Aircraft Noise Measurements at Gardermoen Airport - Sintef

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62 Measurement Program2.1 Measurement site and measurement positionsThe site for the noise measurements was located to the north and east of the western runwaysystem, as shown in Appendix 1. The measurement positions are numbered 1 - 5. Position 1 issituated inside the airport area, directly below the flight path and 400 m from the runway end.Position 2 is also in line with the runway, just outside the airport area at a distance of 1150 m fromthe runway end. Positions 2 - 5 are situated on a straight line slightly tilted to the perpendicular tothe runway extension. The distances from position 2 are 400 m, 800 m and 1250 m for positions 3,4 and 5 respectively.The terrain along the line of measurement positions is relatively flat, although smooth terrainundulation occurs causing terrain height variations of a few meters. The ground type in the area ismainly sandy soil, with varying extent of grass coverage. Position 2 is situated at the border of aspruce forest area. Position 5 is placed in an area sparsely covered by tall spruce or deciduous trees.Else, the area of the measurement positions is open land.An agreement with the Airline Company SAS was vital to the program to attain flight-recorder datafrom selected flights. The SAS operations at OSL mainly consist of narrow-body aircraft of the MD80 family, “Next Generation” B737s and a few MD90s.2.2 Acoustical InstrumentationThe measurement positions 2 - 5 all had microphones at two heights. The lower microphone wasput at 1.5 m above ground. The higher microphone height varied between 6.5 - 10.5 m aboveground. At measurement position 1 only one microphone was used. This microphone was attachedto the runway approach light bar arrangement, approximately 6.5 m above ground.The acoustic measurement equipment consisted of condenser microphones (1/2" with standard 9cm diameter windscreen) connected to Nor-121 Environmental Analysers manufactured byNorsonic AS. Instrumentation is described in detail in Part 2 of the report. A schematic layout isshown in Appendix 1 of this report.The instruments were pre-set to measure LEQ and LMAX(FAST) in 0.25-second intervals in 1/3-octave frequency bands 25 - 10,000 Hz and both A-weighted and C-weighted. The data were storedelectronically at each position and at the end of every session the data were transferred to acomputer and recorded to CD-ROM.2.3 Measurement synchronisationFor synchronisation purposes, the measurement instruments were connected to a PC with speciallydesigned software for generating trigger signals and reading/storing of trigger signal time from anexternal GPS clock. Three GPS clocks were used; one for position no. 1, one for position number 2- 5, and one for synchronisation of aircraft movements on the runway.2.4 Aircraft TrackingThe task was to determine the position of an aircraft at a certain moment of time during the noisemeasurement. Additionally, other flight parameters such as velocity and thrust level had to besynchronised with the noise measurements. Data from the airport radar tracking system wasavailable, as well as flight-recorder data from selected flights. Below is an outline of the proceduresthat were investigated.

8other flight parameters were taken from the flight recorder after time synchronising as described in(2), and correcting as described in (7) and (8).For the 737s and MD90s, the position vs. time were taken from the GPS position data in the flightrecorder, after time synchronising and position adjustment as described in (2), (4) and (6). All otherflight parameters were taken from the flight recorder data after time synchronising as described in(2), and correcting as described in (7) and (8).2.5 Meteorological and Ground Type DataA 10 meters high mast with meteorological equipment was erected at position no. 4 as shown inAppendix 2. The following parameters were recorded every minute:- Temperatures (°C) at two heights, 0.5 m and 9.25 m above ground,- Wind velocity and wind gust (m/s), wind direction, all at 9.25 m height,- Relative humidity (%) at 9.25 m height,- Precipitation (rainfall) (mm)- Net radiation (W/m 2 )The net radiation was measured in an attempt to estimate the relative cloud cover in the sky.All data are average values, except for wind gusts that represent maximum values. Graphicalpresentations are presented in Appendix 2.The acoustic impedance of the ground surface was measured at the measurement positions exceptfor position no. 1. A typical measurement layout is shown in Appendix 3.2.6 Measurement ProceduresThe noise measurements were carried out during June 20 – 27, 2001. The measurements werearranged in two separate sessions each day. The sessions lasted for 2.5 – 4 hours. After acousticcalibration the equipment were brought in position and checked for proper operation. Theequipment were all battery operated. The measurements were started independently at site I(position 1) and site II (positions 2 – 5) by the site PC giving a trigger signal, and simultaneouslyrecording the GPS time. The measurement of sound levels according to section 2.2 then proceededcontinuously through the session. Positions 2 – 5 were manned in order to register events ofbackground noise that might affect the aircraft noise.Personnel situated in the airport control tower registered the aircraft movements as described insection 2.4. The registrations included the GPS time for the special movements along with the flightidentification and the arrival/departure time. All the registrations were saved on data files.At the end of the sessions the measurements were stopped manually by the attending personnel.After the last session each day the equipment were collected for acoustic calibration, transferring ofdata files to a main PC, making backup CDs, etc.

93 Data Reduction and Processing, Overview3.1 Time-Space-Position AnalysisThe position of the aircraft as function of time was extracted from the airport radar tracking system,the aircraft flight recorder, and manual GPS clock operations, as described in section 2.4. For allaircraft, the position data and the other flight parameters were interpolated to have a regular, 0.5-second step length. There were a total of 155 valid flights, 70 with position taken from the aircraftGPS, and 85 with position taken from the airport radar tracking system.The aircraft position data was given as east/north co-ordinates, and height above runway. Using theco-ordinates of the measurement positions and the height of the microphones above ground, thetriplet (east, north, height) was replaced with the triplet (lateral distance, elevation angle, azimuthangle relative to north). In this way the position of the aircraft was expressed in units needed for thefollowing data processing.3.2 Net thrust dataFlight recorder data provide engine thrust settings that has to be transformed into net thrust.Equations for this purpose are found in the SAE AIR 1845 [6]. When the aircraft engines are beingoperated at thrusts other than rated thrust, the thrust developed is a function of the thrust-settingparameter. When engine pressure ratio (EPR) is available the corrected net thrust per engine iscalculated by:( Fn amC A Bam+12/ δ ) = E + FV + G h + G h + HT K ( EPR)(3.1)F n is the net thrust per engine,δ am is the ratio of the ambient air pressure at the aeroplane to the standard air pressure at meansea level,V c is the calibrated airspeed (kts),h is the pressure altitude above sea level,T am is the ambient air temperature,E, F, G A , G B , K 1 and H are constants or coefficients, which are taken from the INM 6.0cdatabase for the relevant operating conditions,EPR, V c and h are available from the flight-recorder data.When the thrust is defined by N 1 , the corrected net thrust is calculated by:22( Fn/ δam) = E + FVC+ GAh+ GBh+ HTam+ K2( N1/ θT) + K3( N1/ θT) (3.2)N 1 is the engine's low pressure rotor speed,θ T is the ratio of absolute total air pressure at the engine inlet to the absolute standard airtemperature at mean sea level,K 2 and K 3 are coefficients, which are taken from the INM 6.0c database for the relevantoperating conditions.3.3 Noise event extraction – exclusion of background noise influenceThe raw noise level measurement results were filtered to determine a background noise level.Background noise level was defined separately for each 1/3-octave band as the level that wasexceeded 90% of the time (L90). The background noise level was determined for a 30-minute widetime window, which was moving in 5-minute steps.

