Wednesday, 5 August 2009
Heathrow, an inauspicious start...
The early development of Heathrow from an airfield into an airport was in response, during World War Two, to the urgent need for a military airfield close to London and as such land, which under normal civilian procedure could not have been acquired for the development of a civilian airport, was requisitioned using the Defence of the Realm Act. The memoirs of Harold Balfour, Aviation Minister at the time, describe how the site had previously been earmarked as suitable for civilian use and that, for individuals within the Air Ministry with a vested interest in civil aviation, the requirement for a military airfield provided a pretext for the acquisition of the land for an airport’s construction, that after the war may be transferred to civilian use (Wings Over Westminster, 1973). Indeed the airport was never used by the RAF (Royal Air Force) and before its completion Heathrow was transferred from the Air Ministry to the Ministry of Civil Aviation.
So, without any consideration to the noise pollution that it would cause local residents, London ended up with an airport just 20 kilometres from Hyde Park Corner with east-west orientated runways, pointing in one direction toward the historical town of Windsor and in the other towards the heavily urbanised areas of west London.
Sunday, 26 July 2009
Aircraft Noise at Source
The International Civil Aviation Organisation (ICAO) promotes a balanced approach to airport noise management consisting of four principle elements, namely: reduction of noise at source; land-use planning and management; noise abatement operational procedures; and aircraft operation restrictions. Each element represents a method of managing noise that, based on the particulars of a given airport, can be used in combination to manage or reduce aircraft noise. One of the most tangible of these four elements in managing aircraft noise levels is the noise at source (that produced by the aircraft itself). Over the last 30 years significant efforts have been aimed at producing quieter planes and, where other elements of the balanced approach have been exhausted or are not feasible, the continued advancement of aircraft technology, producing ever quieter planes, is often seen as a pre requisite to accommodating increased numbers of aircraft movements.
In the
As mentioned above, Annex 16 standards are not designed to correspond with restrictions on the use of a given aircraft per se; however, they do offer a bench mark where by noisier aircraft can be phased out or restricted - on
Although the different body/engine configurations and different series of the same design of aircraft can make it difficult to differentiate a Chapter 2 aircraft from a Chapter 3 or a Chapter 3 from a Chapter 4, for illustrative purposes below are some examples of aircraft belonging to different chapters:
Chapter 2 Aircraft (no longer in use within
Chapter 3 Aircraft (characterised by more modern, quieter, jet aircraft): Boeing 737-300 (in production until 1999); Boeing 737-400 (in production until 2000); Boeing 747-400 (in service since 1989), Boeing 777 (in service since 1995); and Airbus A319 (in service since 1996).
Chapter 4 (at least one third quieter than those currently certified to the Chapter 3 standard, IATA): Airbus A380 (in service since 2007); Boeing 737-600 (in service since 1998).
The ICAO standards represent a useful means of categorizing aircraft (with regard to noise level); however, within each Chapter there is naturally going to be variation between aircraft - a 428 seat 747 'jumbo jet' is significantly more disruptive that an 80 seat Fokker 70, both of which are Chapter 3 aircraft. Indeed, Chapter 3 aircraft that exceed Chapter 3 noise standards but have not yet been reclassified as Chapter 4, may actually be quieter than a Chapter 4 aircraft.
Variation in noise level between different aircraft has important implications for the creation of a noise map based on ground observations. If a continuous series of measurements are taken at a given location, over time the average of those measurements will tend toward the true mean noise level experienced at that location; however, just a single measurement, which might observe a ‘quiet’ or ‘noisy’ aircraft, is prone to be un representative of the typical level of noise.
When considering such a spatially distributed phenomenon as aircraft noise it is not practical to take a continuous series of measurements at all locations. This is especially true in the case with the lhrnoisemap project where data collection is opportunistic, based on volunteered geographical information (VGI). The accuracy of this method must therefore rely either on accommodating this uncertainty or assuming repeated sampling of the same location will occur over time - helping the sample become more representative of the true mean at that location. Although the latter is preferable, to achieve repeated samples comprehensively requires a very large number of observations (together with an according time span), and to a greater or lesser degree methods of accommodating the uncertainty will have to be given consideration.
