For better interpretation and understanding of the NDVI images, the deviation from the long-term mean is also provided. The NDVI deviation describes the amount and direction (positive or negative) of change of the current time period compared to the long-term mean NDVI (2001 to 2010) calculated for the corresponding time period. For example, the NDVI values for 1 to 15 January 2015 will be compared to the average of previous NDVI values from 2001 to 2010 for the first half of January. It therefore offers a good indication of how the current conditions compare with average conditions of the same time of year for many years.