# Inter-Story Drift Ratio Detection of High-Rise Buildings Based on Ambient Noise Recordings
## 1 Introduction
During the transmission process, ambient noise is modified by the medium that it passes through. Therefore, it is possible to analyze the changes in medium, that is, the building structure the ambient noise passes through, and indirectly measure IDRs by analyzing ambient noise recordings. Currently, many experiments using ambient noise provide many valuable ideas. For example, [PERSON] et al. [14] used a long-period signal in the broadband seismic data to detect the tilt change caused by the explosion of the Meakan-dake volcano in Hokkaido, Japan. They successfully understood the relevant characteristics of the propagation medium, such as the inclination of the formation, with the help of the observed ambient noise data. Their findings provide useful knowledge for the experiment of this paper, which intends to understand the inclination characteristics of building structures based on the ambient noise data. Additionally, [PERSON] and [PERSON] [15] analyzed an original set of seismic and meteorological data collected at a newly established PNSN site near the Pacific coast of the Olympic Peninsula in Washington. They found that the correlation of the ambient temperature and wind profiles with the amplitude of the seismic signals was remarkably close for periods greater than 30 s. This discovery provides a preliminary basis for the use of ambient noise to conduct wind-response-related experiments. [PERSON] et al. [16] introduced a system identification technique, which used seismic waves to conduct a structural diagnosis of building damage during earthquakes. This technique was applied to high-rise buildings in 2011 off the Pacific coast of the Tohoku earthquake and achieved a satisfactory result. Moreover, [PERSON] et al. [17] used ambient noise data to conduct a seismic diagnosis of buildings. Their experiments showed that noise measurements can efficiently provide reliable data for understanding the actual building behavior. All these studies provide a theoretical foundation to carry out research on buildings based on ambient noise. However, except for the research mentioned above, there have been few studies concerning measuring IDRs using ambient noise. When a building is free from external influence, the IDRs should be stably maintained at an initial value. However, if the building is under an external force, vertical components will be deformed, causing a change in the IDRs. Since ambient noise mainly exists as Rayleigh waves, if the ambient noise is modified by the vertical components that it passes through, the polarization characteristics of the Rayleigh waves separated from the ambient noise will change accordingly. Therefore, the polarization characteristics of the Rayleigh waves can be analyzed to understand the change in the ambient noise and finally understand the change in the vertical components that the ambient noise passed through, which can reflect the change in the drifts of the whole building and, of course, the change in the IDRs. Since this method is based on seismic waves, control points on the surface of the building, a large space for instruments, and a clear line of sight are all unnecessary. Therefore, the surrounding conditions, e.g., narrow spaces and objects blocking the eyesight, cannot hinder the monitoring. In addition, the survey with instruments can be conducted indoors, which protects the instruments from external disturbances, allowing for undisturbed accuracy, a longer lifespan, and lower maintenance requirements. Therefore, the monitoring can even be conducted in adverse weather conditions, e.g., excessive sunlight, heat, and great gates, which may affect or damage instruments such as total stations. Finally, since the ambient noise is a continuous seismic signal and can be collected at any time, the monitoring conditions for this method are relatively easier to meet, and monitoring can be performed in real time. The monitoring can be conducted in many application areas, even in urban areas and under adverse weather conditions with the help of ambient noise.