// Define the area of interest (AOI) - Shandong, China
var aoi = ee.Geometry.Rectangle([115.5, 34.5, 122.5, 38.5]);

// Function to apply a speckle filter to Sentinel-1 data
function applySpeckleFilter(image) {
  var kernel = ee.Kernel.circle({radius: 7, units: 'pixels', normalize: true});
  return image.convolve(kernel);
}

// Load Sentinel-1A VV and VH polarization data
var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD')
  .filterBounds(aoi)
  .filterDate('2015-01-01', '2015-12-31')
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
  .select(['VV', 'VH'])
  .map(applySpeckleFilter);

// Composite the collection to get median value
var sentinel1Composite = sentinel1.median().clip(aoi);

// Display the results
Map.centerObject(aoi, 8);
Map.addLayer(sentinel1Composite, {bands: ['VV'], min: -30, max: 0}, 'Sentinel-1 VV');
Map.addLayer(sentinel1Composite, {bands: ['VH'], min: -30, max: 0}, 'Sentinel-1 VH');

// Export the results to Google Drive
Export.image.toDrive({
  image: sentinel1Composite,
  description: 'Sentinel1_Composite_Shandong_2015',
  scale: 1000,
  region: aoi,
  maxPixels: 1e13
});