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International conferences on frequency coordination have, in recent years, required new information on radiowave propagation in tropical regions and, in particular, on propagation in Africa. The International Telecommunications Union (ITU-R) initiated ‘radio-wave propagation measurement campaign’ in some African countries some years back. However, none of the ITU-initiated experiments were mounted in Nigeria, and hence, there is lack of adequate understanding of the propagation mechanisms associated with this region of the tropics. The Centre for Basic Space Science (CBSS) of NASRDA has therefore embarked on propagation data collection from the different climatic zones of Nigeria (namely Coastal, Guinea Savannah, Midland, and Sahelian) with the aim of making propagation data available to the ITU, for design and prediction purposes in order to ensure a qualitative and effective communication system in Nigeria. This paper focuses on the current status of propagation data from Nigeria (collected by CBSS), identifying other parameters that still need to be obtained. The centre has deployed weather stations to different locations in the country for refractivity measurements in clear atmosphere, at the ground surface and at an altitude of 100 m, being the average height of communication mast in Nigeria. Other equipments deployed are Micro Rain Radar and Nigerian Environmental and Climatic Observing Program equipments. Some of the locations of the measurement stations are Nsukka (7.4° E, 6.9° N), Akure (5.12° E, 7.15° N), Minna (6.5° E, 9.6° N), Sokoto (5.25° E, 13.08° N), Jos (8.9° E, 9.86° N), and Lagos (3.35° E, 6.6° N). The results obtained from the data analysis have shown that the refractivity values vary with climatic zones and seasons of the year. Also, the occurrence probability of abnormal propagation events, such as super refraction, sub-refraction, and ducting, depends on the location as well as the local time. We have also attempted to identify and calculate the most important propagation factors and associated data, such as k factor, that are relevant in considerations of propagation in tropical regions like Nigeria.
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ORIGINAL PAPER
Radiowave propagation measurements in Nigeria
(preliminary reports)
S. E. Falodun &P. N. Okeke
Received: 16 March 2012 /Accepted: 4 September 2012 / Published online: 6 October 2012
#The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract International conferences on frequency coordina-
tion have, in recent years, required new information on
radiowave propagation in tropical regions and, in particular,
on propagation in Africa. The International Telecommuni-
cations Union (ITU-R) initiated radio-wave propagation
measurement campaignin some African countries some
years back. However, none of the ITU-initiated experiments
were mounted in Nigeria, and hence, there is lack of ade-
quate understanding of the propagation mechanisms associ-
ated with this region of the tropics. The Centre for Basic
Space Science (CBSS) of NASRDA has therefore embarked
on propagation data collection from the different climatic
zones of Nigeria (namely Coastal, Guinea Savannah, Mid-
land, and Sahelian) with the aim of making propagation data
available to the ITU, for design and prediction purposes in
order to ensure a qualitative and effective communication
system in Nigeria. This paper focuses on the current status
of propagation data from Nigeria (collected by CBSS),
identifying other parameters that still need to be obtained.
The centre has deployed weather stations to different loca-
tions in the country for refractivity measurements in clear
atmosphere, at the ground surface and at an altitude of
100 m, being the average height of communication mast in
Nigeria. Other equipments deployed are Micro Rain Radar
and Nigerian Environmental and Climatic Observing Pro-
gram equipments. Some of the locations of the measurement
stations are Nsukka (7.4°E, 6.9°N), Akure (5.12°E, 7.15°N),
Minna (6.5°E, 9.6°N), Sokoto (5.25°E, 13.08°N), Jos (8.9°E,
9.86°N), and Lagos (3.35°E, 6.6°N). The results obtained
from the data analysis have shown that the refractivity values
vary with climatic zones and seasons of the year. Also, the
occurrence probability of abnormal propagation events, such
as super refraction, sub-refraction, and ducting, depends on
the location as well as the local time. We have also attempted
to identify and calculate the most important propagation fac-
tors and associated data, such as kfactor, that are relevant in
considerations of propagation in tropical regions like Nigeria.
1 Introduction
Propagation data are statistically representativeof propagation
behaviour and associated conditions in both the troposphere
and the ionosphere throughout the world. The planning of
broadcasting services above 30 MHz has been based on
Recommendation 370 of the International Telecommunica-
tion Union (ITU-R). However, most of the propagation
curves and formulas used are derived from measurements
performed in Europe, North America, and Japan. Although
the climate is different in Africa, the planning of radio services
in Africa has been based largely on these data and curves.
However, research results (e.g. Hughes 1988) have shown that
optimized planning of radio services in Africa requires data
which take account of the specific climatic conditions. As a
result, the ITU started a radiowave propagation measurement
campaign for Africa in 1984. A number of experiments/proj-
ects were carried out in some locations in Africa.
Unfortunately, none of these experiments were mounted
in Nigeria, and hence, there were no adequate propagation
data in the country for planning. As a consequence, there is
no proper understanding of the propagation mechanisms
associated with this region of Africa.
In response to the ITU-R's call, many researchers in
Nigeria have made substantial contribution to the data base
(Falodun and Ajewole 2006; Kolawole and Owonubi 1982).
However, the propagation data that have been acquired
locally have been, largely, by radiosonde. Until recently,
S. E. Falodun (*)
Department of Physics, Federal University of Technology,
PMB 704,
Akure, Nigeria
e-mail: besfal@yahoo.com
P. N. Okeke
Centre for Basic Space Science CBSSNASRDA,
Nsukka, Nigeria
Theor Appl Climatol (2013) 113:127135
DOI 10.1007/s00704-012-0766-z
researchers in radiowave propagation have relied on these
radiosonde data for their study in radio communications.
