Research Methods for Understanding Aircraft Noise Annoyances and Sleep Disturbance (2014)

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6 Noise Metrics The day-night annual average sound level, DNL, as computed with the FAA’s Integrated Noise Model (INM) will be the independent “noise dose” variable. In addition to using DNL, we suggest including several other noise/aircraft operation based metrics in the annoyance response analyses. These metrics have been chosen as possible supplemental metrics that could account for some of the aspects of noise exposure not explicitly included in DNL. The INM will be used to either compute these metrics directly, or to provide the basic information from which most of the supplemental metrics will be derived. Aspects that may not be sufficiently incorporated in DNL include: • Adverse Effects of Nighttime Noise – DNL does provide a weighting factor of 10 for events occurring during the night, but then sums this weighted nighttime sound energy with the sound energy from the rest of the day, possibly obscuring the adverse effects of nighttime noise. • Speech Interference – DNL does not explicitly count the number of times speech interference could occur. • Different Types of Aircraft Operations – Sound level time histories and frequency content can be quite different for departures and arrivals, and can be different for locations adjacent to a runway as compared with locations affected by overflights. Table 2 lists all the metrics computed at the geographic location of each survey respondent. Table 2 Annual Noise Related Metrics Determined for Each Survey Respondent Energy Average, dB Mean and Median DNL Time Above (TA): 55, 60, 65, 70, 75 Lnight Leq24: Total Arrival Only Departure Only Number Above (NA) 55, 60, 65 Probability of Awakening at least Once ANSI 12.9-2008 / Part 6 – (ANSI, 2008) Locations Affected by Start of Takeoff Noise Lnight (outdoors) is the metric recommended by the World Health Organization for judging adverse effects on sleep, (WHO, 2009). Sleep disturbance, however, results from single events and Lnight averages events so that many combinations of aircraft event noise levels will produce the same Lnight. Nevertheless, we suggest including it to permit further analysis of its relationship to annoyance. Leq24 is identical to DNL with no night time weighting and is included primarily as a means of distinguishing between the predominance of arrival and departure sound energy. Some airports operate almost entirely in one direction of aircraft operations so that some communities experience almost entirely departure noise while others primarily arrival noise. Do these communities judge the annoyance of aircraft with respect to DNL differently? Figure 5 (Brink, 2006) shows the reaction of a sleeping subject to two separate aircraft noise events of equal maximums. Apparently, the rapid rise and fall of the arrival noise was more disturbing, as measured by “motility” – movement of the body – than was the slower rise and fall of the departure noise event. Interestingly, though both events had equal maximums, their SEL values were quite different: departure SEL was 73 dB, while the arrival SEL was 67 dB. These findings suggest that human annoyance reactions to a dominance of departures may be different from that due to a dominance of arrivals. 16

Figure 5 Departure and Arrival Time Histories compared with Motility (body movement) of Sleeping Subject Time above a threshold (TA) and number above a threshold (NA) may correlate with duration or number of incidents of speech interference and may be related to the reported annoyance. Probability of awakening, as computed using the ANSI standard 12.9/2008/Part 6, (ANSI, 2008), accounts for number and level of each night time noise event (10 p.m. to 7 a.m.) and may be better correlated with reports of sleep disturbance than is Lnight (Question 7, Telephone Survey, Appendix A). Finally, the residents who experience start of takeoff noise may react differently from the residents who experience only overflight noise. The sound level time histories and frequency content of overflights and of takeoff differ considerably. Figure 6 and Figure 7 show the difference in time histories of an overhead departure and of a takeoff measured to the side of the runway. 17

Figure 6 A-weighted Time History of Recorded Overhead Departure Figure 7 Time Histories of a Single Jet Takeoff as Recorded ~ 3200 Feet Adjacent the Runway Boeing 737 Departure Directly Overhead 30 40 50 60 70 80 90 0 30 60 90 120 Seconds A -W ei gh te d So un d Le ve l, dB 30 40 60 80 90 0 10 20 30 40 50 60 70 80 90 100 A-level Time (Seconds) C-level Linear 20 Hz OB 18 70 50 S ou nd L ev el (d B )

The following three sections provide graphics that demonstrate the inter-relationships of some of these metrics. They were developed primarily to verify the reasonableness of the INM computed values and to establish a process for efficiently generating the metrics for the national survey airports. The plots also suggest the degree of correlation of the various metrics: NA and TA might provide insight to annoyance versus DNL, while probability of awakening may better relate to awakening reports (and annoyance) than does Lnight. 6.1 Number above a Level versus DNL Figure 8 compares at respondent locations the number of aircraft noise events above various threshold sound levels (dBA) with the DNL value at the same location. For a given threshold, there is considerable correlation at the higher values of DNL. These are locations close to the runway end, but at different distances from the runway, close to the centerline. Hence, the number of events does not vary with DNL (with distance from the runway). As distance increases, the aircraft are higher and hence quieter. However, at lower DNL values, many locations can have different numbers of events above a threshold but similar DNL. Analyses may be able to determine whether annoyance reports are affected by these differences. Figure 8 Number Above Different Threshold Levels versus DNL 6.2 Time above a Level versus DNL Figure 9 shows time above and associated DNL values at the receiver locations. Time above appears closely correlated with DNL for the higher thresholds, but less so at the lower thresholds (blue points). This scatter appears to be in part related to the distance the locations are from the flight tracks / runways. Along runway sideline, but at some distance, presumably many aircraft operations may be heard, but at lower levels than close to the runway. Hence higher numbers are heard, but levels are lower and consequently so is DNL. 19

Figure 9 Time Above Different Threshold Levels versus DNL 6.3 Probability of Awakening versus Lnight Figure 10 shows that the probability of awakening is quite correlated with Lnight, but differently at different locations. This differing relationship is because the probability of awakening is highly dependent on the number of night time aircraft noise events. Hence, locations that are affected by similar numbers of operations have similar ranges of likelihood off awakening, decreasing slightly with decreasing Lnight. Figure 10 Probability of Awakening versus Lnight 20