A pulse synthesis technique for improving ionosonde resolution

Abstract

When an ionosonde sweeps through a given frequency range, the transmitted pulses may be regarded as the frequency components of a synthesized pulse. If measurements are made of the phase and amplitude of the ionospheric echoes observed over this frequency range they may be regarded as the frequency spectrum of the echo of the synthesized pulse. The range of the echo of the synthesized pulse is therefore given by the Fourier transform of the phase and amplitude measurements. Using a frequency range of 128 kHz gives a range quantization of 586 m so that echoes separated by about 1 km in range can be resolved. This paper discusses the principles of the method and presents examples of results obtained using the n/ethod.

A wideband technique for micro-ranging in OTHR

“…The dimension in f forms a frequency series whose Fourier transform can be used to estimate the power estimates in a micro-range domain [4,5,6] and this can be written as…”

On the accuracy and interpretation of Dynasonde virtual height measurements

“…By measuring the phase of the received echo as the frequency is varied over a small interval, the group height may be determined in a manner which thus corresponds approximately to its definition. The principle was first applied to the ionospheric problem by Appleton and Barnett [ 1925] and more recently has formed the basis of pulsed 'phase ionosondes' [Whitehead and Kantarizis, 1967;Hammer and Bourne, 1976;Devlin et al, 1977], and of vernier group path estimation in the Kinesonde [Paul et al, 1974]. It may be noted that the stationary-phase principle is involved implicitly and is then applied explicitly in pulsed experiments, first in attributing a phase measurement within the pulse to that of the continuous wave at f and then in comparing two such phase values at f and f + Af.…”

“…. Using a pulse synthesis method[Devlin et al, 1977], dependent on a sequence of frequencies, an accuracy of +30 m is obtained, provided only a simple echo is present. The Fourier method nicely facilitates resolution of nearby (---___ 1 km) overlapped echoes, but as they show [e.g.,Hammer and Bourne, 1976, Figure 6], it rather curiously suppresses any significaat influence of the precision with which the phase itself may be measured.…”