Surface Refractivity Research Articles

Machine learning-based models for forecasting radio refractivity over the coastal area of South Africa

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.

QUARTERLY VARIATION OF TROPOSPHERIC SURFACE REFRACTIVITY IN ILORIN, NIGERIA

To construct a radio communication system, there is need for extensive knowledge of the refractivity and its variations. This work aims to determine the change in season with tropospheric surface refractivity of Ilorin, Kwara, Nigeria. The refractivity for both dry (1st quarter) and rainy (3rd quarter) seasons for 2000 - 2002 have been calculated using the meteorological data obtained from the Nigerian Meteorological Agency, Ilorin. The result shows that there is a variation between tropospheric surface refractivity during the dry and rainy seasons. High refractivity during the rainy season than in dry season is observed, mainly due to higher amount of water content in the atmosphere (troposphere) in the rainy season.

Comparative Analysis of Surface Refractivity Variations in the Sahel and Coastal Zones of Nigeria

Comparative Analysis of Surface Refractivity Variations in the Sahel and Coastal Zones of Nigeria

Seasonal and latitudinal variations of surface radio refractivity over Nigeria

Refractivity is a significant challenge of radio signal propagation. As it often distorts or leads to loss of signals. The seasonal and latitudinal variations of surface refractivity at three Nigerian tropospheric Observatory stations in Nigeria, namely Port-Harcourt, Lagos, and Makurdi, are presented in this paper. Values of monthly averages of pressure, temperature, relative humidity, and water vapour from the stations were used to compute surface refractivity at each station. The results show that the values of surface refractivity increase from the arid region in the north to the coastal area in the south. There was an increase in the values of surface radio refractivity from the minimum value of about 332.83 N-units at Makurdi station to a maximum value of 386.69 N-units at Lagos station. Seasonal variations are seen to be caused by weather conditions. The values of the surface refractivity increased significantly in the wet season and reduced in the dry season. It also shows that the values of surface radio refractivity are affected by the meteorological components mentioned above. The result of this study is needed for effective planning of good signal reception in these stations.

Digital Maps of Atmospheric Refractivity and Atmospheric Ducts Based on a Meteorological Observation Datasets

The propagation of electromagnetic waves in the troposphere is significantly influenced by atmospheric refractivity and atmospheric ducts. Thus, abundant statistics on atmospheric refractivity and ducts are essential for reliable propagation prediction. In this study, we develop novel digital maps of atmospheric refractivity and atmospheric ducts based on the processing of radiosonde observation (RAOB) data and surface observation (SUOB) data collected from 2005 to 2014, including wet term of surface refractivity, refractivity gradients, and atmospheric ducts. The new digital maps, referred to as RADIO maps are defined as RADIOS and RADIOS2 maps. The RADIOS maps, which are world maps of refractivity gradients and atmospheric ducts, are obtained from data collected at radiosonde stations at 892 sites. The RADIOS2 map, which is a world map of the wet term of surface refractivity, is obtained from data collected at radiosonde and surface stations at 3218 sites. To test the consistency between RADIO maps and ITU-R ERAI (International Telecommunication Union Recommendations employing ERA-Interim (European Centre for Medium-Range Weather Forecasts Re-Analysis-interim) reanalysis data for 36 years from 1979 to 2014) maps; a comparison is performed with the cumulative distributions of refractivity gradients at two radiosonde stations. The accuracy of RADIO maps is checked through comparisons with the maximum, mean, and standard deviation of the relative errors, which are obtained from observed values and predicted values, between RADIO maps and ITU-R ERAI maps. Our results show that: 1) RADIOS2 map is consistent with the current ITU-R ERAI map with respect to the wet term of surface refractivity; 2) <inline-formula> <tex-math notation="LaTeX">$\Delta N_{65\,\mathrm {m}}$ </tex-math></inline-formula>(50) and <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> obtained from RADIOS maps are larger than those obtained from ITU-R ERAI maps in low-latitude coastal and marine areas; and 3) comparisons between RADIOS and ITU-R radios&#x005F;duct maps (i.e., the world digital maps obtained from a 20-year (1977&#x2013;1996) dataset of 661 radiosonde stations released by ITU-R P.453-14) show that ITU-R radios&#x005F;duct maps predict lower occurrences of surface and elevated ducts at low latitudes. Overall, this study demonstrated that the new maps based on observations over the past ten years provide more accurate and reliable information than other traditional maps in terms of atmospheric refractivity, refractivity gradients, and atmospheric ducts.

