JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2020, Vol. 44 ›› Issue (3): 149-156.doi: 10.3969/j.issn.1000-2006.201811012

Previous Articles     Next Articles

Estimation of aboveground biomass in a Chinese fir (Cunninghamia lanceolata)forest combining data of Sentinel⁃1 and Sentinel⁃2

PAN Lei1(), SUN Yujun1(), WANG Yifu1, CHEN Liping2, CAO Yuanshuai3   

  1. 1.State Forestry and Grassland Administration Key Laboratory of Forest Resources & Environmental Management, College of Forest, Beijing Forestry University, Beijing 100083, China
    2.Huizhou University, Huizhou 516007, China
    3.East China Inventory and Planning Institute, State Forestry Administration, Hangzhou 310019, China
  • Received:2018-11-05 Revised:2019-01-24 Online:2020-05-30 Published:2020-06-11
  • Contact: SUN Yujun E-mail:1072344791@qq.com;panlb@bjfu.edu.cn

Abstract: Objective

Forest above-ground biomass (AGB) is the main storage site of carbon, which plays an important role in the regional and global carbon cycle. In studies on AGB estimation based on remote sensing, saturation of optical and radar data is a well-known phenomenon, however, it is unclear so far as to how this problem may be reduced in order to improve AGB estimations. Optical and radar data offer different advantages for recording forest stand structures, thus optimized use of their features may help improve AGB estimation. This study was conducted to assess whether forest AGB estimations can be produced in a subtropical area based on data produced using Sentinel-1 synthetic aperture radar (SAR) and Sentinel-2 multispectral instruments.

Method

A stand of Chinese fir (Cunninghamia lanceolata) in a state-owned forest farm in Jiangle, Fujian Province, China, and Sentinel-1 SAR data and Sentinel-2 multispectral optical data were used. Backscatter coefficients of Sentinel-1 images in different polarization modes (VH, VV, VH/VV) and second-order texture measures of a gray level co-occurrence matrix in different window sizes (3×3, 5×5, 7×7 and 9×9) were recorded, and band values, vegetation indices, and second-order texture measures in 3 × 3 windows of Sentinel-2 image were extracted as remote sensing factors. Models were fitted using multiple linear stepwise regression. AGB estimation models based on Sentinel-2 remote sensing factors only and on cooperative Sentinel-2 and Sentinel-1 remote sensing were established. Determination coefficient (R2), adjusted determination coefficient (Radj2), root mean square error (RMSE), and variance inflation factor were selected for assessing the models. The ability of Sentinel-2 optical data and Sentinel-2 optical data combined with Sentinel-1 SAR data to estimate forest AGB was compared and analyzed.

Result

The results showed that when Sentinel-2 band values, vegetation indices and texture measures were used as dependent variables to predict AGB, the estimation effect was inadequate, and the Radj2 values of the models were 0.319, 0.303 and 0.455, respectively; an AGB estimation model based on all remote sensing factors of Sentinel-2 optical data (Model-1) produced an Radj2 value of 0.501, while RMSE was 64.04 Mg/hm2. When the Sentinel-1 remote sensing factor was added, the AGB estimation model based on Sentinel-2 optical data and Sentinel-1 SAR data was improved, with a model adjustment coefficient (Radj2) and RMSE were 0.575 and 59.13 Mg/hm2. Compared with Model-1, the accuracy of Model-2 was considerably improved, thus the second-order texture measures of Sentinel-1 VH polarimetric imaging plays an important role.

Conclusion

Our study demonstrates that multispectral optical data of the Sentinel-2 satellite can be used as reliable data source for estimating forest AGB in subtropical areas, and the combination of Sentinel-1 SAR data and Sentinel-2 multispectral optical data can substantially improve accuracy of estimating forest AGB. Estimations of forest ABG by combining multispectral optical remote sensing images and space-borne polarimetric SAR data offers considerable advantages. The results of the present study may help improve accuracy of forest AGB estimation, and it provides a reference basis for future studies on forest AGB using different remote sensing data sources.

Key words: Chinese fir forest, aboveground biomass, Sentinel-1, Sentinel-2, texture, regression model

CLC Number: