Soil Moisture from Space

// Define the region of interest (North Morocco)
var roi = ee.Geometry.Polygon([[[-5.5, 35.0], [-2.0, 35.0], [-2.0, 32.0], [-5.5, 32.0]]]);

// Define the date range
var startDate = '2023-01-01';
var endDate = '2023-12-31';

// Load Sentinel-1 GRD data
var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD')
  .filter(ee.Filter.eq('instrumentMode', 'IW'))
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
  .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))
  .filter(ee.Filter.date(startDate, endDate))
  .filterBounds(roi);

//Print the number of images
print('Number of Sentinel-1 images:', sentinel1.size());

// Function to apply a simple speckle filter (e.g., median filter)
var speckleFilter = function(image) {
  var vv = image.select('VV');
  var vvFiltered = vv.focal_median();
  return image.addBands(vvFiltered.rename('VV_filtered')).copyProperties(image, ['system:time_start']);
};

// Apply speckle filtering to the Sentinel-1 data
var sentinel1Filtered = sentinel1.map(speckleFilter);

// Function to calculate Normalized Difference Soil Moisture Index (NDMI)
var calculateNDMI = function(image) {
  var vv = image.select('VV_filtered');
  var vh = image.select('VH');
  var ndmi = vv.subtract(vh).divide(vv.add(vh)).rename('NDMI');
  return image.addBands(ndmi).copyProperties(image, ['system:time_start']);
};

// Calculate NDMI
var sentinel1NDMI = sentinel1Filtered.map(calculateNDMI);

//Composite the images into one image
var composite = sentinel1NDMI.median();

// Export the NDMI image to Google Drive
Export.image.toDrive({
  image: composite.select('NDMI'),
  description: 'Sentinel1_NDMI_Morocco',
  folder: 'GEE_Exports',
  scale: 10,
  region: roi,
  maxPixels: 1e10
});