Equatorial F-region plasma drift measurements and observations using Doppler interferometry at Parit Raja

Abstract

The measurements of ionospheric drift and convection using the digital doppler interferometer at the Wireless and Radio Science centre (Waras) at UTHM, is used to provide high temporal and spatial resolution measurements of the dynamics of the ionosphere at the Parit Raja station in Batu Pahat, Johor. These measurements include Doppler shifts, angles of arrival, as well as group ranges from the significant numbers of ionospheric echo sources simultaneously at the same time. By employing Doppler inteferometry reception technique at four receivers connected to four spaced antennas nearby, it is possible to identify the three dimensional locations of various scattering points reflected back from the ionosphere as a result of vertically-incident HF waves transmitted at frequencies of 5.9MHz, 7MHz, and 8MHz. These three frequencies cover the local F-layers since the critical frequencies lie between 6MHz and 8MHz for this local station. The technique of Doppler interferometry treats signal returns from the ionospheric F-region as reflections from individual scatterers. Spectral analysis is performed on the complex voltages generated from the four receivers’ in-phase (I) and quadrature-phase (Q) detectors to produce Doppler frequency functions. Both spectral phase functions and amplitude functions are generated using Fast Fourier Transform or FFT by the receivers from the Doppler frequency functions. This will then result in a skymap display containing echo coordinates, ranges and Doppler shifts. By further processing of the echoes, drift velocities which can be deduced by a least-squares fitting algorithm can be found. The behaviour of the plasma movements under certain variations of the geomagnetic and solar activities can also be studied so as to be able to estimate the influence of geomagnetic storms and equatorial electrojets on the ionosphere, which is vital for navigation, surveillance and telecommunications.