| # Interferometric DEM Generation using Sentinel-1A SLC and SNAP |
|
|
| This guide walks you through the process of generating a **Digital Elevation Model (DEM)** using **Sentinel-1A IW SLC products** with the **Sentinel Application Platform (SNAP)**. |
|
|
| ## Overview |
|
|
| **Sentinel-1** satellites provide SAR data in SLC format, which can be used to generate interferometric DEMs using InSAR techniques. This involves processing a pair of SLC scenes over the same area, computing their phase difference (interferogram), and unwrapping the phase to generate elevation data. |
|
|
| --- |
|
|
| ## Requirements |
|
|
| - **ESA SNAP Toolbox** with **SAR/InSAR plugins** |
| - **Sentinel-1 IW SLC product (2 scenes, same orbit, different acquisition dates)** |
| - **SRTM 1sec HGT DEM** (automatically downloaded by SNAP during terrain correction) |
| - At least **8 GB RAM** |
|
|
| --- |
|
|
| ## Input Data |
|
|
| - Download **two Sentinel-1 IW SLC scenes** for the same area with temporal baseline of ~6–24 days using ASF Alaska-1 Vertex by uploading the kml file for the targeted event co-ordinates (lat,long). |
| - Make sure both scenes are from the **same orbit direction** (Ascending/Descending). |
|
|
| --- |
|
|
| ## Processing Steps in SNAP GUI |
|
|
| ### 1. **Split (Optional if specific sub-swath needed)** |
|
|
| - Menu: `Radar > Sentinel-1 TOPS > Split` |
| - Select IW1, IW2, or IW3 and the burst as needed |
|
|
| ### 2. **Apply Orbit File** |
|
|
| - Menu: `Radar > Apply Orbit File` |
| - Input: Both SLC images |
| - Output: Orbit-corrected products |
|
|
| ### 3. **Subset (Optional)** |
|
|
| - Use if you want to focus on a smaller area (can speed up processing) |
|
|
| ### 4. **Co-registration: S-1 TOPS Coregistration** |
|
|
| - Menu: `Radar > Interferometric > InSAR Stack Preparation > S-1 TOPS Coregistration` |
| - Input: Master and Slave images |
| - Output: Stack product |
|
|
| ### 5. **Enhanced Spectral Diversity (ESD)** |
|
|
| - Menu: `Radar > Interferometric > InSAR Stack Preparation > Enhanced Spectral Diversity` |
| - Input: Co-registered stack |
| - Output: ESD-corrected stack |
|
|
| ### 6. **Interferogram Formation** |
|
|
| - Menu: `Radar > Interferometric > Products > Interferogram Formation` |
| - Input: ESD-corrected stack |
| - Output: Wrapped interferogram |
|
|
| ### 7. **Deburst** |
|
|
| - Menu: `Radar > Sentinel-1 TOPS > Deburst` |
| - Input: Interferogram |
| - Output: Continuous interferogram |
|
|
| ### 8. **Goldstein Phase Filtering** |
|
|
| - Menu: `Radar > Interferometric > Filtering > Goldstein Phase Filtering` |
| - Output: Filtered interferogram |
|
|
| ### 9. **Phase Unwrapping (SNAPHU Export/Import)** |
|
|
| - Export data for SNAPHU: |
| - Menu: `Radar > Interferometric > Unwrapping > SNAPHU Export` |
| - Run SNAPHU (external tool) |
| - Import unwrapped phase: |
| - Menu: `Radar > Interferometric > Unwrapping > SNAPHU Import` |
|
|
| ### 10. **Phase to Height Conversion** |
|
|
| - Menu: `Radar > Interferometric > Products > Phase to Elevation` |
| - Input: Unwrapped phase |
|
|
| ### 11. **Range-Doppler Terrain Correction** |
|
|
| - Menu: `Radar > Geometric > Terrain Correction > Range-Doppler Terrain Correction` |
| - DEM: Select SRTM 1Sec HGT (auto-download) |
| - Output: Final geocoded DEM |
|
|
| --- |
|
|
| ## Output |
|
|
| - A **GeoTIFF** or **BEAM-DIMAP** file containing your **interferometrically derived DEM**. |
| - You can view, export, or analyze the DEM using QGIS, SNAP, or any GIS tool. |
|
|
| ## Sample Output: |
|
|
| <img src="assets/dem.png" alt="DEM" width="400" height="500"> |
|
|
| --- |
|
|
| ## Additional Notes |
|
|
| - **Temporal Baseline**: Try pairs that are not too far apart in time to maintain coherence. Recommendation [ within 24days and 150 - 250m ] |
| - **Coherence Map**: Check before unwrapping. Poor coherence leads to unreliable DEMs. |
| - **SNAPHU**: Needed for phase unwrapping. Install separately and configure its path in SNAP. |
|
|
| --- |
|
|
| ## References |
|
|
| - [SNAP Documentation](https://step.esa.int/main/doc/) |
| - [Sentinel-1 User Guide](https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar) |
| - [InSAR Principles: ESA Training](https://earth.esa.int/documents/10174/12102/InSAR_Principles_Part1) |
|
|
| --- |
|
|
