Error generating chart: No features contain non-null values of "system:time_start". Landsat 8 Surface Temperature Time-Series Chart (Earth Engine)

Question

I want to create an average surface temperature time series chart (+ per year). However I am encountering this error Error generating chart: No features contain non-null values of "system:time_start".

I already added several .copyProperties(img, ['system:time_start']); but it doesn't seem to work.

Any ideas in fixing this?

// This example demonstrates the use of the Landsat 8 Collection 2, Level 2
// QA_PIXEL band (CFMask) to mask unwanted pixels.

function maskL8sr(image) {
  // Bit 0 - Fill
  // Bit 1 - Dilated Cloud
  // Bit 2 - Cirrus
  // Bit 3 - Cloud
  // Bit 4 - Cloud Shadow
  var qaMask = image.select('QA_PIXEL').bitwiseAnd(parseInt('11111', 2)).eq(0).copyProperties(image, ["system:time_start"]);
  var saturationMask = image.select('QA_RADSAT').eq(0);

  // Apply the scaling factors to the appropriate bands.
  var opticalBands = image.select('SR_B.').multiply(0.0000275).add(-0.2).copyProperties(image, ["system:time_start"]);
  var thermalBands = image.select('ST_B.*').multiply(0.00341802).add(-124.15).copyProperties(image, ["system:time_start"]);

  // Replace the original bands with the scaled ones and apply the masks.
  return image.addBands(opticalBands, null, true)
      .addBands(thermalBands, null, true)
      .updateMask(qaMask)
      .updateMask(saturationMask)
      .copyProperties(image, ["system:time_start"]);
}

var months = ee.List.sequence(1, 12);
var years = ee.List.sequence(2016, 2021);

var byMonthYear = ee.ImageCollection.fromImages(
  years.map(function(y) {
    return months.map(function (m) {
      return collection
        .filter(ee.Filter.calendarRange(y, y, 'year'))
        .filter(ee.Filter.calendarRange(m, m, 'month'))
        .mean()
        .set('month', m).set('year', y);
  });
}).flatten());
print(byMonthYear)

// plot full time series
print(
  ui.Chart.image.series({
    imageCollection: byMonthYear,
    region: table,
    reducer: ee.Reducer.mean(),
    scale: 1000
  }).setOptions({title: 'SST over time'})
);

// plot a line for each year in series
print(
  ui.Chart.image.doySeriesByYear({
    imageCollection: byMonthYear,
    bandName:'sst',
    region: table,
    regionReducer: ee.Reducer.mean(),
    scale: 1000
  }).setOptions({title: 'SST for each year'})
);

access the code here:

Answer 1

Image collection byMonthYear doesn't have values of 'system:time_start'. For fixing this you have to do:

var byMonthYear = ee.ImageCollection.fromImages(
  years.map(function(y) {
    return months.map(function (m) {
      return collection
        .filter(ee.Filter.calendarRange(y, y, 'year'))
        .filter(ee.Filter.calendarRange(m, m, 'month'))
        .mean()
        .set('month', m).set('year', y).set('system:time_start', ee.Date.fromYMD(y, m, 1));
  });
}).flatten());

It is also necessary to use 'ST_B10' band name instead 'sst' in the second chart.

Complete code for an arbitrary geometry (your asset 'projects/ee-cczablan1/assets/NCR' is not accessible) is here.

After fixing these issues, running code in GEE code editor produces following result without any issue.