Abstract
Doppler signatures of local multipath signals provide useful information for target altitude estimation in over-the-horizon radar surveillance. In this paper, we develop a method to improve the resolution of these multipath Doppler signatures and enable enhanced altitude estimation of aircraft target which maintains a constant altitude. Moreover, we consider the impact of ionospheric layer motion on target parameter estimation and show that target parameters can be estimated under both stationary as well as time-varying ionospheric layer conditions. In order to improve the resolution and estimation accuracy of the target parameters and ionosphere velocity with a significantly reduced complexity, we exploit a frequency focused transform to the de-chirped target signals for dimension reduction before applying a least absolute shrinkage and selection operator (LASSO)-based high-resolution spectrum estimation technique. The proposed strategy outperforms fractional Fourier transform and classical subspace-based frequency estimation methods with a much lower computational complexity. The effectiveness of the proposed approach is especially evident for challenging cases where the multipath signal components have spectrally close Doppler signatures. Simulation results confirm the effectiveness of the proposed method.
Highlights
Sky-wave over-the-horizon radar (OTHR) systems provide wide-area long-range surveillance far beyond the limit of the earth horizon [1]–[5]
In [10], the authors obtained a matched-field estimate of aircraft altitude by exploiting multiple OTHR dwells and the altitudedependent structure of the local multipath rays resulting from reflections local to the aircraft
This work was extended in [11] where the altitude and altitude rate were jointly estimated by investigating the effects of a constant altitude rate on the local multipath Doppler frequencies
Summary
Sky-wave over-the-horizon radar (OTHR) systems provide wide-area long-range surveillance far beyond the limit of the earth horizon [1]–[5]. The vertical target velocity was considered as the primary source that generates a detectable Doppler frequency difference between the multipath signals, which enables target altitude estimation. A target usually flies without changing its altitude during most of the flight time In this case, the Doppler frequencies are difficult to resolve using existing methods, making difficult the estimation of the target altitude based on Doppler difference between the local multipath signals. Analysis with a long CPI is often used to enhance the target signal and to mitigate range migration of maneuvering targets [24], [25], our goal is to achieve an improved resolution of local multipath signal components with very small Doppler frequency differences. · 1 and · 2 respectively denote the l1- and l2-norms of a vector, whereas diag(·) represents a diagonal matrix with the elements of a vector as the diagonal entries and E[·] shows the expectation operator
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