Designing an urban-scale auditory alert system

The high tides that periodically flood Venice, locally known as acqua alta, are becoming more serious due to recent changes in the surrounding lagoon as well as atmospheric conditions. A special office of the Municipality of Venice, the Center for Tide Prediction and Warning (Centro Previsioni e Segnalazioni Maree-CPSM), provides a continuous tide forecast based on computational models as well as astronomical and meteorological data. When a significant high tide is expected, city authorities activate a network of electromechanical sirens for a few minutes, usually anticipating the tide peak by a few hours. The sirens, however, emit threatening wails reminiscent of air attack warnings, do not convey the gravity of the threat, and may not reach isolated or distant areas. Drawing on a wide range of computing technologies and methodologies, the authors present a new auditory alert system for high tides in Venice designed to replace the existing network of electromechanical sirens. As part of this research effort, our project team first analyzed the current alert system using off-the-shelf acoustic simulation software and a specially designed visualization tool. We then used a form of constraint logic programming to determine the optimal placement of loudspeakers in Venice, a complex task with many physical, economic, and social constraints. Next, we created the alert sounds for our demanding listening environment. The final phase of the project involved iteratively validating and redesigning the alert signals using human testing.