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Development of a predictive haze index to reflect observed visibility degradation in the city of Cape Town
Author(s)
Witi, Jongikhaya
Date Issued
2006
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Measurement and forecasting of visibility is essential in assessing the extent of
visibility degradation (haze) due to air pollution in Cape Town. Rapid impairment in
visibility over the years forced the City ofCape Town to initiate the Brown Haze I (BH
I) study in September 1997. The main objective of the Brown Haze I Study was to
determine the contribution of all major pollutant sources to the brown haze, and to
determine other factors that contribute to haze formation. However to date no study has
attempted to devise quantitative methods to monitor visibility in Cape Town.
This study reports on a new method of measuting visibility using Digital Image
Processing. An hourly series of time-stamped images of three scenic vistas was
recorded over a period of 8 months (20060318 to 20061031) using three co-located
Sanyo E-6311xP-H digital cameras equipped with E-50500D 20 to lOOrnrn
Variable-focal Auto Iris Lenses. The cameras were orientated in three directions
(approximately due west, north and east). These time- stamped images were archived
for subsequent digital image processing. The average image intensities of selected
areas of each image were calculated using the histogram function of digital image
processing software (PhotoshopTM 7.0), to obtain the inherent and apparent contrast
ratios. The inherent and apparent contrast measurements were then used to calculate
light extinction coefficient (bex') and the visual range (VR).
visibility degradation (haze) due to air pollution in Cape Town. Rapid impairment in
visibility over the years forced the City ofCape Town to initiate the Brown Haze I (BH
I) study in September 1997. The main objective of the Brown Haze I Study was to
determine the contribution of all major pollutant sources to the brown haze, and to
determine other factors that contribute to haze formation. However to date no study has
attempted to devise quantitative methods to monitor visibility in Cape Town.
This study reports on a new method of measuting visibility using Digital Image
Processing. An hourly series of time-stamped images of three scenic vistas was
recorded over a period of 8 months (20060318 to 20061031) using three co-located
Sanyo E-6311xP-H digital cameras equipped with E-50500D 20 to lOOrnrn
Variable-focal Auto Iris Lenses. The cameras were orientated in three directions
(approximately due west, north and east). These time- stamped images were archived
for subsequent digital image processing. The average image intensities of selected
areas of each image were calculated using the histogram function of digital image
processing software (PhotoshopTM 7.0), to obtain the inherent and apparent contrast
ratios. The inherent and apparent contrast measurements were then used to calculate
light extinction coefficient (bex') and the visual range (VR).
Additional information
Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2006
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