 12.255 GHz Frequency
0.18
0.16
0.14
Sigma (dB)
0.12
0.1
Feb, 40.1
May, 40.1
Aug, 40.1
Nov, 40.1
0.08
0.06
0.04
0.02
0
Kebbi
Abuja
Sokoto
Calabar
Enugu
Onitsha
Sites
Figure 2: Scintillation amplitude deviation at elevation angle of 40.1, 12.255 GHz frequency
90810-8383 IJBAS-IJENS @ International Journals of Engineering and Sciences IJENS
International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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0.25
0.2
0.15
Sigma
Kebbi
Abuja
Sokoto
Calabar
Enugu
Onitsha
0.1
0.05
0
Feb, 40.1
Feb, 30.73
May, 40.1
May, 30.73
Aug, 40.1
Aug, 30.73
Nov, 40.1
Nov, 30.73
Month/Elevation Angle
Figure 3a
0.2
0.18
0.16
0.14
Sigma
0.12
Feb, 40.1
Feb, 30.73
0.1
0.08
0.06
0.04
0.02
0
Kebbi
Abuja
Sokoto
Calabar
Enugu
Onitsha
Site
Figure 3b
Figure 3a& 3b: Effect of Elevation Angle on Scintillation at 12.255 GHz
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International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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0.18
0.16
0.14
Sigma (dB)
0.12
Kebbi
Abuja
Sokoto
Calabar
Enugu
Onitsha
0.1
0.08
0.06
0.04
0.02
0
Feb 11.5
Feb 12.255
May 11.5
May 12.255
Aug 11.5
Aug 12.255
Nov 11.5
Nov 12.255
Month/Frequency
Figure 4: Effect of Frequency Variation on Scintillation at 30.73o
Conclusion
From the results, it can be concluded that Scintillation intensity is significantly dependent
on seasons, regions, elevation angle and frequency. The scintillation intensity is high in
the coastal areas and decreases as one moves northward in the Country. It is also
observed that the scintillation is higher in the raining season than in the dry season,
because in the raining season the temperature is low and the humidity is high. Moreover,
it was also confirmed that there is an inverse relationship between scintillation and
elevation angle.
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International Journal of Basic & Applied Sciences IJBAS Vol: 9 No: 10
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Acknowledgement
The authors would like to thank the Nigerian Meteorological Centre (NIMET),
Oshodi, Lagos Nigeria for supplying the ten-year surface data of measured variables of
temperature and relative humidity.
References
[1] Pedro Garcia; Jose M.Riera; Ana Benarroch (2002), “Propagation Impairment
Mitigation for Millimetre wave Radio Systems: Statistics of dry and wet scintillation in
Madrid using Intelsat 50 GHz beacon”, PM3-013 1st international workshop, COST
Action 280.
[2] Joko Suryana; Utoro Sastrokusumo; Kenji Tanaka; Kiyoshi Igarashi; Mitsuyoshi Iida
(2005), “Two-Year Characterization of Concurrent Ku-band Rain Attenuation and
Tropospheric Scintillation in Bandung, Indonesia using JCSAT3”
[3] Mandeep Singh Jit Singh; Syed Idris Syed Hassan; Fadzil Ain; Kiyoshi Igarashi;
Kenji Tanaka and Mitsuyoshi Iida (2007), “Measurement of Tropospheric Scintillation
from Satellite beacon at Ku-Band in South East Asia”, IJCSNS International Journal of
Computer Science and Network Security, Vol. 7 No.2, pp.251-254
[4] C. E. Mayer; B.E. Jaeger;
R. K. Crane (1997), “Ka-Band scintillations:
Measurements and Model Predictions”, IEEE Proc., Vol.85, pp.936-945
[5] ITU-R (2003) “Propagation data and prediction methods required for the design of
Earth-space telecommunication systems”, recommendation ITU-R. 618-8.
[6] ITU-R (2007) “Propagation data and prediction methods required for the design of
Earth-space telecommunication systems”, Recommendation ITU-R. 453-9.
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