# Intention Recognition for Multiple AUVs in a Collaborative Search Mission
## 3 Description of the Intent Recognition Problem in AUV Collaborative Search Mission
### AUV Intention Space  
The collaborative search mission typically involves a long duration and a wide spatial span. In such missions, a swarm of AUVs must collaborate intensively to complete missions such as target detection, tracking, and localization. We assume the entire process as follows:  
At the initial stage of the mission, the AUV swarm performs an area patrol mission aimed at covering a broad marine area and identifying potential targets. Due to the advantages of low power consumption and high concealment, passive sonar sensors are commonly used for detection in the AUV swarm. At the beginning of the mission, one AUV uses its passive sonar sensor to preliminarily detect a target. The AUV then shares the target information with the entire swarm to ensure that other AUVs receive the preliminary location data of the target. To enhance the accuracy of target localization and gather more information about the target, the AUV swarm needs to perform a collaborative localization and tracking mission. The entire mission is divided into two stages:  
1. Positioning Stage: To quickly approach the target and prepare for subsequent collaborative localization, the AUV swarm first needs to design a series of positioning points based on the target's location. The selection of these points takes into account providing better spatial positioning for collaborative detection and localization. Each AUV navigates from its initial position to the corresponding positioning point based on the collaborative localization requirements, preparing for continuous tracking and localization. During this stage, the AUV swarm needs to ensure that no AUV is left behind while reaching the positioning point as quickly as possible. 2. Tracking Stage: Once the AUV reaches the positioning points, the AUV adopts a bearing-only passive target tracking (BOT) method to continuously track and localize the target [43]. The BOT method enables the AUV swarm to adjust its headings and speeds based on the relative direction of the target, thereby improving localization accuracy and stability. In the entire collaborative search mission, in addition to the target position and bearing information, the AUV swarm also needs to share other relevant information in real time, such as detection errors. This allows for flexible strategy adjustment based on changes in the environment and the progress of the mission, ensuring the efficiency and robustness of the mission. To achieve this, we collected the aforementioned information during the decision-making cycle to determine the AUV's behavior in the next cycle, which is essentially the AUV's intent. Specifically, based on the two main phases of the mission, we have designed corresponding intent strategies. In the positioning phase, the AUV's intent can be classified into two types: communication priority and positioning priority. The communication priority intent emphasizes maintaining stable communication connections within the swarm, ensuring smooth information flow and preventing swarm disintegration due to communication interruptions. On the other hand, the positioning priority intent focuses on rapidly reaching the predetermined positioning points to ensure a quick response for the subsequent target tracking mission. In the tracking phase, the AUV swarm must minimize target detection errors to enhance localization accuracy. However, while the BOT method helps reduce detection errors, it overlooks the detection range, which may cause the AUV to exceed the detection radius. To address this limitation, the AUV's intent in this phase can be categorized into two types: detection priority and positioning priority. Under the detection priority intent, the AUV continues to track the target using the BOT method, further refining the target's localization accuracy. Once the distance to the target reaches a predefined threshold, the intent shifts to positioning priority. The positioning priority intent prioritizes rapidly approaching the target within a specified heading range to minimize the distance.