| Abstract: Low-frequency radio observations below 30 MHz is one of the unexplored regions of the radio spectrum and offer insights to a wide range of astrophysical phenomena, including planetary radio emissions, transient solar activity, and the dynamics of the interplanetary medium. Ground-based observations at these frequencies are blocked by ionospheric absorption and radio-frequency interference, thereby necessitating space-based measurements. This thesis tries to addresses both the scientific and technical challenges associated with detecting and interpreting low-frequency radio signals from space.
A central contribution of this work is the development of direction-of-arrival (DoA) and source localisation techniques for low-frequency space-based radio missions. The Snapshot Averaged Matrix Pencil (SAM) method is proposed to improve DoA and polarisation estimation using co-located tri-axial antenna configurations under low signal-to-noise ratios, limited snapshots, and multiple incoherent sources. The performance of the SAM-DoA algorithm is evaluated through electromagnetic simulations and scaled laboratory experiments, demonstrating improved estimation accuracy compared to conventional approaches. In addition, a machine-learning–based localisation framework is developed to enable faster, near–real-time inference for observation and resource constrained scenarios.
In the absence of routine space-based low-frequency observations, this thesis also investigates higher-frequency (327 MHz) observations using Interplanetary Scintillation (IPS) to study the interplanetary medium. IPS measurements capture the modulation of radio signals by solar wind density irregularities through Fresnel filtering effects, enabling remote probing of small-scale density fluctuations. Using long-term IPS datasets, this work examines the temporal evolution of solar wind microturbulence and density modulation, with results compared against in-situ measurements from spacecraft such as the Parker Solar Probe to study the radial evolution of plasma and magnetic field fluctuations in the inner heliosphere.
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