117 research outputs found
SIGNATURE OF ATMOSPHERIC DYNAMICS ON SURFACE OZONE VARIABILITY IN NIGERIA
An examination of analysis revealed that surface ozone concentration over Nigeria varied with direction of the local
trade winds, namely the Harmatan, and the Gulf of Guinea maritime trade winds. In DJF and MAM the period of the dry
dusty Harmatan seasons, surface ozone concentration in the southern Nigeria exceeded that of the north by 21DU and
24DU respectively. Whereas in the JJA and SON, the rainfall season, reversal was the case, the surface ozone
concentration in the northern Nigeria exceeded that of the south by 20DU and 15DU respectively. Maximum temporal
variation gradient of 20DU was also observed in MAM season while the minimum of 11DU occurred in JJA which is the
peak of the raining season
Study of Cloud Impact on Fixed Satellite Communication Link at Ku, Ka and V Bands in Nigeria
The study investigates the effect of clouds on fixed satellite communication link on earthspace
path in Nigeria for 0.01 to 10% unavailability of an average year. The input data (from August
2002 to July 2009) used for the study are base on recent meteorological data measured from space
by the Atmospheric Infrared Sounder satellites (AIRS). The International Telecommunication Union
Radio Propagation Recommendation (ITU-RP, 2009) procedure was used for the computation of cloud
attenuation statistics for each of the 37-stations for link to Nigeria Communication Satellite
(NigComsat-1), for both uplink and downlink frequencies. At Ku band (12/14 GHz), cloud fade is
between 0.2 to 0.55 dB, for Ka band (20/30 GHz), 0.6 to 2.4 dB and for V band (40/50 GHz) 2.0
to 6.0 dB. A Contour map of cloud attenuation at Ku, Ka and V-band for 0.01% unavailability, at
0.1 by 0.1 degree latitude and longitude for downlink and uplink to NigComsat-1 was developed.
The maps show consistently that impact of cloud is generally severe in the southern part of Nigeria
Cloud cover, cloud liquid water and cloud attenuation at Ka and V bands over equatorial climate
Cloud cover statistics and their diurnal variation have been obtained from in situ and satellite measurements for
three equatorial locations. Cloud liquid water content, 0 °C isotherm height and cloud attenuation have also been
obtained from radiosonde measurement using the so-called Salonen model at Kuala Lumpur (Malaysia). The
results show a strong seasonal variation of cloud cover and cloud liquid water content on the two monsoon
seasons. The Liquid Water Content (LWC) obtained from radiosonde and the Tropical Rainfall Measuring Mission
(TRMM) Microwave Imager (TMI) is higher during the Northeast Monsoon season, which corresponds to the
period of higher percentage cloud cover and high rainfall accumulation. The International Telecommunication
Union—Region (ITU-R) model underestimates the cumulative distribution of LWC values at the present station.
The relationship of the cloud attenuation, derived from the profiles of liquid water density and temperature within
the cloud, shows an underestimate by the data obtained from the ITU-R model. The cloud attenuation at Kuala
Lumpur is somewhat underestimated by the ITU-R model up to about 1.2 dB at Ka (30 GHz) and 3.4 dB at V (50
GHz) bands. The results of the specific attenuation can be used for the estimation of cloud attenuation at
microwave and millimetre wave over earth-space paths. The present data are important for planning and design of
satellite communications at Ka and V bands on the Earth–space path in the equatorial region
Some preliminary results of the fine structure profiles of radio refractivity near the surface at Ota, Southwest Nigeria
Some preliminary results are presented of the fine structure profiles of surface radio refractivity, Ns,
over Ota, Southwest Nigeria (6° 42'N, 3° 14'E) computed from in-situ, one minute interval
measurements of surface pressure, temperature and relative humidity. A wireless Davis Vantage
Pro2 Weather Station instrument installed at the Department of Physics, Covenant University, Ota in
April 2012, was used to obtain the measured variables. Hourly, daily and monthly average values of
surface water vapour density, dry, wet and total radio refractivity were obtained for the months of
April 2012 to March 2013. The distance to the radio horizon for a given transmitter height may be
deduced from the observation that Ns is well correlated with the gradient of refractivity over the first
kilometer above ground. Refractivity gradients utilized for the work were those obtained in a previous
work for Oshodi, a meteorological weather station near the coast and close to Ota
Tertiary Conformational Transition In Horse Haemoglobin Induced By Inositol Hexakisphosphate
The red blood cell of the domestic horse contains two haemoglobin types. The
two haemoglobins were separated on a column of carboxymethylcellulose. The
equilibrium constant, Kequ, for the reaction of 5,5'-dithiobis(2-nitrobenzoate) —
DTNB — with the CysF9[93]β sulfhydryl group of each haemoglobin was
determined at 25°C as a function of pH. The reactivity of CysF9[93]β is affected by
allosteric effectors such as the proton (H+) and inositol hexakisphosphate
(inositol-P6). Between pH 5.6 and 9.0 Kequ decreased by about two to four orders
of magnitude, demonstrating that H+ is a heterotropic allosteric effector of
haemoglobin with respect to its reaction with DTNB. Inositol-P6 also decreased
Kequ by about two to four orders of magnitude across the experimental pH range.
