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Remote Sens. 2015, 7(11), 15114-15139; doi:10.3390/rs71115114

Increasing the Accuracy of Mapping Urban Forest Carbon Density by Combining Spatial Modeling and Spectral Unmixing Analysis

1
Research Center of Forestry Remote Sensing and Information Engineering, Central South University of Forestry and Technology, Changsha 410004, China
2
Department of Geography, Southern Illinois University at Carbondale, Carbondale, IL 62901, USA
3
Xianhu Botanic Garden of Shenzhen, Shenzhen 518004, China
4
College of Forestry, South China Agricultural University, Guangzhou 510642, China
*
Author to whom correspondence should be addressed.
Academic Editors: Dengsheng Lu, Guomo Zhou, Conghe Song, Guangxing Wang, Alfredo R. Huete and Prasad S. Thenkabail
Received: 21 September 2015 / Revised: 25 October 2015 / Accepted: 3 November 2015 / Published: 11 November 2015
(This article belongs to the Special Issue Carbon Cycle, Global Change, and Multi-Sensor Remote Sensing)
View Full-Text   |   Download PDF [1311 KB, uploaded 11 November 2015]   |  

Abstract

Accurately mapping urban vegetation carbon density is challenging because of complex landscapes and mixed pixels. In this study, a novel methodology was proposed that combines a linear spectral unmixing analysis (LSUA) with a linear stepwise regression (LSR), a logistic model-based stepwise regression (LMSR) and k-Nearest Neighbors (kNN), to map the forest carbon density of Shenzhen City of China, using Landsat 8 imagery and sample plot data collected in 2014. The independent variables that contributed to statistically significantly improving the fit of a model to data and reducing the sum of squared errors were first selected from a total of 284 spectral variables derived from the image bands. The vegetation fraction from LSUA was then added as an independent variable. The results obtained using cross-validation showed that: (1) Compared to the methods without the vegetation information, adding the vegetation fraction increased the accuracy of mapping carbon density by 1%–9.3%; (2) As the observed values increased, the LSR and kNN residuals showed overestimates and underestimates for the smaller and larger observations, respectively, while LMSR improved the systematical over and underestimations; (3) LSR resulted in illogically negative and unreasonably large estimates, while KNN produced the greatest values of root mean square error (RMSE). The results indicate that combining the spatial modeling method LMSR and the spectral unmixing analysis LUSA, coupled with Landsat imagery, is most promising for increasing the accuracy of urban forest carbon density maps. In addition, this method has considerable potential for accurate, rapid and nondestructive prediction of urban and peri-urban forest carbon stocks with an acceptable level of error and low cost. View Full-Text
Keywords: forest carbon; integration; Landsat 8 image; k-nearest neighbors; mapping; mixed pixel; regression; Shenzhen City; vegetation fraction forest carbon; integration; Landsat 8 image; k-nearest neighbors; mapping; mixed pixel; regression; Shenzhen City; vegetation fraction
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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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MDPI and ACS Style

Sun, H.; Qie, G.; Wang, G.; Tan, Y.; Li, J.; Peng, Y.; Ma, Z.; Luo, C. Increasing the Accuracy of Mapping Urban Forest Carbon Density by Combining Spatial Modeling and Spectral Unmixing Analysis. Remote Sens. 2015, 7, 15114-15139.

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