T. V. Omotosho

Cloud-Cover Statistics and Cloud Attenuation at Ka- and V-Bands for Satellite Systems Design in Tropical Wet Climate

Cloud-cover statistics, low cloud base height, frequency of precipitation, 0°C isothermal height, and integrated cloud liquid water and cloud attenuation have been obtained for the tropical rain forest climatic zone of Africa. The cumulative distribution of integrated cloud liquid water content shows a departure from the ITU-R model. A comparison of cloud attenuation at Ka-and V-bands show that the ITU-R model underestimates the attenuation up to about 1.7 and 2.3 dB at 30 and 50 GHz, respectively.

A simple resistive load I-V curve tracer for monitoring photovoltaic module characteristics

Current-Voltage (I-V) curve tracers are useful implements for solar Photovoltaic (PV) research and manufacturing, particularly when wishing to ascertain module yield viz-a-viz solar irradiation falling on the module in different climatic conditions. This paper presents a simple affordable and easy to fabricate instrument for tracing I-V characteristics of a PV module. It comprises of rapidly varying resistive loads centred on power resistors connected to relays and controlled by an electronic circuitry. The circuit consists of a 555 astable oscillator that is used to send clock pulses to the clock terminal of a 4017 decade counter which in turn produces a sequence of pulses. Each progression of pulse advances by one bit to sequentially turn on individual relays via driver transistors. The speed of the count is made variable from the frequency determining network of the 555 oscillator. The I-V characteristics of the module are thus measured by the sequential selection of the relays which are each connected to a selected load resistor to determine the operating point on the I-V curve. The currents and voltages are then recorded simultaneously with irradiance from a pyranometer, by a datalogger to which the instruments are connected. The circuit was tested on two monocrystalline modules to compare the effect of Harmattan dust on PV output yield.

Dataset of surface refractivity in Southeast, Nigeria

In this data article, analysis of surface refractivity and water vapour density in Southeast, Nigeria were reported. The meteorological data were collected for the period of 39 years between 1973 and 2012 from National Oceanic and Atmospheric Administration (NOAA) Climatology Centre. Five locations considered in the study area includes: Enugu, Onitsha, Abakaliki, Aba and Ihiala. Descriptive statistics were used to show an increase in monthly variation of refractivity of about 299.8 N units at Enugu in January to peak value of about 385.81 N units at Abakaliki in May. Hence, the seasonal variation for South East indicate maximum value within the months of March to May in the rainy season and a minimum value around December to February which is the dry season. The results from this data will help engineers in proper design and planning of radiowave propagation and satellite communication systems in southeastern, Nigeria.

Total atmospheric absorption of fixed satellite communication signal due to oxygen and water vapor in Nigeria

Total atmospheric absorption values due to oxygen and water vapor on terrestrial and Earth-space paths at frequencies between 1 GHz and 50 GHz were evaluated for 1% unavailability of an average year at two elevation angles of 5° and 55°, which are typical for terrestrial and Earth-space links, respectively. Practical links to the Nigerian communication satellite (NigComsat1) uplink/downlink in the Ku (12/14 GHz), Ka (20/30 GHz), and V (40/50 GHz) bands for 1% unavailability of an average year were also investigated. The basic input climatic data used included monthly and yearly mean meteorological parameters for each station, such as surface and vertical profiles of pressure, temperature, and relative humidity, obtained from the Atmospheric Infrared Sounder (AIRS) instrument on NASAs Aqua spacecraft for seven years (2002 to 2009). The International Telecommunication Union Radio Propagation Recommendation (2009) procedure was used for the computation of gaseous attenuation for each of the 37 stations in Nigeria. The results obtained at various elevation angles (of 44° to 55°) for Earth-space links to NigComsat-1 showed that in the absence of rain, 99% availability was possible at Ku, Ka, and V bands for uplink and downlink at all of the 37 stations in Nigeria, as the gaseous attenuation values obtained were between 0.05 dB to 4.81 dB. For low elevation angles of 5°(terrestrial link) at V band, 99% availability was not practical, as atmospheric loss was between 15.30 dB to 17.62 dB in Nigeria. The results consistently showed that gaseous attenuation was very high at six stations across Nigeria; Calabar (South-South regions), followed, in descending order, by the Ikeja (South-West), Abakaliki (South-East), Abuja (Middle-Belt), Dutse (North-East), and Kastina (North-West) regions. The present results of gaseous attenuation will be very useful for satellite communication-system design engineers across the six regions in Nigeria.

