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Google Earth Engine implementation of the popular R bfast package

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Introduction

geeBFASTmonitor is a reimplementation of R bfastmonitor with only some slight variations.

BFASTmonitor

BFASTmonitor is a variation of bfast for monitoring purposes. Since geeBFASTmonitor is mostly a reimplementation, the original documentation is still relevant.

Running geeBFASTmonitor

It's as easy as including the following code in the beginning of your script :

var engine = require('users/andreim/geeMonitor:monitor.js');

in your gee script. Afterwards, you'll have access to the function engine.bfastMonitor(roi,historyStart,historyEnd,monitoringStart,monitoringEnd,h,period,alpha,magnitudeThreshold,harmonics)

The parameters are similar to the R version of bfastMonitor:

  • roi: region of interest as a Feature
  • historyStart: The starting date of the stable period.
  • historyEnd: The end date of the stable period.
  • monitoringStart: The starting date of the monitoring period.
  • monitoringEnd: The end date of the monitoring period.
  • h: numeric scalar from interval (0,1) specifying the bandwidth relative to the sample size in MOSUM/ME monitoring processes
  • period: maximum time, relative to the history period, that should be monitored. The default is 10 times the history period.
  • alpha: Significance level of the monitoring (and ROC, if selected) procedure, i.e., probability of type I error.
  • magnitudeThreshold: Threshold for magnitude level for which a change should be considered. Default is 0.
  • harmonics: Order of the harmonic term.

A typical way of using the function is to save its result:

var result = engine.bfastMonitor(roi,historyStart,historyEnd,monitoringStart,monitoringEnd,h,period,alpha,magnitudeThreshold,harmonics)

The most important results are:

  • the time of change found in bfastResults.timeCnk2
  • magnitude of change found in bfastResults.Cnk

Applications

If you want to play with the algorithm interactively, please check:

https://andreim.users.earthengine.app/view/bfastmonitor

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Google Earth Engine implementation of the popular R bfast package

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