Radio Refractivity Research Articles

Investigating tropospheric radio refractivity variation with weather parameters in Kampala, Uganda: implications for communication systems

Investigating tropospheric radio refractivity variation with weather parameters in Kampala, Uganda: implications for communication systems

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.

Investigation of Tropospheric Radio Refractivity and other Relevant Parameters across Some Selected Locations in the Sahelian Region of Nigeria

The troposphere's internal processes are complex and exhibit nonlinear trends, which have a significant impact on the transmission and reception of high-quality signals worldwide. This study used measured monthly climatic data of temperature, relative humidity, and atmospheric pressure for Maiduguri and Sokoto from the National Aeronautic and Space Administration (NASA) over a forty-two-years period (1981 to 2022) to estimate the seasonal tropospheric radio refractivity and examine its variations with other meteorological parameters and refractive index. The refractivity gradiant, effective earth radius, and percentage contribution of the dry and wet term radio refractivity were also examined. According to the results, radio refractivity was found to be highest at the two locations during the rainy season and lowest during the dry season. In Maiduguri, during the rainy season and dry seasons are 361.4837 N-units in August, 272.4506 N-units in March while for Sokoto are 366.7093 N-units in August, 277.1162 N-units in February. For Maiduguri and Sokoto, the wet term (Nwet) contributes to the significant variation with 19.9753 % and 21.1831%, respectively, while the dry term (Ndry) contributes 80.0247 % and 78.8169 % to the total value of radio refractivity. The average refractivity gradients in the studied locations were found to be -42.3746 and -42.3928 N-units/km. Furthermore, it was discovered that Maiduguri and Sokoto had average effective earth radiuses (k-factors) of 1.3697 and 1.3698, respectively. These values implied super refraction propagation condition.

Autoregressive modelling of tropospheric radio refractivity over selected locations in tropical Nigeria using artificial neural network

Autoregressive modelling of tropospheric radio refractivity over selected locations in tropical Nigeria using artificial neural network

Performance Analysis of Tropospheric Radio Refractivity along with Refractivity Gradient and Effective Earth Radius in the Coastal Zone of Nigeria

Study’s Excerpt Analysis of the variability in tropospheric radio refractivity in Ogoja and Warri, Nigeria, was carried out by examining a 42-year dataset (1981-2022) of meteorological factors obtained from NASA. The contributions of dry and wet terms to radio refractivity variations were identified and key parameters such as refractivity gradients and the effective earth radius (k-factor) for both locations were evaluated. The radio wave propagation in the region is lowest during the dry season. Full Abstract Radio refractivity is the ratio of the velocity of radio waves in a specific medium to that in free space. Radio waves propagate according to variations in tropospheric radio refractive index. This study used the refractive index and other pertinent meteorological factors to calculate the radio refractivity of the seasonal troposphere and analyse its variability with monthly temperature, relative humidity, and atmospheric pressure measurements that were collected from the National Aeronautic and Space Administration (NASA) for Ogoja and Warri over a forty-two-year period (1981 to 2022). We looked at the proportion contributions of the dry and wet term radio refractivity, the refractivity gradient, and the effective earth radius. The outcome signified that in the two locations, radio refractivity values were lowest for the dry season and highest during the rainy season. For Ogoja and Warri, the highest and lowest average radio refractivity values recorded in the wet and dry seasons are, respectively, 382.9085 N-units in May, 346.4311 N-units in January, and 390.9042 N-units in April, 370.3009 N-units in January. For Ogoja and Warri, the wet term (Nwet) provides 31.5210 % and 30.1793%, respectively, to the primary variation in radio refractivity's overall value, whereas the dry term (Ndry) adds up to 69.8207 % and 68.4790 %. Mean refractivity gradients of -43.8326 and -44.5326 N-units/km were found in the subject areas under examination. Furthermore, it was discovered that the mean effective earth radius (k-factor) for Warri and Ogoja were 1.3959 and 1.3873, respectively. The values provided represent the propagation conditions of superrefraction.

