NDVI time series with Sentinel-2 in Google Earth Engine

Question

I want to calculate the time series of the NDVI with Sentinel-2 of a specific area of Australia.

I started from this code:

Time series analysis of NDVI using Google Earth Engine

Substituting Landsat with Sentinel and modifying the data extraction start date.

  //Importing image and geometry:
var l8 = ee.ImageCollection("COPERNICUS/S2")
var geometry = //Graigzone
    ee.Geometry.Polygon(
        [[[147.232246, -25.695369],
          [147.230186, -25.654525],
          [147.173195, -25.627907],
          [147.353439, -25.648645],
          [147.347946, -25.686707],
          [147.389145, -25.623573],
          [147.398758, -25.622954],
          [147.398758, -25.682994],
          [147.438583, -25.692894],
          [147.431717, -25.702794],
          [147.408371, -25.699082],
          [147.374039, -25.725684],
          [147.298164, -25.747023],
          [147.275848, -25.75228],
          [147.256622, -25.762793],
          [147.259369, -25.772687],
          [147.384338, -25.835123],
          [147.393265, -25.859841],
          [147.345886, -25.934582],
          [147.288208, -25.931495],
          [147.275848, -25.856752],
          [147.240829, -25.789072],
          [147.23774, -25.763103],
          [147.221947, -25.755372],
          [147.232246, -25.695369]]], null, false);
          
  

//Filtering date, polygon, and cloudiness
    var image = l8.filterDate ('2016-01-01', '2021-07-26')
                .filterBounds (geometry)
                //.filterMetadata ('CLOUD_COVER', 'less_than', 20);

    //NDVI calculation:
    var ndvi_func = function (i) {
      var ndvi = i.normalizedDifference (['B8', 'B4']).rename ('NDVI')
      return i.addBands(ndvi);
    }

    var image_ndvi = image.map(ndvi_func);

    //Calculating year wise NDVI
    var year = ee.List.sequence(2015,2021);
    var year_func = function(y){
      var range = ee.Filter.calendarRange (y, y, 'year');
      return image_ndvi.select('NDVI').filter(range).median().set ('Year', y)
    };
    var yearwise_ndvi = ee.ImageCollection(year.map(year_func));
    print (yearwise_ndvi);
    Map.addLayer (yearwise_ndvi)
    
    //Creating time-series chart:
var chart = ui.Chart.image.series ({
  imageCollection: yearwise_ndvi,
  region: geometry,
  reducer: ee.Reducer.median(),
  scale: 10,
  xProperty: 'Year'
}).setOptions ({title: "NDVI over time",
  hAxis: {title: 'Time of the year', format: 'year'}
});

print(chart);

The Error I get is : Error generating chart: Invalid JSON:

What is wrong with the code?

Answer 1

Maybe because you used median reducer instead of mean. Try using mean and see if it works.

The error you mentioned is about the creating chart part. But i can't find the problem.

This might help you as well. Google Earth Engine Failed to decode JSON