Estimating Savanna Clumping Index Using Hemispherical Photographs Integrated with High Resolution Remote Sensing Images

Jucai Li,Wenjie Fan,Gaolong Zhu,Xiru Xu,Jingjing Peng,Yuan Liu

doi:10.3390/rs9010052

Jucai Li, Wenjie Fan + Show 4 more

Open Access

https://doi.org/10.3390/rs9010052

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Journal: Remote sensing	Publication Date: Jan 8, 2017
Citations: 7	License type: CC BY 4.0

Affiliation: Peking University, Minjiang University

Abstract

In contrast to herbaceous canopies and forests, savannas are grassland ecosystems with sparsely distributed individual trees, so the canopy is spatially heterogeneous and open, whereas the woody cover in savannas, e.g., tree cover, adversely affects ecosystem structures and functions. Studies have shown that the dynamics of canopy structure are related to available water, climate, and human activities in the form of porosity, leaf area index (LAI), and clumping index (CI). Therefore, it is important to identify the biophysical parameters of savanna ecosystems, and undertake practical actions for savanna conservation and management. The canopy openness presents a challenge for evaluating canopy LAI and other biophysical parameters, as most remotely sensed methods were developed for homogeneous and closed canopies. Clumping index is a key variable that can represent the clumping effect from spatial distribution patterns of components within a canopy. However, it is a difficult task to measure the clumping index of the moderate resolution savanna pixels directly using optical instruments, such as the Tracing Radiation and Architecture of Canopies, LAI-2000 Canopy Analyzer, or digital hemispherical photography. This paper proposed a new method using hemispherical photographs combined with high resolution remote sensing images to estimate the clumping index of savanna canopies. The effects of single tree LAI, crown density, and herbaceous layer on the clumping index of savanna pixels were also evaluated. The proposed method effectively calculated the clumping index of moderate resolution pixels. The clumping indices of two study regions located in Ejina Banner and Weichang were compared with the clumping index product over China’s landmass.

Highlights

Earth surface vegetation presents various canopy morphologies [1]
Chen et al [16] demonstrated the importance of clumping index (CI) for leaf area index (LAI) estimation and carbon cycle modeling, since it allows a better segmentation of the solar radiation distribution in sunlit and shaded leaves as compared to models that relate carbon absorption only to the intercepted solar radiation
The clumping index of moderate resolution images of savannah regions was calculated using the theory of average transmittance

Summary

Introduction

Earth surface vegetation presents various canopy morphologies [1]. In contrast to herbaceous canopies and forests, savannas are grassland ecosystems with sparsely distributed individual trees, so the canopy does not close [2,3]. Of Earth’s land area [6,7,8] They are anticipated to be among the ecosystems most sensitive to future land use and climate changes [9,10], and it is important to gain a mechanistic understanding of Remote Sens. Woody cover growth is related to available water, climate, human activities [12], and herbivory level [11] in the form of porosity, leaf area index (LAI), and clumping index (CI). Open ecosystems, and the canopy openness presents a challenge for evaluating canopy LAI and other biophysical parameters, since most remotely sensed methods were developed for ideal and closed canopies [13,14]. CI is a very important parameter to describe spatial heterogeneity and clumping effects of savanna canopies

Results

Discussion

Conclusion