University of Africa Toru-Orua
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- This contains the intellectual works of the faculty members in Agriculture
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Recent Submissions
Machine learning-based models for forecasting radio refractivity over the coastal area of South Africa
(Learning Gate, 2025-02-04) Yusuf Babatunde Lawal1*, Pius Adewale Owolawi2, Chunling Tu3, Etienne Van Wyk4, Joseph Sunday Ojo5
Surface refractivity is a crucial parameter that determines the bending of radio signals as they
propagate within the troposphere. It is greatly influenced by the atmospheric weather conditions and
changes rapidly, especially in the coastal areas. This research utilized 50 years (1974-2023) surface
temperature, pressure, and humidity data from six coastal stations in South Africa to forecast radio
refractivity in the Mediterranean climate. Five machine learning models: Gated Recurrent Unit (GRU),
Light Gradient Boosting Machine (LightGBM), Long-Short Term Memory (LSTM), Prophet, and
Random Forest were trained for future prediction of surface refractivity at any coastal area in South
Africa. The stations latitude, longitude, altitude, surface refractivity and date were applied as the input
parameters to train the models. The models were optimized through the randomized searchCV
hyperparameter tuning to improve their efficiency. The LightGBM outperformed other models with
RMSE and adjusted determination coefficients of 1.67 and 0.96, respectively. The model is
recommended for future prediction of surface refractivity needed for the improvement of point-to-point
wireless communication, terrestrial radio and television transmissions, and mobile communication
networks in the coastal sub-tropical regions.
Investigation of Point Refractivity Gradient and Geoclimatic Factor at 70 m Altitude in Yenagoa, Nigeria
(Nigerian Society of Physical Sciences, 2023-03-05) Y. B. Lawala,∗, E. T. Omotoso
The quality of services provided via Inter-Terrestrial radio communication links such as GSM networks, Wide Area Network (WAN), Radio and
TV broadcasts is largely influenced by some meteorological parameters such as temperature, pressure and humidity. Proper knowledge of these
parameters, specifically at microwave antenna heights (about 70m) is important in order to maintain an effective line-of-sight (LOS) link even
during the worst weather conditions. The geoclimatic factor is an important quantity that must be considered in the design of terrestrial links for
effective wireless communication. This work utilized satellite data from the European Center for Medium-Range Weather Forecasts (ECMWF)
to compute the point refractivity gradient and geoclimatic factor for Yenagoa and its environs. The research was necessitated by the paucity of
research on this subject matter for Yenegoa. The results of the research show that point refractivity gradient and geoclimatic factor in the study
area vary with season. The average point refractivity gradient and geoclimatic factor at 70 m above the ground level are:136.433 N-unit/Km and
6.638633E-05 respectively. This implies that radiowaves propagating in this region at the said altitude is most likely to be super refractive in
both rain and clear air atmospheric conditions. Rain or worst condition refers to the period when atmospheric components such as hydrometeor,
lithometeor, aerosol have significant effects on propagated radio signals. Clear-air conditions means when maximum possible signal is received
such that the most threatening atmospheric components (rain drops) have negligible effects on propagated signal. The results will be useful for
radio engineers in the design and configuration of inter-terrestrial microwave links in Yenagoa and Its environs for optimum quality of service
INVESTIGATION OF NON-STANDARD REFRACTION IN A COASTAL AREA OF NIGERIA USING RADIOSONDE DATA
(FUTA Journal of Research in Sciences, 2015-02-05) S.E. Falodun* and B.Y. Lawal
ABSTRACT
Radio meteorological data obtained by radiosonde measurements in Lagos (3.350E, 6.060N)
were used to calculate the refractivity, N at different altitudes as well as at the ground surface,
in order to derive the refractivity gradient. The values were computed to a height of about
12km being the highest level for which complete radiosonde data were available. The
refractivity profile were plotted versus altitude for all the data analysed. The observed
refractivity distribution is more nearly an exponential function of height than a linear function
as assumed by the 4/3 earth atmosphere. It was also observed that the N-values decrease with
altitude from the earth surface. Other parameters, such as the k-factor and the values of the
gradient exceeded for given percentages of the time were also derived. The analysis of the
results have shown that most of the values of the refractivity gradient for this coastal area are
larger than the standard (normal) value of -40 N-units/km and therefore the propagation
conditions are super-refractive. The shapes of the curves have confirmed the exponential
dependence of refractivity on height, irrespective of the season.
Impact of Rain Heights on Rain-Induced Attenuation for Communication Systems Operating at Ka and V Bands in Pretoria, South Africa
(IEEE, 2025-12-12) Yusuf Babatunde Lawal, Pius A. Owolawi, Chunling Tu, Etienne A. van Wyk and Joseph Sunday Ojo
Wireless communication networks, such as 5G
networks, inter-terrestrial, and earth-space links, transmit radio
signals at high-frequency bands. However, the signal quality of radio
communication systems operating at frequencies above 10 GHz in
tropical and subtropical regions is often degraded due to rain
induced attenuation. Rain rate and rain height are the most
influential meteorological parameters determining the level of
attenuation. This research investigates the effects of seasonal
variations in rain height on rain-induced attenuation and its impact
on radio links operating at typical downlink and uplink frequencies
in the Ka (30/20 GHz) and V (40/50 GHz) bands in Pretoria, South
Africa. The research revealed that maximum rain heights
experienced in the summer resulted in the worst rain-induced
attenuation at all frequencies. The estimated attenuations would
assist to determining the minimum fade margins required to achieve
99.9%, 99.99% and 99.999% signal availability annually at these
frequencies in the study location. The results are expected to serve as
a database for future planning of high-frequency link budgets.
Geoclimatic characterization and latitudinal dependence of rain heights over Nigeria
(IOP Publishing, 2021-04-06) Y. B. Lawal, J. S. Ojo, S. E. Falodun and E. O. Olurotimi
Attenuation due to rain remains the most severe threat to terrestrial and satellite
communication links in the tropics. Rain height is a precipitation parameter that plays important
role in the determination of rain-induced attenuation. In this paper, a statistical study was carried
out to establish the relationship between rain height and earth station latitude using rain heights
derived from Zero Degree Isotherm Height (ZDIH) data retrieved from Global Precipitation
Measurement (GPM). A strong positive correlation of 0.83 propelled the attempt to model
equations for the estimation of rain height based on latitude. The research recommends a
polynomial function of order 3 which has the best coefficient of determination (0.8). The annual
mean values of rain heights were also computed and recommended for each of the four geo
climatic zones in Nigeria.