Validity of Reference Time Intervals in Noise Indicators for Aircraft Noise Policy in Vietnam

Many decibel-based noise indicators are used in noise policy to evaluate aircraft sound in the environment. Among those, day–evening–night-weighted sound pressure level ( Lden ), day–night-weighted sound pressure level ( Ldn ), and nighttime average sound pressure level ( Lnight ) are the most widely used. However, the designation of reference time intervals (e.g., day, evening, and night) differs depending on the country’s lifestyle and culture. A dataset—extracted from socio-acoustic surveys conducted in Vietnam (2005–2019)—was analyzed to investigate temporal patterns of the Vietnamese lifestyle and changes in Lden , Ldn , and Lnight when temporal interval segmentations in these indicators were adjusted. Traffic congestion hours, go-to-bed time, and wake-up time in southern Vietnam were approximately one hour later than those in northern and central Vietnam. Further, a small-scale and Internet-based questionnaire survey on Vietnamese life rhythms was conducted to examine Vietnamese people’s daily behaviors. These data were compared with the relevant data of Japanese individuals, extracted from the Survey on Time Use and Leisure Activities of Japan. Differences in sleeping times and mealtimes were found between Japanese and Vietnamese data. We suggest an appropriate reference time interval for aircraft noise policy in Vietnam, referring to the current national and international noise standards and regulations.