Six Polar Derivative National Phenological Maps Used in Multivariate Clustering
  1. Julian Day of Start of Spring, Defined by Day Accumulating 15% of Total Area Under the NDVI Annual Profile.
  2. Julian Day of Center of the Growing Season, Defined by Day Accumulating 50% of Total Area Under the NDVI Annual Profile.
  3. Duration of the Growing Season, Defined by the Difference Between Day Accumulating 15% GPP and Day Accumulating 85% GPP
  4. Degree of Seasonality, Shown as the Magnitude of the Resultant NDVI Force Vector, or Radial Assymetry in the Polar Plot
  5. Mean NDVI During the Growing Season
  6. Standard Deviation of NDVI During the Growing Season

All 6 of these polar derivative maps are highly orthogonal; that is, they have little cross-correlation with each other - Each map carries unique and different information