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Remote Sens. 2017, 9(8), 853; doi:10.3390/rs9080853

Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model

1
College of Surveying and Geo-Informatics, Tongji University, No. 1239, Siping Road, Shanghai 200092, China
2
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, No. 3663, North Zhongshan Road, Shanghai 200062, China
*
Author to whom correspondence should be addressed.
Received: 29 June 2017 / Revised: 13 August 2017 / Accepted: 15 August 2017 / Published: 17 August 2017
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Abstract

The intensity value recorded by terrestrial laser scanning (TLS) systems is significantly influenced by the incidence angle. The incidence angle effect is an object property, which is mainly related to target scattering properties, surface structures, and even some instrumental effects. Most existing models focus on diffuse reflections of rough surfaces and ignore specular reflections, despite that both reflections simultaneously exist in all natural surfaces. Due to the coincidence of the emitter and receiver in TLS, specular reflections can be ignored at large incidence angles. On the contrary, at small incidence angles, TLS detectors can receive a portion of specular reflections. The received specular reflections can trigger highlight phenomenon (hot-spot effects) in the intensity data of the scanned targets, particularly those with a relatively smooth or highly-reflective surface. In this study, a new method that takes diffuse and specular reflections, as well as the instrumental effects into consideration, is proposed to eliminate the specular reflection effects in TLS intensity data. Diffuse reflections and instrumental effects are modeled by a polynomial based on Lambertian reference targets, whereas specular reflections are modeled by the Phong model. The proposed method is tested and validated on different targets scanned by the Faro Focus3D 120 terrestrial scanner. Results imply that the coefficient of variation of the intensity data from a homogeneous surface is reduced by approximately 38% when specular reflections are considered. Compared with existing methods, the proposed method exhibits good feasibility and high accuracy in eliminating the specular reflection effects for intensity image interpretation and 3D point cloud representation by intensity. View Full-Text
Keywords: intensity correction; terrestrial laser scanning; incidence angle; Lambertian; specular reflections; highlights intensity correction; terrestrial laser scanning; incidence angle; Lambertian; specular reflections; highlights
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Tan, K.; Cheng, X. Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model. Remote Sens. 2017, 9, 853.

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