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This paper studies the Arctic ionospheric environment using ionosonde data and assesses the potential of high-frequency surface-wave radar (HFSWR) surveillance for surface vessels and low-altitute air targets. The evaluation is based on sporadic-E (Es) interference in the HFSWR signal. For surveillance problems up to 150 km, such as in the Northwest Passage through Canada's Arctic islands, the ionospheric Es clutter is the dominant clutter that may degrade the performance of the future HFSWR systems. The results show that Es occurs least often at Eureka in winter and at Resolute Bay in summer. Generally, Es occurs less often in the Arctic than at midlatitudes. Observations also suggest that the best time to perform HFSWR surveillance in the Arctic is between approximately 07:00-15:00 UT and 21:00-24:00 UT. During these hours, the number of days that Es interference occurs in a month and the range of frequencies (in the 4-7 MHz range) reflected are minimized compared to other times of the day. These observations suggest that the future HFSWR systems in the Northwest Passage should be designed to operate at higher radio frequencies. For example, a radio frequency higher than 7 MHz can be operated in order to minimize the Es interference during the hours of 07:00-15:00 UT and 21:00-24:00 UT. It is concluded that the Es interference in the HFSWR signal in the Arctic can be equal to or less than that at midlatitudes (e.g., off the east coast of Newfoundland). Furthermore, the overall performance of HFSWR will be better in the Arctic than at midlatitudes due to lower levels of interference of sea clutter and man-made-related noises combined with a much better level of HFSWR propagation.