Calculating LST from Landsat 8 in Google Earth Engine display a blank image

Question

Why is it that when the following GEE code is used to calculate the lst of landsat8, the data statistics are correct, between 29°C and 55°C, but the output image is blank and the file is only 14.9MB?

https://code.earthengine.google.com/c69b5ae83bcb80b30341fbaacd365d22

// 载入你的区域
Map.addLayer(chifeng);

// 云、阴影遮蔽函数
function maskL8sr(col) {
  var cloudShadowBitMask = (1 << 3);
  var cloudsBitMask = (1 << 5);
  var qa = col.select('QA_PIXEL');
  var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0)
                 .and(qa.bitwiseAnd(cloudsBitMask).eq(0));
  return col.updateMask(mask);
}

// 可视化参数
var vizParams2 = {
  bands: ['SR_B4', 'SR_B3', 'SR_B2'],
  min: 0,
  max: 30000,
  gamma: 1.4,
};

// 载入影像集合
var coll = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
  .map(maskL8sr)
  .filterDate('2019-01-01','2019-12-31')
  .filterBounds(chifeng);

// 打印原始影像集合
print(coll, 'rawcoll');

// 热红外波段校正函数
function calibrateTemperature(image) {
  var thermal = image.select('ST_B10');
  var temperature = thermal.multiply(0.1);
  return image.addBands(temperature.rename('Surface_Temperature'));
}

// 去除异常值函数
function removeOutliers(image) {
  var temperature = image.select('Surface_Temperature');
  var validRange = [-50, 70];
  var validTemperature = temperature.mask(temperature.gt(validRange[0]).and(temperature.lt(validRange[1])));
  return image.addBands(validTemperature.rename('Valid_Surface_Temperature'));
}

// 应用校正和去除异常值到影像集合
var calibratedcoll = coll.map(calibrateTemperature);
var processedcoll = calibratedcoll.map(removeOutliers);

// 打印处理后的影像集合
print(processedcoll);

// 影像降采样
var image = processedcoll.median();
print(image, 'image');
Map.addLayer(image, vizParams2);

// 计算 NDVI
var ndvi = image.normalizedDifference(['SR_B5', 'SR_B4']).rename('NDVI');
var ndviParams = {min: -1, max: 1, palette: ['blue', 'white', 'green']};
print(ndvi, 'ndvi');
Map.addLayer(ndvi, ndviParams, 'ndvi');

// 选择热红外波段
var newthermal = image.select('Valid_Surface_Temperature');
var b10Params = {min: -50, max: 70, palette: ['blue', 'white', 'green']};
Map.addLayer(newthermal, b10Params, 'newthermal');

// 计算 Fractional Vegetation
var minMax = ndvi.reduceRegion({
  reducer: ee.Reducer.minMax(),
  geometry: chifeng,
  scale: 30,
  maxPixels: 1e13
});

var min = ee.Number(minMax.get('NDVI_min'));
var max = ee.Number(minMax.get('NDVI_max'));

var fv = ndvi.subtract(min).divide(max.subtract(min)).pow(ee.Number(2)).rename('FV');
print(fv, 'fv');
Map.addLayer(fv);

// 计算 Emissivity
var a = ee.Number(0.004);
var b = ee.Number(0.986);
var EM = fv.multiply(a).add(b).rename('EMM');
var imageVisParam3 = {min: 0.9865619146722164, max: 0.989699971371314};
Map.addLayer(EM, imageVisParam3, 'EMM');

// 计算 Land Surface Temperature (LST)
var LST = newthermal.expression(
  '(Tb/(1 + (0.00115* (Tb / 1.438))*log(Ep)))', 
  {
    'Tb': newthermal.select('Valid_Surface_Temperature'),
    'Ep': EM.select('EMM')
  }
).rename('LST');
Map.addLayer(LST, {min: -50, max: 70, 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');

// 将结果导出到 Google Drive
Export.image.toDrive({
  image: LST,
  description: "LST2019",
  scale: 30,
  region: chifeng,
  maxPixels: 1e13
});

Answer 1

I do not fully understand your code, but I see two main issues. In the first place, when calculating the temperature, you multiply by 0.1, but according with the documentation (https://developers.google.com/earth-engine/datasets/catalog/LANDSAT_LC08_C02_T1_L2#bands) that is not the way to go. You have to do it like this:

function calibrateTemperature(image) {
  var thermal = image.select('ST_B10');
  var temperature = thermal.multiply(0.00341802).add(149.0);
  return image.addBands(temperature.rename('Surface_Temperature'));
}

After applying this function, you have the temperature in kelvin. Therefore, your valid range cannot be [-50,70]. I suggest using [223, 343] which is equivalent.

function removeOutliers(image) {
  var temperature = image.select('Surface_Temperature');
  var validRange = [223, 343];
  var validTemperature = temperature.mask(temperature.gt(validRange[0]).and(temperature.lt(validRange[1])));
  return image.addBands(validTemperature.rename('Valid_Surface_Temperature'));
}

Secondly, LST is still empty because in your formula you need Ep, but Ep is not included in newthermal. You can create a combined ee.Image and apply the function to it.

var combined = ee.Image([newthermal, EM]);
// 计算 Land Surface Temperature (LST) with combined instead of newthermal
var LST = combined.expression(
  '(Tb/(1 + (0.00115* (Tb / 1.438))*log(Ep)))', 
  {
    'Tb': newthermal.select('Valid_Surface_Temperature'),
    'Ep': EM.select('EMM')
  }
).rename('LST');

Finally, you can visualize LST, but don’t forget to change the min and max:

Map.addLayer(LST, {min: 223, max: 343, palette: [ // hmsp
  '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');