NDVI anomaly over Europe
NOAA-AVHRR data are received and processed at DLR-DFD on a daily time step since the beginning of the 1990th. The raw data are calibrated and geo-located to get technical albedo values for the visible and near-infrared channels while the thermal infrared channels are converted to temperatures.
The first and second channel of NOAA-AVHRR is used to calculate the Normalized Difference Vegetation Index (NDVI), a measure of the greenness of vegetation. No atmospheric correction is applied. The data of three daylight passes are used to build a daily NDVI composite of Europe. The NDVI ranges from -0.1 to 0.7, typically. The value of -0.1 corresponds to bare soil while high NDVI values are related to green vegetation.
Daily, weekly and monthly composites are available from our archive. In the near future, also 10-day composites will be available on an operational basis.
For determining the NDVI anomaly, we calculated for each decade of a month the mean 10-day composites as reference. 10-day composites from 1995 to 2005 are used for getting the mean. Subtracting the actual 10-day composite and the reference 10-day composite gives the NDVI anomaly, which can be regarded as a view on the growing characteristics in comparison to the long term mean (anomaly).
Dark green pixels in the anomaly map represent an increase of the actual 10-day composite of 0.2 compared to the long term mean while light orange pixels mark a decrease of -0.2. White pixels indicate no difference of the long term mean and the actual 10-day composite. Blue pixels indicate an increase of more than 0.2. Water is colored dark grey and no data (clouds or snow) are indicated by black color.
Processed anomaly maps starting with the first decade of April 2009 are accessible from our data library as .tif files.
Please use the active link on this site.
The anomaly maps have dimension of 4300 lines and 4100 samples. The data are given as byte (0-255).
For converting the digital numbers (DN) to NDVI, the following equation will be applied
for 2 <= DN <= 183:
NDVI = (DN-2)*0.0022099 - 0.2
DN = 0 is equivalent to water.
DN = 1 represents anomaly less than -0.2.
DN = 184 represents anomaly more than 0.2.
DN = 185 is equivalent to no data.
The anomaly files are named as:
yy represent the last two number of the year,
mm represent the month (01 - 12) and
d represents the number of decades per month (1-3).
Example: 09_04_1_diff.tif is the coding for the anomaly map for the first decade of April 2009.
For comparison, the actual long term decadal mean is shown in the figure below.
If you want to download the actual 10-day composites go to:
The description of the actual 10-day composites can be found here