Google Earth Engine – Fixing ‘No Features Contain Non-Null Values of system:time_start’ Error

Question

1. I'm getting the following error while generating the time series chart for Image Collection:

       Error: No features contain non-null values of "system:time_start".

2. Here is the code that I have returned for generating the time series chart:

    // Study Area
    var Bhagwanpur = ee.FeatureCollection('projects/ee-omkarjadhav296/assets/Bhagwanpur_Merge');
    Map.addLayer(Bhagwanpur, {}, 'Bhagwanpur', false)
    Map.centerObject(Bhagwanpur, 10);
   
   
    // Load the Sentinel-1 ImageCollection, filter to Jun-Sep 2020 observations.
    var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD')
                      .filterDate('2021-05-01', '2022-06-05')
                      .filterBounds(Bhagwanpur)
   
   
    // Filter the Sentinel-1 collection by metadata properties.
    var vvVhIw = sentinel1
      // Filter to get images with VV and VH dual polarization.
      .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
      .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
      // Filter to get images collected in interferometric wide swath mode.
      .filter(ee.Filter.eq('instrumentMode', 'IW'));
   
    print(vvVhIw);
   
    var RVI = vvVhIw.map(function (image){
   
      var rvi = image.expression('sqrt(vv/(vv + vh))*(vv/vh)',
        {'vv': image.select('VV'),
         'vh': image.select('VH')
        }
   
        );
   
        return rvi;
      })
   
   
    var imageVisParam = {"opacity":1,
                         "bands":["VV"],
                         "min":0.01548,
                         "max":0.46221,
                         "gamma":1};
   
    Map.addLayer(RVI.first().clip(Bhagwanpur), imageVisParam, 'RVI', false);
   
              /*---------------------------------------------------------*/
   
    // Plotting of the graph:
   
    var chart =
        ui.Chart.image.seriesByRegion(
              RVI,
              Bhagwanpur,
              // .filter(ee.Filter.eq('Field_ID', 10)),
              ee.Reducer.mean(),
              'VV',
              10,
              'system:time_start'
            )
            .setSeriesNames(['RVI'])
            .setOptions({
              title: 'RVI',
              hAxis: {title: 'Date', titleTextStyle: {italic: false, bold: true}},
              vAxis: {
                title: 'RVI',
                titleTextStyle: {italic: false, bold: true}
              },
              lineWidth: 5,
              colors: ['#fc0303'],
              curveType: 'function'
            });
   
    print(chart);
   

Answer 1

With following correction it will be enough:

 var RVI = vvVhIw.map(function (image){
  
   var date = image.get('system:time_start');
  
   var rvi = image.expression('sqrt(vv/(vv + vh))*(vv/vh)',
     {'vv': image.select('VV'),
      'vh': image.select('VH')
     }

     );

     return rvi.set('system:time_start', date);

   });

I used complete code with point (76.8576, 29.5632) in your ROI. Change for your Bhagwanpur layer in corresponding asset.

After running complete code in GEE code editor, chart was printed without any problem.