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26 GLOSSARY A-weighting--a frequency-weighting network used to Nnight = Number of vehicle passbys between 2200 and account for changes in human auditory sensitivity as a 0700 hours, local time; and function of frequency. 49.4 = A normalization constant which spreads the Actigraph--a watch-sized device that records human move- acoustic energy associated with highway vehicle ment and can provide an indication of sleep. passbys over a 24-h period; that is, 10*log10 Annoyance--any bothersome or irritating occurrence. (86,400 s per day) = 49.4 dB. Anxiety--a feeling of apprehension, uncertainty, and fear Decibel (dB)--a unit of sound level when the base of the without apparent stimulus. It is associated with physiolog- logarithm is the tenth root of ten and the quantities are ical changes (tachycardia, sweating, tremor, etc.), the proportional to power. source of which is often nonspecific or unknown to the Dose-response--the dose-response relationship is one that individual. describes the change in effect on an organism caused by Arrhythmia--any irregularity in the rhythm of the heart's differing levels of exposure to a stressor, in this case, beating. noise. Audiometry--the measurement and testing of hearing, Epinephrine--a hormone secreted by the adrenal medulla including aspects other than hearing sensitivity. (inner or central portion of an organ) in response to stimu- Auditory threshold--the minimum audible perceived sound. lation of the sympathetic nervous system. Back-country visitor--a visitor to wilderness areas or national Equivalent sound level (TEQ, denoted by the symbol LAeqT parks who ventures into the so-called back-country areas; or Leq)--Equivalent sound level is 10 times the logarithm to that is, those undeveloped areas of the park that do not have the base 10 of the ratio of time-mean-squared instantaneous developed camp grounds, picnic areas, and where solitude A-weighted sound pressure, during a stated time interval T, and quiet are an expected amenity (see front-country visitor to the square of the standard reference sound pressure. for contrast). LAeqT is related to LAE by the following equation: Cardiovascular--a term used when referring to the heart and blood vessels. LAeqT = LAE - 10*log10(t2 - t1) (dB) Change in aircraft SEL (sound level exposure)--is a noise where: metric developed for analyzing noise impacts in national LAE = Sound exposure level in dB. parks and is abbreviated LAE,Tac. CNEL (community-noise equivalent level)--a term used in FICAN (Federal Interagency Committee on Aircraft California and nearly identical to DNL (day-night average Noise)--a federal committee organized to coordinate sound level), except that CNEL includes a 5 dB penalty for federal research and policies on aircraft noise (see the evening time period from 7 p.m. to 10 p.m. www.FICAN.org). Cross-sectional--those data collected by observing many FICON (Federal Interagency Committee on Noise)--is a subjects (such as individuals) at the same point of time. federal committee organized to coordinate federal policies Analysis of cross-sectional data usually consists of compar- on noise. ing the differences among the subjects. For example, in Front-country visitor--a visitor to a park who utilizes the de- airport noise studies, a cross-sectional study compares veloped camp grounds, picnic area, day-use areas (see responses in one group with another group in a different back-country visitor for contrast). location. Cross-sectional data differ from longitudinal data, GIS (geographic information systems)--a computer soft- which follow one subject's changes over the course of time. ware program used to analyze spatial data that can be es- Curvilinear--in the context used in this synthesis, refers to a pecially useful in examining noise distribution over a geo- particular statistical method of plotting a smooth curve graphic area. through scattered data. Ground absorption--as sound propagates near the ground, Day-Night Average Sound Level (DNL, denoted by the ground absorption is the interaction of the sound wave symbol Ldn)--the 24-h average sound level for a given with the ground that results in attenuation of the sound. day, after addition of 10 db to levels from midnight to Hard ground, such as water, has less attenuation than soft 0700 hours and from 2200 hours to midnight. Ldn is com- ground (most other surfaces). (Also known as lateral puted as follows: attenuation. Hearing impairment--decreased ability to perceive sounds Ldn = LAE + 10*log10(Nday + 10*Nnight)--49.4 (dB) as compared with what the individual or examiner would where: regard as normal; the result is an increase in the threshold LAE = Sound exposure level in dB (also known as SEL); of hearing. Nday = Number of vehicle passbys between 0700 and Hearing threshold--for a given listener and specified signal, 2200 hours, local time; a hearing threshold is the minimum: sound pressure level
