The role of ionospheric clutter in mid-latitude and arctic regions for assessment of HFSWR surveillance

The ionosphere is the region of the earth’s atmosphere in which gases are ionized by radiation such as ultraviolet light from the sun and cosmic rays from outer space. The unwanted radar echoes from the ionosphere are collectively called ionospheric clutter. This paper studies the arctic and mid-latitude ionospheric environment using ionosonde data and assesses High-Frequency Surface-Wave Radar (HFSWR) surveillance for surface vessels and low-altitute air targets. Although there are various types of ionospheric clutter, in this study we concentrate only on the sporadic-E (Es) ionospheric clutter. The evaluation is based on sporadic-E interference in the HFSWR signal. Our studies show that the Es is reasonably common in the arctic regions. The best time to perform HFSWR surveillance is between approximately 06:00-15:00 UT and 20:00-00:00 UT. During these hours, the number of days that sporadic-E interference occurs in a month and the range of frequencies reflected is minimized compared to other times of the day. Of the sites considered, Resolute Bay is the most favourable site for HFSWR surveillance in the summer since sporadic-E interference occurs least often, resulting in reduced signal interference. Similarly, Eureka is the preferred site during the winter months. In addition, the ionosphere at Eureka generally reflects the lowest range of maximum frequencies (∼ 4− 8MHz), again resulting in less clutter interference. In all the observations, polar cap sites Eureka and Resolute Bay yield results that are less prone to sporadic-E interference than the mid-latitude site Cambridge Bay. The general behaviour of the morphology of polar cap Es that is observed in this study is explained by gravity waves and metallic ions. DRDC Ottawa TR 2004-093 i