Exploring vertical gradients of radio refractivity and their significance for radio wave propagation in Abuja, Jos and Makurdi of North-Central Nigeria

Vertical radio refractivity gradients are essential for monitoring propagation conditions when designing and planning terrestrial radio links for communications in the lower atmosphere. Average data gathered from meteorological factors such as temperature, pressure, and relative humidity was used from 1980 to 2020 n this study. This study focuses on the vertical gradient of radio refractivity within the lower atmospheric layer, investigating its influence on factors like signal propagation, route clearance, and line-of-sight communication. The analysis encompasses three cities - Abuja, Makurdi, and Jos. In Figure 2 monthly average changes in the refractivity gradient are presented for Abuja. In addition, the seasonal radio refractivity gradient shows mean values of -110.000N/km for Abuja which shows that the refractivity condition is Super-Refraction, -77.553N/km for Jos which shows that the refractivity condition is Normal-Refraction and -97.209N/km for Makurdi which shows that the refractivity condition is Normal-Refraction respectively. Higher gradient values, G1, G2, and G3 were observed during the dry season (December-February) which could be attributed to dry air and steeper refractivity gradients. In contrast, lower gradient values were observed during the wet season (June-October) due to increased atmospheric moisture. Similarly, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Jos displayed consistent fluctuations throughout the year. Similarly, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Jos displayed consistent fluctuations throughout the year. Notably, wetter months exhibit higher refractivity gradient values, while drier months show lower values. G2 consistently records the highest gradient values, and despite varying magnitudes, the trends remain consistent. Finally, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Makurdi indicate distinct fluctuations with the most negative values observed in November and December. The Dry Season witnesses relatively lower gradient values, while the Transition and Wet Seasons experience rising values, influenced by atmospheric shifts. The Higher negative values during the wet season suggest pronounced variations in the refractive index, affecting radio wave propagation. These findings emphasize the significance of refractivity gradient variations and their implications for radio wave behaviour particularly during different seasons.

Assessment of Tropospheric Radio Refractivity and its Variation with Climatic Variables in the Guinea Savannah Region of Nigeria

In studies involving terrestrial atmospheric electromagnetic propagation, such as point-to-point microwave communication, terrestrial radio, television radio, television broadcast, and mobile communication systems, radio refractivity—the bending of a radio signal as it propagates through media—is crucial. In this study, the seasonal tropospheric radio refractivity was estimated and its variations with other meteorological parameters and refractive index were investigated using the measured monthly climatic data of atmospheric pressure, relative humidity, and temperature obtained from the National Aeronautic and Space Administration (NASA) for Makurdi and Ibadan during the period of forty-two (42) years (1981 to 2022). The refractivity gradiant, effective earth radius, and percentage contribution of the dry and wet term radio refractivity were examined. The findings indicated that for the two locations, high values of radio refractivity were observed during the rainy season and low values during the dry season. The maximum and minimum average values of radio refractivity observed for Makurdi and Ibadan during the rainy and dry seasons are, respectively, 380.0641 N-units in the month of May, 331.9776 N-units in January, and 379.9479 N-units in the month of May, 352.2143 N-units in January. The dry term (Ndry) contributes 70.8764 % and 69.4504 % to the total value of radio refractivity, while the wet term (Nwet) contributes to the major variation with 29.1236 % and 30.5496 % for Makurdi and Ibadan, respectively. The study areas under investigation yielded average refractivity gradients of -43.8583 and -43.1480 N-units/km. Additionally, the average effective earth radius (k – factor) for Makurdi and Ibadan was found to be 1.3876 and 1.3790, respectively. These values align with the conditions of super refraction propagation.

INVESTIGATION OF TROPOSPHERIC RADIO REFRACTIVITY AND OTHER RELEVANT PARAMETERS USING METEOROLOGICAL VARIABLES OVER BAUCHI, NIGERIA

The National Aeronautics and Space Administration (NASA) archives were used in this work to obtain the measured monthly average daily temperature, relative humidity, and atmospheric pressure over a 41-years period (1981–2021) for Bauchi (latitude , longitude ) to calculate the monthly tropospheric radio refractivity. The site is located in Nigeria's midland climate zone. We also looked into the variation with other factors, the refractivity gradient, and the percentage contribution of the dry term (Ndry) and wet term (Nwet) radio refractivity. The results showed that during the rainy and dry seasons, respectively, the months of August and February had the highest and lowest average values of radio refractivity, measuring 355.032 (N-units) and 273.255 (N-units), respectively. This suggests that radio refractivity is higher during the rainy season than it is during the dry season. The wet term contributes to the significant fluctuation in radio refractivity values, while the dry term makes up 77.60 % of the total value. The average refractivity gradient estimate was found to be – 40.854 N – units/km suggesting super-refraction propagation for Bauchi indicating that electromagnetic waves are often bent downward towards the earth when the super refraction condition occurs.

