DETECTING AIR POLLUTION IN VIETNAM BY OPTICAL SATELLITE IMAGES Dr. Hab. Luong Chính Ke Msc.Ho Thi Van Trang; Msc.Tran Ngoc Tuong; BA. Nguyen Le Đang Research Center for Remote Sensing Science and Technology National Center for Remote Sensing Abstract: Optical satellite images have been used in many fields but researching aspects and applications have only concentrated in terrain mapping without delving into studying and applying to establish thematic maps – one of remote sensing technology applied strong postures. This article describes the study results about mapping air environment pollution based on processing of spectral and geometric Landsat ETM+ and SPOT images for 2 areas in Vietnam (Hanoi and Cam Pha).
Optical satellite data can be used to enhance current understanding in climate prediction caused by aerosols. A variety of numbers of optical satellites provides diversified products to supply many tasks in related fields and aerosol optical depth determination is one of those. With the spatial and spectral resolution varying from low, moderate to high, aerosol optical depth (AOD) can be specified in different conditions. For detecting air pollution, aerosols are considered as one of the major air pollutants responsible for human health problems related to the respiratory system (). The determination of aerosol optical depth (AOD) from satellite image data can be used as a tool for assessing air pollution in any area of interest (Kaskaoutis, Sifakis, Retalis, Kambezidis, 2010; Retalis, Sifakis, 2009) The monitoring of aerosol concentrations becomes a high environmental priority particularly in urban areas. The proposed algorithm has been developed to allow the quantification of the aerosol optical thickness (AOT) over land. The algorithm compares multitemporal satellite data sets and evaluates radiometric alterations due to the optical atmospheric effects of aerosols (Sifakis., Soulakellis , Paronis, 1998). This article will present the AOD determination by using optical satellite data for Hanoi and Cam Pha area in Vietnam. For the purpose of this study, both optical satellite data and field observing station data were used to assist mutually in mapping air pollution and in verifying the correctiveness. By using Landsat ETM+ has high spatial resolution 1
(Hutchison, 2003; Lorraine, Tanré, Kaufman).
2. DETECTING AIR POLLUTION BY OPTICAL SATELLITE IMAGE
From the early of 70s, while American civil satellite called Landsat-1 was launched for monitoring Earth surface resources, scientists in industrialized countries mentioned about polluted air environment studying problems by satellite images data. Air pollution primarily occurs in troposphere that forming an atmospheric cloudy layer called aerosol layer. In several countries in EU group like Netherlands, Germany…, having updated daily air environment pollution level to websites by using remote sensing data. 2.1. Methodology The entire methodology of this study is briefly presented as below: a/ Spectral processing of satellite images involves the following steps: at first, digital numbers (DN) values were converted to radiance values; then the radiance values were calibrated temporally (Jesen, 1996). b/ Geometric correction of satellite images and geo-reference of each image at the WGS-84 projection system was implemented. The affine transformation was used to do geometric correction with the Root Mean Square Error (RMSE) lower than 1 pixel. c/ The next radiometric processing is calculating ρTOA reflected image at the top of atmosphere, using following formula ( Sifakis., Soulakellis , Paronis, 1998 )
ρTOA = G ( L; Eoλ ; cos θ ; d )
where: L: radiance values were converted from DN values [W / (m 2 .Ster.μm )]
E0 λ : Solar spectral irradiances [W / (m μm)]
d: Astronomical distance from Earth to Sun θ: Sun elevation angle. d/ ρTOA image derived with 2 modules developed by our technical team, integrated into ENVI to detect air...
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