Investigation of anomalous propagation conditions in Central and West African stations using high-resolution GPS radioso
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Investigation of anomalous propagation conditions in Central and West African stations using high-resolution GPS radiosonde observations SAMUEL KAISSASSOU1,6,*, A LENOUO2, R S TANESSONG3,4, KAMSU TAMO3, A VONDOU3, W POKAM3,5 and J KANKO6 1
Department of Electrical and Telecommunication Engineering, National Advanced School of Engineering, Cameroon. University of Yaounde 1, P.O. Box 8390, Yaounde, 2 Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon. 3 Cameroon. LEMAP, Department of Physics, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde, 4 Faculty of Agronomy and Agricultural Sciences, School of Wood, Water and Natural Resources, University of Dschang, P.O. Box 786, Ebolowa, Cameroon. 5 Department of Physics, Higher Teacher’s Training College, University of Yaounde 1, P.O. Box 47, Cameroon. Yaounde, 6 Department of Meteorology, Climatology, Hydrology and Soil Sciences, National Advanced School of Engineering, University of Maroua, P.O. Box 46, Maroua, Cameroon. *Corresponding author. e-mail: [email protected] MS received 13 December 2019; revised 23 May 2020; accepted 10 July 2020
A comprehensive study on the anomalous propagation (AP) conditions occurring over the central and west African stations was made from 2 years (January 2005–December 2006) high-resolution data measured by GPS (Global Positioning System) radio survey observations. Through data quality control and diagnostic analysis, the probability of AP occurrence and characteristic quantities of the three typical anomalous propagation conditions were given. The sub-refraction, super-refraction and ducting cases were investigated statistically using the vertical proBle of modiBed refractivity gradient. Strong diurnal variation in the percentage occurrence of the AP had its peak during the wet months, while the dry months had the lowest values. From 0600 to 1800 local time (LT) at day (1800–0600 LT at night), the total percentage occurrence of super-refraction, sub-refraction and ducting were 82.5% (78.5%), 11% (15.5%) and 6.5% (6%), respectively. Besides statistical results, local meteorological conditions prevailing over central and west Africa have also been discussed. Keywords. Anomalous propagation; west-central Africa; duct; radiosonde.
1. Introduction Atmospheric refraction has a significant impact on the propagation of electromagnetic waves. The discovery of this eAect dates as far back as the emergence of the radio wave technology (Freehafer 1988). We noticed that anomalous atmospheric conditions for propagation occur generally below
the tropopause. The AP conditions can conduct to a propagation of nonstandard electromagnetic telecommunication systems such as RADARs, LIDARs and other wireless tools. It has been shown that, the electromagnetic waves are bending because of the spatial stratiBcation of the refractive index of air sometimes alter the wave direction and intensity.
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