Assessment of Tropospheric Radio Refractivity and Its Variation with Climatic Variables Over Zaria, Nigeria

To achieve optimal performances, radio link/system planning and design must take radio refractivity estimation very seriously. This study utilizes measured average daily temperature, relative humidity, and atmospheric pressure for forty-one-year period (1981–2021) obtained from the National Aeronautics and Space Administration (NASA) archives for Zaria (latitude 11.100 N, longitude 7.680 E) strategically located in Nigeria’s midland climate zone to calculate the monthly tropospheric radio refractivity and look into how it varies with other meteorological factors and radio refractive index. The percentage of the contribution of dry term (Ndry) and wet term (Nwet) to radio refractivity and refractivity gradient were investigated. The findings indicated that radio refractivity was higher during the rainy season (August) and lower’during the dry season (February), with a maximum mean value of 350.8733 N-units and a minimum mean value of 284.1975 N-units, respectively, found in those months. The wet term contributes to the significant fluctuation of the radio refractivity, whereas the dry term makes up 76.03% of the total value. The gradient of mean refractivity estimated for Zaria was found to be – 43.8709 N – units/km indicating super-refraction propagation condition.

The Investigation of Surface Radio Refractivity Over Lokoja, Kogi State Nigeria

This research investigated the variation of Surface Radio Refractivity and its propagation effects on radio signals over Lokoja, Kogi State, Nigeria. The study used six years (2015-2020) of satellite data on temperature, pressure, relative humidity and rainfall at the surface (12 km) above ground level. The data retrieved were used to determine the monthly, seasonal, and annual Surface Radio Refractivity value for Lokoja Kogi State. Results show that high Surface Radio Refractivity values were recorded generally during the wet season months compared to the dry season months in all Six years (2015-2020). The average values of Surface Radio Refractivity 307.7407 (N-units) and 323.4674 (N-units) were obtained during the dry and wet season, respectively. The minimum surface radio refractivity values of 280.7245, 284.6583, 308.0021, 285.2304, 304.2521 and 285.9139 (N-units) were recorded for the years 2015, 2016, 2017, 2018, 2019, and 2020 respectively. On the other hand, the highest values of 330.8153, 331.8133, 330.3580, 330.9278, 332.4704, and 331.1316 (N-units) were recorded for the years 2015, 2016, 2017, 2018, 2019 and 2020, respectively. Higher values of Surface Radio Refractivity were recorded generally during the wet season compared to the dry season months in all years (2015-2020) in Lokoja, Kogi State. This implies higher radio signal attenuation due to Ns during the wet season compared to the dry season. The correlation coefficients between Surface Radio Refractivity Ns and temperature are -0.41, -0.51, -0.49, -0.48, -0.46, -0.50, pressure 0.07, -0.15, -0.28, -0.08, -0.11, -0.26, relative humidity 0.89, 0.84, 0.75, 0.84, 0.77, 0.83, and the amount of rainfall 0.76, 0.64, 0.73, 0.58, 0.51, 0.65 respectively in the year 2015, 2016, 2017, 2018, 2019, 2020. The overall findings of the work will be useful to radio engineers for properly planning a reliable power budget for terrestrial radio communication over Lokoja, Kogi State.

Harnessing the Radio Frequency Power Level of Cellular Terminals for Weather Parameter Sensing

In light of recent extreme weather events, it is imperative to explore innovative methodologies for promptly and accurately measuring various meteorological parameters. The high spatial and temporal variability in precipitation often surpasses the resolution capabilities of traditional rain gauge measurements and satellite estimation algorithms. Therefore, exploring alternative methods to capture this variability is crucial. Research on the correlation between signal attenuation and precipitation could offer valuable insights into these alternative approaches. This study investigates (a) the feasibility of the classification of precipitation rate using signal power measurements in cellular terminals and (b) the impact of atmospheric humidity as well as other meteorological parameters on the signal. Specifically, signal power data were collected remotely through a specialized Android application designed for this research. During the time of analysis, the power data were processed alongside meteorological parameters obtained from the meteorological station of the Physics Department at the University of Ioannina gathered over one semester. Having in mind the radio refractivity of the air as a fascinating concept affecting the way radio waves travel through the atmosphere, the processed results revealed a correlation with signal attenuation, while a correlation between the latter and absolute humidity was also observed. Moreover, a precipitation rate classification was attained with an overall accuracy exceeding 88%.

Behaviour of ultra-short radio waves refraction in the lower atmospheric layer of the coastal zone of the Bolshye Yeravninsky Lakes

The propagation of ultra-short waves is influenced by weather conditions. Meteorological inhomogeneities in the atmosphere cause refraction of the ultra-short wave beam. Measurements of meteorological parameters at h1 = 2 and h2 = 10 m have been carried out using an atmospheric-soil measuring complex installed in the coastal zone of Big Eravninsky Lakes at the Forest-Steppe permafrostecological station “Eravninsky” in Buryatia. There is a strong daily variability of the refractive gradient, and the refractive gradient values scatter ranges from –0.820 to +0.307 N-units In the lower ten-meter layer of the troposphere. It is discovered that in summer, meteorological conditions favorable for the superrefraction appearance are observed in this area.

