# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 3 USVs for Natural Disasters
### Hurricanes  
Hurricanes or typhoons depending on the part of the Earth are tropical cyclones with wind speed higher than 74 mph (about 119 Km/h) that are created due several factors such as the sea-surface temperature, low tropospheric moisture, sea-level pressure etc. [78]. Hurricanes can have disastrous effects, including casualties and damage to buildings. Their effect on the sea can even lead to floods which can cause further problems to the affected region. Such disasters can be monitored from space, as well as by the forecasting of ocean behavior as they pass. In this sense, USVs can serve as a tool in the event of hurricanes, for weather forecasting, disaster response, and recovery missions, providing observations that are not presently available through manned platforms and satellites. In such extreme events, USVs may be used since it avoids the high risk to personnel operating in these dangerous and remote environments [65]. Below are described the current applications of USV for disasters caused by hurricanes. For the recovery phase of DM, [PERSON] et al. [61] investigate the cooperation of a USV with a rotary-wing UAV to detect damages to seawalls and piers. The USV named AEOS-1 is a catamarandesign with two polyethylene pontoons connected with a central T-shaped chassis that supports the instrumentation. The USV is designed to determine the extent and severity of the damage to the seawall and bridges. It is equipped with a camera to perform the inspection above the waterline, while an underwater acoustic camera detects structural damage below it. The UAV is a battery powered T-Rex miniature helicopter, which contains a miniature pan-and-tilt visible light camera to provide a bird's-eye view. This view allows the USV pilot to localize the vehicle for navigation relative to the structure, as well as identifying when GPS data is not available. Tests were performed in Marco Island after Hurricane Wilma (2005) to check the USV mobility to work underneath small docks, as well as how it operates around bridges in significant current. It was observed that the USV offered advantages over manned surface vehicles and UUVs since it is easier to deploy in disaster conditions, reaching places manned boats cannot reach. Furthermore, the bird's-eye view provided by the UAV can help with general safety and control by determining safe lanes for sea navigation. The cooperation of the USV with UAV is further applied in inspecting littoral environments for military and environmental applications [79]. For post-disaster bridge inspection after hurricane Ike, a category four storm that struck Galveston, Texas in 2008, [PERSON] et al. [62] and [PERSON] et al. [63; 64] use a combination of a Sea-RAI USV with two UUVs (YSI EcoMapper and a tethered VideoRay) to inspect the bridge footings by searching for scour and mapping the debris field around the bridge. The Sea-RAI USV is a platform based on two 6 ft catamaran hulls that carry an acoustic camera for sub-surface inspection and three video cameras for viewing above the waterline. Tests to assess the bridge substructure were performed in the Rollover Pass Bridge located in Galveston Bay, Texas. They found out that it is essential to map the debris first with USVs, and then use the mapping as input for UUV collision avoidance. GPS problems near the bridge piers were also reported during the inspection of affected structures. [PERSON] and [PERSON] [67] perform observations of the ocean's response to a tropical cyclone (hurricane) using a Wave Glider [80; 81]. The glider left from San Francisco, California, heading to Australia, came close to the category three Tropical Cyclone Freda (2012). The closest approximation of the glider with the tropical cyclone took place near New Caledonia, where the glider collected data of the evolution of the wind, the directional wave field, the sea-surface temperature, and the Stokes drift profile as Freda passed near the vehicle. Measures obtained by the glider agree with recent hurricane marine boundary layer studies [82].