How to create σ0 data from Sentinel-1 SLC data

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Dear all,

I would like to create σ0 data using Sentinel-1 SLC data, and I would greatly appreciate it if you could guide me on the workflow in SNAP. Any documentation or website references are also welcome. I understand that you may be busy, but I would be grateful for your assistance.

Thank you in advance for your cooperation.

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Step-by-Step Workflow to Generate σ0\sigma^0σ0 Data from Sentinel-1 SLC in SNAP:

Step 1: Open SNAP and Import Sentinel-1 SLC Data**

  1. Open SNAP and navigate to the “Radar” toolbox.
  2. Go to File → Open Product.
  3. Browse to your Sentinel-1 SLC data (in .SAFE format) and open it. SNAP will load the metadata and display the data in the Product Explorer.

Step 2: Apply Orbit File

  1. Radar → Apply Orbit File.
  2. Select your product and apply the most recent orbit file. This step ensures precise orbit correction and better geolocation.
  • Keep the default settings.
  • Click Run.

Step 3: Split the SLC Data (Optional)

If you’re working with IW (Interferometric Wide Swath) or EW (Extra-Wide Swath) modes and only need specific sub-swaths or bursts, split the data first.

  1. Radar → Sentinel-1 TOPS → S-1 TOPS Split.
  2. Choose the sub-swath (IW1, IW2, IW3 for IW mode) and polarization (VV, VH, HH, HV) you need.
  3. Specify the burst range if necessary, or leave it to process all bursts.
  4. Click Run.

Step 4: Calibration to σ0\sigma^0σ0

  1. Radar → Radiometric → Calibration.
  2. In the Calibration window:
  • Choose the Sentinel-1 SLC product you opened.
  • Select the relevant polarization.
  • Ensure that the Output Sigma0 Band checkbox is checked. This will produce σ0\sigma^0σ0 (backscatter coefficient).
  1. Click Run to perform the calibration, generating σ0\sigma^0σ0 bands for each polarization selected.

Step 5: Deburst the Data (For IW or EW Modes)

If you are working with IW or EW mode, you’ll need to deburst the data to combine the individual bursts into a continuous image without gaps.

  1. Radar → Sentinel-1 TOPS → S-1 TOPS Deburst.
  2. Select the calibrated product that contains the σ0\sigma^0σ0 band.
  3. Click Run to merge the bursts into a continuous image.

Step 6: Terrain Flattening (Optional)

Terrain flattening is useful for correcting σ0\sigma^0σ0 values over regions with varying topography.

  1. Radar → Radiometric → Terrain Flattening.
  2. In the dialog box:
  • Select the DEM (Digital Elevation Model). SRTM 1Sec HGT is commonly used and can be automatically downloaded if you’re online.
  • Select the product and polarization.
  • Keep other parameters as default unless specific changes are required.
  1. Click Run to flatten the terrain.

Step 7: Multilooking (Optional)

Multilooking reduces the resolution and speckle noise in your SLC data by averaging pixels, which can improve the visual quality and signal-to-noise ratio.

  1. Radar → Multilooking.
  2. Choose the product.
  3. Set the number of Range Looks and Azimuth Looks. A common setting is 4 x 1 for Sentinel-1.
  4. Click Run to apply multilooking.

Step 8: Geocoding (Terrain Correction)

After debursting and (optionally) multilooking, perform terrain correction to convert the image from radar geometry to geographic coordinates.

  1. Radar → Geometric → Terrain Correction → Range-Doppler Terrain Correction.
  2. In the dialog box:
  • Select the DEM (SRTM 1Sec HGT is usually fine).
  • Choose the interpolation method (leave default settings).
  • Specify the output pixel spacing if needed (typically 10m for Sentinel-1).
  • Check the Mask out areas without elevation option to avoid empty data regions.
  1. Click Run to apply terrain correction and geocode the image.

Step 9: Export Your Data

  1. Once all processing steps are complete, export the data in your preferred format.
  2. Go to File → Export → Geotiff (or another format of your choice).
  3. Specify the filename and folder, then click OK to export.

Summary of Key Steps:

  1. Open Sentinel-1 SLC data .
  2. Apply Orbit File to correct the orbit information.
  3. Split the SLC data if needed (optional).
  4. Calibrate to σ0\sigma^0σ0 (backscatter coefficient).
  5. Deburst (if working with IW or EW mode).
  6. Terrain Flattening (optional for hilly or mountainous areas).
  7. Multilooking (optional to reduce speckle noise).
  8. Geocoding (Terrain Correction) to project the data into geographic coordinates.
  9. Export the processed data.

This workflow will help you generate σ0\sigma^0σ0 data from Sentinel-1 SLC products in SNAP.

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Dire Damien

Thank you for your response and advice.
I’ll give it a try !!
Just a quick note to express my gratitude.
I look forward to your continued support.