The Surface Reflectance Daily L2G Global 250m of MODIS is selected as the input for generating normalized difference vegetation index (NDVI). The L2G product has two bands – Band1 (620-670 nm) and Band2 (841-876 nm) that represent respectively red and near-infrared band. Therefore, the equation for computing daily NDVI is as follows:
Resulted data are in the range of [0, 250].
RVCI stands for the ratio of current NDVI to previous year for the same periods – either weekly or biweekly. The equation is listed as:
RMVCI stands for the ratio of current NDVI to the median of previous years since 2000 for the same periods – either weekly or biweekly. The equation is listed as:
Where, c is the current year.
Vegetation Condition Index (VCI) is an index that represents the weather condition or the vegetation condition. The following is the basic equation:
Where, NDVI is the value at a given pixel, NDVImin is the minimum across multiple years at that pixel, NDVImax is the maximum across multiple years. This is basically normalized across years at a given pixel.
Mean Vegetation Condition index (MVCI) represents the deviation of the vegetation to “normal” vegetation or multiple-year mean. The equation is listed:
In general, the value range should be mainly around -100% to 100% although the actual range can go beyond these limits.