3.2. Tweet Categories and Keywords during Different Disaster Phases
Emergency management typically consists of four phases: mitigation, preparedness, response, and recovery [1]. However, mitigation is not included in this work because it concerns the long-term measures or activities to prevent future disasters or minimize their effects. Examples include any action that prevents a disaster, reduces the chance of a disaster happening, or reduces the damaging effects of a disaster, e.g., building levies or elevating a building for a potential hurricane. Therefore, this paper focuses on the other three phases. We additionally identified tweets on impact, which is crucial for disaster response. During a disaster, only some of the messages posted by Twitter users contribute to situational awareness. Therefore, we first need to filter out the messages that are irrelevant to the disaster before mining useful information from the massive social media data for disaster analysis. We start by listing all hashtags from the collected data using a program we developed using Java, which can automatically extract the hashtags of the tweets and count the word frequency of each hashtag. Top hashtags related to Hurricane Sandy are then selected and provided as follows