Washita Battlefield National Historic Site: Acoustic monitoring report

Job, Jacob

In 2017, the Natural Sounds and Night Skies Division (NSNSD) received a request to collect baseline acoustical data at Washita Battlefield National Historic Site (WABA). Between October and December 2017, a single acoustical monitoring station was deployed within the park. The goal of the study was to establish a baseline soundscape inventory of the park, especially with regards to noise emanating from a nearby highway, airport, and local industry. This inventory will be used to establish indicators and thresholds of soundscape quality. This will support the park and NSNSD in developing a comprehensive approach to protecting the acoustic environment through soundscape management planning. Additionally, results of this study will help the park identify major sources of noise within the park, as well as provide a baseline understanding of the acoustical environment as a whole for use in potential future comparative studies. In this deployment, sound pressure level (SPL) was measured continuously every second by a calibrated sound level meter. Other equipment included an anemometer to collect wind speed and a digital audio recorder collecting continuous recordings to document sound sources. In this document, “sound pressure level” refers to broadband (12.5 Hz–20 kHz), A-weighted, 1-second time averaged sound level (LAeq, 1s), and hereafter referred to as “sound level.” Sound levels are measured on a logarithmic scale relative to the reference sound pressure for atmospheric sources, 20 µPa. The logarithmic scale is a useful way to express the wide range of sound pressures perceived by the human ear. Sound levels are reported in decibels (dB). A-weighting is applied to sound levels in order to account for the response of the human ear (Harris, 1998). To approximate human hearing sensitivity, A-weighting discounts sounds below 1 kHz and above 6 kHz. Trained technicians calculated time audible metrics after monitoring was complete. See Methods section for protocol details, equipment specifications, and metric calculations. Median existing (LA50) and natural ambient (LAnat) metrics are also reported for daytime (7:00–19:00) and nighttime (19:00–7:00). Prominent noise sources included aircraft, vehicles, and a lift station. Table 1 displays time audible values for each of these noise sources during the monitoring period, as well as ambient sound levels.

Washita Battlefield National Historic Site: Acoustic monitoring report

Series

Collections