Diurnal Variation of Surface Radio Refractivity over Sokoto, North-western Nigeria

The knowledge of good refractivity profile is vital for proper planning of terrestrial communication links; surface refractivity profile of a station is particularly required for enhanced planning and prediction of performance of terrestrial radio links especially in tropical regions where International Telecommunication Union Recommendations (ITU-R) has called for such local propagation data. The diurnal surface radio refractivity Ns over Sokoto was investigated for a period of three years (2008-2010). High values of Ns were recorded in the early morning hours while low values were recorded during afternoon hours. The least mean hourly Ns varied between 270-280 N-units in January (a typical dry season month in Sokoto) while the mean maximum was recorded between 345-360 N- units in July (a typical rainy season month). Also, average seasonal variation of Ns was 356-440 N-units in rainy season and 270-285 N-units in dry season. The result of this investigation also showed that relative humidity and temperature have major influence on the variation of surface radio refractivity, while pressure has relatively less influence. The study further showed that coverage of a radio transmitter of 200 m height may have a variation of up to 0.5 km between morning and afternoon hours in Sokoto.

The theoretical study of anticancer rhodium complexes and methyl groups effect on ligands in chemical reactivity, global descriptors, ADMET by DFT study

As there are a potential application of rhodium (0) complexes and rhodium (II) complexes in anticancer drug discovery, the key point of this study is to design new rhodium(0) complexes with amine ligand, and was estimated their properties. To predict the thermo-physical, chemical reactivity and biological activity of most expected rhodium (0) complexes with amine and alkyl amine were conducted by the computational method of density functional theory (DFT). The thermo-physical parameters, such as free energy, entropy, dipole moment, binding energy, nuclear energy, electronics energy and heat of formation were calculated, as well as chemical reactivity, for example, Highest Occupied Molecular Orbital (HOMO), Lowest Unoccupied Molecular Orbital (LUMO) and HOMO-LUMO gap. Some descriptors, such as ionization potential, electronegativity, hardness, softness and electron affinity were estimated of rhodium (0) complexes. To explain about biological indication, the charge density, surface area grid, volume, LogP, polarizability, refractivity and molecular mass had also calculated. The ADMET was illustrated through the online database AdmetSAR for the safe uses and toxicological evidence. Regarding the chemical reactivity study in view of softness and LUMO HOMO gap, the L03 is a more suitable drug than others, and stands for that secondary alkyl amine as ligand is more effective than primary and tertiary amine ligands.

Estimation of radio refractivity from satellite-derived meteorological data over a decade for West Africa

Radio refractivity, which is the bending of a radio signal as it propagates through media, is very important in works involving terrestrial atmospheric electromagnetic propagation such as point-to-point microwave communication, terrestrial radio and television broadcast and mobile communication system. This study focused on the West African region where it was found that the refractivity varies exponentially with height (N=NoeH/h) and from the coast towards the desert: the average surface refractivity (No) for West Africa was found to be around 342 N-units, while the average scale height (h) was found to be around 8.01 km. Generally, the refractivity gradient was found to range between −46.48 and −29.51 N-units/km (k-factor value of between 1.23 and 1.42) across West Africa, splitting the region between sub- and super-refraction. The variation in refraction type was found to follow a seasonal pattern across the West African region, with sub-refraction dominating during the dry season and super-refraction dominating most part in the coastal area during the wet season.

