0

I am a beginner in learning about GEE. I am now calculating sediment using Sentinel 2a satellite images in GEE, but I encountered an issue as follows:

NDSSI Mosaic: Layer error: ImageCollection.mosaic: Error in map(ID=null): 
Date: Parameter 'value' is required.

Below is the code I have:

    // Display catchment boundary
    Map.addLayer(boundary, {}, 'Boundary');
    
    // Import the global surface water layer
    var gsw = ee.Image("JRC/GSW1_3/GlobalSurfaceWater");
    
    // Select the 'max_extent' band
    var water = gsw.select('max_extent').clip(boundary); 
            
    // Keep the water areas only (1)
    var masked = water.updateMask(water);
    
    // finally masking out 0 values and retain only water areas (1)
    var masked = water.selfMask();
    Map.addLayer(masked, {}, 'Water');
    
    //////
    var masks2a = function (image) {
      var qa = image.select('QA60');
      var cloudBitMask = 1 << 10;
      var cirrusBitMask = 1 << 11;
      var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
        .and(qa.bitwiseAnd(cirrusBitMask).eq(0));
      return image.updateMask(mask).divide(10000);
      };
    
      // Function to calculate NDSSI and add time as a band.
    var addVariables = function(image) {
      // Get the timestamp and convert it to a date.
      var timestamp = ee.Number(image.get('system:time_start'));
      var date = ee.Date(timestamp);
      var yearStart = ee.Date.fromYMD(date.get('year'), 1, 1);
      var fractionalYear = date.difference(yearStart, 'day').divide(365);
      
      // Calculate NDSSI.
      var ndssi = image.normalizedDifference(['B2', 'B8']).rename('NDSSI');
      
      // Add NDSSI and fractional year as bands.
      return image.addBands(ndssi)
                  .addBands(ee.Image(fractionalYear).rename('fractional_year').toFloat());
    };
    
    var filtermasks2a = ee.ImageCollection('COPERNICUS/S2')
      .filterBounds(boundary)
      .filterDate('2020-01-01', '2023-10-30')
      // Pre-filter to get less cloudy granules.
      .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20))
      .map(masks2a)
      .map(addVariables)
                      
    // Display RGB parameters
    var rgb = filtermasks2a.select('B4', 'B3','B2');
    
    
    // Plot a time series of NDSSI at a single location.
    Map.centerObject(boundary, 15);
    
    // Load and define a continuous palette
    var palettes = require('users/gena/packages:palettes');
    
    // Choose and define NDSSI display palette
    var palette = palettes.colorbrewer.RdBu[10];
    var viz = {min: -1, max: 1, palette: palette};
    
    // Display the NDSSI map
    Map.addLayer(filtermasks2a.select('NDSSI'), viz, 'NDSSI Mosaic');

Is there a solution?

1 Answer 1

0

This fails because addVariables() expects the image to have a system:time_start property. You lost all properties in masks2a(). Just tweak that function, to add the properties back:

var masks2a = function(image) {
  var qa = image.select('QA60')
  var cloudBitMask = 1 << 10
  var cirrusBitMask = 1 << 11
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
    .and(qa.bitwiseAnd(cirrusBitMask).eq(0))
  return image.updateMask(mask).divide(10000)
    .copyProperties(image, image.propertyNames())
}

https://code.earthengine.google.com/a17aae96293dd56503726e2aeff69535

1
  • Thank you for your response, I just realized that I need to add that, I can now run the code. It's very helpfull !
    – Ikrima
    Nov 23, 2023 at 10:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.