New NDVI-derived variables

Within the Seasonal Analysis Topic, GDA has added new derived variables for GDA-processed crop-specific NDVI to compare a given year with the prior year, 5 Yr Avg or 10 Yr Avg.  These variables are Timeshift and Delta.  Timeshift calculates the difference in days for a given date and the same NDVI from a prior year/5 Yr Avg/10 Yr Avg.  Delta calculates the difference in NDVI from a given date and the same date from the prior year/5 Yr Avg/10 Yr Avg.