Research on validating MODIS/LAI product in a typical semi-arid steppe of Xilinhot in Northern China

Abstract

Abstract: MODIS/LAI product in a typical semi-arid steppe of Xilinhot in Northern China was validated based on three comprehensive field surveys which were carried out during July-August 2008 in the study area. LAI was measured in 25 m×25 m plots by a destructive harvest method of 80 intensive plots and 20 scattered plots. Three TM/ETM+ images acquired during the field survey periods were collected and processed. The validation work covered two parts: Time series analysis and spatial pattern analysis. In time series analysis, MODIS/LAI track in the intensive sampling region extracted from DOY169 to DOY241 were compared with ground measured values. In spatial pattern analysis, LAI map with 30 m spatial resolution were first derived by building a regression line between LAI and TM band 5 (1.6 μm), and then aggregated to 1 km spatial resolution based on MODIS grids. Results indicated that in the temporal domain MODIS/LAI product can correctly reflect grass growth trends; In the spatial domain it showed a similar pattern with TM/LAI (1 km). Using the TM/LAI as reference, the relative RMSE of MODIS/LAI was about 24% and a positive bias (10.8%) existed, suggesting slight over-estimation. Error distribution analysis revealed that the MODIS/LAI product was less accurate in regions with lower LAI values, probably due to soil contamination. Moreover, the relative RMSE of the MODIS/LAI product was higher at the beginning of July and the end of August when the heterogeneity of grass cover increased as a result of human activities.

CLC Number:

S812.3

WANG Yuan-yuan, WANG Meng, LI Gui-cai, WANG Jun-bang, YANG Zhong-dong, RONG Zhi-guo. Research on validating MODIS/LAI product in a typical semi-arid steppe of Xilinhot in Northern China[J]. Acta Prataculturae Sinica, 2011, 20(4): 252-260.

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