In this work, the impact of the COVID-19 outbreak on the environmental noise generated by the air traffic at the Hannover Airport, Germany, is assessed. For this purpose, a comparative study of the air traffic noise in the years 2019 and 2020 is conducted by means of publicly available measurement data and computational simulations. Based on environmental noise directives defined by the responsible German authorities, the comparative study is conducted in terms of A-weighted equivalent sound pressure level metrics computed for the six months of the forecast years with the largest number of flights. In comparison with the year of 2019, the measurement data indicates that the , and were reduced in average by 2.4, 4.2, and 3.7 dBA, respectively, in the year 2020. Furthermore, the results based on the computational simulations show that the isocontour areas of the and noise protection zones defined by the German federal government were reduced by and , respectively, in the year of 2020.
Environmental noise is a large burden on public health. In 2011, the World Health Organisation (WHO) published a study stating that in western Europe, each year, a number of approximately 1.0–1.6 × 106 disability-adjusted life years (DALYs), a quantity accounting for the number of healthy life years lost due to illnesses, are lost due to long-term exposure to environmental noise (World Health Organization, 2011). A thorough review of the negative effects of environmental noise on sleep is given in the work of Basner and McGuire (2018). Moreover, the concept of annoyance due to environmental noise is of special importance for the assessment of noise sources since, according to the WHO, approximately half of the DALYs lost are due to noise annoyance. A concise review of the relation between environmental noise exposure and annoyance is provided by Guski (2017). Environmental noise is caused by various sources, but literature suggests that traffic noise (comprising road, rail, and aircraft noise) is among the major contributors (European Environmental Agency, 2020). With respect to the number of affected people, aircraft noise ranks third among traffic noise sources. However, especially for communities located around airports, the long-term exposure to aircraft noise is prone to trigger annoyance (Baudin , 2018). Long-term annoyance due to aircraft noise is usually quantitatively assessed by means of dose-response metrics (Brink , 2019; Guski , 2017), while short-term annoyance can be assessed through psychoacoustic-based metrics (Felix Greco , 2021; Merino-Martinez , 2019; More, 2010; Vieira , 2019). Since annoyance is one of the major causes of lost DALYs, aircraft noise becomes of high importance to public health.
The COVID-19 pandemic, due to the spread of the SARS-CoV2 virus, led to enormous efforts in policy and society to assure people's safety. The COVID-19 pandemic presumably took its start on December 12, 2019, in Wuhan, China, with the outbreak of an unidentified pneumonia disease (Zhou , 2020). The first person tested positive in Germany was confirmed on January 27, 2020. Suspension of flights from/to China started in different parts of the world around January 29, 2020, after the WHO named the virus a public health emergency of international concern (PHEIC) (Allam, 2020; von Tigerstrom and Wilson, 2020). In the following days, many countries issued travel restrictions and/or closed borders (Germany: March 16, 2020) (Lüdecke and von dem Knesebeck, 2020). Moreover, major policy actions included the implementation of lockdowns (Germany: March 22, 2020) and curfews in order to restrict social contact only to essential needs. Accordingly, passenger travel dramatically declined on an international scale, resulting in a decline in aircraft movements. This directly leads to the hypothesis that the decline in aircraft movements results in less aircraft-caused environmental noise, especially in the vicinity of airports.
The effect of the COVID-19 pandemic on environmental noise has been studied from several viewpoints of which some shall be highlighted in the following. The effect on noise levels in cities and the associated soundscape is investigated in a quantitative manner in Madrid, Spain (Asensio , 2020), Girona, Spain (Alsina-Pagès , 2021), Stockholm, Sweden (Rumpler , 2021), and some major cities in India (Mimani and Singh, 2021). Generally, a decrease in ambient noise levels during phases of lockdown and/or curfew is reported. Accordingly, ambient noise levels increased again when restrictions were relieved, as shown by Kumar (2022) at a school site in Guildford, United Kingdom. A quantitative analysis especially focusing on aircraft noise in Lima, Peru, is reported in the work of Montano and Gushiken (2020), with similar findings regarding noise reductions during lockdowns. A combination of qualitative and quantitative analyses of the altered soundscapes in Turkey is provided by Şentop Dümen and Şaher (2020), which shows that traffic noise-associated annoyance was reduced while the fact that people spent more time at their homes during the lockdown increased their annoyance due to noise at their own house but not due to neighbor noise. Moreover, the qualitative study of Maggi (2021) shows that the reduced traffic noise levels during lockdown led to increased feelings of happiness and tranquility, and a decreased feeling of irritation. Hence, the reduction of environmental noise may be associated with increased well-being.
