Effects of Aircraft Noise: Research Update on Select Topics (2008)

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26 A-weighting—a frequency-weighting network used to account for changes in human auditory sensitivity as a function of frequency. Actigraph—a watch-sized device that records human move- ment and can provide an indication of sleep. Annoyance—any bothersome or irritating occurrence. Anxiety—a feeling of apprehension, uncertainty, and fear without apparent stimulus. It is associated with physiolog- ical changes (tachycardia, sweating, tremor, etc.), the source of which is often nonspecific or unknown to the individual. Arrhythmia—any irregularity in the rhythm of the heart’s beating. Audiometry—the measurement and testing of hearing, including aspects other than hearing sensitivity. Auditory threshold—the minimum audible perceived sound. Back-country visitor—a visitor to wilderness areas or national parks who ventures into the so-called back-country areas; that is, those undeveloped areas of the park that do not have developed camp grounds, picnic areas, and where solitude and quiet are an expected amenity (see front-country visitor for contrast). Cardiovascular—a term used when referring to the heart and blood vessels. Change in aircraft SEL (sound level exposure)—is a noise metric developed for analyzing noise impacts in national parks and is abbreviated ΔLAE,Tac. CNEL (community-noise equivalent level)—a term used in California and nearly identical to DNL (day-night average sound level), except that CNEL includes a 5 dB penalty for the evening time period from 7 p.m. to 10 p.m. Cross-sectional—those data collected by observing many subjects (such as individuals) at the same point of time. Analysis of cross-sectional data usually consists of compar- ing the differences among the subjects. For example, in airport noise studies, a cross-sectional study compares responses in one group with another group in a different location. Cross-sectional data differ from longitudinal data, which follow one subject’s changes over the course of time. Curvilinear—in the context used in this synthesis, refers to a particular statistical method of plotting a smooth curve through scattered data. Day-Night Average Sound Level (DNL, denoted by the symbol Ldn)—the 24-h average sound level for a given day, after addition of 10 db to levels from midnight to 0700 hours and from 2200 hours to midnight. Ldn is com- puted as follows: Ldn = LAE + 10*log10(Nday + 10*Nnight)—49.4 (dB) where: LAE = Sound exposure level in dB (also known as SEL); Nday = Number of vehicle passbys between 0700 and 2200 hours, local time; Nnight = Number of vehicle passbys between 2200 and 0700 hours, local time; and 49.4 = A normalization constant which spreads the acoustic energy associated with highway vehicle passbys over a 24-h period; that is, 10*log10 (86,400 s per day) = 49.4 dB. Decibel (dB)—a unit of sound level when the base of the logarithm is the tenth root of ten and the quantities are proportional to power. Dose-response—the dose-response relationship is one that describes the change in effect on an organism caused by differing levels of exposure to a stressor, in this case, noise. Epinephrine—a hormone secreted by the adrenal medulla (inner or central portion of an organ) in response to stimu- lation of the sympathetic nervous system. Equivalent sound level (TEQ, denoted by the symbol LAeqT or Leq)—Equivalent sound level is 10 times the logarithm to the base 10 of the ratio of time-mean-squared instantaneous A-weighted sound pressure, during a stated time interval T, to the square of the standard reference sound pressure. LAeqT is related to LAE by the following equation: LAeqT = LAE − 10*log10(t2 − t1) (dB) where: LAE = Sound exposure level in dB. FICAN (Federal Interagency Committee on Aircraft Noise)—a federal committee organized to coordinate federal research and policies on aircraft noise (see www.FICAN.org). FICON (Federal Interagency Committee on Noise)—is a federal committee organized to coordinate federal policies on noise. Front-country visitor—a visitor to a park who utilizes the de- veloped camp grounds, picnic area, day-use areas (see back-country visitor for contrast). GIS (geographic information systems)—a computer soft- ware program used to analyze spatial data that can be es- pecially useful in examining noise distribution over a geo- graphic area. Ground absorption—as sound propagates near the ground, ground absorption is the interaction of the sound wave with the ground that results in attenuation of the sound. Hard ground, such as water, has less attenuation than soft ground (most other surfaces). (Also known as lateral attenuation. Hearing impairment—decreased ability to perceive sounds as compared with what the individual or examiner would regard as normal; the result is an increase in the threshold of hearing. Hearing threshold—for a given listener and specified signal, a hearing threshold is the minimum: sound pressure level GLOSSARY

27 or force level that is capable of evoking an auditory sensa- tion in a specified function of trials. Hedonic—a term used by both economists and other scientists. Basically, it means that one item or measure is judged better than another. Hedonic studies are commonly used for estimating the impact of aircraft noise on property values. Noise is considered as one of the many variables that may affect property values. Hertz (Hz)—a unit of frequency representing the number of times a phenomenon repeats itself in a unit of time. ICBEN (International Commission on Biological Effects of Noise)—a commission that meets and publishes a report every five years. INM (Integrated Noise Model)—an FAA-developed com- puter program used to compute noise contours around an airport. Ischemic—a medical term that refers to a restriction in blood supply, generally owing to factors in the blood vessels, with resultant damage or dysfunction of tissue. LAE (see sound exposure level). Lateral attenuation—as sound propagates near the ground lateral attenuation is the interaction of the sound wave with the ground resulting in attenuation of the sound. Hard ground, such as water, has less attenuation than soft ground (most other surfaces). Also known as ground absorption. Lden—Similar to day-night noise level (DNL), but includes an evening weighting period like CNEL. Ldn (see day-night average sound level). LAeq (see equivalent sound level). Leq (see equivalent sound level). Longitudinal—a longitudinal study is one that follows one subject’s or group’s changes over the course of time. It differs from a cross-sectional study in that the effect of a change in exposure is measured in the same subjects, whereas with a cross-sectional study the differences are observed by comparing different subjects. Longitudinal studies are superior to cross-sectional studies. Lmax (maximum noise level)—the maximum noise level, in A-weighted decibels, that occurs during an aircraft flyover. Lnight—the equivalent noise level (Leq), computed for night-time hours, 10 p.m. to 7 a.m. Maximum noise level (Lmax)—the maximum noise level, in A-weighted decibels, that occurs during an aircraft flyover. Meta-analysis—in statistics, a meta-analysis is an analysis of data that combines the results of several studies that address a set of related research hypotheses. NDI (Noise Depreciation Index)—a common method used to report the change in property value as a function of noise exposure. Neuroendocrine—a clinical term referring to a specialized group of nerve cells (neurons) that produce hormones. Noise—any unwanted sound. Noise-induced temporary threshold shift—temporary hearing impairment occurring as a result of noise exposure, often phrased temporary threshold shift. Noise-induced permanent threshold shift—permanent hear- ing impairment occurring as a result of noise exposure, often phrased permanent threshold shift. Norepinephrine—a hormone produced by the adrenal medulla similar in chemical and pharmacological properties to epinephrine, but chiefly a vasoconstrictor with little effect on cardiac output. NPD (Noise Power Distance)—NPD curves are the basic data used in the Integrated Noise Model to define the source noise levels for different aircraft types. It defines the noise level as a function of distance and engine power setting. Paracusis—any hearing abnormality or disorder. Peak-sound pressure level—peak-sound pressure level is the level of peak-sound pressure with stated frequency weighting, within a stated time interval. Parsimonious—a term signifying an unwillingness to spend money or resources; stinginess or frugality. Pathological—any condition that is a deviation from the normal. Percent Time Above Ambient (%TAA)—a noise metric devel- oped for use in analyzing noise levels in national parks. Psychological morbidity—an incidence of mental health illness, including but not limited to depression and anxiety. Physiological—refers to the branch of biology dealing with the functions and vital processes of living organisms or their parts and organs. Presbyacusia, Presbycusis—a condition referring to hearing deterioration occurring after middle age. Psychophysiological—a term describing the promotion of or combination of the normal or healthy functioning of the mind or mental processes. Recruitment (loudness)—refers to abnormal loudness perception. Reverberation—a sound that persists in an enclosed space, as a result of repeated reflection or scattering, after the source has stopped. Reverberation time—reverberation time of an enclosure, for a stated frequency or frequency band, is the time that would be required for the level of time-mean-square sound pressure in the enclosure to decrease by 60 dB, after the sound source has stopped. Schultz Curve—the dose-response relation curve that relates DNL to the percentage of the population who are “highly annoyed.” It is named for Theodore Schultz, who first proposed and developed this curve. The curve has been updated by others and the updated curves are often also referred to as the Schultz Curve in honor of the original author. Sound exposure level (SEL; denoted by the symbol LAE)— over a stated time interval, T (where T = t2 − t1), is 10 times the base-10 logarithm of the ratio of a given time integral of squared instantaneous A-weighted sound pressure, and the product of the reference sound pressure of 20 micropas- cals, the threshold of human hearing, and the reference duration of 1 s. The time interval, T, must be long enough to include a majority of the sound source’s acoustic energy.

As a minimum, this interval should encompass the 10 dB down points (see Figure 1). In addition, LAE is related to LAeqT by the following equation: LAE = LAeqT + 10*log10(t2 − t1) (dB) where: LAeqT = Equivalent sound level in dB (see definition above, also know as Leq). 28 Sound pressure level (SPL)—SPL is 10 times the base-10 logarithm of the ratio of the time-mean-square pressure of a sound, in a stated frequency band, to the square of the reference sound pressure in gases of 20 micropascals. Steady-state—steady-state noise is a continuous, constant noise as compared with a noise that varies over time. Stress—the sum of the biological reactions to any adverse stimulus (physical, mental, or emotional, internal, or exter- nal) that tends to disturb the organism’s state of stability. Threshold of hearing—(see hearing threshold). Tinnitus—a condition that causes a sound of ringing or whistling in the ears, excluding hallucinations of voices. It is an otological condition in which sound is perceived by a person without an external auditory stimulation. Vasoconstriction—a tightening or compressing of the blood vessels. WECPNL (Weighted Equivalent Continuous Perceived Noise Level)—is a noise metric commonly used in Japan, it is similar in concept to DNL, but uses a different algorithm to compute and includes an evening weighting similar to CNEL and Lden. FIGURE 1 Schematic diagram of aircraft flyover noise metrics (Mestre Greve Associates 2007).