Study of Seasonal Surface Refractivity over North-Central Nigeria

Tropospheric radio wave signals experience loss due to multipath effect, scattering and other forms of attenuation through the atmospheric medium, primarily due to variations in weather conditions with time. The knowledge of surface refractivity profile is important for optimal planning of Very High Frequency/Ultra High Frequency (VHF/UHF) terrestrial radio links in a region. The study of surface refractivity (Ns) over the North-Central Nigeria was carried out using meteorological data from seven locations in North-Central zone of Nigeria. The seasonal variations of Ns were also derived using the monthly summaries of surface data obtained from Nigerian Meteorological Agency (NIMET) over seven stations of Abuja, Lafia, Lokoja, Makurdi, Jos, Minna and Ilorin between 2005 and 2010.The results indicated that the monthly averages of radio refractivity during the rainy season months (April to October) are greater than the Ns values during the dry season months (November to March) for all the locations throughout the years of the study. The computed of mean monthly Ns over all the seven stations in the first 1 km above the ground level is 348 N-units, which gives mean refractivity gradient (dN/dh) of -49 N/k, these shows that the region is characterised by low scale super-refraction. The mean k-factor over the entire region in the first 1 km above the ground level is 1.4; the mean Field Strength Variability (FSV) in first 1 km of height in the region was calculated to be 14 dB. The mean Radio Horizon distance within 1 km height for a transmitter height of 100 m over the stations is 42 km. The results provide useful information needed by radio engineers to set up new terrestrial radio propagation links or to improve on the existing ones especially at VHF, UHF in the North-Central region of Nigeria, as recommended by International Telecommunication Union Recommendations (ITU-R P.453, 2013), which observed the need for local reference data on refractivity and refractivity gradients all over the world.

The influence of primary radio climatology parameters on radio refractive index over the African region: a 30-year satellite study

In the lower part of the atmospheric boundary layer, structure of the radio refractive index plays a vital role when planning and designing microwave communication link. The effects of primary radio climatic parameters on radio wave propagation at UHF and microwave frequencies are crucial in studying radio refractive index. 1951 to 1980 satellite data has been used to investigate the mean values of both the primary radio climatic variables and surface radio refractive index over the Africa. The mean value of water vapor pressure, temperature and pressure ranges from 3-23 mbar, 284-302 K and 800-1000 mbar respectively across Africa. The high values of water vapor pressure around the Coastal and Rainforest reduce towards the Savanna and Steppe region (semi-arid). The mean variation value of surface refractivity over Africa ranges from 160 - 340 N-units. The refractivity values in larger part of the savanna range between 250 – 280 N-units.

Surface Radio Refractivity of Akure and Ondo town, Southwest Nigeria

The surface radio refractivity, refractivity gradient at 1km above ground surface and the effective earth radius factor, K over Akure and Ondo town of South west Nigeria has been investigated using Ten (10) years daily data of the meteorological parameters of Pressure, air temperature and humidity. The result showed that the mean monthly value of the surface refractivity at the Ondo station is generally slightly higher than that of Akure. The monthly mean value of refractivity at the two stations was found to be strongly correlated with a value of 0.915. The most negative refractive gradient value observed at Ondo and Akure are of -46.48N-units/km and -45.64N-units/km respectively and the least effective earth radius factor, k value of 1.421 and 1.410 were observed at the station respectively. These results showed that the Ondo and Akure station were generally super-refractive. The Ondo station was however found to be slightly more super-refractive than the Akure station.

Seasonal surface refractivity patterns in the part of Lagos-Nigeria

The surface refractivity(SF) is essential in estimating the performance of terrestrial radio links. In the troposphere, there are lots of meteorological updraft and downdraft that influence the refractive index. In this study, we examine the seasonal variation of an emerging community in Lagos to design a reliable and efficient radio communication system based on the meteorological parameters.Thirty-nine years dataset between 1980-2018 was used to examine both the surface refractivity and the meteorological drivers that determine the SF patterns. It was observed that early wet season and late dry season were seen to have higher SF values, i.e., 262.03 N-unit and 262.07 N-unit respectively, while early dry and late wet had lower SF, i.e., 261.71 and 261.76 respectively. It is now possible to use the weather forecast to predict the likely SF pattern over the tropics.

Determination of areas for surface refractivity variation analysis over Quebec

For the aim of surface refractivity analysis, the overall territory of Quebec has been divided in a desired number of areas from North to South using clustering analysis. The meteorological data used in the analysis are collected from 50 stations located in various climatic regions over Quebec for the year 2013. It is found that the best input data for the identification of areas is the water vapour pressure. The results show that the surface refractivity increase from North to South and the maximum values for all areas are observed in July or in August. However, the variation of the surface refractivity remains in a relatively small interval in comparison to the variation observed in some tropical countries, particularly Nigeria.

