Application of Digital Camera Data for Air Quality Detection
2.0 STUDY AREA
The selected air quality station was located in USM campus at longitude of 100 0 17.864’ and
latitude of 5 0 21.528’ (Figure 1). The site consists mainly of undulating land has many assets that
make it an ideal University campus. University Sains Malaysia is situated in the northeast district of
Penang island (Figure 1).
Figure 1 Study area and Air Quality Station
3.0 METHODOLOGY
The digital images were captured for a period of five days from 8-7-2004 until 11-7-2004 starting
from 9.00 am. to 5.00 p.m. This air pollution station was selected in this study due to several
reasons, 1. It is in the USM campus, so it is easy to capture the digital images hourly. 2. The
presence of a construction site near the station, so we expected that the PM10 level to be high
during working time. 3. The USM bus stop was near to the station, so we expected that the CO
levels to be high during busy times in the morning and evening. 4. A building near the station can
be used to stick up the colour paper on its wall for reference surface. The air quality station belongs
to ASMA is shown in Figure 1. The digital images were captured hourly because the air quality
data were also collected hourly by ASMA through the network.
We used a red colour paper and the wall of the building as our reference targets. The camera
axis was at 90 0 with the plane the red colour paper. We captured the digital images of the reference
targets by using the digital camera at near and far distances from the targets. The far distance
between the building and the camera was 100 meter. The air pollution station was located between
the reference target and the digital camera.
In this study a modification was made to the model developed by Ahmad and Hashim
(1997). Skylight is an indirect radiation, which occurs when the radiation from the sun being
scattered by elements within the air pollutant column. It is not a direct radiation, which is
dominated by pixels on the reference surface. Figure 2 shows electromagnetic radiation path
propagating from the sun towards the digital camera penetrating through the air pollutant column.
(Source: Modified after Ahmad and Hashim, 1997).
Figure 2 The skylight parameter model (Source: Modified after Ahmad and Hashim, 1997)
The modified model is described by:
