# The Cloud-to-Edge-to-IoT Continuum as an Enabler for Search and Rescue Operations
## 2 Related Work
### Sensor Networks and IoT for SAR Operations  
Sensor networks have seen broad application in areas such as healthcare, transportation, logistics, farming, and home automation, but even more in search and rescue operations. Sensors capture signals from the physical world and increase the information available to make decisions. The IoT as an extension of the sensor network includes any type of device and system such as vehicles, drones, machines, robots, human wearables or cameras with a unique identifier that can gather, exchange and process data without explicit human intervention. The use of IoT systems has been widely explored to extend the capabilities of SAR teams in disaster situations. Drone and UAV capabilities allow access to remote areas in less time, deploy communications systems, improve area visibility and transport light cargo if necessary [37]. Acoustic source location based on azimuth estimation and distance was proposed to estimate the victim's location [38; 39]. Image/video resources in drone-based systems are also used for automatic person detection by applying deep convolutional neural networks and image processing tools [40]. SARDO [41] is a drone-based location system that allows locating victims by locating mobile phones in the area without any modification to the mobile phones or infrastructure support. Collaborative multi-robots have a high impact on SAR operations. providing real-time mapping and monitoring of the area [42]. The multi-robot systems in SAR operation have been explored for urban [43], maritime [44] and wilderness [45] operational environments. Several types of robots are involved in multi-robot systems such as UAVs, unmanned surface vehicles (USVs), unmanned ground vehicles (UGVs) or unmanned underwater vehicles (UUVs). Serpentine robots are useful in narrow and complex spaces [46]. The snake robot proposed in [47] has a gripper module to remove small objects and a camera to move the eyes and look in all directions without moving the body. There are also more flexible and robust ground units with long-term autonomy and the capacity to carry aerial robots to extend the coverage area using an integrated vision system [48]. Maritime SAR operations are supported by UAVs, UUVs and USVs, where the UUV includes seafloorpressure sensors, hydrophones for tsunami detection and a sensor for measuring water conditions such as temperature, the concentration of different chemicals, depth, etc. [49]. Other fundamental elements in SAR operations are personal devices such as smartphones and wearables [23]. One of the constraints during a disaster is infrastructure failure where electricity is off or communications equipment is destroyed, damaged or saturated. COPE is a solution to exploit the multi-network feature of mobile devices to provide an alert messages delivery system based on smartphones [50]. COPE considers several energy levels to use the technologies available in smartphones nowadays (Bluetooth, Wi-Fi, cellular) for alert diffusion in the disaster area. Drones are used to collect emergency messages from smartphones and take the messages to areas where there is connectivity. This approach is explored in [51] to propose a collaborative data collection protocol that organizes wireless devices in multiple tiers by targeting fair energy consumption in the whole network, thereby extending the network lifetime. Wearables are also important in SAR operations because they can monitor the vital signs such as temperature, heart rate, respiration rate and blood pressure of the victims and rescuers [51]. This information can be collected by the rescuer or the robot-based system to determine the victim's status and provide a more convenient treatment depending on the conditions [52]. SAR dogs have also been involved in disaster events to locate victims even in limited vision and sound scenarios. A wearable computing system for SAR dogs is proposed in [53], where the dog uses a deep learning-assisted system in a wearable device.