10The personnel at each measurement site registered random noise disturbances like vehicle noise,bird singing, voices, etc. Not all of these possible disturbances had significant sound levelscompared to the aircraft noise. Therefore, the time intervals of these disturbances had to bemanually defined afterwards, based on the shape of the time history. Both the A-weighted and the1/3-octave band data were used to find and define the time intervals of the significant disturbances.To locate noise data corresponding to a specific flight, and to eliminate the effects of backgroundnoise and noise from preceding/succeeding flights, the following criteria were applied in the orderlisted (only landing criteria are listed; takeoff criteria were similar):1. Noise data time window must be inside time window of aircraft position data (the delay of thesound propagation is accounted for).2. Noise data must not include time intervals with disturbance.3. A peak must be found within 60 seconds before touchdown, and minima must be foundbetween touchdown and 90 seconds before touchdown.4. Noise level must be higher than 10 dB above the levels at the minima.5. Noise level must also be higher than 10 dB above the background noise level.6. The remaining noise data must span at least 10 dB down at either side of peak.The table below shows the number of valid flights after the criteria above were applied to the A-weighted noise data. For the 1/3-octave band data, the number of valid noise events were dependenton frequency.Table 3.1Number of valid noise events after applying filtering criteriaAircraft type Pos. 1 Pos. 2 Pos. 3 Pos. 4 Pos. 5 TotalB736 31 20 24 27 30 132B737 35 23 31 31 27 147B738 2 1 2 1 1 7MD81 24 18 17 19 19 97MD82 48 35 36 38 40 197MD83 1 1 1 1 1 5MD87 11 8 9 7 7 42MD90 3 3 3 3 2 14Total 155 109 123 127 127 641The result of the extraction process was data files containing one line per aircraft position andmeasurement position, at a time resolution of 0.5 second. Each line contained all relevant flightparameters and the corresponding measured sound level, i.e. the 0.5-second LEQ was the energyaverage of two consecutive 0.25-second LEQ.3.4 SEL calculationFor each flight, the closest point of approach (CPA) was assumed to equal the position where thelateral distance to the measurement position was smallest. At this point, the lateral distance,elevation angle and slant distance was extracted, together with all the other flight parameters. Fromthe noise data the sound exposure level (SEL) was determined according to:Leq /10( ∑0.5⋅10)SEL = 10log(3.3)

11The sum is taken over all 0.5-second time steps for the current noise event, which fulfil the criterialisted in section 3.3. In addition the maximum level (MAX) was found, based on 1-secondequivalent sound pressure levels derived from the 0.5-second equivalent sound pressure levels.3.5 Aircraft noise spectraFor all aircraft types, average noise spectra were found for takeoff and landing. The spectra werebased on SEL values for each 1/3-octave band. Only data from measurement positions 1 and 2 wereused. The sound attenuation in air was accounted for by using the ISO 9613-1 standard [4]. Atemperature of 20 degrees Celsius and a relative humidity of 60% were used, in accordance withmeasured average weather conditions. The distance used for the sound attenuation was the height ofthe aircraft above the microphone at CPA.3.6 Meteorological and Ground Type dataThe meteorological data are already suitably processed by recording values for subsequent 1 minuteintervals. This is assumed to be sufficient to link meteorological parameters to single flights.As can be seen from the accumulated weather description in Appendix 2, wind speeds were mostlylow (i.e. wind speeds well below 5 m/s). The wind direction was mostly due North or South, whichmeans minor components of down- or up-wind at the measurement positions. The temperaturegradient revealed prevailing negative values, corresponding to summer conditions with varyingsunlight brightness.The acoustic impedance of the ground surface was assumed to follow the Delaney/Bazley model.The important parameter is the flow resistivity (Pa s/m 2 ) which was determined from acousticmeasurements according to Nordtest standard [3], for a number of test areas at the measurementpositions. The main result is the average flow resistivity relevant to positions 2 - 5, as given inTable 3.2.Table 3.2 Measured Flow Resistivity (kPa s/m 2 )Pos. no. 2 Pos. no. 3 Pos. no. 4 Pos. no. 5400 250 250 - 400 100

124 Data AnalysisThe data analysed in this chapter are all based on the 155 valid flights shown in Table 3.1.4.1 Noise source directivityThis chapter presents noise source directivity 2 of the measured aircraft types separated for each 1/3-octave frequency band from 25 to 10,000 Hz. The directivity is calculated from the measured data,using a propagation model that eliminates the influence of distance, ground surface and weather,thus giving the actual sound emission from the aircraft. Part 2 of the report includes a memo withall results. This chapter only highlights a few of the major findings.4.1.1 Analysis toolsThe sound pressure level of every measurement sample (2 per second) is propagated back to thesource, using the model Nord 2000 [12]. This is a modern ray-tracing model, which accounts forthe influence of topography, ground impedance, wind- and temperature gradients, and turbulenceeffects in the atmosphere. The calculations are done in a special developed MATLAB® program. Todescribe the 3D directivity as precise as possible, the program accounts for all aircraft angles(heading, pitch and roll), as well as the full source-to-receiver geometry.A separate computer program has been developed to visualise the source directivity. The result isdisplayed as a colour map of the hemisphere below the aircraft, projected to a plane. Thehemisphere above the aircraft is disregarded in these analyses. The projection is a hybrid polarprojection with side angle in the wing-plane (Theta) along the projection circle, and azimuth angle(Phi) displayed as radius. Theta is set to 0 in front, 90 degrees to the right, 180 degrees behind etc.Phi is 0 straight above the aircraft, 90 degrees in the wing-plane, and 180 degrees straight below(see Figure 4.1). This projection is chosen because it preserves the real area of any shape projectedfrom the hemisphere to the plane, which means that grouping, smoothing, and other statisticalanalyses can be based on the x, y co-ordinates of the projection plane. The projection however, doesnot preserve the shape of any object.To help visualise any axis-symmetry in the directivity, lateral lines are added to the diagram (seered lines in Figure 4.1). These connect points in the projection with constant angle to the flightheadingvector. Any axis-symmetry (i.e. cylindrical symmetry) in the data set will display ascoloured areas parallel to these lines.In the source directivity program all source data for one aircraft type can be displayed. Differentfilters can be added to the data to investigate how the directivity changes due to operation (arrivaland departure), thrust interval, frequency, measurement position and microphone height. In additiondata can be excluded based on user defined parameters for background noise, source – receiverdistance, aircraft elevation angle, and quality indicators in the propagation model.2 The term “directivity” used herein is the distribution of backwards propagated sound pressure levels over thehemisphere below the aircraft. This should not be mixed with the normalised directivity that usually characterisessingle sound sources.

13Figure 4.1 Directivity projection. Theta angles in blue (outside circle). Phi angles in grey(inside circle). Lateral lines (axis-symmetric) display equal angle to flight vector.Finally the program is able to calculate statistics for a resulting averaged source directivity, andproduce report files containing source spectra, directivity plots and tables. Directivity parametersare averaged according to a grid. We assume symmetry between right and left side of the aircraft.Thus all data are transferred to the right-hand side of the aircraft before statistical analyses. Tocover all angles, the grid-cells with less than 10 samples are automatic set equal to the closest gridcellwith more than 10 samples. The resulting averaged source directivities with correspondingstatistics are tabulated in ASCII text files. They are not included in this report due to spacelimitations.4.1.2 Backward propagation parametersThe backward propagation from receiver to source is based on:• Nord 2000 algorithms.• Actual geometry including flight position and orientation sampled every 0.5-second.• Actual ground impedance measured close to the receiver.• Air absorption based on actual measured temperature and humidity, smoothed over 30minutes.• Actual wind speed and direction smoothed over 7 minutes.