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27 or force level that is capable of evoking an auditory sensa- Noise-induced permanent threshold shift--permanent hear- tion in a specified function of trials. ing impairment occurring as a result of noise exposure, Hedonic--a term used by both economists and other often phrased permanent threshold shift. scientists. Basically, it means that one item or measure is Norepinephrine--a hormone produced by the adrenal medulla judged better than another. Hedonic studies are commonly similar in chemical and pharmacological properties to used for estimating the impact of aircraft noise on property epinephrine, but chiefly a vasoconstrictor with little effect values. Noise is considered as one of the many variables on cardiac output. that may affect property values. NPD (Noise Power Distance)--NPD curves are the basic Hertz (Hz)--a unit of frequency representing the number of data used in the Integrated Noise Model to define the times a phenomenon repeats itself in a unit of time. source noise levels for different aircraft types. It defines ICBEN (International Commission on Biological Effects of the noise level as a function of distance and engine power Noise)--a commission that meets and publishes a report setting. every five years. Paracusis--any hearing abnormality or disorder. INM (Integrated Noise Model)--an FAA-developed com- Peak-sound pressure level--peak-sound pressure level is the puter program used to compute noise contours around an level of peak-sound pressure with stated frequency airport. weighting, within a stated time interval. Ischemic--a medical term that refers to a restriction in blood Parsimonious--a term signifying an unwillingness to spend supply, generally owing to factors in the blood vessels, money or resources; stinginess or frugality. with resultant damage or dysfunction of tissue. Pathological--any condition that is a deviation from the LAE (see sound exposure level). normal. Lateral attenuation--as sound propagates near the ground Percent Time Above Ambient (%TAA)--a noise metric devel- lateral attenuation is the interaction of the sound wave with oped for use in analyzing noise levels in national parks. the ground resulting in attenuation of the sound. Hard Psychological morbidity--an incidence of mental health ground, such as water, has less attenuation than soft illness, including but not limited to depression and anxiety. ground (most other surfaces). Also known as ground Physiological--refers to the branch of biology dealing with absorption. the functions and vital processes of living organisms or Lden--Similar to day-night noise level (DNL), but includes an their parts and organs. evening weighting period like CNEL. Presbyacusia, Presbycusis--a condition referring to hearing Ldn (see day-night average sound level). deterioration occurring after middle age. LAeq (see equivalent sound level). Psychophysiological--a term describing the promotion of or Leq (see equivalent sound level). combination of the normal or healthy functioning of the Longitudinal--a longitudinal study is one that follows one mind or mental processes. subject's or group's changes over the course of time. It Recruitment (loudness)--refers to abnormal loudness differs from a cross-sectional study in that the effect of a perception. change in exposure is measured in the same subjects, Reverberation--a sound that persists in an enclosed space, as whereas with a cross-sectional study the differences are a result of repeated reflection or scattering, after the source observed by comparing different subjects. Longitudinal has stopped. studies are superior to cross-sectional studies. Reverberation time--reverberation time of an enclosure, for Lmax (maximum noise level)--the maximum noise level, in a stated frequency or frequency band, is the time that A-weighted decibels, that occurs during an aircraft flyover. would be required for the level of time-mean-square sound Lnight--the equivalent noise level (Leq), computed for night-time pressure in the enclosure to decrease by 60 dB, after the hours, 10 p.m. to 7 a.m. sound source has stopped. Maximum noise level (Lmax)--the maximum noise level, Schultz Curve--the dose-response relation curve that relates in A-weighted decibels, that occurs during an aircraft DNL to the percentage of the population who are "highly flyover. annoyed." It is named for Theodore Schultz, who first Meta-analysis--in statistics, a meta-analysis is an analysis of proposed and developed this curve. The curve has been data that combines the results of several studies that updated by others and the updated curves are often also address a set of related research hypotheses. referred to as the Schultz Curve in honor of the original NDI (Noise Depreciation Index)--a common method used to author. report the change in property value as a function of noise Sound exposure level (SEL; denoted by the symbol LAE)-- exposure. over a stated time interval, T (where T = t2 - t1), is 10 times Neuroendocrine--a clinical term referring to a specialized the base-10 logarithm of the ratio of a given time integral of group of nerve cells (neurons) that produce hormones. squared instantaneous A-weighted sound pressure, and Noise--any unwanted sound. the product of the reference sound pressure of 20 micropas- Noise-induced temporary threshold shift--temporary hearing cals, the threshold of human hearing, and the reference impairment occurring as a result of noise exposure, often duration of 1 s. The time interval, T, must be long enough to phrased temporary threshold shift. include a majority of the sound source's acoustic energy.
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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). FIGURE 1 Schematic diagram of aircraft flyover noise metrics Tinnitus--a condition that causes a sound of ringing or (Mestre Greve Associates 2007). whistling in the ears, excluding hallucinations of voices. It is an otological condition in which sound is perceived by As a minimum, this interval should encompass the 10 dB a person without an external auditory stimulation. down points (see Figure 1). In addition, LAE is related to Vasoconstriction--a tightening or compressing of the blood LAeqT by the following equation: vessels. WECPNL (Weighted Equivalent Continuous Perceived Noise LAE = LAeqT + 10*log10(t2 - t1) (dB) Level)--is a noise metric commonly used in Japan, it is where: similar in concept to DNL, but uses a different algorithm to LAeqT = Equivalent sound level in dB (see definition above, compute and includes an evening weighting similar to also know as Leq). CNEL and Lden.