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Article

Diffuse Skylight as a Surrogate for Shadow Detection in High-Resolution Imagery Acquired Under Clear Sky Conditions

Ecosystem Management, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia
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Remote Sens. 2018, 10(8), 1185; https://doi.org/10.3390/rs10081185
Received: 1 July 2018 / Revised: 24 July 2018 / Accepted: 25 July 2018 / Published: 27 July 2018
(This article belongs to the Special Issue Multispectral Image Acquisition, Processing and Analysis)
An alternative technique for shadow detection and abundance is presented for high spatial resolution imagery acquired under clear sky conditions from airborne/spaceborne sensors. The method, termed Scattering Index (SI), uses Rayleigh scattering principles to create a diffuse skylight vector as a shadow reference. From linear algebra, the proportion of diffuse skylight in each image pixel provides a per pixel measure of shadow extent and abundance. We performed a comparative evaluation against two other methods, first valley detection thresholding (extent) and physics-based unmixing (extent and abundance). Overall accuracy and F-score measures are used to evaluate shadow extent on both Worldview-3 and ADS40 images captured over a common scene. Image subsets are selected to capture objects well documented as shadow detection anomalies, e.g., dark water bodies. Results showed improved accuracies and F-scores for shadow extent and qualitative evaluation of abundance show the method is invariant to scene and sensor characteristics. SI avoids shadow misclassifications by avoiding the use of pixel intensity and the associated limitations of binary thresholding. The method negates the need for complex sun-object-sensor corrections, it is simple to apply, and it is invariant to the exponential increase in scene complexity associated with higher-resolution imagery. View Full-Text
Keywords: imagery; shadow; shadow detection; illumination; vector; diffuse skylight; high resolution imagery; shadow; shadow detection; illumination; vector; diffuse skylight; high resolution
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MDPI and ACS Style

Cameron, M.; Kumar, L. Diffuse Skylight as a Surrogate for Shadow Detection in High-Resolution Imagery Acquired Under Clear Sky Conditions. Remote Sens. 2018, 10, 1185. https://doi.org/10.3390/rs10081185

AMA Style

Cameron M, Kumar L. Diffuse Skylight as a Surrogate for Shadow Detection in High-Resolution Imagery Acquired Under Clear Sky Conditions. Remote Sensing. 2018; 10(8):1185. https://doi.org/10.3390/rs10081185

Chicago/Turabian Style

Cameron, Mark, and Lalit Kumar. 2018. "Diffuse Skylight as a Surrogate for Shadow Detection in High-Resolution Imagery Acquired Under Clear Sky Conditions" Remote Sensing 10, no. 8: 1185. https://doi.org/10.3390/rs10081185

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