Differences between MODIS NDVI and AVHRR NDVI in monitoring grasslands change
MODIS NDVI和AVHRR NDVI 对草原植被变化监测差异

In this paper, with grassland of Xilingol as the research site, the average method, unary linear regression model, correlation analysis are used to compare the annual and interannual characteristics of NDVI series, including the MODIS NDVI and the AVHRR NDVI. The precipitation, mean temperature, vapor pressure are taken as climatic variables to compare the relationship between NDVI series and climatic factors over different types of grasslands. The objective is to provide references for reasonable use of NDVI series to monitor vegetation changes. The results show that, (1) Annual characteristics of the MODIS NDVI and the GIMMS NDVI are similar, yet the MODIS NDVI can distinguish each steppe better than that of the GIMMS NDVI. (2) Different interannual characteristics are observed between MODIS NDVI and GIMMS NDVI of grassland vegetation during 2000 to 2003. Compared with MODIS NDVI, vegetation increase trend is stronger in GIMMS NDVI change trend classifi cation image, with a proportion of vegetation increasing area in GIMMS NDVI of 94.25%, while only 83.33% for MODIS NDVI. Consistency of the two NDVI classifi cation images is only 52.88%. (3) Correlation differences between the two NDVI series and climatic factors are signifi cant. Correlation coeffi cients between MODIS NDVI and mean temperature are larger than that of GIMMS NDVI. The proportion of correlation coeffi cients between MODIS NDVI and vapor pressure are lower than that of GIMMS NDVI with a value of 83% (about 10 meteorological stations). Similar results are also observed for the precipitation with a proportion of 67% (about 8 meteorological stations).