# Presentation: 924706

## The Analysis and Protection of the Natural Soundscape in National Parks

- Bill Schmidt
- NRSS
- WASO

## The Basic Ideas

- The “soundscape” is the totality of sounds
- The “natural soundscape” = (the soundscape) – (human noise)
- The natural soundscape is a protected natural resource of the National Park Service.
- It is neither necessary nor practical to return NPS soundscapes to their pre-1492 conditions.
- Monitoring the soundscape is neither as difficult as you might fear nor as easy as you might hope.
- There is no time like the present to start.

## Fundamentals of Sound (pressure)

## Fundamentals of Sound (frequency)

## Fundamentals of Sound (loudness)

## Frequency Weighting

## Soundscape Metrics

-  **Decibel** – The dB = 20 Log10 ((sound pressure in Pascals)/20 x 10-6 Pascals))
-  SEL (Sound Exposure Level) – This metric is the unit used to describe the total amount of sound for an event compressed into 1 second.
**L****max**** and L****min** – The highest and lowest instantaneous sound levels within a certain time period
**L****eq** (Equivalent sound level) – The average sound level in a period of time.

**Notes:**
(20 x 10-6 is the reference pressure in air.  1 x 10-6 is the reference pressure in water.)

, e.g. the Lmax during that hour was 112 dBA. 

## Soundscape Metrics

**T****A** (Time above) – The amount of time in a given period that the sound level exceeds a specified threshold.
**Ln**  (Exceedance levels) – These are statistical values for a series of readings.  For example, L90 = 43 dBA means 43 dBA was exceeded 90 percent of the time.
- DNL Day night level (also called Ldn) – This is a 24-hour average hourly noise level with a 10 dB penalty for nighttime noise events between 10 PM and 7 AM.

**Notes:**
(20 x 10-6 is the reference pressure in air.  1 x 10-6 is the reference pressure in water.)

, e.g. the Lmax during that hour was 112 dBA. 

## Some useful facts and rules of thumb.

- Low frequency sounds, e.g., mechanical noise, can be heard at greater distances than high frequency sounds.
- The decrease in sound pressure levels from a point source, i.e., one whose lateral dimension is small, is about 6 dB per doubling of distance – about 5 dB over water.  For example, a boom box whose SPL at 50 feet is 80 dB, would have a SPL of about 74 dB at 100 feet, 68 dB at 200 feet, etc.
- The decrease in SPL for a line source, e.g., a highway, is about 3 dB for each doubling of distance.

## Why worry about the soundscapes?

**Because it is part of our job**
**Because the critters are depending on you**
**Because it is important to visitor enjoyment**

## Why worry about the soundscapes?- Job Related 

- The natural soundscape is a natural resource and the Organic Act says: “Thou shall protect natural resources.”
- Director’s Order 47:
- Develop soundscape plans (or components of GMPs, RMPs, WMPs, etc.) (Sections C.3, 6, and 7)
**Inventory and monitor the soundscape** (Section C.5)

**Notes:**
Deference to agencies plans in EIS

## DO 47 also 

- Directs the parks to use the natural soundscape as the “affected environment” for NEPA matters related to the impacts of sound. (Section C.7 )
- Unless there is better information, parks are to use the L90 exceedance levels as the level of the natural ambient,i.e., the value for the natural soundscape in C.7. (Section D.4)

**Notes:**
Better information can be developed through detailed monitoring of a park’s soundscape but the L90, also referred to as the background level, is commonly used as a baseline for determining normal conditions under state and municipal codes around the country.

## Tactical use of the L90/Natural values

- In a defense of the park’s soundscapes, get the discussion revolving around your concepts and issues rather than those of the proponents of an action.
- Avoid allowing use of “assumed” ambient values.
- Don’t let the proponents choose the “appropriate” metrics – it’s your park.

**Notes:**
The St George case.

## Why worry about the soundscapes?- Critters 

- Most studies of effect of noise on wildlife are ad hoc – a species or two and short term.
- Most acoustic studies of wildlife are for “trophies.”
- There is a growing interest in studies of the biophony – the biota in the context of the ecosystem.

## Why worry about the soundscapes?- Visitors

- The NPS is the keeper of some of the quietest places in the US.
- The natural soundscape is a major reason visitors come to the parks.
- approximately 93 % of surveyed visitors reported that the reason for their visit was to view the natural scenery.
- 91 per cent reported that their reason for the park visit was to enjoy the “natural quiet.”

**Notes:**
system-wide visitor survey.  15,000 visitors were surveyed during the busiest 2 months of the season at 39 parks across the country. 

## Monitor a park?How? 

- A few thoughts:
- This park-wide area acoustics is new – the NPS is helping write the book.
- A park’s soundscape is dynamic, varying with time and place. You will never have all the answers.
- If you wait to get the data until a crisis hits, it is generally too late to be able to use them.

## Monitor a park?How as an I&M effort? 

- Use consultants
- Expensive $1–1.5K/day + expenses
- Come with expertise (and equipment)
- Use rotating teams
- Collateral duty
- Assemble a lot of data in a few years
- Use equipment from pool
- Funding being sought
- Park funded people and equipment
- Can meet more urgent or specialized needs

## Monitor a park?How? 

- Define your goals.
- Plan your study before you get to the field.
- Do a reconnaissance study first.
- Build on the reconnaissance.
- Keep things simple.

## Monitor a park?What type of instrumentation?

- What are you trying to do?
- Measure park-caused noise? A $50 Radio Shack 33-2055 will probably work just fine.
- Do reconnaissance or have an observer document levels? An $850 CEL 254 may be just the ticket.
- Longer term logged monitoring? One of the logging meters from Larson Davis, B&K, or Norsonics -- $3,000-$10,000.

**Notes:**
Brüel & Kjær

## Monitor a park?What is measured?

- The meters take instantaneous pressure level data and assemble it as you specify – generally 1 second Leq values.
- A-weighting is the lingua franca of the industry.
- 1/3 OB. narrow band, and analyses like d-prime or FFT (and more) may serve specialized needs.

**Notes:**
Brüel & Kjær

## Monitor a park?Where to measure?

- Unless obvious noise sources are of interest, e.g., a proposed highway expansion, stay out of their area of influence when monitoring.
- Try for representative conditions and seasons – (reconnaissance).
- Absent a better hypothesis, try for balanced geographic coverage.

**Notes:**
Brüel & Kjær

## Some Current Issues

- Microphone Height
- Bird spikes etc.
- Acoustic Zoning
- To .WAV or not to .WAV
- Noise floor of mics
- Duration of monitoring
- Wind-mic interaction
- Form of the record

## Some other available tools

- NPS Acoustic database
- Data viewers
- NMSIM, NPS version.
- ISIS

## Data viewers

- The common database allows common data structure and useful tools like this viewer.

## NMSIM

- Prospective actions generally require noise modeling.  The NPS is about to acquire its own.