Characteristic Investigation of Ionospheric Clutter of a Coastal High-Frequency Radar

Abstract

High frequency (HF) radar can overcome the limits caused by the curvature of the earth when its electromagnetic wave operated over high conductivity sea water. The HF radar spectrum is critical for large-area current mapping because of mechanism of Bragg resonance. Taiwan is located in an equatorial ionization anomaly area, in which the ionosphere causes strong interference on HF radar bands that may limit system performance. The unwanted radar echoes, called ionospheric clutter, are of various types with time-variable and range-specific properties, which require different suppression techniques. Additionally, these radar echoes could yield ionospheric information as a by-product of an HF radar system function. It is therefore critical to understand the regional characteristics of these ionospheric clutter phenomena. In this study, we first identify the ionospheric clutter boundaries for the Doppler spectrum range. Then, the distribution pattern of the spectra for identified areas was analyzed to determine the characteristics of ionospheric clutter and the extent to which the ionospheric clutter affects the system. The identified echoes at these ranges are presumed mainly to come from the E-layer, which may influence the system performance in those areas. The results show there exist a similarity of distribution in spectral density and DOAs which ionospheric clutter occurs. Hence, through aforementioned analysis can help distinguish the regions in which ionospheric clutter occurs and provide an opportunity for noise suppression strategies.