00015_lake_elevation

/*
Tutorial Code by Amirhossein Ahrari
YouTube: https://www.youtube.com/@amirhosseinahrarigee

This code is part of a tutorial series on Earth Engine programming techniques
presented on the Amirhossein Ahrari YouTube channel. You are free to use and modify
this code for academic and non-academic purposes. Don't forget to subscribe to
the Amirhossein Ahrari channel and follow the videos to support the instructor!
*/


var cor = [
  [44.86557382828752,37.08659871132482],
  [46.08505625016252,37.08659871132482],
  [46.08505625016252,38.34669285754838],
  [44.86557382828752,38.34669285754838],
  [44.86557382828752,37.08659871132482]
  ]

var roi = ee.Geometry.Polygon(cor)

Map.centerObject(roi)

var modis2001 = ee.ImageCollection("MODIS/061/MOD09Q1")
.select('sur.*')
.filterDate('2001','2002')
.map(function(img){
  var band = img.multiply(0.0001);
  var ndwi = band.normalizedDifference(['sur_refl_b01','sur_refl_b02']).rename('ndwi');
  return ndwi
  }).median();
  
Map.addLayer(modis2001.clip(roi),[],'ndwi_2001', false)  

print(
  ui.Chart.image.histogram(modis2001,roi,250)
  )
  
var thr = modis2001.gt(0.1);

Map.addLayer(thr.clip(roi),[],'lake_thr', false)

var mask2001 = thr.updateMask(thr);

Map.addLayer(mask2001.clip(roi),[],'mask2001',false)

var vector2001 = mask2001.reduceToVectors({
  geometry: roi, scale: 250
  });
  
Map.addLayer(vector2001,[],'lake2001', false)

var dem = ee.ImageCollection("JAXA/ALOS/AW3D30/V3_2")
.mean().select('DSM')

Map.addLayer(dem,[],'dem',false)


var lake_elevation_2001 = ee.Number(dem.reduceRegion({
  reducer: ee.Reducer.percentile([55]), geometry:vector2001, scale: 250
  }).values().get(0));
  
print('lake elevation for 2001', lake_elevation_2001)


Export.table.toDrive({
  collection: vector2001, description: 'lake2001', folder: 'lake_border', fileFormat: 'SHP'
  })


var modis2023 = ee.ImageCollection("MODIS/061/MOD09Q1")
.select('sur.*')
.filterDate('2023','2024')
.map(function(img){
  var band = img.multiply(0.0001);
  var ndwi = band.normalizedDifference(['sur_refl_b01','sur_refl_b02']).rename('ndwi');
  return ndwi
  }).median();

var thr2 = modis2023.gt(0.1);
var mask2023 = thr2.updateMask(thr2);

var vector2023 = mask2023.reduceToVectors({
  geometry: roi, scale: 250
  });

Map.addLayer(vector2023,[],'lake2023', false)

var lake_elevation_2023 = ee.Number(dem.reduceRegion({
  reducer: ee.Reducer.percentile([55]), geometry:vector2023, scale: 250
  }).values().get(0));
  
print('lake elevation for 2023', lake_elevation_2023)