Scholarly works

Permanent URI for this collectionhttps://repository.ui.edu.ng/handle/123456789/420

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Start date: 2020

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    Worst month rain rate characterization for line-of-sight link performance in tropical locations
    (2021) Osita, I.; Nymphas,E.F.
    Communication equipment operating in the 30 to 300GHz frequencies avails large bandwidth and high speed data transmission but suffers greatly from attenuation by rain. The design of radio communication equipment has been based on predicted rain rate from the International Telecommunication Union-Radio (ITU-R) recommendations. This equipment fails in the tropics due to the differences in tropical and temperate rainfall structure on which the ITU-R recommendation is based. Five minutes rainfall data from two tropical locations in Nigeria – Jos (9.93 oN, 8.89oE, 1280 m) and Minna (9.61 oN, 6.56 oE, 223 m) were analysed. The 1- minute and ITU-R predicted rain rate (RR) were obtained with the Lavergnat and Gole model and MatLab rain rate statistics respectively while the logarithmic scale was used to convert the RR to exceedance time percentages (0.001 to 1%). The two parameter conversion factors, Q1 and β were generated with the ITU-R P. 841-6 recommendation; these were compared with the conversion factors recommended by ITU-R for global rain rate application. The results showed that at 0.01% exceedance, the ITU-R predicted rain rate for Jos and Minna were 87.1mm/hr and 91.6mm/hr respectively while the estimated rain rate from these locations were 84.5mm/hr and 110.0mm/hr respectively. The ITU-R conversion factor for the computation of the mean annual worst month from mean annual rain rate percentage exceedence were Q1 = 2.83 and β = - 0.15 while these parameters at Jos is, Q1 = 3.17 and β = - 0.19 and at Minna, Q1 = 3.12 and β = - 0.18. The results showed that there is a very strong relationship between the distribution of rain rate in the worst month and the annual rain rate distribution with coefficient of determination of 0.9994 and 0.9984 respectively. Thus for optimum link design budgeting, the modified values of Q and β should be adopted in these locations in order to enhance radio equipment performance in Nigeria.
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    Characterization of tropical rainfall structure for some selected locations in Nigeria
    (2021) Osita, I.; Nymphas,E.F.
    Rainfall rate for any location is required for rain attenuation modeling for the region of interest. The characteristics of tropical rainfall structure in Nigeria have been investigated. The data was collected from the Tropical Data Acquisition network (TRODAN) set up by the Center for Atmospheric Research (CAR) in Nigeria. The rainfall rates were measured at 5-minutes integration time. The results were then compared with those predicted by the ITU-R model, and those from other tropical locations. The results revealed that the ITU-R model performs best only in the Southern Guinea Savannah (SGS) region of the country. In other geographical locations, the ITU-R model either under-estimates or over-estimates rainfall rates. The Cumulative Distribution Functions (CDFs) at the 0.01% time of exceedence showed that the percentage difference in the measured rain rate and the ITU-R estimates varied from a minimum of 4.89% in SGS to a maximum of 22.93% in the Derived Savannah (DS). At the 0.001% of time, these differences varied from a minimum of 11.90% to a maximum of 38.80% in these respective regions. These results and others from the tropics suggest the need for the modification of the ITU-R model for predicting rain attenuation in the tropical region to take into account the peculiar characteristics of rainfall in the region.
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    Comparison analyses of different models used to determine soil thermal conductivity and diffusivity at nimex site, Ibadan
    (2021) Nwaokoro,E.; Nymphas,E.F.
    Soil thermal properties regulate the separation of energy fluxes at the ground surface and they control the exchange of energy and mass between the soil and the atmosphere. The knowledge of these properties is needed in order to ascertain the heat flux distribution in the soil under steady and non-steady conditions. In this study, which lasted for 11 months starting from March 2006 to January 2007, we estimated soil thermal conductivity and thermal diffusivity at Nigeria Mesoscale Experiment (NIMEX) site, Ibadan using Johansen and Kersten models and Horton Numerical method. The aim of this work is to compare the results obtained from these models and to ascertain the level of agreement of the results. The result showed that for Johansen and Kersten models, the highest mean