GEE时序——利用sentinel-2（哨兵-2）数据进行地表物候学分析（时间序列平滑法估算和非平滑算法代码）

///
// Land Surface Estimation (LSP) with Sentinel-2 in the Arctic
//
// This is a demo code for the estimation of the start and end of season (SoS and EoS) with the threshold method with
// time series smoothing (20-day composition and cubic interpolation).
//
// The LSP method is the threhsold method
//
// Adrià Descals - a.descals@creaf.uab.cat
// CREAF - Centre de Recerca Ecològica i Aplicacions Forestals
var textSections = '' +
  "\n SECTION 1 - Define parameters and setup " +
  "\n SECTION 2 - Define function for cubic interpolation " +
  "\n SECTION 3 - Prepare Sentinel-2 data " +
  "\n SECTION 4 - Generate composites  " +
  "\n SECTION 5 - Increase window size for empty composites  " +
  "\n SECTION 6 - Interpolate time series " +
  "\n SECTION 7 - Estimate phenology metrics " +
  "\n SECTION 8 - Plot results " +
  "\n SECTION 9 - Display legends " 
print(textSections)
 
 
//_______________________________________________________________________________________________________________________
// SECTION 1 - Define parameters and setup
Map.setOptions('satellite')
var geom = /* color: #ff0000 */ee.Geometry.Point([17.07398, 67.7578]);
var point = geom // inspect results for this location
var roi = point.buffer(100000).bounds() // display results around the point of interest
var vegIndex = 'evi' // Specify the vegetation index (VI): 'ndvi', 'evi', 'gcc', or 'ndpi'.
var th = 0.5 // Define the percentage of amplitude for the estimation of the threshold 
var threshMin = 0.2 // minimum NDVI value for the reclassification of snow values
var scale = 50 // scale of the analysis
var year1 = 2019 // year of processing
var lag = 20 // temporal resolution of the composites
var startDate = year1+'-04-15'
var endDate = year1+'-12-20'
Map.centerObject(roi,7)
//_______________________________________________________________________________________________________________________
// SECTION 2 - Define function for cubic interpolation
var cubicInterpolation = function(collection,step){ 
var listDekads = ee.List.sequence(1, collection.size().subtract(3), 1);
var colInterp = listDekads.map(function(ii){
  var ii = ee.Number(ii);
  
    var p0 = ee.Image(collection.toList(10000).get(ee.Number(ii).subtract(1)));
    var p1 = ee.Image(collection.toList(10000).get(ii));
    var p2 = ee.Image(collection.toList(10000).get(ee.Number(ii).add(1)));
    var p3 = ee.Image(collection.toList(10000).get(ee.Number(ii).add(2)));
  
    var diff01 = ee.Date(p1.get('system:time_start')).difference(ee.Date(p0.get('system:time_start')), 'day');
    var diff12 = ee.Date(p2.get('system:time_start')).difference(ee.Date(p1.get('system:time_start')), 'day');
    var diff23 = ee.Date(p3.get('system:time_start')).difference(ee.Date(p2.get('system:time_start')), 'day'