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Distribution of tropospheric amplitude scintillation on Ku Band earth-space link over a tropical station

Ashidi Ayodeji Gabriel, Ojo Joseph Sunday, Ajewole Moses Oludare, Adediji Adekunle Titus

Acta Geophysica

2022

Vol. 70, no 1

415--427

This work utilized three years of measured satellite radio beacons to examine the statistical and temporal characteristics of tropospheric scintillation intensity and amplitude on the earth-space link over Akure, Southwest Nigeria (7.17 °N, 5.18 °E, 358 m). The signal measurement from Eutelsat W4/W7 satellite was taken between January 2016 and December 2018. The instrument used is Tektronix Y400 NetTek spectrum analyzer at a sampling rate of 1-s, downlink frequency 12.254 GHz, and path elevation of 036°E. Analysis involving cumulative distribution and probability density functions was performed over seven sampling intervals for characterizing the distribution of scintillation phenomenon on an annual and sub-annual basis. The results show scintillation intensity (σχ) to be well approximated by lognormal, Gamma, and generalized extreme value (GEV) distributions, while scintillation amplitude (χ) was suitably described by Gaussian distribution model. Also, as the sampling interval increased, the accuracy of the distribution models decreased. Analysis of mean and standard deviation equally revealed that scintillation intensities measured over longer intervals are less variable. Finally, a two-part exponential model developed for scintillation intensity prediction performed well as indicated by a least R2 value of 0.97 just as highest sum of square error (SSE) and root-mean-square error (RMSE) values of 0.192 and 0.087, respectively, were returned for both the goodness of ft and goodness of validation tests.

Statistics of tropospheric amplitude scintillation over selected locations in tropical Nigeria

Ashidi Ayodeji Gabriel, Ojo Joseph Sunday, Kareem Afan Idowu, Ojo Olusola Samuel, Emmanuel Israel

Acta Geophysica

2021

Vol. 69, no. 3

947--957

Tropospheric scintillation depends signifcantly on any location’s prevailing weather condition, and its variation must be statistically analyzed to ensure accurate fade margin determination. This study examines the distribution of Ku-band amplitude scintillation across selected locations in tropical Nigeria. Eight years of daily averaged data of surface temperature and relative humidity were employed for computing scintillation intensity (σ) and amplitude (χ) using international telecommunications union recommended model across eighteen (18) stations, that are subdivided into four (4) regions and spread over tropical Nigeria. The data, spanning January 2010 to December 2017, were obtained from the archive of the European center for medium-range weather forecasts (ECMWF) with a resolution of 0.125° by 0.125°. Three (3) years of in-situ data of concurrently measured satellite radio beacons and primary radio-climatic parameters at Akure (7° 17′ N, 5° 18′ E, 358 m), South-west Nigeria, were employed for comparison and validation. Statistical analyses involving time series, probability density, and cumulative distribution functions were performed on the scintillation dataset annually. Results indicate that the magnitude of tropospheric amplitude scintillation varies across diferent locations; nevertheless, it exhibits a similar distribution pattern characterized by the generalized extreme value (GEV) probability density function (pdf). The study has shown the need to incorporate the scintillation component into the fade mitigation architecture of telecommunication systems in tropical Nigeria while considering its regional variability. Also, experimental validation of the observations raised in this study should be encouraged at all the locations for better prediction accuracy.