Geography Reference
In-Depth Information
medium-hard soles, when walking on hard surfaces (asphalt, concrete, or bricks)
and when holding the microphone horizontally at waist height, volume levels about
55-60 dB were recorded. In the case of shoes with a slim hard heel measured values
reach up to 70 dB. Smaller contributions can also be caused by rustle of pants
'
fabric. Therefore, it is appropriate that each user, who intends to measure the noise
during his/her walk, will measure (or set) the noise level, which he/she emits while
walking on different surfaces (user
s footwear noise profiles should be created).
Even though the noise level of ca. 60 dB forms a relatively high threshold, below
which there is virtually no measurement resolution during walk, this threshold is
still sufficient for measuring noise in cities. If the level of residual noise is more
than 10 dB below the level of the phenomenon, residual noise is traditionally seen
as irrelevant.
When measuring quiet locations, user can make regular stops, and measure noise
during these stops. If each stop lasted longer than ca. 5 s, it should be possible to
reliably separate data collected during walking from the data measured during
stops.
'
Effects of Mobile Phone on Noise Measurements
Operation of the mobile phone itself may also have a significant effect on measured
noise levels. This includes activities associated with calling, sending data, or the
loudness of hardware components. For example, pressing hardware buttons can
greatly distort measurement results (measured noise level can be around 80 dB), so
it is necessary to exclude samples recorded during other user activity with the
phone. This may not apply to clicks on the touch screen if the user is careful enough.
Data Aging
Noise data become gradually outdated, like any other environment data. Noise
situation changes occur as a result of new infrastructure construction, as well as
changes in traffic flows, individual devices (e.g. cars) loudness, etc. Infrastructure
changes can be detected with base spatial data updates, or they can be detected also
by volunteers themselves. However, it is more difficult to determine which sites are
affected by this change and that therefore what data is already outdated. This
situation can be verified by observation, or, better, by direct measurement. At
places, where was no fundamental change, environmental noise data are considered
as obsolete 5 years after acquisition (European Commission
2006
).
