Investigation of Low Clouds Attenuation on Earth Space Path for some West-Africa Stations

The study investigate the contribution of low clouds, to signal fade rate, at Ka band in the satellite communication links on earth-space path(s) to NigComSat 2, from three tropical locations in West Africa. Extracted cloud cover statistical data such as average cloud amount, average base height, and frequency of occurrence, were used to obtain the monthly variations and seasonal variations for Lagos (6.55o, 3.35o), Bouake (7.73o, -5.07o) and Bamako (12.53o, -7.95o). Cloud attenuation statistics were computed for each of the three stations for their respective uplink and downlink. The uplink and downlink attenuation ranges between about 0.2 to 1.6 dB and 0.1 to 0.8 dB respectively for Lagos; for Bouake between 0.005 to 0.035 dB and 0.003 to 0.016 dB respectively; finally, for Bamako between about 0.2 to 2 dB and about 0.1 to 1 dB respectively. The stations downlink attenuation sets of values are generally about twice their corresponding uplink attenuation values

Seasonal Variation of Surface Radio Refractivity and Water Vapour Density for 48 Stations in Nigeria

The monthly and seasonal variation of surface refractivity and water vapour density were studied using thirtynine years meteorological data for forty-eight stations in Nigeria. The factors which influence the transmission of radio signals operating within the troposphere are water vapour and refractivity. The results show that the surface refractivity and water vapour density generally have higher values during the rainy season than dry season at all station studied. Furthermore the results show that the value of surface refractivity and water vapour density varies from about 263 N-units and 3 g/m3 in arid region of Nigeria (North East) to about 393 N-units and 23 g/m3 in the coastal area of Nigeria (South West) respectively. For optimal performance of terrestrial radio link across Nigeria it is required to account for the variability of these parameters for optimal systems design

Tropospheric Scintillation and its Impact on Earth- Space Satellite Communication in Nigeria

The study investigates the impact of tropospheric scintillation on fixed satellite communication link on earth-space path for frequencies between 10 and 50 GHz for 37 stations in Nigeria. Elevation angles of 5º, 55º which are typical look angles for links over the Atlantic Ocean region and Indian Ocean region, look angles to the Nigeria Communication Satellite was also considered. Meteorological climatic data retrieve from satellite such as; profiles of temperature, pressure, and relative humidity, were validated with the available ground data in Nigeria. These data were reprocessed to derive radio propagation input parameters, such as; water vapour density integrated water vapour content and radio refractivity. Secondly, the International Telecommunication Union Propagation model (ITU-P 618, 2009) was used to estimate tropospheric scintillation for time unavailability between 0.01 to 10% in an average year. The result shows that scintillation fade depth is between 4.0 to 19.0 dB and 0.2 to 1.3 dB at 5º and 55º elevation angles respectively. For links to NigComsat scintillation fade depth is between 0.05 to 1.26 dB for all the 37-locations. The results will help in designing, planning and quick integration and expansion of satellite telecommunication services in the six regions of Nigeria

Four Year Cloud Attenuation Study in a Tropical Station

The paper present four year results of Cloud attenuation measurements carried out at Covenant University, Ota, Nigeria. The links operate at frequency of 12.245 GHz and the cumulative distribution function for monthly Cloud attenuation have been estimated from the 4-year measured spectrum analyser data. The result of the visually measured Cloud and Satellite Cloud cover data are presented. The monthly variability shows that the highest cloud attenuation at the station occur in August, reaching a maximum of 3.96 dB for 0.01% of time; which corresponding to an average cloud cover of 89.86% and 75.36% by ground and satellite data respectively of which Nimbostratus (Ns) is average of 29.1%. The lowest cloud attenuation at the station occur in September, with a value of 2.5 dB for 0.01% of time; corresponding to an average cloud cover of 90.3% and 77.26% by ground and satellite data respectively, of which Nimbostratus (Ns) is average of 28.9%

ATMOSPHERIC GASES ATTENUATION IN WEST AFRICA

Atmospheric gases variations were evaluated to have major effect on Ku-band and above at 0.01 % unavailability of an average year on both uplink and down link. The International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676, 2012) data bank was used for the computation of gaseous attenuation for West Africa. Monthly and yearly mean of temperature, pressure and relative humidity were used as input parameters obtained from ITU-R study group 3 data base. The results presented on contour map show that total atmospheric absorption signal fade attenuation values at C, Ku, Ka and V bands is between 0.015 to 0.09 dB, 0.04 to 0.9 dB, 0.04 to 1.4 dB and 0.2 to 3.2 dB respectively for both uplink and downlink frequencies. Generally, consistent signal absorption due to Oxygen and water vapour are higher in the western region than southern part of West Africa