14• Temperature gradient is set to –1 degrees per 100 meter, in accordance with measuredmeteorology and expert judgement [13] of the total weather situation.• No topography corrections (horizontal ground assumed).• After backward propagation, the data is normalised to a fixed thrust setting of 10,000Lbs. This is done by subtracting 1.1 dB per 1000 Lbs. thrust exceeding 10,000 Lbs.4.1.3 Data filteringA series of test calculations of source directivity were done to verify the quality, and find optimumsettings for filtering parameters. The goal was to exclude suspicious data, and gain highest possiblestatistic strength in the results. Preliminary results indicated that the directivity does not changemuch with varying thrust, so the figures display the directivity as an average for all measured thrustsettings, after separation between arrival and departure.The optimised filter settings where:• No specific adjustment for background noise other than what was done with the rawmeasurement data (se Section 3.3).• All data propagated more than 2 km where excluded.• On departures, all data propagated at an elevation angle less than 15 degrees wereexcluded. 3 On arrivals no data where excluded due to elevation angle.• All data with air and ground attenuation more than 30 dB were excluded.4.1.4 Directivity resultsIn the technical memo in part 2 of the report the directivity plots are shown for each aircraft type.The data is organised as one spectrum table and 27 directivity plots, one for every 1/3-octave band.The table covers all measured directions from the aircraft, and has the following columns:• Freq.: 1/3-octave centre frequency from 25 to 10,000 Hz.• Num.: Number of 0.5-second measurement samples.• Avg.: Arithmetic average sound level 1 meter from a point representing the aircraft• Std: Standard deviation of the 0.5-second sound levels.• 95%Avg: The +/- deviation for the average sound level, within 95% confidence interval.• P1, …P6: Average level for each engine power setting, grouped according to the NPDtable. (No data is denoted –1).The directivity plots show all 0.5-second samples as noise levels 1 meter from a point representingthe aircraft. They are plotted in the projection of the hemisphere below the aircraft, describedabove, as one small circle per sample. The colour of the circle indicates the deviation from theaverage of all samples, according to a colour scale ranging +/- 15 dB. Black circles indicate that thesample is outside the colour scale.At the top of both tables and directivity plots, the aircraft type is indicated, along with the one letterindicator “A” for arrival and “D” for departure. In the plots, the 1/3-octave centre frequency, andaverage sound level is indicated.Table 4.1 and 4.2 show examples of directivity data for the aircraft B737-600 and MD82 ondeparture.3 This filter only removes data in front of the aircraft and does not influence data to the side or behind.

15Table 4.1B737 600 mean spectrum on departureSPECTRUMSource EmissionB736DFreq. Num. Avg. Std 95%Avg P1 P2 P3 P4 P5 P625 7426 120.2 6.7 0.2 -1.0 -1.0 119.4 120.3 -1.0 -1.031.5 8568 121.9 6.0 0.1 -1.0 -1.0 121.1 121.9 -1.0 -1.040 8738 122.5 5.6 0.1 -1.0 -1.0 121.9 122.6 -1.0 -1.050 9146 123.1 5.2 0.1 -1.0 -1.0 122.1 123.2 -1.0 -1.063 9345 124.2 5.0 0.1 -1.0 -1.0 122.5 124.4 -1.0 -1.080 9799 125.4 4.7 0.1 -1.0 -1.0 122.9 125.6 -1.0 -1.0100 9982 125.3 4.3 0.1 -1.0 -1.0 122.5 125.6 -1.0 -1.0125 10195 124.6 4.3 0.1 -1.0 -1.0 122.0 124.8 -1.0 -1.0160 10203 123.6 4.6 0.1 -1.0 -1.0 120.7 123.9 -1.0 -1.0200 10298 123.0 5.0 0.1 -1.0 -1.0 119.5 123.3 -1.0 -1.0250 10331 122.5 4.9 0.1 -1.0 -1.0 120.0 122.7 -1.0 -1.0315 10365 121.4 5.3 0.1 -1.0 -1.0 118.0 121.7 -1.0 -1.0400 10344 120.5 5.6 0.1 -1.0 -1.0 117.1 120.8 -1.0 -1.0500 10330 119.9 6.0 0.1 -1.0 -1.0 116.0 120.3 -1.0 -1.0630 10286 119.0 5.7 0.1 -1.0 -1.0 115.1 119.3 -1.0 -1.0800 10254 118.1 5.3 0.1 -1.0 -1.0 113.9 118.5 -1.0 -1.01000 10210 117.5 5.4 0.1 -1.0 -1.0 113.2 117.9 -1.0 -1.01250 10219 117.2 5.5 0.1 -1.0 -1.0 112.8 117.5 -1.0 -1.01600 10188 117.3 5.6 0.1 -1.0 -1.0 112.8 117.7 -1.0 -1.02000 9856 118.2 6.1 0.1 -1.0 -1.0 114.1 118.6 -1.0 -1.02500 9198 119.0 5.2 0.1 -1.0 -1.0 116.7 119.2 -1.0 -1.03150 7390 120.7 5.2 0.1 -1.0 -1.0 120.1 120.8 -1.0 -1.04000 4334 121.2 5.4 0.2 -1.0 -1.0 121.2 121.2 -1.0 -1.05000 1772 121.1 5.2 0.2 -1.0 -1.0 120.8 121.1 -1.0 -1.06300 463 120.7 5.8 0.5 -1.0 -1.0 121.6 120.6 -1.0 -1.08000 81 119.5 7.2 1.6 -1.0 -1.0 122.0 119.1 -1.0 -1.010000 7 111.6 7.4 5.5 -1.0 -1.0 -1.0 111.6 -1.0 -1.0

16Figure 4.2Noise source directivity pattern B737-600 Departure for some 1/3 octave bands

Figure 4.3 Noise source directivity pattern B737-600 Arrival for some 1/3 octave bands17

18Table 4.2MD 82 mean spectrum on departureSPECTRUMSource EmissionMD82DFreq Num Avg Std 95%Avg P1 P2 P3 P4 P5 P625 13546 124.2 8.3 0.1 -1.0 -1.0 -1.0 -1.0 125.2 -1.031.5 14365 126.1 8.1 0.1 -1.0 -1.0 -1.0 -1.0 127.1 -1.040 15589 127.0 8.0 0.1 -1.0 -1.0 -1.0 -1.0 128.0 -1.050 15535 128.3 8.2 0.1 -1.0 -1.0 -1.0 -1.0 129.3 -1.063 15698 130.0 8.5 0.1 -1.0 -1.0 -1.0 -1.0 131.0 -1.080 16139 131.4 8.1 0.1 -1.0 -1.0 -1.0 -1.0 132.4 -1.0100 17310 131.5 7.4 0.1 -1.0 -1.0 -1.0 -1.0 132.3 -1.0125 18411 131.0 6.3 0.1 -1.0 -1.0 -1.0 -1.0 131.6 -1.0160 18694 130.6 5.8 0.1 -1.0 -1.0 -1.0 -1.0 131.0 -1.0200 18727 130.4 5.9 0.1 -1.0 -1.0 -1.0 -1.0 130.8 -1.0250 18716 130.4 5.6 0.1 -1.0 -1.0 -1.0 -1.0 130.7 -1.0315 18689 130.2 5.7 0.1 -1.0 -1.0 -1.0 -1.0 130.3 -1.0400 18745 129.8 5.8 0.1 -1.0 -1.0 -1.0 -1.0 129.8 -1.0500 18690 129.3 5.6 0.1 -1.0 -1.0 -1.0 -1.0 129.2 -1.0630 18749 129.1 5.5 0.1 -1.0 -1.0 -1.0 -1.0 129.0 -1.0800 18610 128.8 5.4 0.1 -1.0 -1.0 -1.0 -1.0 128.7 -1.01000 18695 128.3 5.5 0.1 -1.0 -1.0 -1.0 -1.0 128.3 -1.01250 18687 127.6 5.6 0.1 -1.0 -1.0 -1.0 -1.0 127.6 -1.01600 18675 126.9 5.7 0.1 -1.0 -1.0 -1.0 -1.0 126.9 -1.02000 18504 126.6 5.7 0.1 -1.0 -1.0 -1.0 -1.0 126.6 -1.02500 17610 126.8 5.6 0.1 -1.0 -1.0 -1.0 -1.0 126.9 -1.03150 13494 126.5 5.6 0.1 -1.0 -1.0 -1.0 -1.0 127.0 -1.04000 7188 126.0 5.7 0.1 -1.0 -1.0 -1.0 -1.0 126.7 -1.05000 2948 124.4 6.5 0.2 -1.0 -1.0 -1.0 -1.0 124.7 -1.06300 803 121.0 7.6 0.5 -1.0 -1.0 -1.0 -1.0 121.5 -1.08000 150 117.1 8.5 1.4 -1.0 -1.0 -1.0 -1.0 117.1 -1.010000 19 110.9 10.4 4.7 -1.0 -1.0 -1.0 -1.0 117.2 -1.0

