Ionospheric clutter models for high frequency surface wave radar

Chen, Shuyan (2017) Ionospheric clutter models for high frequency surface wave radar. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

High frequency surface wave radar (HFSWR), operating at frequencies between 3 and 30 MHz, has long been employed as an important ocean remote sensing device. These high frequency (HF) radars can provide accurate and real-time information for sea state monitoring and hard-target detection, which is greatly beneficial for planning and executing oceanographic projects, search and rescue events, and other commercial marine activities. Ideally, in HFSWR operation, the radio waves may be coupled with ocean waves and propagate along the curvature of the ocean surface with ranges well beyond 200 km. However, during transmission, a portion of the radar radiation may travel upwards to the ionosphere from the transmitting antenna. This may be partially reflected back to the receiving antennas directly (vertical propagation) or via the ocean surface (mixed-path propagation). This ionospheric clutter may significantly impact the performance of HFSWR. Furthermore, the high intensity and random behaviour of the ionospheric spectral contamination of radar echoes make the suppression of this kind of clutter challenging. In this thesis, comprehensive theoretical models of the ionospheric clutter are investigated. The physical influences of the ionospheric electron density on HF radar Doppler spectra are taken into account in the ionospheric reflection coefficient. Next, based on previous modeling involving the scattering of HF electromagnetic radiation from the ocean surface and a first-order mixed-path propagation theory, the second-order received electric field for mixed-path propagation is derived for a monostatic radar configuration. This is done by considering the reflection from the ionosphere and scattering on the ocean surface with second-order sea waves. Then, the field integrals are taken to the time domain, with the source field being that of a vertically polarized pulsed dipole antenna. Subsequently, the second-order received power model is developed by assuming that the ocean surface and the ionosphere may be modeled as stochastic processes. The ionospheric clutter model including a pulsed radar source is further investigated for the case of vertical propagation for a monostatic configuration and mixed-path propagation for a bistatic configuration. Next, a theoreticalmixed-path propagationmodel is developed by involving a frequencymodulated continuous waveform (FMCW) radar source. In order to investigate the power spectrum of the resulting ionospheric clutter and its relative intensity to that of the first-order ocean clutter, the normalized ionospheric clutter power is simulated. Numerical simulation results are provided to indicate the performance of the ionospheric clutter under a variety of radar operating parameters, ionospheric conditions and sea states.

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