Geography Reference
In-Depth Information
Table 1 Typical urban noise situations from a road traffic, letters in parentheses correspond to the
labeling in Fig.
2
Closer measurement point
(
A
)
Most distant measurement
point (
B
)
Cell
diameter (
r
)
(m)
Noise
level
(dB)
Noise
level
(dB)
Situation [car
speed (km/h)]
Distance from
source (
a
) (m)
Distance from
source (
b
) (m)
Passenger car,
30
5
3
60
8
52
7
10
49
8.5
11.5
48
Passenger car,
50
5
3
70
8
62
7
10
59
8.5
11.5
58
Passenger car,
65
5
15
64
20
62
7
22
61
8.5
23.5
60
Passenger car,
105
5
15
70
20
68
7
22
67
8.5
23.5
66
person. Localities with both noise levels 52 and 60 dB can be still considered as
quiet (in urban environments, Kang (
2007
)). The most acceptable universal cell size
for noise in the urban environment is an area with a diameter of 7 m. The data for
common distances and speeds is summarized in Table
1
.
In case of GPS position measurement, reducing the cell size under 5 m will not
lead to better spatial accuracy, because, according to Modsching et al. (
2006
), the
spatial error of typical GPS receiver can be well one order of magnitude above.
However, in such a homogeneous space layout, it was necessary to perform a
large number of measurements, even in the case when sufficient noise measurement
accuracy is secured. Based on the observations of the noise situation in cities, it is
clear that (especially in the case of linear noise sources, e.g. from road traffic), the
average noise level values along certain segments of this source (e.g. road seg-
ments) in a given measurement period is virtually the same. (As long as the source
is in the same condition. For road traffic the surface condition is considered to be the
same if the same number of vehicles passes through individual measurement
positions at the same speed.) The noise situation in a direction transverse to the
linear source is also predictable, and is possible to generalize its behavior.
Therefore, in the case of noise from surface traffic, which passes through city
streets, it is appropriate to adjust cell shape and orientation to the street directions
and generalize the measured data into some form of linear map which indicates the
average noise level on each homogeneous street segment. The method of allocating
street segments to homogenous units is shown in Fig.
2
.
Usually the pedestrian moves on the street, on Fig.
2(a)
is volunteer
s path noted
as a
blue line
. Error in position recorded by GPS device is then expressed by
violet
vectors
. Measured point values of noise level can be in map then represented by
'
