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Question

The original code was for MODIS data, but I would like to do a time series with Landsat8 Tier 2 Level 2, which already has the LST values, you just have to apply the scalling factor. I modified the code to use Landsat8 collection, however, I get absurd numbers for the LST, like negative hundreds. I don't understand what I'm doing wrong with this code.

// Import image collection
var landsat = ee.ImageCollection('LANDSAT/LC08/C02/T2_L2');
// A start date is defined and the end date is determined by advancing years from the start date.
var start = ee.Date('2025-08-04');
var dateRange = ee.DateRange(start, start.advance(10, 'year'));

// Filter the LST collection to include only images from time frame and select day time temperature band

var modLSTday = landsat.filterDate(dateRange).select('ST_B10');

// Scale to Kelvin and convert to Celsius, set image acquisition time.
var modC = modLSTday.map(function(image) {
  return image
    .multiply(0.00341802)
    .add(149.0)
    .subtract(273.15)
    .copyProperties(image, ['system:time_start']);
});
// Chart the time-series
var temp_trend = ui.Chart.image.series({
  imageCollection: modC,
  region: roi,
  reducer: ee.Reducer.mean(),
  scale: 30,
  xProperty: 'system:time_start'})
  .setOptions({
    lineWidth: 1,
    pointSize: 3,
    trendlines: {0: {
        color: 'CC0000'
      }},
     title: 'LST  Time Series',
     vAxis: {title: 'LST Celsius'}});
print(temp_trend);

//Clip to roi
var LSTclip = modC.mean().clip(roi);

// Add clipped image layer to the map.
Map.addLayer(LSTclip, {
  min: 0, max: 40,
  palette: ['blue', 'limegreen', 'yellow', 'darkorange', 'red']},
  'Mean temperature');