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DInSAR service specifications

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Service Description

The DInSAR Displacement Mapping (DInSAR) service performs an interferometric computation between a pair of SAR complex imagery to obtain Line of Sight (LOS) displacement, interferometric phase and coherence.

Cover

Figure 1 - Interferometric phase map highlighting the co-seismic ground deformation induced by the Crete M6.0 Earthquake, September 2021. The interferometric phase derived from the DInSAR service using Copernicus Sentinel-1 mission data. Reference 24th and secondary 30th Sep 2021.

The coherence between the reference and the secondary indicates the quality of the interferometric phase. High coherence values highlight a strong similarity in the interferometric pair and creates the better condition for processing (e.g. Displacement mapping in LOS). Instead, low coherence values result into poor interferometric results (e.g. over vegetation in C-band due to volumetric scattering).

The DInSAR service relies on the ESA SNAP1,2 software which is a common architecture for all Sentinel Toolboxes and is ideal for Earth Observation processing and analysis. The flowchart in the next section describes the entire DInSAR workflow. For the two-dimensional phase unwrapping DInSAR employs the SNAPHU3 software from the Stanford Radar Interferometry Research Group. In the creation of the interferogram the Goldstein4 phase filtering is applied to enhance the signal-to-noise ratio of the interferometric phase image and better identify fringes. To Subtract topographic phase and in the Geocoding and Back Geocoding steps DInSAR uses the Copernicus DEM, COP-DEM5, at 30m resolution as Digital Elevation Model. In the geocoding DInSAR employs an automatic UTM zone reprojection of results.

Once Line of Sight (LOS) displacement, interferometric phase and coherence single-band assets are generated, the service also derives three overview products after a normalization of the each single-band asset in its valid range (e.g. [-3.14,3.14] for the interferometric phase) and a rescaling to 8-bit range. The color maps6 adopted in the creation of the RGBA are the followings:

  • Sequential Black to White color map Gray for the interferometric coherence (higher coherence values in white tones),

Legend-001

  • Multicolor Jet color map for the interferometric phase,

Legend-002

  • Diverging Red to Blue RdBu color map for the LOS displacement (negative LOS displacement values in red shadows and positive in blue shadows).

Legend-003

Note

The here given legend for LOS Displacement is just an example since min and max are derived by the asset.

Info

A negative LOS displacement value (red color) indicates a movement of the surface farer away from the sensor along the LOS. Viceversa, positive displacement (blue color) for a surface moving closer to the sensor along the LOS. Negative or positive values indicates a surface movement consistent with the satellite orbit direction.

Warning

Signed LOS displacement values are always relative to the reference image. A convention is to set the reference as the oldest SAR acquisition in the pair. Thus, the most recent acquired image of the pair can be used as secondary to check how the motion was evolved.

Workflow

The DInSAR service implements the workflow depicted below.

graph TB c[(COS-2<br>&<br>External EO data catalogues)] style c fill:#ffde86,stroke:#ffb900,color:#282828,stroke-width:2px c --> b2(Reference SLC Dataset/s) c --> b1(Secondary SLC Dataset/s) b2 --> a2[input 2] b1 --> a1[input 1] subgraph Inputs style Inputs fill:#e8e8e8,stroke:#818181,color:#282828 a1[/Reference/s/] style a1 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px a2[/Secondary/ies/] style a2 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px a3[/AOI as WKT/] style a3 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px end subgraph DInSAR Displacement Mapping a1 --> r1[Read] a2 --> r2[Read] r1-->check{is AOI set?} r2-->check{is AOI set?} a3-.->check{is AOI set?<br> and/or <br>is AOI between two consecutive frames along the orbit?} check--yes--> subRef[Split and Assemble] check--yes--> subSec[Split and Assemble] check--no--> aofRef[Apply Orbit File] check--no--> aofSec[Apply Orbit File] aofRef --> bg[Back Geocoding] aofSec --> bg[Back Geocoding] subRef --> aofRef[Apply Orbit File] subSec --> aofSec[Apply Orbit File] bg --> esd[Enhanced Spectral Diversity] esd --> ifg[Interferogram] ifg --> tdb[TOPSAR-Deburst] tdb --> tfr[Topo Phase Removal] tfr --> ml[Multilook] ml --> gpf[Goldstein Phase Filtering] gpf --> unw[Phase Unwrapping] unw --> ptd[Phase to Displacement] ptd --> tc[Terrain Correction] tc --> sub[Subset] a3 -.-> sub[Subset] tc --> cog[Convert to COG] cog --> p1(Coherence) style p1 fill:#cfdfff,stroke:#87afff,color:#282828 cog --> p2(Wrapped Phase) style p2 fill:#cfdfff,stroke:#87afff,color:#282828 cog --> p3(LOS Displacement) style p3 fill:#cfdfff,stroke:#87afff,color:#282828 p1 --> over1[Overview and legend creation] p2 --> over2[Overview and legend creation] p3 --> over3[Overview and legend creation] over1 --> p4(Coherence-overview) style p4 fill:#cfdfff,stroke:#87afff,color:#282828 over2 --> p5(Phase-overview) style p5 fill:#cfdfff,stroke:#87afff,color:#282828 over3 --> p6(Displacement-overview) style p6 fill:#cfdfff,stroke:#87afff,color:#282828 p1 --> stac[Create STAC item] p2 --> stac[Create STAC item] p3 --> stac[Create STAC item] p4 --> stac[Create STAC item] p5 --> stac[Create STAC item] p6 --> stac[Create STAC item] end subgraph Outputs style Outputs fill:#e8e8e8,stroke:#818181,color:#282828 stac --> o1[/Interferometric Coherencee/] style o1 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px stac --> o2[/Interferometric Phase/] style o2 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px stac --> o3[/LOS Displacement/] style o3 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px stac --> o4[/Coherence-overview/] style o4 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px stac --> o5[/Phase-overview/] style o5 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px stac --> o6[/Displacement-overview/] style o6 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px end

Inputs

Input of the DInSAR service are at least a couple of SLC Datasets (interferometric pair) from supported SAR sensors.

