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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:

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.

Interferometric DEM Generation using Sentinel-1A SLC and SNAP