Soundscape Inventorying and Monitoring

The fundamental purpose of a soundscape inventory is to provide a baseline of ambient sound conditions for the primary acoustic zones in a park. Specifically, a soundscape inventory provides natural ambient and existing ambient sound levels for the primary acoustic zones in a park in order to provide a basis for soundscape management, and against which potential impacts can be assessed. Acoustic data, associated metrics, and sound source information should be collected for the primary acoustic zones in a park. With this knowledge, known and proposed non-natural sounds can be modeled and sound levels of those activities calculated.

The purpose of soundscape monitoring is to provide park managers with knowledge about the status and condition of park soundscapes relative to laws, policies, and management documents for that park. Effective monitoring is achieved by identifying where monitoring should be done, under what conditions, and how intensive the monitoring should be. Long-term soundscape monitoring efforts should be developed in consideration of acoustic conditions in the primary acoustic zones and soundscape management plans specific to that park.

Soundscape inventory and monitoring efforts must follow specific, standardized methodology and protocols to be scientifically defensible and comparable to other studies.

Data Collection: Planning and Preparation

Planning for data collection should focus on the primary acoustic zones of each park, but should also consider specific management areas and associated soundscape management objectives, as well as acoustically sensitive areas, such as endangered species habitat or cultural areas. Preparation for data collection includes identifying acoustic zones, selecting representative acoustic areas, selecting specific measurement locations, and defining the season and period of time for taking measurements.

Identifying Acoustic Zones

Acoustic zones are areas of similar vegetation, land cover, topography, elevation, and climate that typically contain similar animals, physical processes, and other sources of natural sounds. These areas with similar attributes have similar natural sound sources, sound levels, propagation and attenuation properties, and other acoustic qualities. Once the primary acoustic zones have been identified, measurement locations should be selected to insure that all of the primary acoustic zones of the park are sampled.

In developing park acoustic zones, land cover and climate regions are the two greatest technical factors influencing ambient sound levels. Specific measurement locations within acoustic zones should be considered relative to other factors such as park resources, park management zones, visitor-use, wildlife habitats, and other factors.

Measurement Season

Ideally, for soundscape management in national parks, acoustic data for all seasons shall be collected. Although, two seasons, summer and winter, are usually adequate. For assessment of specific sound sources, such as the development of ATMPs, acoustic data should be collected during the season(s) in which the activity occurs. For example air tours are typically concentrated during the summer months. Few if any are conducted in the winter. In this case, measurements should be conducted during the summer season. For those parks at which regular air tours occur year-round, more data from different seasons will be needed to adequately model potential air tour impacts. Typically, one summer measurement period and one winter measurement period are adequate.

Measurement Location

In most situations, the principal consideration in selecting measurement locations is to insure data are collected in all of the primary acoustic zones of the park. Additional considerations include, in rough order of priority:

• Park management zones and soundscape management objectives of those zones;
• Specific sound-sensitive areas;
• Specific acoustic data needs;
• Proximity to natural and human-caused sounds; and
• Equipment considerations (security, solar exposure, visibility, etc.).

Final selection of measurement locations is made through a screening process of potential sites considering all of the above factors, and in consideration of site access, equipment availability/capability, and availability of personnel to deploy and service the equipment.

Measurement Duration

Acoustic conditions in most parks vary daily and seasonally, and this variability must be considered in determining adequate measurement periods. Measurements at a particular site should not only be of sufficient duration to ensure statistical confidence in the data, but also be reasonable in light of practical and other resource considerations. Based on review of acoustic literature, the ambient data collected in various national parks, a minimum 25-day measurement period has been shown to generally limit measurement uncertainty to less than 3 decibels. For some situations or environments, shorter or longer measurement periods may be needed.

Data to be Collected

Acoustical

Continuous, one-second, A-weighted sound levels and one-third octave band measurements from 20 to 20,000 Hz should be collected. When measuring in very low acoustic conditions (<15 dBA), measurements should be made using ultra-sensitive, low-noise microphones whenever possible.

Meteorological

Meteorological data is important because previous studies in National Parks have established a strong correlation between land cover, wind speed, and ambient sound level. Sounds also travel differently in cold or hot temperatures. Continuous, one-second wind speed data should be collected. Wind data is particularly important because a substantial change in noise level can occur as wind speeds increase. Wind direction, outside air temperature data, and humidity should also be collected when possible, as they can also affect the characteristics of sound in the environment.

Source identification/Observer Logging

In addition to sound level data, knowledge of the source, duration, and distribution of sound sources is important in characterizing natural and non-natural acoustic conditions in a park. Thus, during sound-level data collection, periods of observer logging and high-quality digital recordings will be conducted in order to discern the type, timing, and duration of different sound sources.

Digital Recordings

Advancements are continuously being made in acoustic data analysis. Therefore, it is crucial to obtain high-quality archival recordings that can be used to compute any conceivable metric for future analysis. It is almost certain that metrics specified today will be inadequate to meet all future needs, thus making high-quality digital recordings is important. Digital recordings also provide an archival record of the biological acoustics of the area.