Google Earth Engine – Troubleshooting Image Time Series Chart and Band Name Property

bandgoogle-earth-engineland-surface-temperaturetime series

Here is part of my code for creating a time series chart in GEE.

 var addLST = function(image) {
  var LST = thermal.expression(
'(Tb/(1 + (0.00115* (Tb / 1.438))*log(Ep)))-273.15', {
 'Tb': thermal.select('B10'),
'Ep': EM.select('EMM')
}).rename('LST');
Map.addLayer(LST, {min: 20.569706944223423, max:29.328077233404645, palette: [
'040274', '040281', '0502a3', '0502b8', '0502ce', '0502e6',
'0602ff', '235cb1', '307ef3', '269db1', '30c8e2', '32d3ef',
'3be285', '3ff38f', '86e26f', '3ae237', 'b5e22e', 'd6e21f',
'fff705', 'ffd611', 'ffb613', 'ff8b13', 'ff6e08', 'ff500d',
'ff0000', 'de0101', 'c21301', 'a71001', '911003'
 ]},'LST');
  return image.addBands(LST);
};
 
var withLST = imageCollection.map(addLST);

 // Create an image time series chart.
var chart = ui.Chart.image.doySeriesByRegion
({imageCollection: imageCollection, 
bandName: "LST", 
regions: geometry,
//regionReducer: geometry, 
scale: 200, 
yearReducer: ee.Reducer.mean(), 
//seriesProperty, 
startDay: 153, 
endDay: 244});

// Add the chart to the map.
chart.style().set({
  position: 'bottom-right',
  width: '500px',
  height: '300px'
});
Map.add(chart);

I have created the variable called 'LST' and added it to the whole collection so that each image in the collection should have a band called 'LST'. I hope I am correct in that. Then, I want to create the time series chart where it only shows the 'LST' band and not all 11 bands in the chart. However the bandName: 'LST' code is not working. I get this error:

Collection.first: Error in map(ID=LC08_026029_20130520): Image.select:
Pattern 'LST' did not match any bands.

and this error:

Cannot read properties of null (reading 'awa')

Best Answer

Your code has some issues but the part corresponding to print chart works well. Problem is in imageCollection used. I think you have to use withLST collection where 'LST' band is. As your code is incomplete, I arbitrarily assumed a wrong way for estimating 'LST' bands (by using 'B1' band instead 'EMM') but, it was correctly added to withLST collection for printing a chart without any error.

Complete code is:

var geometry = ee.Geometry.Polygon(
        [[[-1.9540705233485922, 40.29915610852847],
          [-1.9540705233485922, 40.27296656861284],
          [-1.9156183749110922, 40.27296656861284],
          [-1.9156183749110922, 40.29915610852847]]]);

Map.centerObject(geometry);

var imageCollection = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
  .filterDate('2020-05-01','2020-08-1')
  .filterBounds(geometry);

print('imageCollection', imageCollection);

function addLST (image) {
  var LST = image.expression(
  '(Tb/(1 + (0.00115* (Tb / 1.438))*log(Ep)))-273.15', {
  'Tb': image.select('B10'),
  'Ep': image.select('B1') //I assumed 'B1' as 'Ep'
  }).rename('LST');
  
  return image.addBands(LST);
  
}

var withLST = imageCollection.map(addLST);

print('withLST', withLST);

 // Create an image time series chart.
var chart = ui.Chart.image.doySeriesByRegion
  ({imageCollection: withLST, 
  bandName: "LST", 
  regions: geometry,
  //regionReducer: geometry, 
  scale: 200, 
  yearReducer: ee.Reducer.mean(), 
  //seriesProperty, 
  startDay: 153, 
  endDay: 244});

// Add the chart to the map.
chart.style().set({
  position: 'bottom-right',
  width: '500px',
  height: '300px'
});

Map.add(chart);

After running it in GEE code editor, chart was printed as follows.

Related Solutions

Google Earth Engine – Formatting H-Axis of Time Series Chart

Yes, ui.Chart.image.series is expecting system:time_start to be in it's own format, and you should always do it that way. You can always add a new property with your custom data. This is how I'd solve this:

// Filters images annualy-monthly
var map_m = function(i) {
  i = ee.Number(i);
  var filtered_col = years.map(function(j) {
    var filtered = series
        .filter(ee.Filter.calendarRange(i, i, 'month'))
        .filter(ee.Filter.calendarRange(j, j, 'year'))
    var max =filtered.reduce(ee.Reducer.max())
    var time = ee.Date.fromYMD(j,i,1)
    var custom_time = ee.Number.parse(time.format('YYYYMMDD'))
    return max.set('system:time_start', time.millis())
              .set('custom:time_start', custom_time)
              .addBands(ee.Image(custom_time).rename('time'))
  });
  return filtered_col;
};

Google Earth Engine – Getting Table Instead of Chart for Time Series of Multiple Polygons

The ui.Chart.image.seriesByRegion function actually wraps some reduction computations and then does the plotting for you, which is very nice for exploring and creating quick charts but doesn't give you the data in a variable you can use. You can simulate that functionality with you own function to extract the time series for your featureCollection and have a list of arrays. Here is an example:

// Define a FeatureCollection: regions of the American West.
var regions = ee.FeatureCollection([
  ee.Feature(    // San Francisco.
    ee.Geometry.Rectangle(-122.45, 37.74, -122.4, 37.8), {label: 'City'}),
  ee.Feature(  // Tahoe National Forest.
    ee.Geometry.Rectangle(-121, 39.4, -120.8, 39.8), {label: 'Forest'}),
  ee.Feature(  // Black Rock Desert.
    ee.Geometry.Rectangle(-119.15, 40.8, -119, 41), {label: 'Desert'})
]);


var modis = ee.ImageCollection('MODIS/006/MOD11A1');
var modisLST = modis.filterBounds(regions)
                    .filterDate('2003-12-25', '2004-02-25')
                    .select('LST_Day_1km');

// Convert temperature to Celsius.
modisLST = modisLST.map(function(img){
  return img.multiply(0.02).subtract(273.15).copyProperties(img, ['system:time_start']);
});              


function imageCollection_to_timeSeries(imageCollection,featureCollection,reducer,scale){
  var noDataValue = -999; // internal no data value to use

  // loop over all of the images in the collection
  var series = modisLST.map(function(img){
    var t = ee.List([img.date().millis()]); // get time information
    var fc = img.reduceRegions(regions,reducer,scale); // get the mean values
    // loop over the results and check if the value is non null
    fc = fc.map(function(feature){
      var v = ee.List(feature.get('mean'));
      // set no data if value is null
      var setter = ee.Algorithms.If(v,v,noDataValue);
      return feature.set('result',setter);
    });
    // get a list of the results
    var results = ee.List(fc.aggregate_array('result'));
    // return a feature with time and reduction values for each feature
    return ee.Feature(ee.Geometry.Point(0,0),{'values':results,'time':t});
  });

  // extract some information to format the time series arrays
  var keys = ee.List.sequence(0,featureCollection.size().subtract(1));
  var x = ee.Array(series.aggregate_array('time'));
  var y = ee.Array(series.aggregate_array('values'));

  // loop over all of the features
  var df = keys.map(function(i){
    i = ee.Number(i);
    // slice out time series for feature
    var v = y.slice(1,i,i.add(1));
    // create mask for array
    var mask = v.neq(noDataValue);
    // return dictionary with time index and values
    return ee.List([ee.Dictionary({'index':x.mask(mask),'values':v.mask(mask)})]);
  }).flatten();

  return df;
}

// call custom function
var df = imageCollection_to_timeSeries(modisLST,regions,ee.Reducer.mean(),1000);

// do whatever is needed with the individual arrays after this
print(df);

// get time series for first feature
var x1 = ee.Dictionary(df.get(0)).get('index');
var y1 = ee.Dictionary(df.get(0)).get('values');

// and create a chart from the array
var arrayChart = ui.Chart.array.values(y1,0,x1).setChartType('LineChart');
print('Chart from array',arrayChart);

// Create a graph of the time-series using the default ee.ui.chart functionality.
var graph = ui.Chart.image.seriesByRegion({
  imageCollection: modisLST, 
  regions: regions, 
  reducer: ee.Reducer.mean()
});
print('Default ee.ui.Chart',graph);

This a little bit of a work around to handle different no data information and different length arrays for different features but you will essentially have all of the array information you need and can extract/manipulate how you want for further processing. Here is the link. I hope this helps!

Best Answer

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