Comparison of Surface Radio Refractivity Variability in the Northern and Southern Parts of Quebec, Canada

AbstractThirty‐nine years of archived meteorological data measured at two stations located in the northern and southern parts of Quebec, Canada are used to estimate the surface refractivity and its dry and wet components. The results of the comparison of the obtained estimates showed that for all months the values of the dry component are higher in the northern part, whereas the values of the wet component are higher in the southern part. Due to this, for several months of the year, the values of the surface refractivity are higher in the northern part and for the remaining months in the southern part. Moreover, in both parts, August is the month where the highest values of the surface refractivity were recorded. In this particular month, the slope of the surface refractivity trend in the northern part is several times higher than that in the southern part. The obtained results show that the performance of the used direct smoothing forecasting technique depends on the deviation between the values of N in the current year and the previous year.

The effect of halogen atoms at propanoate anion on thermo physical, vibrational spectroscopy, chemical reactivity, biological properties of morpholinium propionate Ionic Liquid

The morpholinium cation based ionic liquids are designed to evaluate the thermophysical, chemical reactivity, and biological activity. To estimate and design the bioactive ILs, propionate and trihalopropanoate were considered under theoretical study by Density Functional Theory (DFT). To make effect of halogens atom on anion, propionate, trifluro propionate, trichloro propionate, and tribromo propionate were taken for optimization. Some thermodynamic and thermophysical properties such as free energy, entropy, dipole moment, binding energy, nuclear energy, electronics energy, and heat of formation were calculated using DFT method and make a comparative effect for halogen atoms activity on anion. The free energy, binding energy, and heat of formation were the highest on morphonium trifluro propionate (IL02) and the second is on tribromo propionate (IL04). Quantitative Structure Activity Relationship (QSAR) like charge density, surface area grid, volume, LogP, polarizability, refractivity, and molecular mass were simulated and recorded, from which the biological activity was calculated. The chemical reactivity like HOMO, LUMO, HOMO-LUMO gap, ionization potential, hardness, softness electronegativity and electron affinity were calculated. The vibrational spectroscopy and UV spectroscopy data provide them the identification and characterization. To sum up, the thermophysical properties are highly affected by trifluro propionate anion then tribromo propionate, trichloro propionate, and propionate respectively. On the other hand, the chemical reactivity increases in order IL04, IL03, IL02, IL01 but biological activity is inversely changed.

Surface Refractivity Profile Construction on One-Fourth Kilometer Square Area for 1800 to 1900 Mhz Frequency

The meteorological parameters review the impact of refractivity on received signal strength for the one-fourth kilometre square area is confer for frequency 1800 to 1900 MHz. It is necessary to know the refractivity profile of radio frequencies in the surface layer of the atmosphere to predict the execution of a radio system for the consistent gradient of refractivity. The data were accumulated from the Atoll software and then an experimental setup was used on the same investigated area to compare both figures and find out the effect of refractivity on received signal strength. It has been analyzed that environmental parameter such as temperature, humidity, and height above the ground level play a major role in varying refractivity. The information recorded from the experimental arrangement shows that when refractivity is high (more particularly around the afternoon time and in the morning time, the humidity is high) the quality of the signal strength is degraded, while at that point when the refractivity is low (more particularly during the daytime when humidity is low due to high temperature) the quality of the signal strength is better. Refractivity and signal strength are inversely proportional to each other. It is essential to apply an accurate path loss prediction technique to demonstrate the need for a precise accounting of the refraction and ducting when planning future radio networks.