Dataset of surface water vapour density in southeast, Nigeria

In this data article, analysis of surface water vapour density in Southeast, Nigeria were reported. The meteorological data were obtained for the period of 39 years between 1973 and 2012 from National Oceanic and Atmospheric Administration (NOAA) Climatology Centre. Five stations considered in the research area includes: Enugu, Onitsha, Abakaliki, Aba and Ihiala. Descriptive statistics were used to show an increase in monthly variation of surface water vapour density (SWVD) minimum value of about 7.15 g/m3 at Enugu in January to maximum value of about 21.96 g/m3 at Onitsha in April. Hence, the seasonal variation for South East indicate peak value within the months of March to May in the rainy season and a lower value around December to February which is the dry season. The results from this data will help engineers in proper design and planning of radiowave propagation and satellite communication systems in southeastern, Nigeria.

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.

Performance and Evaluation of Eight Cloud Models on Earth—Space Path for a Tropical Station

This is a review of eight cloud models and a statistical analysis of radiosonde data and cloud cover data in order to obtain attenuation distributions and cloud cover statistics for a tropical location, Ota (6.7oN, 3.23oE) at a computed elevation angle of 56.18o to an Astra 2B satellite located at 31.5oE. Cloud models are mathematical algorithms scientifically designed to predict cloud attenuation impact on propagating electromagnetic signals in the troposphere, using data on each model’s required parameters such as temperature, pressure, cloud height, cloud occurrence and liquid water content of clouds. The station’s cloud cover statistics, namely average amount of cloud, cloud base height, and frequency of occurrence were computed from extracted cloud data to obtain their monthly and seasonal variations. The results show that minimum attenuation values were predicted by both the Gun and East and the ITU-R models, while the Liebe and Slobin models predicted consistently maximum values of attenuation for all the cloud models tested. Cloud attenuation statistics computed for each of the models show that at 0.01% exceedance probability, the averages of the predicted cloud attenuation for uplink and downlink at Ota, ranges between 0.45 dB and 0.44 dB for Ku, 1.85 dB and 0.75 dB for Ka, and 3.50 dB and 2.50 dB for V bands. At 0.1% the averages are between 0.30 dB and 0.27 dB, 0.95 dB and 0.47 dB, 2.45 dB and 1.51 dB at Ku, ka and V bands for both uplink and downlink respectively.

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.

Cloud attenuation modelling for satellite network links performance improvement

All local climate zones need to develop relevant climatic models such as cloud attenuation model which can serve as correlative resources to global satellites applications and a means of determining local link margins for satellite networks services in localities. Effects of suspended water droplets (SWD) and suspended ice crystals (SIC) which constitute clouds are major concern in the design and successful operation of satellite communication system at frequencies above 3GHz because the hydrometeors reduces the services availability critically as frequency increases. This work is a review of cloud attenuation modelling, using as a case study typical research work been carried out, to develop cloud attenuation model for tropical Ota (6.7oN, 3.23oE), southwest Nigeria. Cloud attenuation modelling for a station involve obtaining clouds parametric system equation from their numerical representations, taking into consideration the climatic initial and boundary conditions. The numerical representations are collected climatological and radiometric data, derived from well-designed experiments in which cloud parameters measurements are carried out using radiances change measured by satellites and visual observations from the surface station(s) on land and ships in the ocean. The on-going research work begin with the study of performance of eight foundation cloud models at the station, through their detailed evaluation from cloud cover data and radiosonde data analysis, followed by analysis of collected over three years spectrum analyser signal attenuation data. Then modelling analysis of the station spectrum analyser data collected at computed elevation angle 56.18o to Astra 2(E-G) Satellite located at 28.2oE, which involve comparisons of the derived attenuation distribution curves, both of the spectrum analyser data and those of the existing cloud models for the station, with the derived attenuation distribution curves of output data generated by each run session of the station simulation equation program. The general representation of the station cloud attenuation model is stated and the specific model equation is been worked on.

Comparison between experimental and satellite temperature datasets in Covenant University

This article contains the ground and satellite meteorological data sets of clear-sky temperature events for five years (2012–2016) in Covenant University, Ota, Ogun State, Nigeria. The satellite data were obtained from Atmospheric Infrared Sounder (AIRS) while the ground data information were acquired from Davis weather station data logger-vantage pro2. These data were acquired from propagation study that used same location (Lat: 6.67°N and Long: 3.23°E) for both satellite data and radiometer directed along the same path by providing information about the temperature. The data sets were assessed and evaluated by means of a descriptive statistics. There was perfect agreement between the two data. The peak temperature events occurs between the months of November and April for the five years of observation for both Ota and AIRS Satellite. The data from this article can be used for further studies on non-rainy attenuation effect in the study area.