Abstract
With the rapid development of sensor networks and earth observation technology, a large quantity of high resolution remote sensing data is available. However, the influence of shadow has become increasingly greater due to the higher resolution shows more complex and detailed land cover, especially under the shadow. Shadow areas usually have lower intensity and fuzzy boundary, which make the images hard to interpret automatically. In this paper, a simple and effective shadow (including soft shadow) detection and compensation method is proposed based on normal data, Digital Elevation Model (DEM) and sun position. First, we use high accuracy DEM and sun position to rebuild the geometric relationship between surface and sun at the time the image shoot and get the hard shadow boundary and sky view factor (SVF) of each pixel. Anisotropic scattering assumption is accepted to determine the soft shadow factor mainly affected by diffuse radiation. Finally, an easy radiation transmission model is used to compensate the shadow area. Compared with the spectral detection method, our detection method has strict theoretical basis, reliable compensation result and minor affected by the image quality. The compensation strategy can effectively improve the radiation intensity of shadow area, reduce the information loss brought by shadow and improve the robustness and efficiency of the classification algorithms.
Highlights
Ups and downs in mountainous terrain led to a large number of terrain shadow in remotely sensed images, which lacks direct solar radiation and has problem of widespread incomplete spectral information, darker brightness and fuzzy boundary, seriously affects subsequent interpretation work, like image matching, classification and change detection
Current shadow detection research can be divided into two classes: spectral method (Elbakary, 2014; Tsai, 2006) and geometric method (Li, 2005; Stevens, 1995)
With the consideration of terrain, we proposed a simple and effective automatic shadow detection and compensation method based on radiation transmission theory
Summary
Ups and downs in mountainous terrain led to a large number of terrain shadow in remotely sensed images, which lacks direct solar radiation and has problem of widespread incomplete spectral information, darker brightness and fuzzy boundary, seriously affects subsequent interpretation work, like image matching, classification and change detection. As lack of terrain information, spectral methods provide a solution to the recovery of the spectral information in shadow area. With the consideration of terrain, we proposed a simple and effective automatic shadow detection and compensation method based on radiation transmission theory. With the above factors and radiation transmission model we can calculate the parameters and compensate shadow.
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