XPRESS: X-Band Radar Place Recognition via Elliptical Scan Shaping

Abstract--X-band radar serves as the primary sensor on maritime vessels, however, its application in autonomous navigation has been limited due to low sensor resolution and insufficient information content. T o enable X-band radar-only autonomous navigation in maritime environments, this paper proposes a place recognition algorithm specifically tailored for X-band radar, incorporating an object density-based rule for efficient candidate selection and intentional degradation of radar detections to achieve robust retrieval performance. The proposed algorithm was evaluated on both public maritime radar datasets and our own collected dataset, and its performance was compared against state-of-the-art radar place recognition methods. An ablation study was conducted to assess the algorithm's performance sensitivity with respect to key parameters. ARL Y maritime autopilot systems were primarily designed for open-sea navigation, where the sparse and relatively unstructured environment allowed for sufficient autonomy despite intermittent sensor noise and signal fluctuations. As demonstrated by Han et al. [1] and Jang et al. [2], global positioning system (GPS) signals in maritime environments are frequently subject to degradation and interference, complicating real-time decision-making in safety-critical scenarios. Additionally, these environments are characterized by high traffic density and dynamic obstacles, which complicate situational awareness and hinder robust localization due to the frequent occlusion and unpredictability of surrounding agents. Furthermore, geographic features shift over time under the influence of tidal effects and constructions. These challenges render the estimation of vessel location based solely on fixed Electronic Navigational Chart (ENC) or satellite images unreliable and necessitate the incorporation of real-time place recognition (PR) with perception to account for dynamic environmental changes. Previous studies [3] have utilized camera and Light Detection and Ranging (LiDAR) sensors to perceive complex near-shore environments and enable autonomous sailing.