But, the radiosonde data are not well suited for determining
the refractivity profile in the lower 100 m of the troposphere
because ascent speed restricted only by the free lift is too
large for accurate and detailed measurements. The variation
of the measured values is usually too small due to the time
constants of the sensors which are large compared with
the travelling time inside the atmospheric layer (Bean and
Dutton 1968).
The current research effort by the Centre for Basic Space
Science, CBSS, is therefore aimed at making an input to the
data base by engaging in in-situ measurements of the rele-
vant parameters. This is aimed at enhancing the quality of
radio signals in Nigeria through adequate planning.
1.1 Presentation of basic propagation data
Radiowave propagation data represent the fundamental basis
upon which studies of propagation phenomena are built. The
analysis of suitably large bodies of data leads to an under-
standing of the various propagation characteristics observed
and to an appreciation of the influence of the neutral atmo-
sphere on radiowave propagation. Models can then be devel-
oped allowing propagation to be predicted as a function of the
prevailing conditions of the propagation medium concerned
(Grabner et al. 2003b).
The propagation data give information relating to clear air
effects concerning (1) terrestrial line-of-sight (LOS) paths, (2)
earthspace (ES) paths (fixed, mobile, and broadcasting), and
(3) evaluation of interference and signal levels. In relation to
radiowave propagation, the prediction methods that are usu-
ally used include (1) attenuation due to atmospheric gases
(LOS and ES paths), (2) diffraction fading due to path varia-
tions (LOS), (3) multi-path effects, focusing/defocusing, ray
bending, scintillation (LOS and ES), (4) depolarization (LOS
paths), and (5) super refractive effects and ducting.
2 Data collection by CBSS
The CBSS, Nsukka, embarked on atmospheric data collec-
tion some years ago with particular interest in propagation
data. The following research equipments are being used by
the centre for measurements and data collection for propa-
gation studies at different locations in Nigeria.
1. Nigerian Environmental and Climatic Observing Pro-
gram (NECOP)to monitor real time climatic and en-
vironmental hazards in Nigeria
2. Automatic weather stationsfor propagation studies
3. Rain radarfor rain attenuation studies
4. Field-strength measurementsfor propagation studies
Some of the meteorological parameters that are currently
being measured include wind speed, wind direction, rainfall,
atmospheric temperature, relative humidity, atmospheric pres-
sure, ultraviolet radiation, solar radiation, signal strength, and
rain rate, etc.
2.1 The Nigerian Environmental Climatic Observing
Program
NECOP is a project designed to establish a network of
meteorological and climatological observing stations, spa-
tially located across Nigeria as shown in Fig. 1. The aim of
NECOP is to create a network of stations that can carry out
simultaneous basic measurements of meteorological and
climatological variables, in real time, through telemetry
technology, with 5-min update cycles. The project is being
executed in collaboration with the Centre for Climatic Re-
search, DE, USA; NIMET; and Nigerian universities.
A typical NECOP station is shown in Fig. 2. The equip-
ment can measure air temperature (in degrees Celsius), rela-
tive humidity (in percent), precipitation (in millimetres),
atmospheric pressure (in millibars), wind speed (in metres
per second), direction (in degrees N), solar radiation (in watts
per square metre), soil moisture (in percent), soil temperature
(in degrees Celsius), and rain rate (in millimetres per minute).
All the existing stations across the country are com-
manded and controlled from a central location or server.
The system server is located in CBSS, Nsukka.
2.2 Refractivity measurements
Adequate planning of radio propagation requires a good
knowledge of the variation pattern of the atmospheric param-
eters (conditions) during the different months of the year and
an assessment of their potential effects on a regional radio
range and propagation paths. The calculations involved in-
clude statistics and seasonal variations of surface refractivity
and vertical refractivity gradients for the lowest 100 m height.
The refractive index nof air depends on the atmospheric
pressure P(in millibars), the temperature T(in kelvins), and
the water vapour pressure e(in millibars) of the atmosphere
(Hall 1979). The radio refractivity, N, and the refractive
modulus, Mfor air, for frequencies up to 100 GHz, are
given by the ITU-R formula [ITU-R (1987)] in Eqs. 1and 2.
N¼77:6P
Tþ3:73 105e
T2ð1Þ
M¼n1ðÞ106þh
R106ð2Þ
where Pis the atmospheric pressure; eis the water vapour
pressure which can be calculated from the relative humidity
128 S.E. Falodun, P.N. Okeke
and the saturation vapour pressure, using the relationship
described in Rec. ITU-R.P. 4539(2004); and Tis the
absolute temperature. Also, h(in kilometres) is the height
of the atmospheric layer above the earth's surface, and R(in
kilometres) is the radius of the earth.
In terms of refractive index, whenever the vertical refractivity
gradient, dN/dh, of the atmosphere is less than the standard
refractivity gradient of 40 N-units/km, the radio ray will un-
dergo super refraction. On the other hand, the radio ray will be
sub-refracted whenever dN/dh is greater than 40 N-units/km. If
dN/dh in a layer of the atmosphere is equal to 157 N-units/km,
the curvature of the path is equal to that of the earth. On
occasions when meteorological conditions are such that the
vertical gradient is less than 157 N-units/km, trapping or
ducting of the rays may occur depending on the wavelength
and duct thickness (Barclay 2003).
A consequence of super refraction and ducting is the
extension of the radio range, which sometimes leads to radio
interference between neighbouring transmission links. On
the other hand, sub-refraction reduces radio horizon.
For an ideal condition of the atmosphere, the atmosphere
is uniformly stratified, and the vertical gradient of the re-
fractive index is assumed constant and defined by
k¼1
1þRdn
dh
¼1
1þRdN
dh 106¼106
RdM
dh
ð3Þ
where kis the effective earth-radius factor.
In temperate climates, the average variation of the refrac-
tive index near the ground is about 40 N/km (CCIR, 1974).
Then, putting R06,370 km gives a value of k04/3. It is
therefore, common practice to use a 4/3 earth radius in the
design of microwave communication links.