CysF9[93]β exists in two tertiary conformations, r and t, in dynamic equilibrium.
Krt, the equilibrium constant for the r t conformational transition, was
determined for each of the two horse haemoglobins from an analysis of the pH
dependence of Kequ. The calculations from the pH dependence of Kequ showed
that the pKa values of the ionisable groups coupled to the DTNB reaction vary
between 5.0 and 8.9. The equilibrium constants, Krt, for the r t tertiary
structure transition, were 0.143 ± 0.05 and 0.446 ± 0.22 for the fast and slow
stripped horse haemoglobins respectively. In the presence of inositol-P6, Krt for
the fast and slow were 2.219 ± 0.79 and 2.214 ± 0.83 respectively. The results
show that inositol-P6 increases the relative population of the t tertiary
conformation. So, it increases the affinity of CysF9[93]β by changing the relative
distribution of two protein conformations
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
STUDIES OF PROPAGATION IMPAIRMENTS FOR FIXED SATELLITE COMMUNICATION LINKS AT THE MICROWAVE FREQUENCIES IN NIGERIA
The study investigates the effect of propagation impairments such as rain, cloud, gases and tropospheric scintillation on fixed satellite communication link on earth-space path for frequencies between 10 and 50 GHz at Ku, Ka and V bands for 37 locations in Nigeria. Two standard elevation angles of 50, 550 as well as some elevation angles for links to recently launched Nigeria Communication Satellite, (NigComsat-1) were used in the computation of the propagation impairments for the 37 locations. Linearly and circularly polarized waves were considered. The International Telecommunication Union Radiowave Propagation models (ITU-RP) were used in the investigation of the propagation impairments. The study is divided into three parts; firstly, the collection and analysis of meteorological data from Tropical Rain Measurement Mission (TRMM) and Atmospheric Infrared Sounder (AIRS) satellites such as rain accumulation, profiles of temperature, pressure, and relative humidity, surface temperature and pressure were validated with the available ground data in Nigeria to form statistics on monthly and annual basis. These are reprocessed to derive propagation parameters, such as; one-minute rainfall rate, water vapour density, total cloud liquid water content, and integrated water vapour content. Secondly, an appropriate ITU-RP propagation model was selected for each of the propagation impairment and was used to calculate each attenuation distribution for a percentage of time unavailability. Thirdly, the attenuation due to all impairments were combined based on the annual cumulative distribution and percentage of time unavailability between 0.01 to 10%. The calculation of the propagation parameters are based on the measured mean annual data in each location for the period of 4 to 9 years. Propagation impairments were also computed at Ku, Ka and V bands for links to NigComsat-1 at 0.01 to 10% of time unavailability in an average year. The results of all impairment were compared on regional basis by using a colour chart for all the 37 locations in Nigeria. The results of the predicted propagation impairments are as follows: rain attenuation is highly severe in Abakaliki the South-East (SE) region followed, in descending order, by Yenagoa the South-South (SS), Ibadan South-West (SW), Jos Middle-Belt (MB), Damaturu North-East (NE), and Kastina North-West (NW) regions. Cloud attenuation is highly severe in Abakaliki the SE region followed, in descending order, by Jos (MB), Gombe (NE), Dutse (NW), Ikeja (SW), and Calabar (SS) regions. Gaseous attenuation is highly severe in Calabar the (SS regions) followed, in descending order, by Ikeja (SW), Abakaliki (SE), Abuja (MB), Dutse the (NE) and Kastina (NW) regions. Tropospheric scintillation is very high in Calabar (the SS region) followed, in descending order, by Ikeja (SW), Owerri (SE), Abuja (MB), Dutse (NE) and Kastina (NW) regions. Combined impairments due to multiple sources of simultaneously occurring atmospheric attenuation is highly severe in Abakaliki the (SE region) followed, in descending order, by Uyo (SS), Ikeja the (SW), Markudi (MB), Maiduguri (NE) and Katsina (NW) regions. For links to NigComsat-1 the combined impairments due to multiple sources of simultaneously occurring atmospheric attenuation is highly severe in Yenagoa the (SS region ) followed, in descending order, by Owerri (SE), Ibadan (SW), Jos (MB), Damaturu the (NE), and Katsina (NW) regions. Overall, Sokoto and Katsina appear as good locations to site fixed satellite earth stations (operating at Ku band and above) for deep space exploration as the results obtained showed consistently that the two locations are less affected by all propagation impairments investigated
Cloud attenuation studies of the six major climatic zones of Africa for Ka and V satellite system design
