Analysis of direction‐of‐arrival aliasing for MF/HF Doppler‐sorted interferometry measurements of ionospheric drift

Abstract

Abstract. The determination of accurate direction of arrival (DOA) of echoes is paramount when performing Doppler-sorted interferometry (DSI) at MF/HF to measure the drift of ionospheric plasma. Important factors affecting the accuracy include inadequate signal-to-noise ratio (SNR) and coherency of ionospheric echoes. As the SNR deteriorates, there is an increase in the errors in the phases measured at the individual antennas of an array, and this leads to ambiguities in DOA equivalent to directional aliasing. In this paper we model this effect, the effects of Doppler-frequency aliasing, and the finite resolution of Doppler spectra. We thereby show the importance for vertical incident sounders of rejecting echoes with large off-vertical angles, and the choice of appropriate signal-processing parameters for the accurate estimation of ionospheric motions. As an example, we consider the situation for vertical incident ionosondes and show that a low SNR can produce spurious echoes at relatively large zenith angles, which can, however, be avoided or minimized by the suitable choice of operating parameters.

The effects of thunderstorm-generated atmospheric gravity waves on mid-latitude F-region drifts

“…Nevertheless, at high latitudes, the electric fields are often large and the observed Doppler shifts are dominated by E Â B/B 2 motion. Parkinson et al (1997), Smith et al (1998, and many others found good agreement between the velocities measured using ionosondes and the ionospheric convection patterns inferred from magnetometers, satellites, ISR, and SuperDARN radar. Parkinson et al (2001) and Kumar et al (2008) found that the average ionosonde velocities exhibited diurnal variations very similar to those measured by the Millstone Hill ISR (i.e., they were E Â B/B 2 drifts).…”

“…Basically, the Bundoora DPS-4 recorded ionograms by scanning between 2 and 12 MHz in steps of 100 kHz for less than 2 min, once every 10 min. During the intervening 8 min, Doppler sorted interferometry (DSI) (Parkinson et al, 1997) measurements were made using ordinary mode polarization at licensed fixed frequencies. The standard Digisonde Data Analysis (DDA) software was used to estimate the 3D drift velocity in a Cartesian reference frame.…”

Thunderstorm-associated responses in the vertical motion of the mid-latitude F-region ionosphere

“…During the intervening 8-min, Doppler sorted interferometery (DSI) (Parkinson et al, 1997) measurements were made using ordinary mode polarization at licensed fixed frequencies.…”

No‐search algorithm for direction of arrival estimation

“…The estimation of direction of arrival (DOA) is an important problem in radar, sonar, seismology and geophysics. DOA estimation is used to measure the drift in ionospheric plasma [ Parkinson et al , 1997] and to separate the source signals [ Hirari and Hayakawa , 1999]. Superresolution DOA estimation methods are popular due to their close to optimum use of the sensor signals and high resolution [ Tuncer et al , 2007].…”