19Figure 4.4Noise source directivity pattern MD82 Departure for some 1/3 octave bands

20Figure 4.5Noise source directivity pattern MD82 Arrival for some 1/3 octave bands

214.1.5 CommentsThe directivity analyses can be summarised in the following main results:• The directivity is strongly dependent on frequency.• The directivity is fundamentally different between the aft-fuselage mounted-engineaircraft (MD8x, MD90) and wing-mounted-engine aircraft (B73x). This is especially thecase below 1000 Hz, which is the dominating frequency range in noise zoningsituations. Aft-fuselage-mounted-engine aircraft has a very distinct directivity lobebehind and below the aircraft at mid and low frequencies, while wing-mounted-engineaircraft are more omni directional.• There is no fundamental difference in directivity between MD8x and MD90, eventhough the engine type is different.• There is a fundamental difference between the directivity of B73x and MD90, eventhough the engine type is similar. Connected to the above two points, this indicates thata major difference in directivity depends more on engine placement, than engine type.• The sound radiation downwards is generally stronger than to the side. This is clearlymost evident behind aft-fuselage- mounted-engine aircraft, at mid and lowerfrequencies.• The directivity does not change significantly within the thrust intervals covered by themeasurements.4.2 Lateral AttenuationTwo methods have been used to determine lateral attenuation:• Through measurements where the A-weighted data were used to estimate the lateral attenuationby comparison of noise levels measured directly below the flight and at positions to the side.• Through simulations based on the source directivity spectra found in 4.14.2.1 Lateral attenuation as measuredIt was assumed that the measurement positions 2 – 5 were situated on a line orthogonal to the flightpath. The lateral attenuation (LA) was calculated according to equation (4.1):LA⎛ d ⎞k k2 k ⎜ ⎟ kK (4.1)⎝ h2⎠k( l , θ ) = SEL − SEL −10log⎜⎟ − Φ k = 3 5Here, k is the measurement position, (l k ,θ k ,d k ) is the lateral distance, elevation angle and slantdistance from the measurement position to the aircraft respectively, and h 2 is the height of theaircraft above the microphone at position 2. Φ k is the A-weighted air absorption from the aircraft toposition k, which was calculated according to equation (4.2) :Φ[ S ] − A[ S − α( T,RH,)]= A (4.2)kd kHere A[] represents A-weighting, S is the noise source spectrum of the aircraft, T is thetemperature, RH is the relative humidity, and α( ) is the frequency dependent air absorption for thegiven temperature, humidity and distance. For each flight, the temperature and relative humidityvalues at the time of closest point of approach were used.

224.2.1.1 Comparison of measured lateral attenuation and SAE 1751The estimated lateral attenuation was developed per aircraft type and split on landing (LA) andtakeoff (TO) operations.In Figure 4.6 the estimated lateral attenuation is compared with the standard lateral attenuationgiven in SAE AIR 1751 [5]. The straight line in the figure indicates conformity of values.Figure 4.6Lateral attenuation, measured versus SAE prediction.

23In Figure 4.7 the estimated lateral attenuation is presented as a function of elevation angle. Alsoshown is the lateral attenuation according to SAE AIR 1751, corresponding to values at 300-mdistance, and to maximum attenuation (distance 914 m or more) which covers the actual span inlateral distance in this study.Figure 4.7Measured lateral attenuation versus elevation angle.4.2.1.2 Comments on measured lateral attenuationThe results indicated above may be influenced by thrust cutback during take off. Cutback isassumed to occur at an aircraft height of approximately 450-500 m above runway elevation. Thismeans that a small part of the takeoffs (TO) may be affected. However, the engine power cutbackrepresents a certain noise level reduction in both SEL 2 and SEL k in equation (4.1). The net effect inFigures 4.6 and 4.7 is therefore expected to be rather small.The measured lateral attenuation shows clearly that SAE AIR1751 overestimates the effect forthese aircraft. Since lateral attenuation in the recommendation combines effects from directivity,installation of engines and ground attenuation, it is not clear what contributes most to thedifferences measured. There is a tendency that B737 models have less lateral attenuation thanMD80 models. This may be due to any of the effects, since both noise source spectra, directivityand installation are different. Further investigations have therefore been undertaken to distinguishbetween the possible causes.4.2.2 Simulated lateral attenuationThe noise resulting from horizontal straight line flights have been simulated. The sound emission ofthe source is modelled by the spectra and directivities described in chapter 4.1. Flight speed is fixedto 160 knots, while flight height is variable.Sound pressure levels are calculated at different receiver points 1.5 meters above the ground belowthe flight line and to the side. Nord 2000 algorithms have been used to calculate the noise

24propagation from points along the flight line to the receiver point. Distance from receiver point toclosest point of approach is kept constant at two distances.The propagation conditions are set to:• Horizontal ground with a flow resistivity = 250,000 Pa s/m 2 .• Temperature = 15° Celsius.• Relative humidity = 70%.• Wind speed = 0.• Temperature gradient = -1°C/100m.• Wind turbulence parameter = 0.5.The turbulence parameter expresses the strength of turbulence due to wind. The value of thisparameter is adjusted by comparison between simulated and measured vertically separated soundpressure levels.The sound pressure levels at the receiver points are accumulated to A-weighted SEL values for thewhole flight.The following figure shows the difference between SEL below the flight line, and SEL to the sideat the same distance from the point. The results are plotted as function of elevation angle for MD82and B737-600. To indicate distance dependency, the curves are given at both 300 and 1200 meters.Simulated propagationLateral Attenuation incl. Ground Effect109876543210-1-20 10 20 30 40 50 60 70 80 90Elevation Angle (degrees)MD82 at 300mB736 at 300mMD82 at 1200mB736 at 1200mFigure 4.8Simulated lateral attenuation (dBA)The spectral source directivity and the ground attenuation both influence the curves. The differencebetween the two aircraft is caused by the spectral source directivity. Since directivity seems to bemore dependent on engine position than engine class, it can be concluded that the main differencebetween the two aircraft lateral attenuation is due to engine position.