Furthermore, because of the convenience of the 4/3 effective
earth's radius, it has been widely used in radio propagation
work and the radar. However, the procedure has several
SPATIAL LOCATIONS
SPATIAL LOCATIONS
Extreme & contrasting weather
Extreme & contrasting weather
conditions
conditions
Rep.
Rep. interland
interland,
,
Major urban
Major urban centres
centres
Weather threat regimes
Weather threat regimes
Fig. 1 Map of Nigeria showing
the locations of NECOP
stations
Fig. 2 A typical NECOP station
Radiowave propagation measurements in Nigeria 129
limitations. It is only an average value and may not be used for
purposes other than general computation. In addition, the
assumption that ndecreases linearly with height is in disagree-
ment with the experimentally observed refractive index struc-
ture of the atmosphere (Bean and Dutton 1968). It is therefore
necessary to use data which are representative of a particular
locality to estimate the appropriate values of kfor a given
region.
2.2.1 Method and instrumentation
The air temperature (in degrees Celsius), the water vapour
pressure (in percent), and the barometric pressure (in millibars)
were measured simultaneously at the ground surface and at a
height of 100 m above the ground surface. The equipment (i.e.
Integrated Sensor Suite) was positioned at a pre-determined
height of 100 m on a communication mast, and the data
loggerwhich is attached to the console allows the data to be
logged in at a regular time interval of 30 min. Another set of the
measuring equipment was positioned at the ground surface to
measure the surface values of these parameters. The data
obtained were used to calculate the refractivity values and the
mean gradient of N-profile for this range of propagation path,
using Eqs. 1and 2.
The present treatment of the parameters is concerned with
the degree to which the average refractivity structure reflects
the gross differences in climate over Nigeria. Furthermore,
the diurnal and the seasonal range graphs of the refractivity
at the earth's surface and at an altitude of 100 m shed light
upon climatic characteristics of the parameters. The appli-
cations of this information are found in practical problems,
such as the prediction of radio field strength and the refrac-
tion of radiowaves.
A better characterization of the refractivity gradient is
thus obtained by the in-situ measurements used for this
study. These values are also used in the analysis of the
occurrence probability of clear air phenomena such as super
refraction and ducting. Figure 3shows the location of the
measurement sites across Nigeria.
2.2.2 Instrumentation
The device used for the measurements is the Davis 6162
wireless Vantage Pro Plus, manufactured by Davis Instru-
ments, Hayward, CA, USA. It is equipped with the Integrat-
ed Sensor Suite (ISS) (Fig. 4), a solar panel (with an
alternative battery), and wireless console, which provides
the user interface, data display, and analogue-to-digital
conversion.
The device uses the combination of fan-aspiration to
minimize the effects of solar radiation-induced temperature
error. The ISS houses the external sensor array for meas-
urements of pressure, temperature, relative humidity, ultra-
violet index, solar radiation, and rainfall rate among others.
The console is connected to a computer through the data
logger from which the stored data are downloaded. The
frequency of transmission of the ISS is 868.0868.6 MHz,
and the error margin of the device for temperature,
pressure, and relative humidity are ±0.10 °C, ±0.5 hpa,
and ±2 %, respectively. The data from the ISS are trans-
mitted to the console via radio, as shown in the block
diagram in Fig. 5.
Fig. 3 Location of the measurement stations in Nigeria Fig. 4 The Integrated Sensor Suite (ISS)
130 S.E. Falodun, P.N. Okeke
3 Results and discussion
3.1 Refractivity values and derived characteristics
The basic data employed for the calculation of the radio
refractivity were radio-meteorological data obtained by in
situ measurements at stations located at Nsukka (7.4°E,
6.9°N), Akure (5.12°E, 7.15°N), Minna (6.5°E, 9.6°N), and
Sokoto (5.25°E, 13.08°N), in Nigeria. These stations were
carefully selected to represent the climatic regions in Nigeria.
For example, Nsukka is representative of Coastal climate
while Minna and Sokoto are representatives of Guinea Savan-
nah and Shelia Savannah, respectively.
The data cover the two main seasons of the years considered
(i.e. the wet and dry seasons). The meteorological data used for
the analysis include the atmospheric pressure P(in millibars),
the temperature t(in degrees Celsius), and the relative humid-
ity R/H(in percent). The measurements were made every
30 min and round the clock for the periods considered (i.e.
February 2007 to March 2009 for Nsukka, November 2007 to
October 2009 for Minna, January 2007 to December 2009 for
Akure, and June 2008 to March 2010 for Sokoto).
For estimation of the refractivity effects, the following
parameters defined in ITU-R Rep. 563 were evaluated from
the refractivity profile.
&Surface value of radio refractivity, N
s
: this is the refrac-
tivity determined at ground level of the station.
&Refractivity at 100 m height, N
1
: the refractivity deter-
mined at 100 m height above the ground level.
&Change of radio refractivity, ΔN: this is the difference
between the surface refractivity, N
s
, and the refractivity
measured at an altitude of 100 m above ground level, N
1
:
ΔN¼NsN1
The refractivity gradients were calculated between the
earth's surface and the 100 m height.
The result obtained for each station shows that the diurnal
variation of the refractivity follows the same pattern for both
dry and wet seasons with the values during the rainy season
Fig. 7 Typical diurnal refractivity variation for the stations, August
2009
Fig. 6 Typical diurnal variation of refractivity values at Sokoto
Fig. 5 The block diagram of the equipment set-up
Fig. 8 Example of the seasonal variation of the mean monthly distribu-
tion of refractive modulus for morning (6:00 AM), evening (6:00 PM),
and night (12:00 AM) at altitude of 100 m in a savannah (Minna) station
Radiowave propagation measurements in Nigeria 131
being higher; the typical result is shown for Sokoto in Fig. 6.
The maximum Nvalues are observed in morning and night
hours, while its minimum values are fixed between 3 pm and
6 pm. The higher values obtained during the morning and night
hours can be attributed to the high values of the relative
humidity recorded for these hours of the day, while the lower
refractivity values in the afternoon can be attributed to the low
relative humidity which resulted from the high temperature
associated with the afternoon hours. The comparisons of the
refractivity values and their diurnal variations at the different
climatic regions have been plotted in Fig. 7. The figure shows
that the values at Nsukka are the highest followed by those
obtained from Akure. But the range of values obtained for
Minna and Sokoto is higher than those obtained for Nsukka
and Akure. As observed in Fig. 6, the variation is similar for the
stations. For example, there are high values in the morning and
evening hours while the values are relatively lower in the
afternoon hours. It was also observed that as the location goes
into the interland, the absolute values reduce while the range of
values increase.
Typical seasonal variations of the refractivity for Minna
are shown in Fig. 8. The figure reflects similarities in the
variation pattern at different hours of the day. The values are
higher during the rainy months of June to October at both
these savannah areas of the country.
The results obtained for Nsukka have shown that large
negative refractivity gradients were obtained for most of the
refractivity profiles measured at the station as observed in
Fig. 9. The values obtained revealed that the propagation con-
ditions are super refractive at both seasons of the year. However,
some events of sub-refraction are also observed (see Table 1).
Cumulative probability curves were also prepared for the
refractivity gradients obtained for this station. These are
presented in Figs. 10 and 11. Deductions from the curves
are presented in Table 1. The results show that during the
rainy season, the propagation layer 0100 m is super refrac-
tive most of the time with the probability of occurrence of
duct being 31 %.
The implications of these results are quite significant on the
propagation conditions of microwave signals through the at-
mosphere in this locality. For example, in a super refractive
condition, the path loss is smaller than in the standard atmo-
sphere. Deductions from the cumulative probability curve
show that the occurrence of super refraction is 80 % in the
rainy season. The high percentage of occurrence suggests that
the worst month with respect to interference is likely to occur in
the rainy season when Nvalues are relatively higher. This
observation agrees with the results reported by Bean and
Dutton (1968) and Grabner et al. (2003a). According to the
reports, the probability of large variations due to anomalous
propagation is very high in the rainy season owing to the fact
that the atmospheric layers are formed above large, flat lakes
which are filled only during the rainy season. This situation
encourages high relative humidityas a result of evaporation
from the surface of the lakes. Super refractive gradients are
responsible for generally extended service horizon and could
cause interference between widely separated radio circuits
Table 1 Probability of occurrence of propagation phenomena
Rainy season (%) Dry season (%)
Probability of occurrence
of sub-refraction
20 5
Probability of occurrence
of super refraction
80 95
Probability of occurrence
of ducting
31 15
-300
-250
-200
-150
-100
-50
0
50
100
00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00 03:00
LOCAL TIME
Fig. 9 Typical refractivity
gradient (in N-units/kilometre)
plotted for Nsukka, December,
2007
132 S.E. Falodun, P.N. Okeke
operating on the same frequency. This phenomenon is com-
monly observed in this locality especially during the raining
season.
Another abnormal phenomenon of interest is sub-
refraction. A sub-refractive layer could be present during
the day, especially at the time of maximum surface heating.
The results for Nsukka have shown that the probability of
occurrence of sub-refractivity is 20 % in the rainy season
while the probability reduces to 5 % during the dry season.
It is therefore possible to experience signal loss or fading in
this locality as a result of sub-refraction.
A consequence of sub-refraction on a nearly horizontal
path is that the wave trajectory comes nearer to the ground.
In extreme cases, if there is an obstacle (for instance a
hill) along the link, the transmitted signal level can be
severely reduced by diffraction resulting in obstruction
fading (Bonkoungou and Low 1993).
On the other hand, a large negative refractivity gradient
causes ducting, the possible effects of which are prolonged
space wave fade-outs, multi-path fading, and excessive field
strengths at distances many times the radio horizon.
The histogram plots shown in Figs. 12,13,and14 give
the summary of the occurrence percentages of super refrac-
tion, sub-refraction, and ducting events for the stations at
Sokoto, Akure, and Minna, respectively. As shown in
Fig. 13, results for Akure station show that the rainy months
of July and August are dominated by super refractive events
with the percentage of occurrence ranging between 56 and
68 %. Duct activity was recorded for about 40 % of events
in August and September. Furthermore, the dry months of
-300
-200
-100
0
100
200
300
400
500
600
700
020406080100120
Probability of M ordinate value
M
Fig. 10 Cumulative distribution
curve for wet condition
-300
-200
-100
0
100
200
300
400
020406080100120
Probability of M ordinate value
M
Fig. 11 Cumulative distribution
curve for dry condition
Radiowave propagation measurements in Nigeria 133
January and February were dominated by sub-refractive
activity with the percentage of occurrence above 60 %.
The results obtained for the station at Sokoto show that
sub-refraction dominates most of the time with the occur-
rence percentage of 80 %. Super refraction was also ob-
served during the rainy months of August, September, and
October. A very low percentage of duct occurrences was
also observed in the month of September, which is the peak
of the rainy season in this locality.
The seasonal and diurnal variations of the wet term in the
refractivity Eq. 1have been observed to correlate with the
variation of VHF and UHF field strengths (Owolabi and
Williams 1970). This observation could partly explain the
low signal level often received in the afternoon periods, espe-
cially from distant stations. For example, the results for the
Minna station shows that, in the time window 3:00 PM to
6:00 PM local time for the rainy months, the potential for the
occurrence of interference between broadcasting stations in
Minna and other stations from far away, transmitting on
the same frequency, will be greatly reduced due to the
lowest refractivity in this time window.
