# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 2 Groundwork
### Existing Surveys about USVs  
The research starts with a critical review of key surveys related to USVs and also DM [22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41], most focusing only on USVs, where a few vaguely focus on USVs for DM. [PERSON] et al. [30] address research on environmental monitoring for USV. Their focus mostly on oceanic survey applications such as mapping/cleaning oil spills, weather/storm forecasting, and water sampling. The survey also lists challenges for real-world applications such as the system endurance for long-term missions and operation under extreme weather conditions. Obstacle avoidance (both above and underwater) is also pointed as a technological challenge. The lack of laws and regulations for the use of USV is a non-technological challenge which increases the investment risk, reducing the number of business opportunities and technology evolution. The authors included the results from interviews with specialists from different areas who are potential users or clients of the USV technology. [PERSON] et al. [42] studies search techniques for environmental monitoring where USVs are marginally mentioned. [PERSON] et al. [43] studies marsupial robotic teams for environment monitoring of water bodies. The authors claim marsupial robotic teams are especially tailored for water body monitoring, due to their versatility, where each robot can compensate the limitation of others. A survey on robots for environmental monitoring is presented by [PERSON] et al. [44] presents a span of robot applications for environmental monitoring where some USVs mentioned in the present work are mentioned--e.g., the Wave Glider USV. Overall, the current environment monitoring surveys do not seem to address USVs for DM usage in a specific way. [PERSON] and [PERSON] [45] review structure inspection using robots. There, a couple of works using USVs are mentioned, one using USVs in post-disaster cases. They conclude that current work on structure inspection often involves case specific needs for sensors and robot motion in challenging environments, with a trend toward non-destructive analysis. The two significant challenges for structure inspection using robots involve massive robot data manipulation and the need for increased autonomy for such robots. A more recent survey on unmanned systems for construction applications is described in [PERSON] et al. [41]. The authors highlight the relevant presence of USVs for structural inspection after disasters. Key DM works on structural inspection, in the scope of the present work, are mentioned. [PERSON] et al. present two sister papers, divided into parts A [37] & B [38] that focus on a clear classification of the levels of autonomy for USVs. Part A presents an approach which divides the autonomy problem of USVs into subsystems and corresponding scores: decision-making (1-10); action taking (1-10); exceptions handling (1-10); and cooperation subsystems. The authors introduce the cooperation subsystem as new information in comparison to the related work presented in the paper. Moreover, the authors argue that developed exception handling and cooperation subsystems are evidence of higher autonomy levels, stating that autonomous Guidance Navigation and Control (GNC) is common to almost all USVs. The authors offer a table with possible combinations of overall subsystem scores and global scores. However, the entire underlying rationale to the scoring system is not explicitly presented. Part B of the same autonomy survey classifies 60 USVs, developed over more than 20 years, according to the autonomy levels defined in part A. They evaluate the USVs and show that most are only able to perform autonomous path following--i.e., Level 3. They also present data showing that most prototypes correspond to scaled models, where the most common type of hulls used are single and double hull (catamaran), while the engine is typically electric with batteries--sometimes charged with solar panels.