Evaluation of the Vertical Profile of Radio Refractivity and its Gradients in a Tropical Atmosphere

This paper evaluates radio refractivity and its gradients over Abuja, the Federal Capital Territory of Nigeria, using five years upper air meteorological data obtained from the Nigerian Meteorological Agency (NiMet). From the results obtained, radio refractivity was observed to decrease with increasing altitude. Also, higher refractivity values were observed in wet season, while lower values were recorded in dry season. An average refractivity value of 326 N-Units was obtained at 1 km altitude, while average refractivity gradient values of -34 N-Units/km and -40 N-Units/km were recorded for the dry and wet season months respectively. A total average value of -38 N-Units/km for refractivity gradient was obtained for the five-year study period, thus making the atmospheric condition over Abuja to be sub-refractive. The effective earth radius factor (k-factor) computed for the location was also observed to be higher in the wet season months than the dry season months. An average k-factor value of 1.32 was obtained for the study period.

Radio Refractivity Impact on Signal Strength of Mobile Communication

This research investigated radio refractivity impact on signal strength of mobile communication. The mobile communication signal strengths of two popular networks in Nigeria, 9Mobile and MTN, were considered. In the 2100 MHz-3 G band, 9Mobile transmits in the downlink spectrum of 2130.00–2140.00 MHz, while MTN transmits in the downlink spectrum of 2110.00–2120.00 MHz. Also, 9Mobile transmits in the downlink spectrum of 791–821 MHz in the 800 MHz band and 1805–1880 MHz in the 1800 MHz, while MTN transmits in the downlink spectrums of 2620–2690 MHz in the 2600 MHz band; all in the 4 G band. Using the instrument of a mobile station in each station (location) in some selected cities in southern Nigeria, the signal strengths were measured. A cell signal monitor (version 5.1.1) mobile application installed in an Android (transceiver) device (having two SIM slots) constituted the mobile station. To achieve high accuracy, there was a restriction in measuring transmission from specific cells. Hourly measurement of signal strengths was carried out and instantaneously corresponding weather parameters were recorded. Weather parameters for this investigation; atmospheric temperature and pressure; and relative humidity were excerpted online from the Nigeria Meteorological Agency (NIMET) hourly weather report for the various cities where the stations were situated. The hourly radio refractivity was computed using the 2015 International Telecommunication Union–Radio-communication sector (ITU-R) recommended model. Overall, the results indicate that there was no established linear relationship between signal strength and radio refractivity since the overall average R value is 0.0123691 and the overall average standard deviation of R values is 0.1112165. The inconsistencies in the linear relationships obtained from different locations and cells could be due to variations in topography, antenna properties, seasonal variations, wind and position, and distance of the receiver from the transmitter.

Evaluation of Refractivity Gradient and k-factor within the Lower Troposphere of Maiduguri and Enugu under Two Climatic Zones in Nigeria

Estimation of radio refractivity is important in the planning and design of terrestrial radio communication links for the availability and accessibility of strong networks and signals. This paper investigates the refractivity gradient, effective earth radius factor (k), and the geo-climatic factor K in the first 1km of the troposphere of two selected stations (Maiduguri and Enugu) under different climatic zones in Nigeria. The indirect method of measuring radio refractivity was employed in this study to take measurements over the two selected stations. Vertical profile values of pressure (hPa), Temperature (°C), and Relative humidity (%) within the first 1 km were extracted from MERRA MAIMCPASM V5.20 database profile obtained from a satellite sounding instrument by NASA in the United States. MatLab programming language was used to evaluate the refractivity gradient, k-factor, and geo-climatic factor using the equations recommended by ITU. The results showed that Enugu was predominantly sub-refractive due to the tropical savannah climate while Maiduguri encountered both sub-refractive and normal refractive conditions due to the hot semi-arid climate, and unstable and extreme weather conditions in the region.