The main goal of this work is to assess the impact of the COVID-19 outbreak on the environmental noise generated by the air traffic at the Hannover-Langenhagen Airport (IATA code: HAJ), located in the state of Lower Saxony, Germany. For this purpose, a comparative study of the air traffic noise at the HAJ Airport region in the years 2019 and 2020 is conducted in two parts. In the first part, the comparative study is performed based on publicly available measurement data (Reinhart, 2019). As measurements provide noise levels only at specific locations, the comparative study is extended to a large assessment area in a second part, which is conducted by means of computational simulations based on the best-practice method established by Doc. 29 of the European Civil Aviation Conference (2005). Based on environmental noise directives from the German federal government and the state of Lower Saxony, the comparative study is conducted in terms of A-weighted equivalent sound pressure level metrics computed for the six months of the forecast years with the largest number of flights.
This manuscript is organized as follows: Sec. II describes the data and methods used to conduct the comparative study, including information related to the noise assessment metrics and criteria (see Sec. II A), the measurement data (see Sec. II B), and the computational simulations (see Sec. II C). Section III presents the results of the comparative study based on the measurement data (see Sec. II A) and on the computational simulations (see Sec. II B). Section IV presents the conclusions of the study.
II. DATA AND METHODS
A. Noise assessment metrics and criteria
To compare the air traffic noise in the years of 2019 and 2020 at the HAJ Airport region, the noise metrics and assessment criteria established by the German federal government and by the state of Lower Saxony are used. The German federal government establishes the criteria for the definition of noise protection zones around airports in the “Act for Protection against Aircraft Noise” (Bundesministerium der Justiz und für Verbraucherschutz, 2007). For existing commercial, civil airports with air traffic exceeding 25 000 movements per year, the protection zones shall encompass the residential areas in which the A-weighted equivalent sound pressure level, , caused by aircraft operations exceeds the following values:
daytime protection zone 1 – ;
daytime protection zone 2 – ; and
nighttime protection zone – .
An additional nighttime protection zone based on the A-weighted maximum sound pressure level, , is defined as the area where at least six aircraft operations exceed the threshold value of . The daytime period is defined from 06 AM to 10 PM, while the nighttime period is defined between 10 PM and 06 AM. The assessment period is defined as the six months of the forecast year with the largest number of flights.
In addition to the directive of the German federal government, the state of Lower Saxony specifies a settlement restriction area (SRA) (Niedersächsisches Ministerium für Ernährung, Landwirtschaft und Verbraucherschutz, 2017), which is defined based on the day-evening-night level . The is defined as the computed for the 24 h of the day, with a penalty of 5 dBA for the evening period (from 6 PM to 10 PM) and a penalty of 10 dBA for the nighttime period (from 10 PM to 06 AM). The computation of the , as well as of the other noise metrics used in this work, are in agreement with the European Environmental Noise Directive 2002/49/EC (Official Journal of the European Communities, 2002) and the ISO 1996-1:2016 (ISO, 2016).
Based on publicly available data published by Arbeitsgemeinschaft Deutscher Verkehrsflughäfen (2020) concerning the monthly number of flight operations at the HAJ Airport (see Fig. 1), the six months of the forecast year with the largest number of flights were determined to be the months of May, June, July, August, September, and October in the year of 2019, and January, February, March, July, August, and September in the year of 2020. The total number of flight operations in these months are 44 721 and 27 787 in the years 2019 and 2020, respectively. Therefore, the total number of flight operations at the HAJ Airport for the six months of the respective years with the largest air traffic has decreased by in the year 2020 compared to the year 2019. In this work, data concerning these months will be used to conduct a comparative study based on noise measurements and computational simulations.
B. Measurement data
The noise monitoring system operated by the HAJ Airport consists of nine measurement stations placed in the vicinity of residential areas. Each station constantly measures the environmental noise using a 1/2 in. calibrated GRAS 41AM microphone and a Norsonic 118 sound pressure level meter. The measurement stations and its monitoring system complies with the DIN 45643:2011 (DIN, 2011) in multiple aspects, such as instrumentation class, microphone placement, noise metrics, and the criteria used for the identification of sound events associated with aircraft movements, among others.
Figure 2 presents the geographical location of the measurement stations, which were kindly provided by the HAJ Airport. In this work, publicly available measurement data (Reinhart, 2019) provided in terms of monthly , and noise levels are analysed (see Sec. III A). For the sake of consistency, the measurement station number “eight” is excluded from the analysis as it was not operating in the months of September and October of 2019. Therefore, the measurement station number “eight” is omitted in Fig. 2, while the nomenclature identifying the measurement stations is kept consistent with the one used in the official document where the measurement data are available (Reinhart, 2019).
