Calculates the green-up day out of true NDVI values extracted through a fast fourier filter applied to NDVI composites
fft.filter(ndvi, filter=8, globalthreshold=0, resvec=c(0.55,0.6,0.65,0.65,0.7))
- NDVI values computed from the daily surface reflectances, values between 0 and 10000 as a numeric vector.
- Smoothing value of the filter. The higher the value, the more the function will be smoothed.
- The algorithm returns the green-up date calculated through a local threshold method if the value of mode is 0 or through a global threshold method (with a global threshold equal to the value of globalthreshold) if the value is greater than 0.
This routine tries to restore the temporal NDVI profile, i.e. separate true observations from noise. An algorithm creates a function by using a fast fourier transfusion applied to NDVI composites.
The computed green-up date as Julian day (Day of Year).
Documentation reproduced from package biseVec, version 1.3-25. License: GPL (>= 2)