254.3 Noise-Power-Distance dataThe measured A-weighted data were used to estimate the noise-power-distance data. Only datafrom measurement positions 1 and 2 were used, i.e. the positions directly below the flight path.4.3.1 Analysis methodThe measured levels were normalised from the actual atmosphere represented by ISO air absorptioncoefficients for the ambient temperature and relative humidity to the atmosphere represented by theair absorption coefficients tabulated in SAE AIR 1845 [6]. The A-weighted SEL levels for eachflight were corrected for speed by adding the correction V corr = 10log(V/160) according to SAE AIR1845, where V is the velocity (kts) of the aircraft at CPA.The A-weighted SEL- and MAX levels were compared to the corresponding noise curves from theNORTIM database noise-power-distance tables. For comparison with the NORTIM curves, thethrust levels of the measured data were grouped in intervals corresponding to the thrust levels of theNORTIM curves. The measured level at a specific thrust value was normalised to the curve valueby linear interpolation between the database noise levels.For the B737-600, the measured noise data are compared with the NPD curves for B737-500 fromthe database, since the latter lacks data for this specific aircraft type. Also, at this point, no data forthe B737-700 were included in the NORTIM database, and comparison for this aircraft type waswith the data for B737-400.4.3.2 ResultsA technical memo with all results is incorporated in Part 2 of the report. The memo contains figureswith comparisons of measurement results and database values for all the different aircraft types thatwere in the study for both SEL and LAMAX values. The following figures show the results for thetwo dominant aircraft types in the study, the MD 82 and the B737-600 (B736). In the followingfigures, the thrust levels of the NORTIM curves are annotated along the curves.

26Figure 4.9Comparison of database (NPD) and measured SEL for B737-600.Figure 4.10Comparison of database (NPD) and measured LAMAX for B737-600.

27Figure 4.11 Comparison of database (NPD) and measured SEL for MD 82.Figure 4.12Comparison of database (NPD) and measured LAMAX for MD82.

28Note that the NORTIM database levels for MD82 has been adjusted by + 1.5 dB for both SEL andLAMAX for the two upper thrust settings as compared to the INM database.4.3.3 Statistical analysisThe deviations (in dBA) between the NPD curves from the database and the normalised data havebeen analysed and the statistics on the differences are given in the following tables: for differencesin SEL values and LAMAX values respectively. The number of observations, mean value, standarddeviation and limits for the 95% confidence interval are shown for each aircraft and operation.A positive mean value suggests that the database NPD curves give too high noise value. Meandifferences are not significant if the number 0 lies between the limits of the 95% confidenceinterval.Table 4.3Statistical analysis of SEL value differencesType Operation No of Obs Mean St.dev CI_low CI_highB736 LA 20 4.1 1.6 3.4 4.9B737 LA 22 3.8 1.4 3.1 4.4B738 LA 3 1.4* 2.1 -3.8 6.6MD81 LA 13 -2.6 0.7 -3.0 -2.2MD82 LA 25 -1.6 1.6 -2.3 -1.0MD87 LA 8 -2.4 1.4 -3.5 -1.2MD90 LA 2 8.9* 6.5 -49.5 67.2B736 TO 31 -0.9 1.2 -1.4 -0.5B737 TO 36 -0.8 1.8 -1.4 -0.2MD81 TO 29 -0.8 1.1 -1.3 -0.4MD82 TO 58 -1.4 1.5 -1.8 -1.0MD83 TO 2 0.1* 1.6 -14.5 14.8MD87 TO 11 -1.1 1.2 -1.9 -0.3MD90 TO 4 -2.0 1.0 -3.5 -0.5* not significantTable 4.4Statistical analysis of LAMAX value differencesType Operation No of Obs Mean St.dev CI_low CI_highB736 LA 20 6.0 2.5 4.9 7.2B737 LA 22 6.3 2.6 5.1 7.4B738 LA 3 4.2* 2.7 -2.4 10.8MD81 LA 13 -1.8 1.1 -2.4 -1.1MD82 LA 25 -0.4* 2.5 -1.5 0.6MD87 LA 8 -1.6 1.8 -3.1 -0.1MD90 LA 2 12.3* 10.9 -85.9 110.5B736 TO 31 0.2* 1.6 -0.4 0.8B737 TO 36 0.4* 2.0 -0.3 1.1MD81 TO 29 -0.5* 1.9 -1.2 0.2MD82 TO 58 -1.2 2.4 -1.8 -0.6MD83 TO 2 0.7* 2.0 -17.1 18.6MD87 TO 11 -1.0* 1.6 -2.1 0.1MD90 TO 4 -3.8 1.0 -5.4 -2.2* not significant

294.3.4 CommentsIt is clear from the results that there are statistically significant differences between measured noisedata and the database values for similar thrust setting and distance for some aircraft. The results forSEL data is generally more stable with higher confidence than the LAMAX data.The deviations for the B737 family is not clear since substitutions have been used from thedatabase. However, the finding of a little, but statistically significant, higher SEL noise levels fortake-off from both –600 and –700 as compared to –500 and –400 respectively, is surprising, sincethe newer variants are supposedly quieter.Norwegian authorities decided that 1.5 dB should be added for MD80 family aircraft at take-offthrust values based on the Yuma tests in the early 1990’s [14]. Still the database underestimates theSEL values with up to 1.4 dB.4.4 Comparison of actual flight profiles with databaseA flight profile is defined as altitude, velocity and engine thrust settings as a function of distancefrom a reference point along the flight track. For a take-off profile, the reference point is the brakerelease point. For approach profiles, the reference point is the runway threshold at the touch downend of the runway.Flight recorder data give the possibility of constructing actual flight profiles. All 155 profiles havebeen extracted for the valid flights. Part 2 includes a technical memo with these profiles comparedto the corresponding database profiles.4.4.1 Examples of resultsBelow are examples for the MD82 aircraft, both for approaches and departures. For the arrivals, astandard glide path of 3 degrees has been assumed for all flights. For the departures, the stagelength has been calculated based on the ICAO code of the destination by the same procedures as isused in NORTIM.The figures show height, speed and net thrust as a function of distance from the reference point.

30Figure 4.13 Comparison of databaseapproach profile and 15 measured profiles forMD 82.Figure 4.14 Comparison of database takeoffprofile and 29 measured profiles for MD82.NOTE: The database thrust level for reverse thrustis not a physical value. It refers to a database noiselevel in the NPD curve.

314.4.2 Comments on database and flight recorder profile comparisonFor approach and landing there is little deviation from the 3 degrees glide slope with a fewexceptions where the aircraft is coming in steeper.Differences in speed and net thrust are evident. Outside 5000 meter (3 NM), the measured speed ishigher than the database profile. Outside 9000 meter (5 NM) the thrust is also generally lower,which results in less noise produced than the database profile would suggest.Between 9000 and 5000 meter from threshold there is an attitude shift in thrust enforcement. Froma stable low thrust, one enters a region with higher mean value and larger variations. Comparedwith the database profile, this higher mean value would result in higher equivalent noise. The noiselevel will fluctuate and prediction of maximum levels will be uncertain. For the shown variationsbetween net thrust 4300 and 8000 Lbs., the database NPD gives a difference in maximum noiselevel of 8-10 dB for this aircraft type.The measured take off profiles show that the INM database profile is based on different climb outprocedures. Lower thrust is applied both during take off run and throughout the climb. Powercutback can only be seen on around half of the events, most likely due to frequently use of deratedthrust procedures. The effects on noise level are mixed and will vary along the flight path and to thesides. A comparison test will be necessary to illustrate the effects of the different procedures.4.5 Influence of meteorology on air absorptionAppendix 2 shows recorded values of meteorology parameters during the exercise. It has previouslybeen argued that the difference in air absorption between the table given in SAE AIR 1845 andnormal Nordic weather conditions in it self would create an under-estimation of predicted aircraftnoise in the order of several dBs. The figure shows the combination of temperature and relativehumidity during the test, sampled at the time of closest approach at the meteorology system.Figure 4.15Temperature and relative humidity relation during each flight.

