## 1 Introduction  
The movements of seafaring vessels are often obstructed by various navigational obstacles, which include objects that have fallen into the water from vessels, known as floating obstacles, as well as vessels that have sunk, run aground, or are in the process of sinking or grounding, referred to as sunken obstacles. Additionally, vessels that are at an imminent risk of sinking or grounding, or for which such outcomes are reasonably foreseeable, are also considered navigational obstacles. This category can be extended further to include objects located on sunken or grounded vessels, as well as parts of vessels that have detached from such sunken or grounded ships [1]. In this study, a collision is defined as the physical impact between a vessel and any of these navigational obstacles, posing significant threats to both navigation safety and environmental protection. Collision risk refers to the likelihood and potential severity of incidents where a vessel comes into physical contact with navigational obstacles. Suchcollisions can result in vessel damage, loss of human life, and subsequent environmental harm. Pollution risk pertains to the potential ecological hazards and environmental degradation that may arise from the leakage or release of hazardous substances into the marine environment. This pollution typically occurs as a secondary consequence of vessel accidents, especially following collisions with navigational obstacles, and is particularly significant when involving sunken or grounded vessels. The Korea Maritime Safety Tribunal reports that between 2017 and 2023, there were approximately 2439 entanglement accidents caused by navigational obstacles, averaging 348.4 accidents per year [2]. These accidents have resulted in significant loss of life, pollution, and economic losses. In 1985, Japan reported 23,848 accidents caused by fishing vessels colliding with navigational obstacles, blockage of cooling water intakes, or entangled propellers, which led to economic losses of approximately 4.4 billion yen [3]. A study conducted in the early 1990s in the coastal areas of Southeast Asia found, through field surveys and interviews, that discarded navigational obstacles became entangled in ship propellers, causing crew injuries and equipment damage [4]. In 1993, a 110-t passenger ferry capsized and sank in the waters off the west coast of South Korea when a navigational obstacle became entangled in the vessel's shaft and propeller, resulting in the deaths of 292 of the 362 passengers on board [5]. Another study found that adverse weather conditions, grounding, collisions, and entanglement in navigational obstacles were among the leading causes of fatalities in fishing boat crews [6]. As these obstacles hinder the safe operation of vessels and contribute to secondary accidents, their prompt removal is critical. To achieve this, it is necessary to assess the hazards posed by the obstacles, considering the magnitude of the risk of collision or pollution [7]. Existing research has assessed the risk of navigational obstacles from two main perspectives. The first is the collision risk, which refers to the risk posed by floating objects falling from ships (including sunken and grounded ships). The second is the pollution risk, which relates to the ecological hazards posed by the sunken and grounded ships. Regarding the first perspective, [PERSON] et al. [8] analyzed the link between climate change and navigational obstacles, whereas [PERSON] et al. [9] conducted a geographical and methodological study on navigational obstacles worldwide. Subsequent studies have focused on specific regions to examine the local conditions [10; 11; 12; 13; 14; 15]. [PERSON] et al. [16] and [PERSON] et al. [17] investigated the optical remote sensing of navigational obstacles, providing insights into various detection methodologies and approaches. [PERSON] et al. [18] calculated the economic losses resulting from warship accidents by investigating the frequency of accidents and the quantity of floating obstacles.