Verification of ionospheric perturbation induced L-band frequency scintillation using HF/VHF bands over the African equatorial and low latitude region, Ethiopia

Abstract

This study verifies the ionospheric perturbation induced scintillation in L-band range of frequency using HF/VHF bands over the African equatorial and low latitude regions with a focus over Ethiopia. The study was conducted using the SCINDA, ionosonde and beacon receivers installed at different regions in Ethiopia. In the F-layer height (hmF2), a reverse decrease of foF2 in combination with significant background TEC reaching up to 10 TECU prior to the depletion was observed during the evening hours. This creates conducive environment for the generation of ionospheric irregularities that can be manifested by Rate of TEC Index (ROTI) and scintillation index (S4) enhancement. Vertical Perturbation Index (PI) was computed using vertically integrated ion density profiles to verify the irregularities from independent source and found that HF inferred PI can potentially identify the existence of ion density irregularity and further verify L-band frequency scintillation. On the other hand, simultaneous observation of S4 in VHF and UHF bands showed excellent agreement despite VHF scintillates more than UHF due the difference of transmitting frequency bands. Besides, Power spectrum density (PSD) was computed using the FFT algorithm for S4 data measured while receiving L-band and VHF signals for selected PRNs observed by the receivers. The calculated slope (m) and the strength of irregularity (beta) using the power spectral law has enabled us to produce a model which better fits the observed spectrum. It shows beta higher for VHF and lower for UHF; while, PSD modelling better matches for UHF than VHF spectral observation.