Understanding the impact of assimilating FORMOSAT‐7/COSMIC‐2 radio occultation refractivity on tropical cyclone genesis: Observing system simulation experiments using Hurricane Gordon (2006) as a case study

AbstractStudies have shown that assimilating the radio occultation (RO) observations, including those from the FORMOSAT‐3/COSMIC (constellation observing systems for meteorology, ionosphere, and climate) (FS3‐C), provides positive impacts on tropical cyclone (TC) forecasts. The FS3‐C's successor, the FORMOSAT‐7/COSMIC‐2 (FS7‐C2), provides denser spatial data coverage over the Tropics and Subtropics, where severe weather systems often occur. This study investigates the impact of FS7‐C2 refractivity profiles on the prediction of TC genesis. A quick observing system simulation experiment is conducted for the period when Hurricanes Helene and Gordon (2006) occurred over the North Atlantic Ocean using a regional ensemble data assimilation system. Though assimilating FS3‐C or FS7‐C2 ROs successfully reproduces Helene's development, assimilating FS7‐C2 ROs better captures the genesis and development of Gordon with abundant moisture and vorticity in Gordon's core region, providing conditions favorable for the development of deep convection. A minimum area‐mean total precipitable water vapor of 54 mm, as well as the existence of mid‐level cyclonic vorticity (e.g., 500 hPa), at the storm core region in the initial condition is required for forecasting Gordon's genesis. Also, the assimilation of FS7‐C2 ROs in our experiments reduces the 500 hPa geopotential error by 22% and improves probabilistic quantitative precipitation forecast compared with assimilating FS3‐C ROs. Two sensitivity tests are conducted to evaluate the impact of low‐level negatively biased FS7‐C2 RO profiles and the removal of FS7‐C2 data below 3 km on Gordon's genesis. The former test does not degrade Gordon's genesis forecast skills due to a dipole error correlation between the background ROs and the moisture field over an observed RO profile near Gordon. The latter test does degrade Gordon's forecast skills but is still better than the assimilation of FS3‐C ROs since the features of low‐level moisture and mid‐level vorticity are preserved to some extent.

Estimation of some Radio Propagation Parameters using Measurements of Surface Meteorological Variables in Ede, Southwest Nigeria

A data acquisition system that utilised the open-source Arduino platform was developed to take real-time ground measurements of primary radio climatological variables of pressure, temperature, and relative humidity at Ede, a tropical station in southwest Nigeria (7.7349^{o} N, 4.4439^{o} E). Surface radio refractivity was deduced from these variables and used to estimate refractivity gradients at 100 m and 1000 m heights from the exponential reference atmosphere model for terrestrial propagation. Secondary radio propagation parameters such as refractivity gradients, the effective-earth-radius-factor, k, and geoclimatic factor, K, essential parameters for quick application in the planning and design of line-of-sight radio link systems, were also deduced. Data acquired from the device were compared to those obtained from the Re-Analyses (ERA-5) satellite database of the European Centre for Medium-Range Weather Forecast (ECMWF) 2020/2021. Aside from logging data on a micro secure digital (SD) card, measurements were displayed on a liquid crystal display (LCD). The peripheral Arduino-compatible meteorological sensors were connected to the analog inputs of the ATMega328 in the Arduino independent development environment (IDE), and the unit was powered by a 12 V battery charged by a 50-watt solar module. Results showed that slightly higher values of the ERA-5 data characterise the dry months from November to March, while the wet months displayed higher values of the Arduino-derived measured data. The accuracies of the data collected were compared using Mean Percentage Error (MPE) performance indicator. The interpretation is that the mean difference between the Arduino inferred measurements and the ERA-5 data is less than 10%, which is an indication of the measurement accuracy.

Determination of radio wave propagation conditions in the atmosphere of Hanoi using the radiosonde data of balloons

This article uses radiosonde data of balloons in Hanoi to determine the radio refractive index and the conditions of radio wave propagation in the atmosphere. The research results in the three years 2016–2018 show the highest average radio refractivity, the maximum radio refractivity difference between the years. Secondly, radiosonde data are used to estimate the accuracy of global ITU models, and showed that the radio refractivity’s difference between the ITU-R model and the observed value by radiosonde method is up to 60 N-units at a lower altitude of atmosphere. In conclusion, it is recommended to use radiosonde data instead of the ITU model (where available) to obtain refractive index when studying wave propagation conditions in the atmosphere.

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.

ИССЛЕДОВАНИЕ ИЗМЕНЧИВОСТИ РАДИОРЕФРАКЦИИ СВЧ-ИЗЛУЧЕНИЯ В ТРОПОСФЕРЕ АРКТИЧЕСКОГО РЕГИОНА РОССИЙСКОЙ ФЕДЕРАЦИИ

Using the dataset of aerological sounding carried out at five Arctic stations, the profiles of the main characteristics that determine radio refraction of the weather radar sounding beam were calculated and analyzed. These characteristics are the refractive index and its gradient. Seasonal parameters of the exponential model of tropospheric refraction were obtained over Naryan-Mar, Salekhard, Norilsk, Tiksi, and Chokurdakh stations. The frequency of occurrence of various refraction types with account of seasonal variability was investigated. The obtained data can be used for software processing of atmospheric radar sounding data over the Arctic region.