# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 2 Groundwork
### Existing Surveys about USVs
The most advanced systems rely on obstacle detection and avoidance using cameras or Light Detection And Ranging (LiDAR). They conclude that the level of autonomy of USVs is rising and that research on USV cooperation is increasing. [PERSON] and [PERSON] [46] discuss mission planning for AMVs, covering some of the work on DM involving USVsrelated to SAR and structure inspection. The following end-user requirements for mission planning are highlighted: survivability; reliability; quality of mission outcomes; and utility. There is plenty of work related to USVs focused on control, most likely due to the harsh conditions which may happen due to waves, currents and winds a vessel may face [39]. The groundwork of Fossen [22] surveys non-linear control of ships. [PERSON] et al. [26] present a review of non-linear tracking and setpoint control for USVs. [PERSON] et al. [32] present a survey on motion control for USVs and UUVs considering different types of propellers. [PERSON] et al. [33] review course keeping control systems for USVs. [PERSON] et al. [47] reviews the use fuzzy logic for the control of USVs and UUVs. [PERSON] et al. [36] present a brief survey focusing on tactical control algorithms for USV path tracking. [PERSON] et al. [35] give a detailed review on USVs, focusing on GNC, but also addressing design & typical sensor characteristics, comparisons with other platforms, such as satellites and UUVs, hybrid cooperation between USVs and other unmanned systems, as well as current applications in a broad sense. [PERSON] et al. [39] describe a review of marine mechatronics focusing on USVs, UUVs, and other marine devices. Regarding USVs, the paper presents three main challenges: the non-linearity of the system; velocity measurement errors; and localization noise--probably the latter is a consequence of the former two. The article performs an overview of techniques involving Dynamic Positioning (DP) control, path tracking, trajectory tracking, and modeling of system uncertainties. [PERSON] et al. [29] focus on the review of existing USV guidance and motion planning methodologies which could be used to implement naval obstacle avoidance rules based on the International Regulations for Preventing Collisions at Sea (COLision REGulations at Sea--COLREGS). According to the authors, the current research problems for USV obstacle avoidance include the ability to work in the presence of environmental disturbances (e.g., waves, currents, wind, etc.) and to operate in real time. Problems also include research involving multiple USVs in formation. More recently, [PERSON] et al. [40] perform a survey on formation control focusing on unmanned vehicles, also including USVs. USV designs and prototypes are surveyed by [PERSON] [23] and later, very briefly, by [PERSON] [31]. [PERSON] [25] reviews 15 years of USV development, mentioning some reference works. The author reinforces the need for research involving USVs and the COLREGS, without direct references to USVs for disasters. [PERSON] [24] surveys USVs with focus on applications. Prototypes, which are mostly military, for SAR missions are briefly mentioned--i.e., the Rescue Dolphin (1995), Seal, and the Search and Rescue Portable, Air-Launchable (SARPAL) USVs. [PERSON] [28] presents applications and an overview of different USVs where SAR USVs are also mentioned--e.g., the Sterling USV. The survey reveals a tendency, in the last decade, to design small-sized USVs. This trend is seen as a critical change in USV research, mostly restricted to the military domain at the time, which eventually enabled USV research in the civil domain as we see today. [PERSON] et al. [48] discuss the numerous projects involving marine robotics, where some DM-related projects are summarized. Regarding DM-related works, [PERSON] [49] briefly reviews a decade of rescue robots, up to 2012, when the presence of USVs for DM was small. Similarly, [PERSON] [19] analyzes the viability of SAR robots, but the use of USVs are briefly discussed. [PERSON] et al.