# Flying Real-Time Network to Coordinate Disaster Relief Activities in Urban Areas +
## 1 Introduction  
Every year, natural and human-made disasters hit urban areas, producing dramatic losses in terms of human lives, damage to property, and psychological after-effects on the civil population. Examples of these extreme events are earthquakes, flash-floods, tsunamis, and landslides. Once the incident occurs, the relief efforts are typically focused on evacuating the civil population and conducting the search-and-rescue (SAR) process. This period lasts up to 72 h [1], and it is known as the golden relief time. During such a period, the SAR teams (which typically include firefighters and military personnel) scout the affected area, searching and evacuating as many people as possible. Given the short time period available to prepare and conduct these activities, the teams are deployed in the area as quickly as possible and without much planning, and then they are relocated according to the process needs. The incident commander (IC), who is in charge of the operations in the field, periodically evaluates the results of the relief activities, adjusts the SAR process plan, and assigns new goals to the teams. These activities require digital communication support between the teams, and also with the IC, since multimedia information should be shared among them (e.g., maps, pictures, and text/audio messages) in order to support decision-making processes at individual, team, and inter-team levels. Moreover, this communication support should be reliable and consider time constraints for message delivery (i.e., to have real-time characteristics) to allow the maintenance of activity coordination and thus improving the effectiveness of the response process. The literature in this area reports a long list of limitations for using mobile phones and Ultra High Frequency/Very High Frequency (UHF/VHF) radio systems to support these processes [2; 3; 4], and it also recognizes the need to advance the research towards providing real-time and stable digital communication in the field, as a way to reduce the impact of these events on the civil population [5; 6; 7; 8]. Examples of recent incidents where the response process was seriously limited by the communication support are the flood and landslides affecting Rio de Janeiro (Brazil) in 2011, where almost nine hundred people died [9], and also the wild fire of Yarnell Hill (USA) in 2013, where 19 firemen died trapped by the fire [10]. Several recent proposals report solutions that try to deal with this communication challenge, and most of them are based on opportunistic networks [6; 7; 8]. Although useful, they are limited to providing time-constrained message delivery, particularly when there is no direct communication between the teams that need to exchange information. This situation is almost the norm in disaster relief efforts. Trying to address such a communication problem, and given that the teams are reallocated frequently, in a previous work the authors proposed the utilization of special devices named _witness units_ (WUs) as intermediary network nodes [1; 11]. The devices act as information repositories, allowing first response teams and also civilians to retrieve and deliver information depending on their roles. For instance, civilians could access the maps of the area and evacuation routes, while first responders could also retrieve or update information about the status of the SAR process in the area and the location of the SAR teams. These WUs could be attached to street light poles (or other static resilient locations) and then connected to the disaster management center through a satellite network. WUs rely on standard Wi-Fi network interfaces and provide access points for the human users. Although useful, the use of these units only partially addresses the challenge of providing time-constrained message delivery in the field, since WUs were initially conceived as stationary devices.