FACULTY OF SCIENCE
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Item Temperature variations and soil thermal properties at the Nigeria mesoscale experiment site, Ibadan, Nigeria(ECRTD-UK, 2019) Nwaokoro, E.; Nymphas, E. F.Soil temperature has been observed to depend on a number of factors, which also determine the surface temperature. In this study, soil temperature at the Nigeria Mesoscale Experiment (NIMEX) site, Ibadan (7.4398° N, 3.8930° E) was investigated and the soil thermal properties were estimated for the period of March, 2006 to January, 2007 using Kersten model. The rainy seasons had increased the soil moisture content and soil thermal properties while the dry seasons had low soil moisture content and soil thermal properties. The maximum temperature of 32.10° C at the 30cm depth was measured in November 2006 during the dry season and the minimum temperature 26.80° C was measured at 5cm depth in September 2016 during the wet/rainy season. Soil moisture, thermal conductivity, thermal diffusivity and volumetric heat capacity had their maximum value of 20.52m3m-3, 1.006 Wm-1K-1, 1.07*10-8m2s-1 and 0.91*108Jm- 3K-1 in September 2006 respectively. The minimum values for soil moisture, thermal conductivity and volumetric heat capacity occurred in January, 2007 with values of 15.75 m3m-3, 0.90 Wm-1K-1 and 0.91*108Jm-3K-1 respectively, and the minimum value of 0.85*10-8m2s-1 for thermal diffusivity occurred in July 2006.Item Estimation of surface energy fluxes from bare ground in a tropical station using priestleytaylor method(2013) Adeniyi, M.O.; Nymphas, E. F.This investigation was designed to test the performance of Priestley Taylor method in the partitioning of the available energy into sensible and latent heat fluxes in a tropical site. Compared to eddy covariance measured fluxes, the conventional Priestley Taylor constant (aPT) of 1.25 gave low coefficient of determination and high bias error for both sensible and latent heat fluxes. It overestimated latent heat flux in the noon and afternoon but underestimated sensible heat flux. The bias error reduced and the coefficient of determination increased for sensible heat flux when aPT value was reduced to 1.0. The bias error for latent heat also reduced but the coefficient of determination did not change with the reduction in aPT value. The root mean square error reduced with the reduction in the aPT value. Compared to measured fluxes, coefficient of determination of sensible heat flux ranged from 0.82 to 0.90 while that of latent heat flux ranged from 0.78 to 0.9. Priestley Taylor method is recommended for partitioning of available energy into its component sensible and latent heat fluxes.Item Validation of analytical algorithms for the estimation of soil thermal properties using de Vries model(2012) Adeniyi, M.O.; Oshunsanya S.O.; Nymphas, E. F.Soil thermal conductivity, and diffusivity together with the damping depth of soil temperature computed using Amplitude decay, Phase shift, Harmonic (amplitude based and phase based), Arctangent, Logarithmic and conduction-convection algorithms were compared with those obtained from de Vries model. The amplitude decay algorithm yielded the most reliable values of the soil thermal properties of all the estimation methods with mean absolute error (MAE), root mean squared error (RMSE) and relative maximum error (RME) of 0.04, 0.05 and 5.63% respectively for soil thermal conductivity. Harmonic algorithm (using the amplitude of the first 4 harmonics) gave values of the soil thermal properties next to the amplitude decay algorithm with MAE, RMSE and RME values 0.41, 0.44 and 47.84% respectively for soil thermal conductivity. Higher error values were associated with the other algorithms. The Arctangent algorithm gave the most deviated values of soil thermal properties with RME of 156.83% for soil thermal conductivity. For soil moisture content between 0.168 and 0.189 (> critical soil moisture content) the values of the soil thermal properties of the loamy sand decreased with increasing soil moisture, while they increased with increasing soil aeration.Item 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.