Cloud cover statistics, cloud base and top height, cloud temperature, frequency of precipitation, freezing height, total cloud liquid water content (TCLWC) and cloud attenuation data have been obtained for the six major climatic zones of Africa. The present results reveal a strong positive correlation between the monthly distribution of low cloud cover, cloud top height, cloud temperature, and frequency of precipitation in the six zones. The cumulative distribution of the TCLWC derived from radiosonde measurement in each climatic zone shows a departure from the
TCLWC recommended by the ITU Study Group 3 data, with an exceedance percentage difference of 32% to 90% occurring 0.01% to 10% of the time. The underestimation of the TCLWC is greatest in the tropical rain forest. A comparison of the cloud attenuation cumulative distribution in the Ka and V bands reveals that the International Telecommunication
Union – Region (ITU-R) is an intergovernmental organization
that develops rain model based on collected data around the world. This model underestimates the cloud attenuation in all of the six climatic zones by 2.0 dB and 4.7 dB for the arid Sahara desert, 1.3 dB and 3.0 dB in semi-arid North Africa, 1.3 dB and 1.5 dB in savannah North Africa, 2.0
dB and 3.6 dB in the tropical rain forest, 1.3 dB and 2.9 dB in savannah South Africa and 0.9 dB and 2.6 dB in semi-arid South Africa, respectively, at 30 and 50 GHz. Overall, the cloud attenuation in the tropical rain-forest zone is very high because of the high annual total cloud cover(98%), high annual frequency of precipitation (4.5), low annual clear sky amount (8%), high cloud depth (10,937 m), high 0°C isotherm height (4.7 km), high TCLWC (4.0 kg/m2 at 0.01%) and low seasonal cloud base height (356 m)
Mathematical Projections of Air Pollutants Effects over Niger Delta Region Using Remotely Sensed Satellite Data
Air pollution due gas–flaring is a major concern in the Niger-Delta region of Nigeria. The short and long term effect of the massive air pollution on the life form within the area requires urgent attention because of the health implication. This research examines the impact of air pollutants in Niger-Delta region using remotely sensed satellite data. The satellite data set was obtained from CALIPSO, MODIS and ARIS. A mathematical software (MATLAB) was used to analyse the results. For Sulphur dioxide (SO2), Uyo had the highest rate of pollution (0.67DU), then Yenegoa (0.66DU), Benin (0.64DU), Asaba (0.60DU), Port Harcourt (0.58DU), Calabar (0.55DU) respectively. For Carbon dioxide (CO2), Yenegoa was the most polluted with (382.01ppmv), Port Harcourt, Calabar and Uyo all had (381.99ppmv) then Benin (381.77ppmv) and Asaba (381.53ppmv) respectively. For Nitrogen dioxide (NO2), Port Harcourt had the highest mean value with (54.65mol/cm2), Asaba (51.05mol/cm2), Uyo (49.08mol/cm2),Calabar (47.84mol/cm2), Yenagoa (46.73mol/cm2), Benin (43.22mol/cm2) respectively. For Methane (CH4), the stations with the highest rate of pollution were Port Harcourt, Yenagoa and Uyo with (3.86E+19mol/cm2), Benin and Asaba had (3.8E+19mol/cm2) while Calabar (3.76E+19mol/cm2). Mathematical projections were made to capture the dilemma- people in this region might encounter in the nearest future
Storm-time variation of the horizontal and vertical components of the geomagnetic fields and rate of induction at different latitudes
The paper presents the hourly mean variation of horizontal (H) and vertical (Z) components of the geomagnetic field and the rate of induction DH/DZ at different latitudes during magnetic storm of 20 March 2001 and 1 October 2001. The results of the analysis revealed that at high latitude stations greater than 60�, the reduction in DH component was noticed after the noon time while other stations less
than 60� experienced reduction of H in the morning time during the geomagnetic storm. Large amplitude of DH and DZ were exhibited during the daytime over the equatorial zone, the amplitude decreases from mid latitudes to the dip equator during the nighttime. The daytime enhancement of DH at AAE, BAN and MBO suggest the presence of a strong eastward directed current which comes under the influence of electrojet. There were strong positive and negative correlations between ring current (DR) and horizontal component of the magnetic field DH. The effect of rate of induction is more significant at high latitudes than lower latitudes, during the geomagnetic storm. More enhancement in rate of induction occurred at nighttime than daytime. This result may be from other sources other than the ionosphere that is magnetospheric process significantly contributes toward the variation of induction.
Keywords: Geomagnetic field; Geomagnetic storm; Electromagnetic induction; Ring current; Coronal mass ejectio
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