The thermo physical, HOMO, LUMO, Vibrational spectroscopy and QSAR study of morphonium formate and acetate Ionic Liquid Salts using computational method

Morphine is considered as the uncountable pain killer drug which is taken by both of mouth or injection. In this case, morpholinium ILs is the most applicable molecules due to liquid range so that the thermo-chemical, chemical reactivity and biological interaction of most expected morphonium formate and acetate ILs is considered under theoretical study by HyperChem 8.010 computer programming method. Some thermodynamic parameters such as free energy, entropy, dipole moment, binding energy, nuclear energy, electronics energy, heat of formation and QSAR properties of molecules like charge density, surface area grid, volume, LogP, polarizability, refractivity, molecular mass, and reactivity properties of molecule like HOMO, LUMO, HOMO-LUMO, ionization potential and electron affinity were determined using the HyperChem 8.0.10 programme. The morphonium formate is less biological active than morphonium acetate because LogP is 1.19 and -0.66 respectively. On the other hand, the HOMO LUMO gap in all transition level almost same that indicate similar chemical reactivity. The binding energy of both molecules is -3078.01 and -3351.25 kcal/mol respectively. The vibrational spectroscopy data provides them the identification and characterization.

Seasonal and diurnal trends of surface refractivity in a tropical environment using ground-based automatic weather stations

The seasonal and diurnal trends of surface refractivity were derived using International Telecommunication Union Radio assembly model (ITU-R P.453-13) in two locations of entirely different vegetation characteristics in Nigeria. Atmospheric refractivity is a function of temperature, pressure as well as humidity. These meteorological variables were applied to the model to compute the refractivity parameter. Atmospheric refraction or refractivity is a key component in radio wave propagation. Real-time measurement data from a network of ground-based automatic weather station (AWS) installed at 3 m height were used and the monthly trends of surface refractivity at both stations (Lagos and Anyigba) were derived; the trends showed a month-to-month variability signifying the dynamic nature of the Earth’s atmosphere. The monthly trends in both stations show high refractivity values in the rainy months and low refractivity values in the dry months. A drop in refractivity value was observed in Lagos in the month of August, due to the cessation in rainfall as a result of a phenomenon referred to as August break. The diurnal variations were also determined and results obtained showed that the lowest refractivity value in the dry season observed in Lagos is higher than the highest refractivity value in rainy season observed in Anyigba. This is attributed to the fact that Lagos is located along the coast of the South Atlantic Ocean, therefore, the monsoon has a direct influence on its atmosphere, while Anyigba is an inland station with a mixture of savannah vegetation. Overall, the diurnal variations show high values in the morning and evening hours and low values in the afternoon hours in both seasons in Anyigba, while in Lagos we observed a surprising result, such as a rise in refractivity value at pre-noon and a post-noon drop. This unacquainted observation is probably due to excessive precipitation in the area caused by the influence of massive emissions from the South Atlantic Ocean, these emissions are mainly a result of the trapped heat due to warming of surface water.

Estimation of Radio Horizon Distance Using Measured Meteorological Parameters over Some Selected Locations in Nigeria

In this study, results of the variation of maximum and minimum radio horizon distance derived from the computation of surface refractivity through measurement of temperature, relative humidity and pressureacrosssevenlocations((Akure (7.15°N, 5.12°E), Lagos (6.30°N, 3.20°E), Abuja (7.10°N, 9.25°E), Jos (9.50°N, 8.50°E), Makurdi (7.30°N,8.53°E), Port-Harcourt(4.20°N,7.00°E), and Nsukka (6.90°N,7.67°E)) in Nigeria are presented. Two years (Jan., 2011–Dec., 2012) archived data as provided by Tropospheric Data Acquisition Network (TRODAN) of the Centre for Atmospheric Research Anyigba, Kogi State were utilized for the study. Results showed that the values of surface refractivity (Ns) were low during the dry season months and high during the wet season months and also there was high value of NS at the coastal areas compared with the inland areas. It was also deduced that the mean value of NS for Abuja, Akure, Jos, Lagos, Markurdi, Nsukka and Port-Harcourt is 355, 362, 303, 391, 375, 361 and 399 N-units respectively. Results showed that the Radio Horizon Distance (RDH) values were generally low during the wet season months and high during the dry season months. The variability of radio horizon distance of transmitting antennas is higher in the Northern part of Nigeria than the southern part.

Variation of Surface Refractivity with Soil Permittivity and Leaf Wetness in a Tropical Location

Variation of Surface Refractivity with Soil Permittivity and Leaf Wetness in a Tropical Location