Regional Amazon basin and global analyses of MODIS vegetation indices: early results and comparisons with AVHRR

摘要

Vegetation indices (VI) have emerged as important tools in the monitoring, mapping, and resource management of vegetation. They are radiometric measures of the amount, structure, and condition of vegetation, which serve as useful indicators of seasonal and inter-annual variations in vegetation. The recently launched Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra platform offers many improvements for land studies and VI production from that provided by the AVHRR sensor. These include improved sensitivity to chlorophyll and contamination by atmospheric water vapor through narrower bandwidths in the red and NIR, respectively. In addition, the finer pixel size provides improved VI monitoring and change detection capability. The MODIS VI products are produced at spatial resolutions of 250m, 500m, 1km and 0.25/spl deg/ and at temporal intervals of 16 days and 1 month. They include two VI formulations, the normalized difference vegetation index, NDVI. An improved, or enhanced vegetation index (EVI) is also produced with the goal of providing complimentary information on vegetation spatial and temporal variations, while minimizing much of the contamination problems present in the NDVI. Whereas the NDVI is chlorophyll sensitive and responds mostly to red band variations, the EVI is more NIR sensitive and, as a result of the penetrating properties of the NIR band, is more responsive to canopy structural variations, including LAI, canopy type, and canopy architecture. In this study, early images from MODIS are used to evaluate NDVI and EVI for global and regional vegetation monitoring.