The propagation factors, i.e. kfactors, were also derived for
the stations using the mean values of the refractivity gradient
αfor all the data sets for each of the stations. Equation 3was
then used to calculate the kfactor with R06,370 km.
The kfactor derived for the station at Nsukka is 1.58
while the values are 1.51 and 1.34 for the stations at Akure
and Sokoto, respectively. These values have shown that the
ITU-R value of k04/3 is not appropriate for these locations.
The values obtained for the stations are generally higher
than the value of k04/3 for the temperate climate.
4 Summary
CBSS, Nsukka, has embarked on radiowave propagation
experiments in different locations in Nigeria. The measure-
ments are ongoing, and it covers both the rainy and dry
seasons of the year.
The results for stations that have at least 2 years of data
have been presented in this report, and the data analysis has
shown that the refractivity values vary with climatic zones
as well as the seasons of the year.
The kfactor derived for the station at Nsukka is 1.58 while
the values are 1.51 and 1.34 for the stations at Akure and
Sokoto, respectively. These values have shown that the ITU-R
value of k04/3 is not appropriate for these locations in Nigeria.
The refractivity measurements made so far at the different
climatic zones of Nigeria have shown that the propagation
conditions are super refractive (ΔN>40 N-units/km) during
the rainy seasons.
Fig. 13 Summary of occurrence of ducting, super refraction, and
subrefraction in Akure, Nigeria. These propagation conditions are
calculated in terms of N-index, and the gradient intervals are: ducting
dN/dh, <157; super refraction dN/dh, 40; sub-refraction dN/dh,
>40
Fig. 12 Summary of occurrence of ducting, super refraction, and
subrefraction in Sokoto, Nigeria. These propagation conditions are
calculated in terms of N-index and the gradient intervals are: ducting
dN/dh, <157; super refraction dN/dh, 40; sub-refraction dN/dh,
>40
Fig. 14 Summary of occurrence of ducting, super refraction, and
subrefraction in Minna, Nigeria. These propagation conditions are
calculated in terms of N-index, and the gradient intervals are: ducting
dN/dh, <157; super refraction dN/dh, 40; sub-refraction dN/dh,
>40
134 S.E. Falodun, P.N. Okeke
These experiments constitute our initial efforts towards
the contribution to the process of acquiring more knowl-
edge about radiowave propagation in Nigeria. Based on
these results and subsequent results to be obtained, mod-
ifications to the propagation zones will be proposed to
the ITU-R.
The measurements are ongoing, and the refractivity
measurements would be performed parallel to the VHF
measurements at the receiver site at each geographic zone
of Nigeria for different seasons of the year. The acquired
data would then be used to prepare the propagation curves
required for the planning of radio services in Nigeria.
5 Remarks
The propagation prediction methods and related informa-
tion concerning clear aireffects on terrestrial line-of-
sight paths, earthspace paths (fixed, mobile, and broad-
casting), and in the evaluation of interfering signal levels
are derived from radio-meteorological data. However,
detailed studies of system outage requires, in addition
to the measurements made in this study, long-term meas-
urements of electric field strength and path loss. Thus,
the present work constitutes our initial efforts at making
systematic empirical in-situ measurements for the study
of microwave propagation in the lower atmosphere in
this part of the world.
The plan is to continue the measurements with a view to
building a data base of radio-meteorological data for micro-
wave propagation studies in Nigeria. In addition to the
above, the centre has acquired a new set of Micro Rain
Radar (MRR) which would be used to collect rain data
required to carry out studies on the effects of rain and other
hydrometeors on earthspace propagation. The measure-
ments will include rain rate and drop-size distribution from
which the rain attenuation can be predicted. The MRR will
also be used to observe the spatial variation of rain intensity,
thus allowing the estimation of the attenuation along the
propagation path. The study will also include observing
spectrum of rain drop sizes which determines the rainfall
rate, as well as the radar reflectivity and microwave radia-
tion emission of the rain drops.
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution License which permits any use, distribution,
and reproduction in any medium, provided the original author(s) and
the source are credited.
References
Barclay L (2003) Propagation of radio-waves (2nd edition). The Insti-
tution of Electrical Engineers, London, pp 103127
Bean BR, Dutton EJ (1968) Radio meteorology. Dover Publication Co,
New York, pp 259273
Bonkoungou Z, Low K (1993) Radio wave propagation measurement
in Burkina Faso. SMR on radio wave propagation in tropical
regions, Trieste, Italy
Falodun SE, Ajewole MO (2006) Radio refractive index in the
lowest 100-m layer of the troposphere in Akure, South West-
ern Nigeria. Journal of Atmospheric and Solar-Terrestrial Phys-
ics 68:236243
Grabner M, Kvicera V (2003a) Refractive index measurement at TV
tower Prague. Radio Eng 12(1):57
Grabner M, Kvicera V (2003b) Clear-air propagation modeling using
parabolic equation method. Radio Eng 12(4):5054
Hall MPM (1979) Effect of the troposphere on radio communication
(IEE electromagnetic waves series). Peter Peregrinus Ltd, UK, pp
105116
Hughes KA (1988) CCIR propagation studies for Africa. ITU Tele-
commun J 55(1/1988):5066
ITU-R (1987) The radio refractive index; its formula and refractivity
data. Rec. 370 ITU-R 453456 pp
Kolawole LB, Owonubi JJ (1982) The surface radio refractivity over
Africa. Nig J Sci 16(nos 1&2):441454
Rec. ITU-R P. 4539 (2004) The radio refractive index: its formula and
refractivity data 455-460 pp
Owolabi IE, Williams VA (1970) Surface radio refractivity patterns in
Nigeria and the Southern Cameroon. J West Africa Science
Association 1:317
Radiowave propagation measurements in Nigeria 135
... As the urbanisation of coastal cities dramatically increases around the world, so the need for radar and microwave communication services continues to surge. It is important to improve on the previous radio meteorological studies over these regions in order to mitigate the adverse effects of weather on radio propagation (Falodun and Ajewole, 2006;Falodun and Kolawole, 2004;Falodun and Okeke, 2013;Hughes, 1993;Kolawole, 1993Kolawole, , 1981Owolabi and Williams, 1970;Willoughby et al., 2002). The weather phenomenon occurs in the troposphere, which is the lowest atmosphere with almost all the atmospheric water vapour content. ...
