A method of image processing, Haar wavelet transform, was first applied to establish a new index and provide accurate digital data to present urban atmospheric visibility, instead of the conventional observing method. Digital images of urban areas in Kaohsiung, a city at the south of Taiwan, are analyzed according to brightness (gray level). An index value for a scene image is calculated with a processor of Haar wavelet transform. As a result, a good correlation between the wavelet index values and the visual range values estimated by three trained observers is affirmed by the correlation coefficient (R2) of 0.81. Convenient transmission and the exchangeability of digital images of the real-time landscape facilitate the demonstration of the results on the web site.