GEE filter by bands

博客内容提及对空波段和空影像进行过滤操作,这在信息技术领域的数据处理等方面有一定意义,可提升数据质量和处理效率。

过滤空波段、空影像
在这里插入图片描述

### Normalized Difference Built-up Index Implementation in Google Earth Engine The **Normalized Difference Built-up Index (NDBI)** is widely used to identify built-up areas from satellite imagery. It leverages the reflectance properties of urban materials such as concrete and asphalt, which typically exhibit higher near-infrared (NIR) and shortwave infrared (SWIR) reflectance compared to vegetation or water bodies. In Google Earth Engine (GEE), implementing NDBI involves calculating the index using Landsat or Sentinel-2 datasets. Below is a detailed explanation along with code examples: #### Formula for NDBI Calculation The formula for NDBI is defined as follows: \[ \text{NDBI} = \frac{\text{(Band SWIR - Band NIR)}}{\text{(Band SWIR + Band NIR)}} \] Where: - `Band SWIR` refers to the Shortwave Infrared band. - `Band NIR` refers to the Near-Infrared band. For Landsat 8 OLI/TIRS sensor, these bands correspond to: - `Band SWIR`: Band 6 (`B6`) - `Band NIR`: Band 5 (`B5`) Similarly, for Sentinel-2 MSI sensors: - `Band SWIR`: Band 11 (`B11`) - `Band NIR`: Band 8 (`B8`) This calculation highlights man-made structures due to their unique spectral characteristics[^2]. #### Code Example Using Landsat 8 Data Below is an example script demonstrating how to calculate NDBI using Landsat 8 data within GEE: ```javascript // Define region of interest (ROI) var roi = ee.Geometry.Rectangle([79.0, 26.0, 79.2, 26.2]); // Load Landsat 8 Surface Reflectance data var landsat8 = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2') .filterDate('2022-01-01', '2022-12-31') // Filter date range .filterBounds(roi); // Filter by ROI // Select required bands (SWIR & NIR) var ndbi = landsat8.map(function(image){ var swir = image.select('SR_B6'); // Band 6: SWIR var nir = image.select('SR_B5'); // Band 5: NIR // Compute NDBI var ndbiValue = swir.subtract(nir).divide(swir.add(nir)).rename('NDBI'); return image.addBands(ndbiValue); }); // Visualize results Map.centerObject(roi, 10); Map.addLayer(ee.Image(ndbi.first()).select('NDBI'), {min:-1, max:1, palette:['blue','white','red']}, 'NDBI'); ``` #### Key Considerations When Implementing NDBI 1. **Cloud Masking**: Ensure cloud-free images are selected before performing calculations since clouds interfere with accurate measurements[^3]. 2. **Sensor Calibration**: Use calibrated surface reflectance products rather than raw digital numbers (DNs). 3. **Temporal Analysis**: For long-term studies, consider seasonal variations when comparing multiple years' worth of data[^4]. #### Potential Applications Beyond Urban Mapping While primarily utilized for detecting built environments, NDBI also finds applications in disaster management scenarios like flood monitoring post-storm events because flooded regions often display altered NDVI/NDBI ratios depending upon land cover type prior to inundation[^5].
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