C. Aircraft noise simulation
The computational simulations are conducted in the commercial software SoundPLAN 8.2 and are based on the third edition of the best-practice method described by the Doc. 29 of the European Civil Aviation Conference (2005). A comprehensive overview of the Doc. 29 methodology is provided in the work of Isermann and Vogelsang (2010). In the following, details concerning the input data and the simulation procedure are provided.
1. Input data
A template with the setup of the HAJ Airport is provided in the software SoundPLAN. It includes all relevant airport data, such as reference points and runway coordinates, as well as a Digital Terrain model (DGM). Historic weather data concerning the air humidity (%), air pressure (mbar), temperature (°C) and headwind (kt) are obtained from the Weather Underground website (Weather Underground, 2022). Monthly averaged values of these weather parameters are used to conduct all computational simulations.
The simulations are conducted using radar tracks in the Flight Track and Noise Monitoring System (FANOMOS) data format, which was provided on request for this study by the German air navigation service provider “Deutsche Flugsicherung (DFS).” The FANOMOS data provides position and operational parameters describing a particular flight trajectory in discrete points with a temporal resolution of four seconds. The provided parameters are: time (s), x (m), and y (m) Universal Transverse Mercator (UTM)-coordinates, altitude above mean sea level (m) and groundspeed (m/s). Moreover, information regarding each flight, such as date, actual time of arrival/departure, origin, destination, runway, callsign, aircraft type, and procedure type are provided.
Radar data concerning all flight operations at the HAJ Airport along the six months of the years 2019 and 2020 with the largest air traffic (see Sec. III A) were requested. The received dataset contains a total of 40 487 and 22 496 flights for the years 2019 and 2020, respectively. The dataset includes radar tracks with unrealistic flight trajectories, circuit and flyover flights, helicopter operations (which are not supported by the Doc. 29 method), and flights with unassigned runway or aircraft types. These radar tracks are automatically excluded during the import process in SoundPLAN.
2. Simulation procedure
The simulation setup and procedure conducted in SoundPLAN 8.2 is briefly described hereafter. First, a situation concerning each case to be simulated is configured. Each situation case is composed by input data concerning the HAJ Airport setup, coordinate settings, weather conditions, terrain topography, receiver positions and the radar tracks.
SoundPLAN can import radar tracks in the FANOMOS data format and automatically correct unrealistic trajectories or discard inappropriate flight tracks according to numerous criteria. Radar tracks do not include any information about the aircraft thrust and flap settings which are necessary for the simulations based on the Doc. 29 method. Therefore, SoundPLAN automatically assigns standard elevation profiles to each flight track based on the aircraft type, flight procedure, and altitude profile. The database containing standard aircraft-specific elevation profiles, which is provided by the Aircraft Noise and Performance database (ANP) from the Eurocontrol Experimental Centre (2022) covers a limited number of aircraft types. Therefore, SoundPLAN automatically discards flight tracks with unrecognized or nonexistent aircraft types or automatically replaces them based on a substitution list provided by the ANP. The final simulated dataset contains 35 008 and 17 338 flight tracks (arrival+departure) for the years 2019 and 2020, respectively.
Finally, each flight track is simulated individually and the noise footprints are computed on a grid of receiver positions with a spatial solution of 10 m and a height of 4 m above the ground. Additionally, in order to gain insight into the accuracy of the simulation results, a validation study (see Sec. III B 1) is performed through comparison with publicly available measurement data. For this purpose, simulations are conducted considering single receiver positions corresponding to the locations of the measurement microphones considered in this work (see Sec. II B). In this case, the noise levels are computed at the actual height of the measurement microphones.
This section presents the results of the comparative study of the noise levels generated by the air traffic at the HAJ Airport region in the years 2019 and 2020. It is important to highlight that the assessment period is defined as the six months of the forecast year with the largest number of flight operations, as previously discussed in Sec. II A. Therefore, the comparative study presented hereafter analyzes and levels for each year, which are averaged for this time period and not throughout a one year time period. Section III A presents the results of the comparative study based on publicly available measurement data (see Sec. II B). Section III B, presents the results of the comparative analysis based on aircraft noise simulations (see Sec. II C).
A. Noise measurements
It is possible to observe in Fig. 3 that, in comparison with the year 2019, the noise levels were reduced in all measurement stations in 2020. This holds for both the day and night periods of the day. Nevertheless, the noise reductions during the nighttime were higher than during the daytime at all measurement locations. When statistically analysing the difference between the noise levels in the years 2019 and 2020 from all measurement stations per period of the day, the average and standard deviation noise reductions for the daytime are observed to be , while for the nighttime .
