This data set is only available for a restricted user group, please contact us if you want to access these data.
RESTRICTED only accessable in ZMAW net or via CliSAP login What does that mean?
This data set comprises the Normalized Differential Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) together with uncertainty estimates and quality flags. Both indices are based on the difference: reflectance observed in the near-infrared (NIR) portion of the electromagnetic spectrum minus reflectance observed in the red portion of the electromagnetic spectrum. Areas with photosynthetically active vegetation absorb much more radiation in the red portion of the electromagnetic spectrum than areas without any or with photosynthetically inactive vegetation. This is due to the pigments in the leaves, needles, etc. In contrast, absorption of NIR radiation is low for both surface types. However, the amount of NIR radiation transmitted and/or scattered is a function of the surface type / roughness. Therefore, the difference of the reflectances is small for areas without any or with photosynthetically inactive vegetation and high for areas with photosynthetically active vegetation. Note that in areas with a lot of vegetation the dependence of the NIR-radiation scattering and/or transmission on the surface type / roughness helps to overcome saturation effects in the red portion of the electromagnetic spectrum and therefore allows a better separation of high NDVI values.
The impact of clouds, aerosols, sensor noise (and other error sources not mentioned here explicitly) is mitigated using radiative transfer modeling on the one hand. On the other hand these impacts are mitigated by normalizing the above-mentioned difference with the sum of the used reflectances (NDVI) or with these reflectances, the reflectance in the blue portion of the electromagnetic spectrum and additional factors (EVI). For more details we recommend to look into the User's Guide.
The data set offered here has monthly temporal resolution and allows to monitor the seasonal cycle of vegetation development.
Coverage, spatial and temporal resolution
Period and temporal resolution:
Coverage and spatial resolution:
This is version 5 of this MODIS data set. Both, NDVI and EVI have been validated in a number of field campaigns and validation studies. The data set with monthly temporal resolution offered here is based on 16-day composites of MODIS NDVI and EVI at 1 km grid resolution. Radiative transfer modeling and a number of filters were used to mitigate or eliminate cloud and aerosol effects. Particularly, for EVI effects of smoke and sub-gridscale thin clouds are taken into account. A short overview about validation activities can be found here.
The data set offered here contains 4 different quality flags; one gives general information about whether the quality is good or acceptable, in the latter case the recommendation is to look into the detailed quality flags, whether there is snow/ice present, or whether data are missing or have not been processed or have been filled with values from climatology. The second quality flag gives more detailed information about the quality (low value = low quality, high value = high quality). The two remaining flag give information about the aerosol load and/or the aerosol model used to correct the observed radiances and the second one details how many useful NDVI or EVI values of the 1 km grid resolution product contribute to CMG-grid data set given here.
Institute of Oceanography, University of Hamburg, Hamburg
E-Mail: antje.tittebrand@ zmaw.de
LP DAAC User Services
U.S. Geological Survey (USGS)
Center for Earth Resources Observation and Science (EROS)
ICDC, CliSAP, Universität Hamburg
E-Mail: stefan.kern@ zmaw.de
Upon using this data please cite as follows:
These data are originally distributed by the Land Processes Distributed Active Archive Center (LP DAAC), located at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center (lpdaac.usgs.gov), distributed in netCDF format by the Integrated Climate Data Center (ICDC, http://icdc.zmaw.de) University of Hamburg, Hamburg, Germany.