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The following pages are to help guide the user through calculating an EMSI for any available EOS platform on Google's Earth Engine.
EMSI is calculated using the NDVI (or some other vegetation spectral index)
The original per pixel EMSI, derived using the formula for the standard score, is computed using the pixel xt NDVI recorded for a given date (t) in a given year, and the NDVI mean (μ) and NDVI standard deviation (σ) for the same date/period across the entire time series or reference time period (T). A coefficient ρ is used to normalize or give a positive or negative sign to the index.
The EMSI of each pixel is thus placed in its distinctive statistical location in a 'normal distribution' that is defined by all a given pixel's EMSI values for the same time period (i.e., same 'Julian' period) across the entire time series.
Tracking the EMSI for each year for a given pixel's 'phenoperiod' roughly yields, with some statistical rigor, interannual trends in (as we like to say) 'climate forcing' and are amenable to inferential analyses.