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Open AccessArticle

Influence of Leaf Specular Reflection on Canopy Radiative Regime Using an Improved Version of the Stochastic Radiative Transfer Model

1
College of Electrical and Information Engineering, Hunan University, Changsha 410082, China
2
Department of Earth and Environment, Boston University, 685 Commonwealth Avenue, Boston, MA 02215, USA
3
State Key Laboratory of Remote Sensing Science, School of Geography, Beijing Normal University, Beijing 100875, China
4
Guangxi Colleges and Universities Key Laboratory of Unmanned Aerial Vehicle (UAV) Remote Sensing, Guilin University of Aerospace Technology, Guilin 541004, China
5
Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
6
Guangxi Zhuang Autonomous Region Environmental Monitoring Centre, Nanning 530028, China
*
Authors to whom correspondence should be addressed.
Remote Sens. 2018, 10(10), 1632; https://doi.org/10.3390/rs10101632
Received: 9 July 2018 / Revised: 27 September 2018 / Accepted: 11 October 2018 / Published: 14 October 2018
(This article belongs to the Special Issue Radiative Transfer Modelling and Applications in Remote Sensing)
Interpreting remotely-sensed data requires realistic, but simple, models of radiative transfer that occurs within a vegetation canopy. In this paper, an improved version of the stochastic radiative transfer model (SRTM) is proposed by assuming that all photons that have not been specularly reflected enter the leaf interior. The contribution of leaf specular reflection is considered by modifying leaf scattering phase function using Fresnel reflectance. The canopy bidirectional reflectance factor (BRF) estimated from this model is evaluated through comparisons with field-measured maize BRF. The result shows that accounting for leaf specular reflection can provide better performance than that when leaf specular reflection is neglected over a wide range of view zenith angles. The improved version of the SRTM is further adopted to investigate the influence of leaf specular reflection on the canopy radiative regime, with emphases on vertical profiles of mean radiation flux density, canopy absorptance, BRF, and normalized difference vegetation index (NDVI). It is demonstrated that accounting for leaf specular reflection can increase leaf albedo, which consequently increases canopy mean upward/downward mean radiation flux density and canopy nadir BRF and decreases canopy absorptance and canopy nadir NDVI when leaf angles are spherically distributed. The influence is greater for downward/upward radiation flux densities and canopy nadir BRF than that for canopy absorptance and NDVI. The results provide knowledge of leaf specular reflection and canopy radiative regime, and are helpful for forward reflectance simulations and backward inversions. Moreover, polarization measurements are suggested for studies of leaf specular reflection, as leaf specular reflection is closely related to the canopy polarization. View Full-Text
Keywords: leaf specular reflection; radiative regime; stochastic radiative transfer model (SRTM); polarization measurements leaf specular reflection; radiative regime; stochastic radiative transfer model (SRTM); polarization measurements
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MDPI and ACS Style

Yang, B.; Knyazikhin, Y.; Xie, D.; Zhao, H.; Zhang, J.; Wu, Y. Influence of Leaf Specular Reflection on Canopy Radiative Regime Using an Improved Version of the Stochastic Radiative Transfer Model. Remote Sens. 2018, 10, 1632.

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