Aperture‐Synthesis Radar Imaging With Compressive Sensing for Ionospheric Research

• Published in: Radio science 2019-06, Vol.54 (6), p.503-516
• Main Authors: Hysell, D. L., Sharma, P., Urco, M., Milla, M. A.
• Format: Article
• Language: English
• Subjects: Algorithms; Apertures; Backscattering; Beamforming; Clutter; coherent scatter; compressive sensing; Detection; Dynamic range; Entropy; imaging; inverse methods; Ionosphere; ionospheric irregularities; Iterative methods; Mathematical analysis; Matrix algebra; Matrix methods; Noise reduction; Optimization; Plasma density; Radar; Radar imaging; Radar targets; Shrinkage; Synthesis; Wavelet
• ISSN: 0048-6604; 1944-799X
• DOI: 10.1029/2019RS006805

Inverse methods involving compressive sensing are tested in the application of two‐dimensional aperture‐synthesis imaging of radar backscatter from field‐aligned plasma density irregularities in the ionosphere. We consider basis pursuit denoising, implemented with the fast iterative shrinkage thresholding algorithm, and orthogonal matching pursuit (OMP) with a wavelet basis in the evaluation. These methods are compared with two more conventional optimization methods rooted in entropy maximization (MaxENT) and adaptive beamforming (linearly constrained minimum variance or often “Capon's Method.”) Synthetic data corresponding to an extended ionospheric radar target are considered. We find that MaxENT outperforms the other methods in terms of its ability to recover imagery of an extended target with broad dynamic range. Fast iterative shrinkage thresholding algorithm performs reasonably well but does not reproduce the full dynamic range of the target. It is also the most computationally expensive of the methods tested. OMP is very fast computationally but prone to a high degree of clutter in this application. We also point out that the formulation of MaxENT used here is very similar to OMP in some respects, the difference being that the former reconstructs the logarithm of the image rather than the image itself from basis vectors extracted from the observation matrix. MaxENT could in that regard be considered a form of compressive sensing. Key Points Compressive sensing inverse methods have been applied to aperture synthesis radar imaging of ionospheric plasma density irregularities Performance of basis pursuit denoisint (BPDN) and orthogonal matching pursuit (OMP) are generally inferior to that of the maximum‐entropy method (MaxENT) Computational speed of OMP is attractive and prompts research into more suitable function library