SAVI time-series chart on Google Earth Engine

Question

I've been trying to generate time-series indexes charts and print it on the panel, but the SAVI index chart ends up looking just the same as the NDVI chart, besides, the range is wrong (0 - 1.5).

Here is the link: https://code.earthengine.google.com/2199b03f692cdd7fba825910b1c667f2#

Here is the code:

var geometry = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[-44.695355502403196, -20.688760721370848],
          [-44.695355502403196, -22.689497956455646],
          [-41.904828158653196, -22.689497956455646],
          [-41.904828158653196, -20.688760721370848]]], null, false);

var l8 = ee.ImageCollection ('LANDSAT/LC08/C01/T1_SR')
    .filterDate('2017-06-01','2018-08-31').filterBounds(geometry)
      .map(function(image){return image.clip(geometry)});
    
//Importando coleção EVI:
var dataset = ee.ImageCollection('LANDSAT/LC08/C01/T1_8DAY_EVI')
                  .filterDate('2017-06-01','2018-08-31')
                  .map(function(image){return image.clip(geometry)});
                  
var evi = dataset.select('EVI');

  var visParams = {
  bands: ['B5', 'B6', 'B4'],
  min: 0,
  max: 5000,
  gamma: 0.7,
};

/*
var l8_mosaic = ee.ImageCollection ('LANDSAT/LC08/C01/T1_SR')
    .filterDate('2017-06-01','2018-08-31').filterBounds(geometry1);

var l8_median_cloud = l8_mosaic.map(addQualityBands).map(maskL8sr);

var rgb = l8_median_cloud.select(['B6', 'B5', 'B4']).median().clip(geometry);
*/

//Vgetation indexes:

//SAVI time-series:
var savi = l8.map(function(image) {
  return image.select().addBands(image.expression(
                        '(1 + L) * ((NIR - RED) / (NIR + RED + L))', {
                        'NIR': image.select('B5'),
                        'RED': image.select('B4'),
                        'L': 0.5
                    }).float()).rename('SAVI')});


//NDVI time-series:
var ndvi = l8.map(function(image) {
  return image.select().addBands(image.normalizedDifference(["B5", "B4"]))
  .rename('NDVI').float();
});



//Params for visualization:
var colorizedVis = {
  min: 0.0,
  max: 1.0,
  palette: [
    'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901',
    '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',
    '012E01', '011D01', '011301'
  ],
};


Map.setCenter(-45.92506211512293,-23.20796402902837, 8);

//Add layers:
//Map.addLayer(rgb,visParams, 'R5G6B4');
Map.addLayer(ndvi.median(), colorizedVis, 'NDVI');
Map.addLayer(evi.median(), colorizedVis, 'EVI');
Map.addLayer(savi.median(), colorizedVis, 'SAVI');


///////Create panel:
var panel = ui.Panel();
panel.style().set('width', '500px');

//labels:
var intro = ui.Panel([
  ui.Label({
    value: 'Gráficos NDVI, EVI e SAVI Inspector',
    style: {fontSize: '20px', fontWeight: 'bold'}
  }),
  ui.Label('Click a point on the map to inspect.')
]);
panel.add(intro);

// Create panels to hold lon/lat values.
var lon = ui.Label();
var lat = ui.Label();
panel.add(ui.Panel([lon, lat], ui.Panel.Layout.flow('horizontal')));

// Register a callback on the default map to be invoked when the map is clicked.
Map.onClick(function(coords) {
  // Update the lon/lat panel with values from the click event.
  lon.setValue('lon: ' + coords.lon.toFixed(2)),
  lat.setValue('lat: ' + coords.lat.toFixed(2));

//Add a red dot for the point clicked on.
  var point = ee.Geometry.Point(coords.lon, coords.lat);
  var dot = ui.Map.Layer(point, {color: 'FF0000'});
  Map.layers().set(1, dot);

//NDVI chart: 
  var ndviChart = ui.Chart.image.series(ndvi, point, ee.Reducer.mean(), 30);
  ndviChart.setOptions({
    title: 'NDVI Over Time',
    vAxis: {title: 'NDVI'},
    hAxis: {title: 'date', format: 'yy-MM', gridlines: {count: 14}},
  });
  
//EVI chart:
  var eviChart = ui.Chart.image.series(evi, point, ee.Reducer.mean(), 30);
  eviChart.setChartType('LineChart').setOptions({
    title: 'EVI Over Time',
    vAxis: {title: 'EVI'},
    hAxis: {title: 'date', format: 'yy-MM', gridlines: {count: 14}},
  });  
  

// SAVI chart:
  var saviChart = ui.Chart.image.series(savi, point, ee.Reducer.mean(), 500);
  saviChart.setOptions({
    title: 'SAVI Over Time',
    vAxis: {title: 'SAVI'},
    hAxis: {title: 'date', format: 'yy-MM', gridlines: {count: 14}},
  });

  
//widgets position:
  panel.widgets().set(2, ndviChart);
  panel.widgets().set(3, eviChart);
  panel.widgets().set(1, saviChart);


});

//cursor:
Map.style().set('cursor', 'crosshair');

//Inserting panel on position 0 on ui.root.
ui.root.insert(0, panel);

Answer 1

Landsat surface reflectance products are scaled by a factor of 10000. So by setting L=0.5 in your expression for calculating SAVI, you are actually calculating 1.5NDVI (since N, R >> 0.5). Example of a work-around:

var savi = l8.map(function(image) {
  return image.select().addBands(image.expression(
                        '1.5 * (NIR - RED) / (NIR + RED + 5000)', {
                        'NIR': image.select('B5'),
                        'RED': image.select('B4')
                    }).float()).rename('SAVI')});