Warning

This service currently supports Sentinel-1 SLC imagery in TOPSAR (IW and EW) mode only.

Parameters

The DInSAR service requires a specified number of mandatory and optional parameters. Table 1 describes the service parameters.

Parameter Description Required Default value
Reference SLC dataset Input reference SLC Dataset with intensity and phase recorded as complex numbers YES
Secondary SLC dataset Input secondary SLC Dataset with intensity and phase recorded as complex numbers YES
Area of Interest Area of interest expressed in WKT NO

Table 1 - Service parameters for the DInSAR processor.

More information about the service parameters are given below.

Reference and secondary SAR SLC datasets

The reference and secondary SAR SLC datasets must come from the same sensor and shall have the same radar geometry (incident angle, orbit path).

Warning

In the choice of reference and secondary be aware that LOS Displacement values are always relative to the master image.

AOI (optional)

This last parameter (optional) may define the area of interest expressed as a Well-Known Text value.

Tip

In the definition of “Area of interest as Well Known Text” it is possible to apply as AOI the drawn polygon defined with the area filter. To do so, click on the :fontawesome-solid-magic: button in the left side of the "Area of interest expressed as Well-known text" box and select the option AOI from the list. The platform will automatically fill the parameter value with the rectangular bounding box taken from the current search area in WKT format.

Outputs

Output products of the DInSAR service are the following single-band geophysical assets:

  • Product A: Interferometric Coherence
  • Product B: Interferometric Phase
  • Product C: LOS Displacement
  • Product D: Interferometric Coherence overview
  • Product E: Interferometric Phase overview
  • Product F: LOS Displacement overview

Output geocoded assets are given in COG format and in the UTM projected coordinate system (WGS84 datum).

The below tables provide Product Specifications for the DInSAR service.

Attribute Value / description
Long Name Interferometric Coherence product
Short Name coh_b_pp_YYYYMMDD_YYYYMMDD (where b the SAR-band [x,c,l], pp is the polarization [hh, hv, vh, vv], YYYYMMDD is the date of Reference and Secondary Dataset
Description Interferometric coherence computed on input SLC couple, it indicates where the phase information is coherent (Single-band Geophysical Asset)
Data Type Float 32 bit
Band 1
Format COG
Projection UTM (WGS84)
Valid Range [0 - 1]
Attribute Value / description
Long Name Interferometric Phase product
Short Name phase_b_pp_YYYYMMDD_YYYYMMDD (where b the SAR-band [x,c,l], pp is the polarization [hh, hv, vh, vv], YYYYMMDD is the date of Reference and Secondary Datasets
Description Interferometric phase computed from input SLC couple (Single-band Geophysical Asset).
Data Type Float 32 bit
Band 1
Format COG
Projection UTM (WGS84)
Fill Value 0
Attribute Value / description
Long Name Line of Sight Displacement
Short Name displacement_b_pp_YYYYMMDD_YYYYMMDD (where b the SAR-band [x,c,l], pp is the polarization [hh, hv, vh, vv], YYYYMMDD is the date of Reference and Secondary Datasets
Description Line of Sight Displacement in m
Data Type Float 32 bit
Band 1
Format COG
Projection UTM (WGS84)
Unit m
Attribute Value / description
Long Name Interferometric Coherence overview
Short Name overview-coherence
Description Visual product derived from the Interferometric Coherence product using the "Gray" color map
Data Type Unsigned 8-bit Integer
Band 4
Format COG
Projection UTM (WGS84)
Valid Range [1 - 255]
Fill Value 0
Attribute Value / description
Long Name Interferometric Phase overview
Short Name overview-phase
Description Visual product derived from the Interferometric Phase product in radians using the "Jet" color map
Data Type Unsigned 8-bit Integer
Band 4
Format COG
Projection UTM (WGS84)
Valid Range [1 - 255]
Fill Value 0
Attribute Value / description
Long Name Line of Sight Displacement overview
Short Name overview-displacement
Description Visual product derived from the Line of Sight Displacement in m using a "RdBu" color map
Data Type Unsigned 8-bit Integer
Band 4
Format COG
Projection UTM (WGS84)
Valid Range [1 - 255]
Fill Value 0

  1. ESA Science Toolbox Exploitation Platform, SNAP Toolbox available at https://step.esa.int. ↩

  2. SNAPISTA, SNAP GPT Python wrapper documentation available at https://snap-contrib.github.io/snapista/. ↩

  3. Stanford Radar Interferometry Research Group, Statistical-Cost, Network-Flow Algorithm for Phase Unwrapping SNAPHU software, available at https://web.stanford.edu. ↩

  4. Goldstein, Richard & Werner, Charles, (1998), "Radar interferogram filtering for geophysical applications", Geophysical Research Letters, 25, 4035-4038. Geophysical Research Letters, 25. DOI: 10.1029/1998GL900033. ↩

  5. Copernicus, "Copernicus DEM - Global and European Digital Elevation Model (COP-DEM)", available at: https://spacedata.copernicus.eu. ↩

  6. Matplotlib, Color maps, available at https://matplotlib.org. ↩