32Just a few of the flights were measured under conditions close to international standardisedatmosphere (ISA) of 15°C and 70% RH. Most of the time the temperature was higher and humiditywas less. The following figure shows the resulting air absorption, expressed in dBA, for themeasured mean noise source spectra for all operations. Three conditions are calculated based on theISO standard, reference [4] together with the absorption based on SAE AIR 1845.Figure 4.16Air absorption in dBA for a mean spectrum of all flights, as a function of source toreceiver distance.The figure shows that air absorption was generally higher than AIR 1845 coefficients during thetest. On colder days the air absorption may be less at some distance away from the source.However, the effect could be at a magnitude of tenths of a decibel and can therefore not aloneexplain the differences that are experienced between long-term measurements and calculations.4.6 Quality check on the noise and flight tracking system at OSLAs part of the investigation, a quality check on the noise and track monitoring system at OSL wasperformed. The quality check consisted of a number of tasks:• Influence on background noise at the measurement positions.• Influence on local microphone placement with respect to microphone height above ground andinfluence of local surroundings.• Validation of calibration and data treatment.• Validation of flight tracks and profiles registered by the flight tracking system.• Validation of information on aircraft type, operation, runway use.In Part 2 a summary of a survey of the monitoring positions is presented. The evaluation of the firsttwo bullet points above is based on this survey. A comparison of the measurement results atposition 1 with the monitoring systems position 4 is given in the following. Further, the flighttracks and profiles reported by the radar tracking system are compared to the flight recorder data.

33The last part of this chapter concentrates on the NTMS aircraft log data as compared to themeasurement crew observations during the program.4.6.1 Evaluation of microphone positions of the airport monitoring systemA technical memo of this survey is posted in the report part 2. Pictures of the microphone locationsare included in the memo.4.6.1.1 The investigationThe microphone positions belonging to the permanent noise and track monitoring system at OSLare numbered NMT 4 - 11. NMT 4 and NMT 5 are located at the north end of runway west andsouth end of runway east respectively. The rest of the microphones are located in areas somekilometres from the runways, mainly north and south of the airport in the runway directions.When judging the influence of local surroundings, a number of parameters were investigated duringan inspection trip to all the positions mentioned above, exclusive pos. 5. The parameters recordedwere:• type of area (rural, residential, urban),• general background noise situation,• noisy equipment/installations/industrial plants close to the microphone location,• distance to the nearest building,• roads near to the location, or audible,• ground cover.4.6.1.2 The findingsThe findings of this survey investigation are listed in Table 4.5 below.Table 4.5Summary of registrations according to the listed parametersType of areaBackgroundnoiseEquipment,installationsDistance tonearestbuilding, mType ofroadsType ofgroundcoverNMT 4 Airfield - - 20 - GrassNMT 5 Airfield - - - - GrassNMT 6 Rural Low / agric. no 275 - AgricultureNMT 7 Rural Low / agric. no 75 local/Rv120 Agriculture100mNMT 8 Rural * Low / agric. no 15 E6, 500 m AgricultureNMT 9 Rural * Low / agric. no 100 Fv462, Agriculture100mNMT 10 Rural Low / agric. no 140 local AgricultureNMT 11 Rural Low / agric. no 30 local Agriculture* Residential area in the vicinity.All locations NMT 6-11 have generally low background noise levels, but the noise level willincrease during periods of agriculture activities. Location NMT 7 is situated close to a local road.Vehicle traffic on this road may occasionally give rise to high maximum noise levels. NMT 8 islocated relatively close (approximately 15 m) from the nearest building. This may represent a causeto sound reflections from the nearest vertical building façade.

34As far as one could experience during the inspection survey, none of the locations NMT 6 - 11 wereexposed to noise from permanent technical installations or local industrial plants. At location NMT8 noise from garden activities (for instance grass cutting) may represent a certain backgroundproblem during summer time. At this location traffic noise from the distant E6 main road wasclearly audible.The nearby ground covers are in most cases agricultural fields. This means that their acousticalproperties will vary during the summer season, typically between 100 and 400 kPa s/m 2 . Inprinciple, this may influence on the recorded aircraft noise levels in the magnitude of a fewdecibels, especially in the lower end of the noise spectra.4.6.1.3 The influence of microphone heightAll the locations have the same microphone height above ground, i.e. approximately 6 m. Aircraftnoise level calculations are made for a receiver height of 1.5 m above ground. The effect of thisdifference was investigated theoretically in an earlier investigation [1].Two examples of the influence of microphone height were prepared. At measurement position 2 thetwo microphone heights were 1.5 and 10.5 m respectively. This position is directly below theaircraft flight path. At measurement position 5 the two heights were 1.5 and 8 m. This position isapproximately 1250 m to the side of the flight track. Measured sound exposure levels averaged overall departure flights with B736 indicate some significant deviations in the low frequency rangebelow approximately 200-250 Hz. Although the deviation amount to 7 dB in some 1/3-octavebands, the influence was measured to 0.7 and 0.3 dBA for position 2 and 5 respectively. The highmicrophone measured higher noise levels than the 1.5-meter microphone.4.6.1.4 Discrimination algorithms in NTMSAccording to [17] the algorithms that discriminate aircraft noise from other noise sources in themeasurements reported by NTMS, are as based on the following criteria:• The noise event must exceed a sound pressure level threshold set individually at each NMT,typically 55 dBA to 57 dBA for positions in the rural area, 75 dBA for the two close to therunways. It is possible to have a different threshold for start and end of the noise event.• Maximum sound pressure level during the noise event must be at least 3 dBA higher thanthreshold.• The noise event must have duration of 5 to 60 seconds for the rural positions, 5 to 140 secondsfor the positions close to the runway.• Measured noise events is correlated to aircraft movements by use of the radar tracking systemand the following criteria apply:- Distance between aircraft and microphone must be less than a given value, set individuallyfor each position, ranging from 1.800 to 3.000 meter.- Time interval between point of closest approach to the position and measured LAMAXmust not exceed 20 second.If a noise event fails to comply with any of these criteria, it is automatically neglected.4.6.1.5 Concluding remarksAll the microphone locations are situated mainly in rural areas, with generally low backgroundnoise. No specific permanent background noise sources were found. But agriculture activities cangive rise to high maximum noise levels during specific parts of the summer season. If the noise

35monitoring system is activated due to aircraft traffic (i.e. all criteria in 4.6.1.4 are fulfilled), there isa chance that a false aircraft noise level may be recorded.The microphone height of 6 m above ground could give slightly higher noise level relative to 1.5 m,as far as A-weighted SEL values are concerned.4.6.2 Noise levels measured by the airport noise monitoring installationThe equipment at each position of the monitoring system is calibrated acoustically every 6 months.This is considered sufficient in addition to the daily actuator calibration checks.Measurement position 1 in this investigation coincides with one of the measurement positions(NMT-4) of the airport noise monitoring installation. Thus, the same noise levels should bemeasured since the microphones of the two systems were less then 0.3 m apart. It should be notedthat the two microphones were not equally oriented. The monitoring system’s microphone has itsdiaphragm positioned horizontally, while the investigation microphone’s diaphragm was verticallyoriented. Taking general microphone response curves and associated tolerances into account, nosignificant difference between the microphones should be anticipated below approximately 3 - 4kHz. The differences in microphone sensitivity at higher frequencies will not be crucial.A comparison of LAMAX and A-weighted SEL levels measured by the two microphones wasdone. The results are shown in Table 4.6 – 4.8 below, given as mean level differences and standarddeviations per aircraft type. Positive level differences indicate that higher noise levels are measuredby the airport noise monitoring installation.The level difference observed seem to be negative for LAMAX and positive for SEL. Themagnitude of the differences is however what can be expected for two independent measuringsystems. In addition the maximum level detection in the two systems may not be quite coincident.

36Table 4.6Differences in measured noise levels at position 1 / NMT-4, landings.Aircraft type Operation MAX St.dev SEL St.dev CountB736 LA -1.3 1.0 0.4 1.2 13B737 LA -1.1 0.7 0.4 0.5 14B738 LA -1.2 0.3 0.3 0.2 2MD81 LA -0.9 0.4 0.4 0.2 7MD82 LA -0.8 0.6 0.3 0.5 16MD83 LA 0MD87 LA -1.0 0.4 0.5 0.4 5MD90 LA -1.3 0.0 -0.5 0.0 1ALL LA -1.0 0.7 0.4 0.7 58Table 4.7Differences in measured noise levels at position 1 / NMT-4, take-off.Aircraft type Operation MAX St.dev SEL St.dev CountB736 TO -0.2 0.3 -0.8 0.4 15B737 TO -0.2 0.3 -0.6 1.0 19B738 TO 0MD81 TO -0.5 0.5 0.4 0.2 17MD82 TO -0.5 0.4 0.5 0.4 32MD83 TO 0.2 0.0 1.1 0.0 1MD87 TO -0.4 0.4 0.5 0.3 6MD90 TO -0.3 0.4 0.1 0.1 2ALL TO -0.4 0.4 0.1 0.8 92Table 4.8Differences in measured noise levels at position 1 / NMT-4, all operations.Aircraft type Operation MAX St.dev SEL St.dev CountB736 TO+LA -0.7 0.9 -0.2 1.0 28B737 TO+LA -0.6 0.7 -0.1 0.9 33B738 TO+LA -1.2 0.3 0.3 0.2 2MD81 TO+LA -0.7 0.5 0.4 0.2 24MD82 TO+LA -0.6 0.5 0.4 0.5 48MD83 TO+LA 0.2 0.0 1.1 0.0 1MD87 TO+LA -0.7 0.5 0.5 0.3 11MD90 TO+LA -0.6 0.7 -0.1 0.3 3ALL TO+LA -0.6 0.6 0.2 0.8 1504.6.3 Comparison of tracks and profiles from flight recorder with NTMSA technical memo on this subject is presented in Part 2. Of the 155 flights investigated, 70 flightrecords included GPS position data. The pressure altitude is also reported in the flight recorder. Acomparison has been made between the flight recorder data and the data reported from the radartracking part of the noise and flight monitoring system at OSL.

37The following two figures compare the position data given in the flight recorder and reported by theradar tracking system. The blue lines represent the GPS position (smoothed). The red dots representthe position given by the radar. The magenta crosses mark the position of the five measurementsites. The western runway is shown as a thick, black line. The co-ordinates are given relative tomeasurement position 1.The figures show that near the ground (i.e. close to the runway), the radar data is subject tosignificant random errors. At greater altitudes, there are no large random errors, although thedeviation is in the order of ± 50–100 m in the north/south direction, and ± 20–60 m in the east/westdirection.

38Figure 4.17Comparison of position data from NTMS (dots) and flight recorder GPS based flighttracks (lines).Figure 4.18Comparison of position data from NTMS (dots) and flight recorder GPS based flighttracks (lines) near the runway.

39The figures below compare the altitude given in the flight records and reported by the radartracking system. Only three randomly selected flights are shown for each operation. The altitudes ofboth sources have been adjusted by setting the altitude at the runway to zero.Figure 4.19Altitudes from flight recorder (thick lines) and NTMS (thin lines) as a function oftime for 3 randomly selected arrivals.Figure 4.20Altitudes from flight recorder (thick lines) and NTMS (thin lines) as a function oftime for 3 randomly selected departures.

40The figure below shows the difference between the reported altitude for all 70 flights. Red dotsrepresent arrivals, while blue dots represent departures. The data show that the average deviation isapproximately –50 m for arrivals, and approximately 50–100 m for departures.Figure 4.21Comparison of altitudes from flight recorder and NTMS as a function of time forarrivals (red dots) and departures (blue).The average deviation may be due to time delay in the altitude reported by the radar trackingsystem. A time adjustment of approximately 1.5 – 3 seconds applied to the radar data results inbetter agreement.4.6.4 Quality check on the monitoring system aircraft logProject personnel at the air traffic control tower kept record of all flight movements in the northwest quadrant of the airport during the exercise. Their log has been compared to the aircraftmovement log produced by the noise and track monitoring system (NTMS) at OSL. The latter is avital input for the GMTIM noise model. Major findings are:• The time difference between observation and NTMS log is typically 1 minute equal to theresolution, where the NTMS systematically is late. NTMS time matches with the time theaircraft is clear from the runway.• There is a one-to-one match between observation and the aircraft registration number in NTMS.• There is a one-to-one match on runway use and on operation type.• Translation from registration number to aircraft type in NTMS has been checked with theNorwegian Civil Aircraft Register or “JP airline – fleets international” (97/98 edition) andshows good match with a few exceptions.

415 ConclusionsThe investigations show that several effects influencing the accuracy of aircraft noise modellinghave been isolated.5.1 DirectivityThe most important result in this study is the directivity patterns that have been extracted.One basic assumption for state of the art models, that never has been certified, is that soundradiation from the aircraft is cylindrical symmetric with the fuselage centre line as the symmetryaxis. The results from this investigation clearly show that this is not the case. All of today’s noisemodels fall short of taking this result into account.3D directivity can only be modelled in full extent with a new method of describing the noisesource. The task is therefore put in the category “long term measures”.5.2 Lateral attenuationBoth measurements and subsequent simulations show that lateral attenuation is less than predictedby SAE AIR 1751. This trend is true for all aircraft types in this study, at both departure andlanding operations. This trend is also recognised in other investigations [7,8].The results also indicate that the aircraft family B737 exhibits less lateral attenuation than theaircraft family MD80. The reason for this is related to effects of engine position (wing mounted andrear fuselage mounted engines respectively). This is also seen in other recent investigations [8,9].The lateral attenuation according to SAE AIR 1751 enters into the noise level prediction performedby the NORTIM/GMTIM methods. Over-estimation of the lateral attenuation leads to underestimationof predicted noise levels. The findings in this study show that typical effect could be inthe order of 2 - 4 dB. The over all effect on the noise zones is dependent on where the calculationpoint is located relative to the flight path.The findings concerning lateral attenuation can be taken into account in “short term measures”.5.3 Noise Power Distance dataThe analyses show that there are statistically significant differences between measured noise andthe database NPD curves. Further analysis need to be performed for the B737-600/700 aircraftwhere new database NPD curves are compared with the measurements.The statistically significant differences can be used as corrections in the NORTIM/GMTIMdatabase as a “short term measure”.5.4 Flight profilesIt is obvious from this investigation that the standard take off profiles generated by INM and usedin GMTIM/NORTIM are based on different procedures than those used by SAS at Oslo Airport.The main reason is probably that SAS uses derated thrust frequently and INM procedures are notconstructed as such. It should be noted that, according to SAS, the procedures they use are inagreement with criteria set by OSL. The resulting noise level difference will vary along the flighttrack and to the sides.

42It is also clear that the thrust adjustments typically seen from 5 NM to touch down are not takeninto account in the standard approach profiles. The effect on maximum levels can be in the order ofup to 10 dB.Both these findings should be corrected for in the noise model. Corrections may be implemented ona short to intermediate term.The noise and track monitoring system at the airport shows results in good agreement with theaircraft recorder data. Actual flight profiles could therefore be taken directly from the NTMS intoGMTIM. The implementation calls for the development of algorithms to estimate applied thrust foreach flight. This effort is therefore seen as an “intermediate term measure”.

436 Recommendations for further WorkThis chapter discusses a number of actions to be taken in order to minimise the difference betweenmeasured and predicted aircraft noise levels. In order to sort different actions, the presentation isdivided into measures on a short-, intermediate- and long term time scale.6.1 Short term measuresThe time scope for these implementations are 3 months.6.1.1 Correcting lateral attenuationThe correction should be based on the results obtained in the present investigation combined withcorresponding results from recent international investigations. The new routines will have anintermediate status until international recommendations are updated.Present proposal will divide aircraft in three categories: propeller driven aircraft, wing mountedturbofan engine aircraft and ditto fuselage mounted. Implementation of the new algorithms intoNORTIM/GMTIM will also affect the routine that handles terrain topography, which must beproperly adjusted.When the implementation is accomplished, the final step is to test the corrected noise levelpredictions against measurement results. This test will be performed on the base of measured noiselevels used in earlier investigations [1,2].6.1.2 Corrections to Noise-Power-Distance dataThe deviations that are statistically significant should be implemented in the database. For theB737-600/700 the comparison should be regenerated with new sets of data (INM 6.0c database forB737-700). New statistical analysis is also recommended for the MD80 family, where the aircraftshould be grouped together.6.1.3 Adjustment to flight profilesFlight profiles as registered by the aircraft flight recorder combined with the airport radar systemcan be implemented in the NORTIM/GMTIM database. Empirically based takeoff profiles can bedeveloped for the limited numbers of aircraft in this study. These aircraft are the dominant types atOslo Airport and such an implementation would improve the modelling accuracy.Standard profiles can also be improved with information from the airline companies on what set ofprocedures are in use. This input can be used to create new database profiles.6.2 Intermediate term measuresThese actions can be accomplished within 12-15 months.6.2.1 Flight profiles from the monitoring systemFurther investigations need to be initiated to determine the difference between height reported bythe radar transponder and the flight recorder. As pointed out in chapter 4.6.3 time synchronisationmay be the cause.When this is sorted out, take off profiles from the track and monitoring system may be importedinto GMTIM and used instead of the standard profiles. An implementation must be supplementedwith algorithms to calculate what thrust have been applied to fly the profile. Take off weight foreach flight will probably be one needed input parameter.

44For landing profiles it is recommended that a small study be initiated to firstly determine the natureof the varying thrust applied, secondly to develop routines to model this in standard profiles. Theseroutines will have a more generic character and be applicable to other noise models.6.2.2 Investigate effects of flight path segmentationThe noise level data collected in the present investigation represent a potential for further analysisof differences between measured and predicted aircraft noise levels. An evident task is to check theflight segmentation procedures used in NORTIM/GMTIM in order to investigate the applicabilityof a point source model in aircraft noise level prediction.6.3 Long term measuresRelevant tasks are not described in detail, but obvious activities are to prepare for a reconsideringof the aircraft noise level prediction basis, including:• New aircraft noise source description, possible point source.• New frame of noise emission data, including 3D directivity.• New ground attenuation/topography model/weather model.• Harmonising with international development on noise level prediction regarding communitynoise.

7 References[1] R. T. Randeberg: “Validating GMTIM", SINTEF Memo 40-2000-5930, 2000-10-18. (InNorwegian.)[2] R. T. Randeberg: “Analysis of differences between measured and calculated aircraft noiselevels at Gardermoen - Statistical analysis of existing data", SINTEF Memo 40-2001-2698,2001-05-15.[3] Nordtest Method NT ACOU 104: "Ground Surfaces: Determination of the AcousticImpedance". Approved 1999-11.[4] ISO 9613-1:1993, " Acoustics -- Attenuation of sound during propagation outdoors -- Part1: Calculation of the absorption of sound by the atmosphere”.[5] SAE AIR 1751:"Prediction Method for Lateral Attenuation of Airplane Noise DuringTakeoff and Landing", 1981.[6] SAE AIR 1845:"Procedure for the Calculation of Airplane Noise in the vicinity ofAirports", March 1986.[7] K. J. Plotkin et al.: ”Examination of the Lateral attenuation of Aircraft Noise”. NASA/CR-2000-210111, April 2000.[8] D. A. Senzig et al.: ”Lateral Attenuation of Aircraft Sound Levels Over an AcousticallyHard Water Surface: Logan Airport Study”. NASA/DR-2000-210127, DOT-VNTSC-NASA-00-01, May 2000.[9] D. A. Senzig et al.: ”Measured Engine Installation Effects of Four Civil TransportAirplanes”. Proc. NOISE-CON 2001, Portland, Maine, October 29-31.[10] J. A. Page et al.: ”Validation of Aircraft Noise Prediction Models at Low Levels ofExposure”. NASA/CR-2000-210112, April 2000.[11] N. P. Miller et al.: ”Examining INM Accuracy Using Empirical sound Monitoring andRadar Data”. Harris, Miller, Miller & Hanson Inc., Report No. 294520.03, October 1999.[12] B. Plovsing, J. Kragh: “Nord2000. Comprehensive Outdoor Sound Propagation Model”, 31.Dec. 2001.Part 1: ‘Propagation in an Atmosphere without Significant Refraction’, Lyngby 2000Part 2: ‘Propagation in an Atmosphere with Refraction’, Lyngby 2000.[13] Personal communication with Dr. Hans Olav Hygen, Det Norske Meteorologiske Institutt.[14] T. Conner et al.: ”Accuracy of the Integrated Noise Model (INM): MD-80 OperationalNoise Levels”. Joint report of Swedish CAA and US DoT, Stockholm/Washington May1995.[15] K. H. Liasjø, I. L. N. Granøien: “Comparison of Aircraft Noise Programs INM-2/6, INM-3/9, INM-3/10, DANSIM and NOISEMAP”, SINTEF Report STF40 A93043. (InNorwegian.) Trondheim, April 1993.[16] H. Olsen et al.: “Topography influence on aircraft noise propagation, as implemented in theNorwegian prediction model, NORTIM”, SINTEF Report STF40 A95038. Trondheim, May1995.[17] “Noise and track monitoring system”, Technical specification in the Contract: OHAS-N-SP-0005 E03 - C-16726, Oslo September 1997.Personal communication with Knut Holen, Manager HSE, Oslo Airport Gardermoen.45

46Appendix 1 Measurement site and measurement positions.2 34 51The measurement positions 1 - 5 are indicated. In the following a picture of the equipment and sitefor all the 5 positions.23451

47Position 1Position 2

48Position 3Position 4

Position 549

50Schematic layout of the measurement system.POS. 2POS. 3POS. 4POS. 5BCDEFGHIPOS. 1NMT4 AHEADQUARTERRUNWAYPOS. 0 (REF)2 PC w/ CD-recorderBatteries, ChargersSpare sound analyserSpare microphonesCalibratorsGround Impedance EquipmentSpare partsTools Cables, Tape etc220VACLIST OF SYMBOLSMicrophoneSound AnalyserBatteryPCTrigger SystemGPS antennaVoltage adapterMeteorology sensorMeteorology loggerMast

51Appendix 2 Meteorological dataPicture shows the 10 meters mast (type Clark QTM) with meteorological sensors.The following sensors were coupled to the meteorology logger Aanderaa Type 3660:• Wind direction (°) at 9.25 m. Sensor adjusted with compass.• Mean and max wind (m/s) speed at 9.25 m.• Air temperature (°C) at 9.25 m.• Temperature difference (°C) between 9.25 and 0.5 m.• Net Radiation (W/m 2 ).• Relative air humidity (%RH) at 9.25 m.• Precipitation (mm) at 1.5 m.

Graphical presentation of wind direction and wind speed (values representing mean speed and gust)52

Graphical presentation of air temperature (at 9.25 m above ground), relative humidity and rainfall.53

Graphical presentation of air temperature difference between 9.25 and 0.5 m height and netradiation.54

55Appendix 3 Estimation of ground impedance by acoustical measurement.Typical measurement layout.15°500 500352001750 mm