... N, E), North Central, Nigeria, with 40% and 10% super-refractive and normal refractive conditions, respectively, which is typical of Sahelian climatic zone. These results are inconsistent with the ITU values and statistics (Falodun and Okeke, 2013). ...
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Radio engineers and researchers in conjunction with the International Telecommunication Union (ITU) have established the pivotal role of radio refractivity to the propagation of electromagnetic energy in the troposphere. In particular, the refractivity gradient statistics for the lowest 100m in the troposphere are used to determine the probability of occurrence of anomalous propagation conditions known as ducting. The major challenge to characterising the propagation condition over any environment is accessing the data of the lowest boundary layer of the atmosphere, which is highly dynamic and turbulent in evolution. High resolution radiosonde data from the Nigerian Meteorological Agency (NiMet) were used for a synoptic study of the rain-harmattan transition phase. The rain-harmattan transition phase marks the onset of the dry season due to the movement of the intertropical convergence zone interplay between (north-easterly and south-westerly) trade winds and monsoonal circulation. The lowest 100 m data were analysed to determine the frequency of ducting per month. Progressive increase in the occurrence of ducting was observed during the rain-harmattan transition phase, which coincides with the West African Monsoon retreat. The results show significant divergence from previous studies, which reported that the tropospheric condition over Lagos (Geo. 6.5 ºN, 3.3 ºE), Nigeria, is predominantly super-refractive.
... The NECOP project was designed to establish a network of meteorological observing stations, spatially located across Nigeria. The aim of NECOP is to create a network of stations that can carry out simultaneous basic measurements of meteorological and climatological variables, in real time, through telemetry technology, with 5-min update cycles (Falodun and Okeke, 2013). For the purpose of this work, ambient temperature and soil temperature data spanning from 2011 and 2012 were obtained from the Centre for Basic Space Science (CBSS), Nsukka. ...
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The radiation coming from the sun to the earth is the only form of incoming radiant energy that determines the heat balance and thermal regime of the earth. Variation of solar radiation is the single most important factor affecting the earth’s surface temperature. This study seeks to investigate the relationship between ambient temperature and soil temperature with a view to determine the existence of space-earth coupling. With a view to achieving this aim, the research was narrowed to the correlation between air temperature and soil temperature for the Nsukka area of Enugu State in Nigeria. The data used in this study was a two-year data of air temperature and soil temperature measurements collected by the Nigerian Environmental Climactic Observing Program (NECOP) station situated at Nsukka, which carried out simultaneous basic measurements of meteorological and climatological variables, in real time, through telemetry technology, with 5-min update cycles. In order to visualize the relationship between the two variables under study, the soil and air temperatures were co-plotted with time for each month of the year for 2011 and 2012, daily and annual range using Microsoft Excel, OriginPro 2018 64-Bit and Python Programming. From the findings of this work, the air and soil temperature variation patterns over each day, month, and year depict a pattern of correlation. The soil temperature fluctuated alongside the variations observed in air temperature with the addition of time lags (response time) due to difference in their thermal conductivities and heat capacities. This time lag was observed from this work to be up to 2 to 3 h for Nsukka region. On cooling, a delay was also observed in the air temperature, as the air temperature cools about an hour after the reduction in soil temperature was observed in a daily cycle.
... Expressing N in terms of our local meteorological parameters (relative humidity, atmospheric pressure, and ambient temperature) has been made possible by recommendations from the International Telecommunication Union (ITU). The Union had approved the relationship to expressed as (Akpootu and Iliyasu 2017;Kaissassou et al. 2015;Adediji et al. 2011;Falodun and Okeke 2013;Alam et al. 2016;Alam et al. 2017;Emerete et al. 2015): ...
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Trend analysis of meteorological parameters (temperature, pressure, and relative humidity) as well as calculated refractivity, equivalent potential temperature (EPT) for a pseudo-adiabatic process, and field strength in Calabar, Southern Nigeria has been analyzed using Mann-Kendall (M-K) trend test and Sen’s slope estimator (SSE). Data of the meteorological parameters were obtained from the Nigerian Meteorological Agency (NiMet) in Calabar for 14 years (2005–2018). Results show that the maximum and average temperature, atmospheric pressure, refractivity, EPT, and field strength all exhibited a positive Kendall Z value with 2.52, 0.33, 3.83, 0.77, 0.44, and 3.18 respectively which indicated an increase in trend over time, with only maximum temperature, atmospheric pressure and field strength showing a significant increase at 5% (0.05) level of significance, since their calculated p values (0.012, 0.0001, and 0.001) were less than 0.05. The relative humidity and minimum ambient temperature had a decrease in trend over time as they both had negative Kendall Z values (− 0.11 and − 1.09 respectively); however, together with the average ambient temperature and refractivity, their trend was not significant at 5% level of significance since their calculated p values were all more than 0.05. Linear regression, correlation, and partial differentiation showed that relative humidity has the most effect on the changes in seasonal refractivity and an indirect relationship with field strength variability. The novel relationship between EPT and refractivity has been discovered to be very strong and positive. Descriptive statistics has been used to portray the seasonal and annual trend of all parameters.
... This can be seen in both civil and military operations the world over and are applied in transmitting voice, data and video to various location [2,3,4]. In the bid to improve on the coverage, capacity and quality of service for radio wave communication systems, experts have found that the propagation of radio signals through the atmosphere is greatly influenced by the effective earth radius factor k [5,6,7,8]. Particularly, the k-factor is largely dependent on one of the most important parameters of radio wave propagation known as refractivity gradient as considered in the lowest 65m from the ground level [9,10,11]. Variations in refractivity may cause radio waves to bend while propagating through dissimilar layers of the atmosphere [12]. ...
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Understanding the relationship between the variations of meteorological parameters is vital in tackling the climatic problem. This paper presents methods for analyzing parameters that directly or indirectly relate to each other, and accurate methods for interpreting their results. Using obtained and calculated data for 14 years, we adopt the Mann–Kendall (M–K) test for the trend analysis; the Pettit and the standard normal homogeneity test (SNHT) was also used to test for homogeneity or change points for the annual series. Using the Python programming software, the correlation matrixes and linear regression pair plots have been adopted to discern the relationship between all parameters. To crystalize results, partial derivatives relating to the equivalent potential temperature (EPT) for a pseudo-adiabatic process with parameters affecting its variation from equations are obtained. The magnitude of these derivatives’ gradients was used to bolster regression results, showing the mixing ratio (MR) of air as the parameter with the most effect on EPT variation. The MK test results show that the atmospheric pressure (AP) and average ambient temperature (AT) were all increasing significantly for all variations (annual, dry and wet seasons). In contrast, others varied between dry and wet seasons after adopting a benchmark significance level of 5% (0.05). The correlation matrixes and linear regression pair plots show a strong relationship between the variations of refractivity, EPT, the temperature at the lifting condensation level (TL), MR, vapor pressure (VP), specific humidity (SH), and the dew point temperature (DPT). The potential temperature (PT), saturated vapor pressure (SVP), saturated mixing ratio (SMR), and the AT relationships showed a robust positive correlation/regression. This correlation offers a connection between the AT and the PT. The processes, including the partial derivatives, pair plots, correlation matrixes, and tests for trends, provide a solution to the meteorological analysis problem. Results and methods can be applied in other regions. Graphical abstract
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The radio refractive index structure of the lower section of the atmospheric boundary layer is critical in the planning and construction of microwave communication connections. This study analyses the refractivity profile carried out in Mowe (6.8085° N, 3.4367° E) South – Western Nigeria. Ground measurements of air pressure, temperature, and relative humidity used in this investigation were collected from the rain gauge of the Tropospheric Observatory Data Acquisition Network (TRODAN). The radio refractivity, associated refractivity gradient and climatic factor were computed using data from January 2012 to December 2013. The vertical distributions of radio refractivity were then calculated using these parameters. Seasonal fluctuations in refractivity are visible over the location, with high values in the wet season and low values in the dry season. The findings also suggest that propagation circumstances fluctuate in frequency, with sub-refractive situations being most common between April and September. This is an indication that microwave link in Mowe will suffer higher signal loss during wet season, while the loss may be mild during the dry season. The refractivity values in this study are expected to aid in determining the necessary mitigation to be put in place to reduce loss of signal in Mowe.
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Understanding the relationship between the variations of meteorological parameters is vital in tackling the climatic problem. This paper presents methods for analyzing parameters that relate directly and indirectly to each other and accurate methods for interpreting their results. Using obtained data for 14 years and calculated data for other parameters, we adopt the Mann-Kendall (M-K) test for the trend analysis of the annual and seasonal variations, the correlation matrixes, and linear regression pair plots to discern the relationship between all parameters using the python programming software. To crystalize results, partial derivatives relating the equivalent potential temperature (EPT) for a pseudo-adiabatic process with parameters affecting its variation from equations are being obtained. The magnitude of these derivatives' gradients was used to bolster regression results, showing the mixing ratio (MR) of air as the parameter with the most effect on EPT variation. The MK test results show that the atmospheric pressure (AP) and average ambient temperature (AT) were all increasing significantly for all variations (annual, dry and wet seasons). In contrast, others varied between dry and wet seasons after adopting a benchmark significance level of 5% (0.05). The correlation matrixes and linear regression pair plots show a strong relationship between the variations of refractivity, EPT, the temperature at the lifting condensation level (TL), MR, vapor pressure (VP), specific humidity (SH), and the dew point temperature (DPT). The potential temperature (PT), saturated vapor pressure (SVP), saturated mixing ratio (SMR), and the AT relationships showed a robust positive correlation/regression. This correlation offers a connection between the AT and the PT. The processes, including the partial derivatives, pair plots, correlation matrixes, and tests for trends, provide a solution to the meteorological analysis problem. Results and methods can be applied in other regions.
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A comprehensive study on the anomalous propagation (AP) conditions occurring over the central and west African stations was made from 2 years (January 2005-December 2006) high-resolution data measured by GPS (Global Positioning System) radio survey observations. Through data quality control and diagnostic analysis, the probability of AP occurrence and characteristic quantities of the three typical anomalous propagation conditions were given. The sub-refraction, super-refraction and ducting cases were investigated statistically using the vertical proBle of modiBed refractivity gradient. Strong diurnal variation in the percentage occurrence of the AP had its peak during the wet months, while the dry months had the lowest values. From 0600 to 1800 local time (LT) at day (1800-0600 LT at night), the total percentage occurrence of super-refraction, sub-refraction and ducting were 82.5% (78.5%), 11% (15.5%) and 6.5% (6%), respectively. Besides statistical results, local meteorological conditions prevailing over central and west Africa have also been discussed.
