Google Earth Engine JavasSript codes for computing z-score and harmonic analysis based on MODIS time series data.
Harmonic analysis: https://code.earthengine.google.com/09281ea1ffe1ac32d2799e3a7faa68db
z-score analysis: https://code.earthengine.google.com/82043ea84850d0c8ac6173f259c73b63
Philipp, M.; Wegmann, M.; Kübert-Flock, C. Quantifying the Response of German Forests to Drought Events via Satellite Imagery. Remote Sens. 2021, 13, 1845. https://doi.org/10.3390/rs13091845