Sunday 19 July 2009

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:

  • The phone's microphone is quite sensitive and ambient noise, including wind and traffic, can easily mask the noise signature of aircraft - as with many types microphone wind caused particular problems, with even a light gust registering twice the noise intensity of a landing aircraft (the need to find a sheltered location contributed to why I only had time to survey two locations);

  • Different aircraft cause different levels of noise (it was for this reason that five samplings were taken at each location and the average taken); and

  • Landing aircraft cause less noise than those taking off (on the afternoon that I visited aircraft were approaching from the east to land on the northern runway).
  • 1 comment:

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