Even if repeated sampling were comprehensively achieved this makes the additional assumption that these observations are random, namely that the incidence of ‘noisy’ aircraft balances those of ‘quiet’. Rather than aiming to achieve a random sample another approach might aim to sample only a selected class of the total population (i.e. only record the noisy aircraft). Doing so would mean that a resulting visualization would represent only that class of the population rather than the population itself; however, would result in more standardised samples, thus reducing the need for repeated sampling. To facilitate this approach in the final analysis of data volunteers are asked to include the type of aircraft in the description of their sample. Whilst it is not realistic to identify most aircraft types the Boeing ‘jumbo’ 747 represents one that, if visible, is recognisable to many people.
References
Aircraft Noise, International Civil Aviation Organization Air Transport Bureau:
http://www.icao.int/env/noise.htm
Balanced Approach to Noise Management around Airports, IATA:
Emissions Impossible, Aviation Environment Federation:
http://www.hacan.org.uk/resources/reports/emissions.impossible.pdf
Noise Certification Standards, IATA:
Sunday, 19 July 2009
AudioBoo
Using the iPhone’s location awareness Boos are geotagged so that, on the AudioBoo website, the sound file / media player is accompanied by an embedded Google Map showing the location where the recording was made (from this the position's latitude and longitude can be extracted). In addition to the sound recording and its location the website also provides the time at which the recording was made, the author, and the title of the boo.
AudioBoo represents an alternative approach to conducting a participatory noise survey using mobile phones: rather than measuring the level of a noise event in situ AudioBoo offers the facility to record the event its self, geographically reference its location and publish it remotely to a location where it can be readily accessed and shared.
Applying a predetermined tag (lhrnoise) to each Boo means that, using the website’s search facility, Boos collected and published for the LhrNOISEsurvey can be easy identified. Recorded as MP3 files software capable of Acoustic Analysis can be used to analyse the recordings and identify the levels of aircraft noise experienced. Transferring the analysis of the noise events from the 'front end' (the phone) to the 'back end' (me) provides a significantly more user friendly method of collecting data and facilitates an approach to the analysis of noise levels with the potential of distinguishing aircraft noise from other noise sources (such as wind of traffic) that might otherwise distort the measurement.
Possibly the greatest advantage of AudioBoo is its capacity to communicate peoples experiences of aircraft noise as real audio, rather than just numbers. The map below shows markers identifying the location of recordings, hyperlinking them to the AudioBoo website means the respective recording can be heard.
Second noise survey
With aircraft taking off in an westerly direction from the northern runway the levels of noise pollution experienced were universally high, indeed, at a number of locations the maximum sound level of the passing aircraft reached the maximum that can be measured using dBMeter Pro inconjuction with the iPhone - found to be 103.3 dB(lin).
At each location a number of measurements were made and an average calculated. The accuracy of the average value is dependent on the samples used in its calculation forming a representative, random, sample of all aircraft noise events experienced at that location. Multiple readings were used; however, it is likely that the sample size was not sufficient to avoid the average being biased by a greater proportion of large, noisy, aircraft during the period of observation at a given location or small, quieter, aircraft during the period of observation at another. Because of this the average values given in the survey results must be interpreted with care; however, the ability of the phone to measure noise events is a great encouragement.
First noise surveys
To begin exploring how mobile phones could be used to survey aircraft noise I visited the village of Cranford, located at the end of Heathrow's northern runway, to take some samples using my iphone. Using the NoiseMeter app by Treascovery I was able to measure noise levels and with the GPS Tracker app by Instamapper I had a means of recording location (both applications were downloaded onto my iphone via Apple’s App Store).
NoiseMeter does not record in dB but instead uses its own scale of intensity ranging from 0 to 150. Once activated the application displays the real time reading together with the average and maximum experienced during that period of measurement. It should be stressed that I neither calibrated nor tested the accuracy of the NoiseMeter and it is not envisaged that this app be used beyond these conceptual trials.
NoiseMeter does not permit noise readings to be saved so each observation was recorded manually using the phone’s notepad, nor does it possess ‘location awareness’, so, before making each noise reading the location was tagged using GPS Tracker. These locations were later downloaded and manually matched with their respective noise reading.
Starting in Cranford my intention was to move away from the airport, periodically taking noise reading and tagging my location, to investigate whether the (expected) decrease in noise levels could be detected using my phone.
The above map, with markers to the north east of the airport, show where measurements were taken. It is pretty obvious that my plan to take multiple measurements at progressively increased distances from the airport was a little ambitious and, with measurements only being taken in a small geographical area, the survey was inconclusive in determining whether the the phone could detect variability in the noise levels. Despite this the trial was successful in bringing to my attention a number of important points: