Detecting shadows in multi-temporal aerial imagery to support near-real-time change detection
Year: 2017
Type: article
Abstract: Multi-temporal aerial imagery captured via an approach called repeat station imaging (RSI) facilitates post-hazard assessment of damage to infrastructure. Spectral-radiometric (SR) variations caused by differences in shadowing may inhibit successful change detection based on image differencing. This study evaluates a novel approach to shadow classification based on bi-temporal imagery, which exploits SR change signatures associated with transient shadows. Changes in intensity (brightness from red–green–blue images) and intensity-normalized blue waveband values provide a basis for classifying transient shadows across a range of material types with unique reflectance properties, using thresholds that proved versatile for very different scenes. We derive classification thresholds for persistent shadows based on hue to intensity ratio (H/I) images, by exploiting statistics obtained from transient shadow areas. We assess shadow classification accuracy based on this procedure, and compare it to the more conventional approach of thresholding individual H/I images based on frequency distributions. Our efficient and semi-automated shadow classification procedure shows improved mean accuracy (93.3%) and versatility with different image sets over the conventional approach (84.7%). For proof-of-concept, we demonstrate that overlaying bi-temporal imagery also facilitates normalization of intensity values in transient shadow areas, as part of an integrated procedure to support near-real-time change detection.
Source: GIScience & Remote Sensing
Authors: Emanuel A. Storey, Douglas A. Stow, Lloyd L. Coulter, Christopher Chen
Institution: San Diego State University
Language: English
Subfield: Media Technology
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
Awards: G3057660377, G3553680491
OpenAlex ID: W2582328766