values of thermal conductivity and thermal diffusivity were obtained in the month of September 2006. For Johansen model the values are 4.18±0.08 Wm-1K-1 and 4.56±5.57*10-8m2s-1 for thermal conductivity and thermal diffusivity respectively and for Kersten model the thermal conductivity and thermal diffusivity values are 1.00±0.05 Wm-1K-1 and 1.07±0.22*10-8 m2s-1 respectively. This may be due to the observed increase in the soil moisture content within this month. The result obtained using Horton Numerical method showed that the highest mean thermal conductivity and thermal diffusivity values of 9.76 ±3.00 Wm-1K-1 and 10.70±3.30*10-8m2s-1 respectively were obtained in the month of December 2006 while the lowest mean values of -0.44 ±14.68 Wm-1K-1 for thermal conductivity and 0.10±12.70*10-8m2s-1 for thermal diffusivity were obtained in the month of September contrary to the results obtained with the first two models. The negative mean thermal conductivity value of -0.44 ±14.68 Wm-1K-1 obtained in the month of September 2006 using Horton Numerical method was probably due to the increase in soil moisture content which is as a result of increase in the amount of rainfall within this month that lowered the temperature at the near soil surfaces. Kersten model is in agreement with Johansen model but has low values making it unsuitable for very low soil moisture. Johansen model is likely the best model for estimating thermal conductivity and diffusivity.
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    An artificial neural network estimation of global solar radiation at Ibadan, Nigeria using meteorological data
    (2020) Nymphas, E.F.; Udomboso, C.G.
    This paper estimates global solar radiation (Rs) from routinely measured meteorological parameters in the city of Ibadan, Nigeria, using artificial neural network method. Six combinations were used to estimate Rs namely (i) daily mean air temperature (T) and day of the year as inputs and global solar radiation as output, ((ii) daily mean relative humidity (RH) and day of the year as inputs and Rs as output (iii) daily mean T, daily mean RH and day of the year as inputs and Rs as output (iv) daily mean minimum relative humidity (RHmin) and day of the year as inputs and Rs as output, (v) daily mean minimum temperature (Tmin), daily RHmin and day of the year as inputs and Rs as output (vi) daily mean maximum temperature (Tmax), daily mean Tmin, daily mean RHmin, daily maximum relative humidity (RHmax) and day of the year as inputs and Rs as output. The neural network was trained with 3653 measured data between 1995 and 2004 and tested with data for 731 days between 2003 and 2004. The data for testing the neural network were not used for the training. The results obtained showed that the combination of RHmin, RHmax and day of the year gave the best estimate of Rs with MSE of 3.4124. This is followed by RHmin and day of the year with MSE of 3.4424. Daily mean air temperature and day of the year could not mimic the measured Rs; it gave MSE of 5.3345. It is concluded that Rs can be estimated for locations where only temperature and relative humidity data are available.
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    Determination of rainfall attenuation at millimeter wave band for the design of 5g and higher bandwidth radio equipment for terrestrial paths in the tropical region
    (2020) Osita, I.; Nymphas, E. F.
    Millimeter Wave (mmW) radio systems operating at 30 to 300GHz band provides higher bandwidth, frequency reuse and communications security. With the available wide bandwidth, millimeter wave equipment is capable of achieving 10 Gbps full duplex capacities. The mean annual 1-minute RR (mm/hr) ranged from 87.25 in the coastal region to 51.0mm/hr in semi-arid region. The ITU-R predicted RR ranged from 109.10mm/hr in the coast to 91.90mm/hr in the semi-arid region. The ITU-R overestimated the rain rate by 23.83% in the semi-arid region while at the coastal region, it was over-estimated by 12.47%. The highest value of specific attenuation (R g) at horizontal polarization (Hp) and vertical polarization (Vp) for the two regions occurred at 120 and 150GHz MWFs and R P g H > R P g V. The clear signal band at 20km Path length were estimated to be 40 and 45GHz across the regions, while the predicted value by ITU-R is also 40GHz. However, the ITU-R over predicted the value of attenuation at this frequency band by 13.16% and 35.29% at the coastal and semi-arid locations respectively. included 150GHz which overlaps with 45GHz band. The path attenuation across the regions at 40GHZ ranged from 112.58dB to 164.14dB while at 45GHZ, it ranged from 122.02dB to 175.57.45dB. The range of the ITU predicted value of path attenuation at 40GHz and 45GHz were 170.20dB to 192.18dB and 181.83 dB to 204.43dB respectively.