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

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Xingwen,He,Binbin,Wang,Yong,Tang,Zhi,Li,Xing Quan (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: An extended Fourier approach was presented to improve the retrieved leaf areaindex (LAIr) of herbaceous vegetation in a time series from an alpine wetland. The retrievalwas 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 inversionof a two-layer canopy reflectance model (ACRM). To reduce the uncertainty (the ACRMinversion is ill-posed), we used NDVI and NIR images to reduce the influence of the soilbackground and the priori information to constrain the range of sensitive ACRM parametersdetermined using the Sobol"s method. Even so the uncertainty caused the LAIr versus timecurve to oscillate. To further reduce the uncertainty, a Fourier model was fitted using theperiodically LAIr results, obtaining LAIF. We note that the level of precision of the LAIFpotentially may increase through removing singular points or decrease if the LAIr data weretoo noisy. To further improve the precision level of the LAIr, the Fourier model wasextended by considering the LAIr uncertainty. The LAIr, the LAI simulated using the Fouriermodel, and the LAI simulated using the extended Fourier approach (LAIeF) were validatedthrough 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-squareerrors (RMSE) were 0.31, 0.30 and 0.29, respectively, on DOY 177 (early July 2011). In lateAugust (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 resultsOPEN ACCESSRemote Sens. 2014, 6 1172demonstrate that the extended Fourier approach has the potential to increase the level ofprecision of estimates of the time varying LAI.

Additional Information

Publication

Other

Language: English

Date: 2015

Keywords

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

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