Unable to read DEM data on GEE

Question

I have prepared the code for flood mapping risk. But when I am using the below code, the error show dem is not a function. Can anyone help me.

Thanks in advance.

// Import a satellite image of the Houston area
var image = ee.Image('COPERNICUS/S2_SR/20221225T101057_20221225T132927_T32UMA')
  .clip(roi);

// Extract the elevation data from the image
var elevation = image.select('elevation');



// Create a digital elevation model (DEM) from the elevation data
var dem = ee.Terrain.hillshade(elevation);

// Calculate the flood risk for each pixel in the image
var floodRisk = dem.expression(
  'exp(-((x - mean)^2) / (2 * sigma^2))', {
    'x': dem,
    'mean': dem.mean(),
    'sigma': dem.stdDev()
  }
);

score 0 · Answer 1 · answered Dec 28 '22 at 21:32

You need to calculate the mean and sigma using reduceRegions, not mean() and stdDev(). Also, ** is the correct exponent operator, not ^. So,

// Import a satellite image of the Houston area
var image = ee.Image('COPERNICUS/S2_SR/20221225T101057_20221225T132927_T32UMA')
  .clip(roi);

// Extract the elevation data from the image
var elevation = image.select('elevation');

// Create a digital elevation model (DEM) from the elevation data
var dem = ee.Terrain.hillshade(elevation);

var mean = dem.reduceRegion(ee.Reducer.mean(), roi).values().getInfo();
var sigma = dem.reduceRegion(ee.Reducer.stdDev(), roi).values().getInfo();


// Calculate the flood risk for each pixel in the image
var floodRisk = dem.expression(
  'exp(-((x - mean)**2) / (2 * sigma**2))', {
    'x': dem,
    'mean': mean,
    'sigma': sigma
  }

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Unable to read DEM data on GEE

1 Answers1