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Gao, BC (2000). A practical method for simulating AVHRR-consistent NDVI data series using narrow MODIS channels in the 0.5-1.0 mu m spectral range. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, 38(4), 1969-1975.

Over the past two decades, a key indicator of climate change has been the long time series of global maps of the normalized difference vegetation index (NDVI), derived from remotely sensed data acquired with a series of NOAA advanced very high resolution radiometer (AVHRR) instruments from space. These NDVI values are calculated from relatively broad AVHRR channels in the red (similar to 0.58-0.68 mu m) and near-infrared (similar to 0.73-1.0 mu m) regions. Continuation of this long term data set is extremely valuable for climate-related research, However, sometime in the coming decade, the AVHRR time series measurements will no longer be continued, Instead, the measurements will be made using newer generation satellite instruments having narrower channels and improved spatial resolution, For example, the moderate resolution imaging spectroradiometer (MODIS) onboard the Terra spacecraft has several narrow channels in the 0.4-1.0 spectral range. The NDVI values derived from the MODIS red channel (similar to 0.62-0.67 mu m) and near-IR channel (similar to 0.841-0.876 mu m) will be biased compared to those derived from the broader AVHRR channels because of differences in channel positions and widths for the two instruments. The narrow MODIS near-IR channel is-only slightly affected by atmospheric water vapor absorption, while the broad AVHRR near-IR channel is strongly affected by water vapor absorption, As a result, the largest bias comes from the near IR channels on the two instruments. To a lesser extent, the bias also comes from the differences between the red channel positions and the widths of MODIS and AVHRR instruments, In this paper, we describe a practical method for simulating AVHRR NDVI values using several narrower MODIS channels in the 0.4-1.0 mu m spectral range, including the MODIS green channel (similar to 0.545-0.565 mu m) and the ater vapor absorption; channel (similar to 0.915-0.965 mu m), For this study, hyperspectral imaging data acquired with the airborne visible/infrared imaging spectrometer (AVIRIS) are used in the simulation of MODIS and AVHRR channels. This same method can, in principle, be used to derive AVHRR-consistent NDVI data series from other future satellite sensors that have similar capabilities as MODIS.



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