Analysis of non-rainy attenuation on earth-space path in Ota, Southwest Nigeria

Propagation effects due to atmospheric gases and tropospheric scintillation requires accurate modelling in the design of satellite communication systems. The combination of the two attenuation phenomena was observed within the period of August 2014 to December 2015. The result of this paper presents the on-going observation and data analysis of non-rainy attenuation on earth-space path in Ota, Southwest Nigeria. Results of clear-sky attenuation vary between 0 dBm and 4.85 dBm in January and February 2015 respectively. While a value of 4.23 dBm and 4.75 dBm were observed in October 2014 and 2015 respectively. The results will be useful for satellite communication system design and will be submitted to ITU-R Study group 3 Databank

Analysis and comparison of tropospheric scintillation prediction models at Covenant University

Knowledge of tropospheric scintillation is an important phenomenon in the design of satellite communication system. One year (January 2015-December 2015) scintillation data extracted from Astra 2E/2F/2G Satellite link measurement installed at Covenant University, Ota (Lat: 6.7 oN, Long: 3.23 oE) southwest Nigeria, at an elevation angle of 59.9o and a frequency of 12.245 GHz was used in this study. The analysis and the result were compared with some reputable scintillation prediction models so as to obtain best performance model for Ota region. From the result, it was discovered that the Karasawa model gives the lowest percentage error rate for both fade and enhancement of about 0.57% at 0.1 percentage of time and 6.93% at 0.01 percentage of time respectively and therefore was best found fit for the prediction of propagation impairment for the region. However, the model should be tested further using higher frequency band such as Ka and V bands to confirm the accuracy of the model. The information provided in this study will help in fade margin for antenna sizing and performance needed for satellite communication link in the region

Earth-Space Rain Attenuation Prediction: Its Impact at Ku, Ka and V-band Over Some Equatorial Stations

Attenuation due to rain predictive models have been used to calculate the impact of rainfall on satellite communication for six stations in Malaysia. The impact of rainfall is very important for designing a modern satellite system for heavy rainfall climatic regions like Malaysia, with large annual rainfall accumulation exceeding 3000 mm and rainfall rate exceeding 150 mm/h at Ku (12/14 GHz), Ka (20/30 GHz) and V (40/50 GHz) bands. The present result shows that the avalibility of link for 99.99% at the three bands for uplink and downlink to Malaysian Communication Satellite (MEASAT-3a) is not practicable. The results suggest link availability of 99.9% for Ku-uplink and Ka downlink, while 99% for Ka uplink and 99% for V band uplink and downlink due to high annual rainfall rates for most of the stations. The overall result shows that the impact of heavy rainfall on satellite communication will be more severe in the Eastern part than the Western of Malaysia

Freeze-thaw Resistance of an Alluvial Soil Stabilized with EcoSand and Asbestos-free Fiber Powder

Stabilization of poor soils subjected to large daily temperature variations requires careful selection of suitable stabilizer for improvement of such soils. This study investigated the freeze-thaw resistance of an alluvial soil stabilized with EcoSand and asbestos-free fiber powder (AFP). Physical and mechanical properties of the soil were determined. The soil sample was stabilized with 5 variants of equal mixtures of the EcoSand and AFP in proportions of 2, 4, 6, 8 and 10%, with 1% sodium silicate and 1% fly ash, by weight of the soil. UCS tests were conducted before and after three freeze-thaw cycles, while keeping the sample at 0ºC for 8 hours and later at 30ºC for 8 hours for each cycle. It was found that the 8% EcoSand + AFP with 1% sodium silicate and 1% fly ash content provided an optimized increase of the freeze-thaw resistance of the soil. The use of a mixture of EcoSand and AFP as a soil stabilizer for regions of the world experiencing large temperature variation has the potential to improve the resistance of sand to freezing and thawing

STUDY OF OXYGEN AND WATER VAPOUR ATTENUATION IN WEST AFRICA

Atmospheric gases such as Oxygen and water vapour attenuation has become a major concern on earth-space path at higher frequencies both uplink and down link at 0.01% unavailability of an average year. Moreover, few studies of non-rainy attenuation have been reported and the statistical analysis is still not clear most especially in West Africa. The meteorological data used in this study is obtained from Atmospheric Infrared Sounder (AIRS) satellites between 2002 and 2009, while the International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676) model is used to validate and estimate gaseous attenuation for West Africa. The results show on contour map that total atmospheric absorption signal fade attenuation values at C band is between 0.015 to 0.09 dB, Ku band is 0.04 to 0.9 dB, Ka band is 0.04 to 1.4 dB and V band is 0.2 to 3.2 dB respectively for both uplink and downlink frequencies. The results also show consistent increase in attenuation due to gases are higher in the western region than in the southern part of West Africa