Furthermore, Fig. 3 shows that the noise reductions during the daytime have a similar magnitude for all measurement stations, which is expressed by the relatively small standard deviation around the mean value. On the other hand, a relatively larger standard deviation around the mean value is observed for the nighttime. This is mainly due to the noise reduction measured at the station “six,” which is substantially higher than the noise reductions at the other measurement stations. As the measurement station “six” is located near the runway 09R/27L (see Fig. 2), this may indicate that the reduction of observed in this location is associated with a decreased number of flight operations in this particular runway.
By analysing publicly available data concerning the number of flight operations per runway (Reinhart, 2019) (see Fig. 4, where helicopter operations and flight operations on the runway 09C/27C are not included), it is possible to argue that the larger noise reductions observed for the nighttime in comparison to the daytime may be attributed to the substantial decrease in flight operations in this period of the day for the year of 2020 in comparison to the year of 2019. In comparison with the year 2019, a reduction in night flight operations of and is observed in the runways 09L/27R and 09R/27L, respectively, in the year 2020. In counterpart, the reduction of flight movements during the daytime is observed to be of and in the runways 09L/27R and 09R/27L, respectively. The substantial reduction of flight movements during the nighttime in the runway 09R/27L may explain why the noise reductions observed in the measurement stations “one” and “six” are the largest among all measurement stations for this period of the day.
In Fig. 3, the noise reduction on locations which the noise levels in the year of 2019 exceed the critical values determined by the German federal legislation (see Sec. II A) are of particular interest. During the daytime, the measured noise levels in the year 2019 do not exceed the determined threshold values of and at any of the measurement stations. However, the noise levels measured in the year 2019 by the measurement stations “two” ( ) and “nine” ( ) are above the value established for the nighttime protection zone. These measurement stations are particularly located near the runway 09L/27R (see Fig. 2) which, according to Fig. 4, is the main runway used at the HAJ Airport during the daytime and nighttime. For the measurement stations “two” and “nine,” noise reductions of and , respectively, are observed, meaning that the levels in these measurement locations were reduced below the recommended critical values for the nighttime in the year 2020.
Figure 5 presents a comparison between the levels measured in the years 2019 and 2020 per measurement station. The results are expressed in terms of level differences, which are computed in the same fashion as Eq. (1). It is possible to observe that, except for the measurement stations “four” and “five,” the levels measured in the year of 2019 at all remaining measurement stations exceeds the criteria defined by the state of Lower Saxony (see Sec. II A). In counterpart, the levels measured at the stations “one,” “three,” “six,” and “seven” have been reduced to levels below the criteria in the year of 2020. Therefore, in the year 2020, the levels are observed to be below the established criteria in a total of six measurement stations and only exceed the criteria at measurement stations “two” and “nine.” In general, the mean and standard deviation reductions computed when considering all measurement stations are observed to be with respect to the year 2019.
B. Computational simulations
The comparative study conducted hereafter is based on the computational simulations described in Sec. II C. First, a validation study is presented in Sec. III B 1 in order to evaluate the accuracy of results provided by the simulations. Later, a comparative study between the isocontour area of the , and noise protection zones in the years of 2019 and 2020 is presented in Sec. III B 2.
1. Validation study
In order to ensure that the computational simulations provide representative predictions, a validation study is performed by means of comparison with publicly available measurement data (Reinhart, 2019). For this purpose, monthly , and levels are considered, corresponding to each one of the six months of the respective forecast years with the largest air traffic (see Sec. II A). Figure 6 presents a comparison between the simulation results and the measurement data in terms of relative noise level differences (simulation minus measurement), meaning that negative values express an underestimation of the simulation results in relation to the measurements and vice versa. The validation study is conducted by statistically analysing the relative differences in the monthly noise levels at all measurement stations considered in this study. The analysis is grouped by forecast year and noise metrics. Therefore, each data group comprises a total of N = 48 relative noise level difference values, corresponding to the location of the eight measurement stations considered in this work (see Fig. 2) times six noise levels per year.
It is possible to observe an acceptable agreement between simulations and measurements for all noise metrics and forecast years in Fig. 6. For the , the mean differences for both years are not larger than 0.1 dB, while the standard deviation is not bigger than 1.1 dB. Concerning the , the simulation results for the year of 2019 underestimate the measurement data by mean and standard deviation differences of , while for the year 2020, the mean and standard deviation differences are . The relatively large standard deviation, in this case, is attributed to overestimations of the simulation results by up to 11 dB in relation to the measurement results. Finally, the mean and standard deviation differences between simulations and measurements are and for the years 2019 and 2020, respectively. For the year 2020, differences up to 7 dB were observed. The acceptable agreement between simulations and measurements means, among other factors, that the dataset of radar tracks used for the simulations provides a representative description of the air traffic at the HAJ Airport during the daytime and nighttime periods for both forecast years. The observed differences between measurements and simulations may be attributed to uncertainties related to the accuracy of the weather and air traffic input data. Moreover, it is shown by Merino-Martinez (2019) that the use of standard elevation profiles may have a relevant influence on the predictions provided by simulations based on the Doc. 29 method.
2. Noise protection zones
Figure 7 presents a comparison between the and isocontours in the years of 2019 and 2020. It is possible to observe that the isocontours mainly encloses the airport premises and do not reach any of the measurement stations, which is in agreement with the results presented in Sec. III A. Nevertheless, residential areas located west from the airport premises and close to runway 09R/27L are verified to be within the daytime protection zone 2. In this particular region, a relevant decrease in the isocontour is observed during the year 2020, meaning that fewer residential areas were impacted by critical noise levels during the daytime.
Concerning the night protection zone, the results presented in Fig. 7 show a relevant reduction of the isocontour in the year 2020, especially around the runway 09R/27L. This may be due to the substantial decrease in the number of flight operations on this particular runway during the nighttime, as previously discussed in Sec. III A. Nevertheless, it is possible to observe that the residential areas close to the noise measurement stations “two” and “nine” also benefited from the decreased number of flight operations on the runway 09L/27R. This means that the number of residential areas affected by noise levels above during the nighttime in the year 2020 may be substantially lower than in the year 2019.
Figure 8 presents a comparison between the isocontours in the years 2019 and 2020. It is possible to observe that, in the year 2019, only the residential areas near the measurement stations “four” and “five” were not inside the settlement restriction area defined by the isocontour. In counterpart, during the year 2020, a substantial reduction of the isocontour in comparison to the year 2019 is observed and only the residential areas near the measurement stations “two” and “nine” are observed to experience above the recommended level. This is mainly due to the proximity of these two measurement stations to the runway 09L/27R which, according to Fig. 4, is the main runway utilized in the HAJ Airport in both years 2019 and 2020.
Table I provides the isocontour area of each one of the noise protection zones and the relative percentage change in area size with respect the reference year 2019. It is possible to observe that isocontour is reduced by 54.08% in the year 2020, which is the largest isocontour area reduction observed, followed by a 49.03% reduction of the . Finally, compared to the year 2019, the is reduced by 40.29% in the year 2020.
|.||2019 .||2020 .||2020 minus 2019 .|
|Protection zone .||Area (km2) .||Area (km2) .||% change .|
|.||2019 .||2020 .||2020 minus 2019 .|
|Protection zone .||Area (km2) .||Area (km2) .||% change .|
The results of the comparative study based on publicly available data show that, in comparison to the year 2019, the noise levels were reduced in all considered measurement stations in the year 2020. By statistically analysing the differences between the noise levels in the years 2019 and 2020 at all considered measurement stations, it is shown that the noise reductions during the nighttime were higher than the ones observed during the daytime. This fact is discussed to be mainly due to the substantial decrease in the number of flight operations during the nighttime in 2020.
The results of the comparative study based on the computational simulations complements the findings observed by analysing the measurement data. In comparison to the year of 2019, the isocontour area is reduced by 40.29% and encloses mainly the airport premises. Moreover, in the year of 2020, the isocontour area of the night protection zone established by is reduced by 54.08% in comparison with the year of 2019. With the reduction of the nighttime protection zone, no residential areas near the measurement stations are observed to experience noise levels above the criteria established by the German federal government. Finally, the isocontour area of the settlement restriction area is observed to be reduced by 49.03% and only the residential areas near the runway 09L/27R—which is the main runway used at the HAJ Airport—are observed to experience noise levels above the recommended in the year of 2020.
We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy–EXC 2163/1–Sustainable and Energy-Efficient Aviation, Project-ID 390881007. Furthermore, we acknowledge the support of the Open Access Publication Funds of the Technische Universität Braunschweig. The authors would like to thank the Deutsche Flugsicherung GmbH (DFS) for providing the radar tracks (FANOMOS data) used in this work for the aircraft noise simulations. Moreover, the support provided by Mr. Michael Staats from the Noise Management Department of the Hannover-Langenhagen Airport is greatly acknowledged. This paper is part of a special issue on COVID-19 Pandemic Acoustic Effects. The authors declare that they have no conflict of interest.