Broadband Excess Noise Estimation via Sample Distribution Field Calibration

The Marine Strategy Framework Directive (MSFD) of the European Union currently requires meaningful noise level-based indicators to be obtained either through field data observations or computer modeling. Acoustic recordings in the 20–1000 Hz frequency band were performed 6 h a day during June 2018 in three moorings to the southwest of the Islands of Faial and Pico (Azores). Anthropogenic noise was modeled due to ship traffic drawn from AIS data, and environmental sound was attributed to wind. Comparing field and model data at these three locations allowed to introduce a field calibration procedure based on the linear transformation of sample distribution probability density functions in the sound pressure-level domain. The broadband version of the excess noise level (ENL) appears as the sum of the 1/3-octave bands transformed power over the data recording frequency band. The results show that field-calibrated broadband ENL sound maps are in line with the main shipping routes, fishing activity, and leisure paths in the area revealing; however a significant noise spread due to sound propagation conditions to the east and the southwest of the Faial-Pico Islands. Field-calibrated broadband ENL may be seen as a reliable quantity for establishing continuous anthropogenic noise pollution MSFD indicators.