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Trend analysis of meteorological parameters (temperature, pressure, and relative humidity) as well as calculated refractivity, equivalent potential temperature (EPT) for a pseudo-adiabatic process, and field strength in Calabar, Southern Nigeria has been analyzed using Mann-Kendall trend test and Sens slope estimator. Data of the meteorological parameters were obtained from the Nigerian Meteorological Agency (NiMet) in Calabar for 14 years (2005 - 2018). Results show that the maximum and average temperature, atmospheric pressure, refractivity, EPT and field strength all exhibited a positive Kendall Z value with 2.52, 0.33, 3.83, 0.77, 0.44 and 3.18 respectively which indicated an increasing trend over time, with only maximum temperature, atmospheric pressure and field strength showing a significant increase at 5% (0.05) level of significance, since their calculated p-values (0.012, 0.0001, and 0.001) were less than 0.05. The relative humidity and minimum ambient temperature showed a decrease in trend over time as they both had a negative Kendall Z values (-0.11 and -1.09 respectively), however, together with the average ambient temperature and refractivity, their trend was not significant 5% level of significance since their calculated p-values were all more than 0.05. Linear regression, correlation and partial differentiation showed that relative humidity has the most effect on the changes in seasonal refractivity and an indirect relationship with field strength variability. The relationship between EPT and refractivity has been discovered to be very strong and positive. Descriptive statistics has been used to portray the seasonal and annual trend of all parameters.
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The effect of evaporation ducting on millimetre electromagnetic wave on sea surface may lead to path loss, poor line of sight and sometime complete loss of signal due to refraction in shadow zone and noise in the signal. In Nigeria, the refractive gradient varies due of the significant change in climatic condition from the coastal region to southern region through semi-arid region and to the northern region. These effects are more pronounced in Lagos, which fall in a coastal region in Nigeria. The data used for the study were collected from NIMET in Lagos state. This study characterised the monthly variation of refraction types " base on refractivity gradient and estimate the evaporation duct height using P-J model technique. The evaporation ducting only occurred in few months and the mean height is 14.52+0.52m with standard deviation of 1.80m.
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Propagation of radio waves under clear-air conditions is affected bythe distribution of atmospheric refractivity between the transmitterand the receiver. The measurement of refractivity was carried out onthe TV Tower Prague to access evolution of a refractivity profile. Inthis paper, the parabolic equation method is used in modelingpropagation of microwaves when using the measured data. This paperbriefly describes the method and shows some practical results ofsimulation of microwave propagation using real vertical profiles ofatmospheric refractivity.
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Propagation related parameters are used for design and frequencyplanning of microwave networks. Atmospheric refractive index is theimportant parameter that influences the propagation of electromagneticwaves during so-called "clear sky" conditions. The refractive indexmeasurement, which was launched in TESTCOM, is presented in this paper.Some statistical characteristics and their utilization are introduced.
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International conferences on frequency co-ordination have urgently required new information on radio-wave propagation in tropical regions and, in particular, on propagation in Africa. Therefore, the International Telecommunication Union (ITU) initiated a radio-wave propagation measurement compaign in Africa in 1984. Two experiments were performed in Burkina Faso between July 1986 and March 1989: long-term field-strength measurements in the VHF range and refractivity measurments in clear atmosphere. Near Bobo Dioulasso, the signal level of a transmitter located in the Cote d'Ivoire was recorded on 469 days between 16h00 and 23h00 when the transmitter was in operation. The path length was 280 km. The different influences of the dry and rainy seasons as well as the durinal variation are investigated. Refractivity measurements were performed at the receiver site. The refractivity was determined indirectly by means of a meterologic probe, i.e. the parameters temperature, relative humidity and air pressure were measured during the balloon ascent and the refractivity profile was computed off-line afterwards. These refractivity profile are compared with other refractivity measurements carried out in this region. The impact on the VHF field-strength measurements is examined.
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The structure of the radio refractive index “in altitudes of” first 100 m of the troposphere is important for the planning and design of microwave communication “links”. For this reason, measurements of atmospheric pressure, temperature, and relative humidity were conducted in Akure “(7.15°N, 5.12°E)” to determine the radio refractive index. “Wireless meteorological sensors were positioned at the ground surface and at 100 m altitude on a 202 m high tower owned by the Nigerian Television Authority (hereafter NTA) which is now idle due to the relocation of the television house”. The measurements were “made” every “30 min” and round the clock. “Statistical” distributions of the refractive index modulus, “its” vertical gradient, and the diurnal and seasonal variations of the refractivity modulus were determined from the measured “data”. The results obtained show that the local climate has an appreciable influence on the radio refractivity. The curve of the seasonal variation of the vertical gradient of the radio refractive modulus has some minima points corresponding to the dry and the rainy seasons in Akure. The results obtained also show that the values of the refractive modulus at the “100 m” altitude were high in the morning and late evening/night hours while they “show” minima during the afternoon hours. Thus, the worst propagation condition obtained for Akure was observed in the afternoon “within” the time window “from 15:00 to 18:00” local time (hereafter LT) during the dry months and from roughly 17:00 to 19:00 LT during the rainy season.
Propagation of radio-waves The Insti-tution of Electrical Engineers Radio meteorology
  • Barclay
Barclay L (2003) Propagation of radio-waves (2nd edition). The Insti-tution of Electrical Engineers, London, pp 103–127 Bean BR, Dutton EJ (1968) Radio meteorology. Dover Publication Co, New York, pp 259–273
Radio wave propagation measurement in Burkina Faso. SMR on radio wave propagation in tropical regions Radio refractive index in the lowest 100-m layer of the troposphere in Akure, South West-ern Nigeria
  • Z Low
Z, Low K (1993) Radio wave propagation measurement in Burkina Faso. SMR on radio wave propagation in tropical regions, Trieste, Italy Falodun SE, Ajewole MO (2006) Radio refractive index in the lowest 100-m layer of the troposphere in Akure, South West-ern Nigeria. Journal of Atmospheric and Solar-Terrestrial Phys-ics 68:236–243