2

I try to apply an expression to the satellite image and then try to chart the mean of the series of images but I'm getting this error:

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

Link to the code: https://code.earthengine.google.com/c977a6ea5b61ec830b15835036e64c97

Code:

var app = function (image)
{
var conv = image.expression(
    'band/(4.4615*10**-4)',  //formula for coverting mol/m2 to DU(Dobson)
    {
        band: image.select('SO2_column_number_density'),   
  });

return  conv;
};

// Load the sentinel data
var sentinel = ee.ImageCollection('COPERNICUS/S5P/NRTI/L3_SO2')
.filterDate('2019-04-01', '2019-04-21')
.map(app)


//Identify country
var region = ee.FeatureCollection("ft:1p_3AqEj1T9fG0BNu6pGqmP6_HdDOalruzpk54Ne8");
Map.addLayer(region);

Map.addLayer(sentinel)



var TS5 = Chart.image.series(sentinel, region, ee.Reducer.mean(),1000, 'system:time_start').setOptions({
          title: 'pollutants Full Time Series',
          vAxis: {title: 'mol/m2'},
});
print(TS5);

2 Answers 2

1

using an image expression, the image will losse it's original properties. Copy the properties of the source (image) to the new image (conv):

var app = function (image)
{
var conv = image.expression(
    'band/(4.4615*10**-4)',  //formula for coverting mol/m2 to DU(Dobson)
    {
        band: image.select('SO2_column_number_density'),   
  });

return  ee.Image(conv.copyProperties(image)).set('system:time_start', image.get('system:time_start'));
};
1
  • Thank you very much that was very helpful. May 7, 2019 at 13:08
1

This has helped me too. I was unable to plot my time series of NDVI due to the same error. I narrowed it down to the part of my code where there is a mathematical calculation

 return image.updateMask(mask).divide(10000)

}

I fixed it by changing it to

  return image.updateMask(mask).divide(10000).copyProperties(image).set('system:time_start', image.get('system:time_start'));

}

Works perfectly now.

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