Google Earth Engine API 提供空的 ImageCollection

Question

我是 Google Earth Engine 的新手，我正在尝试获取从 2024/05/01 到 2024/06/01 的 Sentinel-2 图像，以获取从 aeronet 位置获取的坐标](https://aeronet.gsfc.nasa .gov/aeronet_locations_v3.txt).

# Define date range for dataset filtering
start_date = '2024-05-01'
end_date = '2024-06-01'
dataset = (
    ee.ImageCollection('COPERNICUS/S2_HARMONIZED')
    .filterDate(start_date, end_date)
    # .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20))
    .map(mask_s2_clouds)
)

count = 4466

def export_image_for_day(image, date_str, location):
    global count
    if not image.Not():  # Ensure image is not None

        # Define the export task without region parameter
        export_task = ee.batch.Export.image.toDrive(
            image=image,
            description=f"image_{date_str}_{location[0]}_{location[1]}",
            folder='Sentinel2_Images',
            fileNamePrefix=f"image_{date_str}_{location[0]}_{location[1]}",
            region=ee.Geometry.Point(location).Buffer(500),
            fileFormat='GeoTIFF',
            maxPixels=1e13
        )
        export_task.start()
        print(f"{count}: Export task started for {date_str} at {location}")
    else:
        print(f"{count}: No image found for {date_str} at {location}")

    count += 1

# Loop through dates and locations
for date_str in pd.date_range(start_date, end_date).strftime('%Y-%m-%d').tolist():
    # Calculate the next day as the end date for filtering
    next_day = (datetime.strptime(date_str, '%Y-%m-%d') + timedelta(days=1)).strftime('%Y-%m-%d')
    
    # Use date_str as the start date and next_day as the end date for filtering
    daily_images = dataset.filterDate(date_str, next_day)
    
    for _, row in stations_df.iterrows():
        location = (row['Longitude(decimal_degrees)'], row['Latitude(decimal_degrees)'])
        image = daily_images.first()  # Retrieve first image of the day
        export_image_for_day(image, date_str, location)
        time.sleep(.2)  # Small delay between exports

函数 mask_s2_clouds 定义为：

def mask_s2_clouds(image):
  """Masks clouds in a Sentinel-2 image using the QA band.

  Args:
      image (ee.Image): A Sentinel-2 image.

  Returns:
      ee.Image: A cloud-masked Sentinel-2 image.
  """
  qa = image.select('QA60')

  # Bits 10 and 11 are clouds and cirrus, respectively.
  cloud_bit_mask = 1 << 10
  cirrus_bit_mask = 1 << 11

  # Both flags should be set to zero, indicating clear conditions.
  mask = (
      qa.bitwiseAnd(cloud_bit_mask)
      .eq(0)
      .And(qa.bitwiseAnd(cirrus_bit_mask).eq(0))
  )

  return image.updateMask(mask).divide(10000)

输出为：

4466: No image found for 2024-05-01 at (-56.070214, -15.555244)
4467: No image found for 2024-05-01 at (-56.104453, -9.871339)
4468: No image found for 2024-05-01 at (-63.068552, -9.19907)
4469: No image found for 2024-05-01 at (-110.953003, 32.233002)
4470: No image found for 2024-05-01 at (-76.839833, 38.9925)
4471: No image found for 2024-05-01 at (-74.476387, 39.802223)
4472: No image found for 2024-05-01 at (-48.41, -10.7)
4473: No image found for 2024-05-01 at (-47.900002, -15.917)
4474: No image found for 2024-05-01 at (-72.188, 42.532)

所有地点都会如此。由于我对GEE不太熟悉，所以我被困在这里。

Answer 1

“if not image.Not():”语句始终为 False。 图像是存储在服务器中的

ee.Image

对象。除非您调用 getInfor 或实际使用导出方法下载图像，否则该图像实际上并不是由服务器计算的。

此外，Not也不是用来检查图像是否存在，它只是检查像素是否为空（并且是按像素进行的）。

如果您确实需要在集合为空或不为空时更改此行为，您可以检查集合的大小：

def export_image_for_day(collection, date_str, location):
    global count
    if not collection.size().getInfo():  # Ensure image is not None

        # Define the export task without region parameter
        export_task = ee.batch.Export.image.toDrive(
            image=collection.mosaic(),
            description=f"image_{date_str}_{location[0]}_{location[1]}",
            folder='Sentinel2_Images',
            fileNamePrefix=f"image_{date_str}_{location[0]}_{location[1]}",
            region=ee.Geometry.Point(location).Buffer(500),
            fileFormat='GeoTIFF',
            maxPixels=1e13
        )
        export_task.start()
        print(f"{count}: Export task started for {date_str} at {location}")
    else:
        print(f"{count}: No image found for {date_str} at {location}")

    count += 1

请注意，您需要将 daily_images 提供给函数而不是

image

。