An Extended Fourier Approach to Improve the Retrieved Leaf Area Index (LAI) in a Time Series from an Alpine Wetland

Remote Sensing

Xingwen Quan¹  Binbin He¹  Yong Wang¹  Zhi Tang¹ 

[1] School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu 611731, China; E-Mails:

关键词: alpine wetland;    extended Fourier approach;    ill-posed inversion problem;    leaf area index;    uncertainty;   

DOI  :  10.3390/rs6021171

来源: mdpi

【 摘 要 】

An extended Fourier approach was presented to improve the retrieved leaf area index (LAI_r) of herbaceous vegetation in a time series from an alpine wetland. The retrieval was performed from the Aqua MODIS 8-day composite surface reflectance product (MYD09Q1) from day of year (DOY) 97 to 297 using a look-up table (LUT) based inversion of a two-layer canopy reflectance model (ACRM). To reduce the uncertainty (the ACRM inversion is ill-posed), we used NDVI and NIR images to reduce the influence of the soil background and the priori information to constrain the range of sensitive ACRM parameters determined using the Sobol’s method. Even so the uncertainty caused the LAI_r versus time curve to oscillate. To further reduce the uncertainty, a Fourier model was fitted using the periodically LAI_r results, obtaining LAI_F. We note that the level of precision of the LAI_F potentially may increase through removing singular points or decrease if the LAI_r data were too noisy. To further improve the precision level of the LAI_r, the Fourier model was extended by considering the LAI_r uncertainty. The LAI_r, the LAI simulated using the Fourier model, and the LAI simulated using the extended Fourier approach (LAI_eF) were validated through comparisons with the field measured LAI. The R² values were 0.68, 0.67 and 0.72, the residual sums of squares (RSS) were 3.47, 3.42 and 3.15, and the root-mean-square errors (RMSE) were 0.31, 0.30 and 0.29, respectively, on DOY 177(early July 2011). In late August (DOY 233), the R² values were 0.73, 0.77 and 0.79, the RSS values were 38.96, 29.25 and 27.48, and the RMSE values were 0.94, 0.81 and 0.78, respectively. The results demonstrate that the extended Fourier approach has the potential to increase the level of precision of estimates of the time varying LAI.

【 授权许可】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland