Sentinel-1 L1 calibration

Ingested Sentinel-1 GRD or SLC products are systematically calibrated in the ESA Charter Mapper using the Radar Products Calibration (SAR-Calib) processor.

Sentinel-1 GRD sigma nought

Figure 1 - Full resolution overview from a calibrated Sentinel-1 GRD HR IW product in VV polarization acquired in 2022 over the Bangkok bay near the mouth of the Chao Phraya river, Thailand. Image credit: Copernicus, ESA.

Input

The input is a Sentinel-1 Dataset derived from an ingested Sentinel-1 GRD or SLC product, see details here.

Workflow

Sentinel-1 GRD and SLC acquisitions¹ are calibrated using SNAP²,³, the open source common architecture for ESA Toolboxes ideal for the exploitation of Earth Observation data.

GRD

The workflow for the systematic generation of Radar Calibrated Datasets from Sentinel-1 GRD products is described in the below graph.

graph TB i[(COS-2)] style i fill:#ffde86,stroke:#333,color:#282828,stroke-width:2px i --> a1(EO data product) subgraph Inputs style Inputs fill:#e8e8e8,stroke:#333,color:#282828 a1[/Sentinel-1 GRD Dataset<br>in IW, or EW mode/] style a1 fill:#acc8ff,stroke:#333,color:#282828,stroke-width:2px end subgraph SAR-Calib for Sentinel-1 GRD a1 --> orbcor[Orbit Correction] orbcor --> bornore[Border Noise Removal] bornore --> calib[Radiometric Calibration] calib --> ml[Multilooking] ml --> tc[Terrain Correction] tc --> ltodb[Linear to dB] ltodb --> p1(Sigma Nought) style p1 fill:#cfdfff,stroke:#333,color:#282828 p1 --> overcreat[Image stretching and RGB composite creation] overcreat --> p2(overview/s) style p2 fill:#cfdfff,stroke:#333,color:#282828 p1 --> cog[Convert to COG] p2 --> cog[Convert to COG] cog --> stac[Create STAC item] end subgraph Outputs style Outputs fill:#e8e8e8,stroke:#333,color:#282828 stac --> out[/Sentinel-1 GRD Calibrated Dataset/] style out fill:#acc8ff,stroke:#333,color:#282828,stroke-width:2px out --> o1[/Single band assets: s0_db_c_vv, s0_db_c_vh/] style o1 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px out --> o2[/overview assets: overview-dual, overview-vv, overview-vh/] style o2 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px end

This diagram represents the application of the SAR-Calib processor workflow applied for Sentinel-1 GRD Datasets. More details about this systematic processor can be found here.

Note

The calibration of Sentinel-1 GRD products has the objective to offer the following assets:

Sigma Nought single band assets at each polarization to be used for visualization in the map (with Select or Combine asset and binarization on the fly) and for processing (e.g. drag and drop a s0_db_c_vv asset into IRIS Change Detection service),
multiple overview assets to be used only for visualization purposes (e.g. to visually compare with the slider in the map the overview-vv asset with a similar one from another calibrated dataset).

SLC

The workflow for the systematic generation of Radar Calibrated Datasets from Sentinel-1 SLC products is described in the below graph.

graph TB i[(COS-2)] style i fill:#ffde86,stroke:#333,color:#282828,stroke-width:2px i --> a1(EO data product) subgraph Inputs style Inputs fill:#e8e8e8,stroke:#333,color:#282828 a1[/Sentinel-1 SLC Dataset<br>in IW, or EW mode/] style a1 fill:#acc8ff,stroke:#333,color:#282828,stroke-width:2px end subgraph SAR-Calib for Sentinel-1 SLC a1 --> read[Read] read --> p1(magnitude) style p1 fill:#cfdfff,stroke:#333,color:#282828 read --> p2(metadata) style p2 fill:#cfdfff,stroke:#333,color:#282828 read --> tss[TOPSAR-Split] tss --> aof[Apply-Orbit-File] aof --> cal[Calibration] cal --> bg[Back-Geocoding] bg --> tsdb[TOPSAR-Deburst] tsdb --> tsm[TOPSAR-Merge] tsm --> ml[Multilook] ml --> tc[Terrain Correction] tc --> ltdb[Linear to dB] ltdb --> overcreat[Image stretching and <br> grayscale co-pol overview creation] overcreat --> p3(overview) style p3 fill:#cfdfff,stroke:#333,color:#282828 p3 --> cog[Convert to COG] p1 --> stac[Create STAC item] p2 --> stac[Create STAC item] cog --> stac[Create STAC item] end subgraph Outputs style Outputs fill:#e8e8e8,stroke:#333,color:#282828 stac --> out[/Sentinel-1 SLC Calibrated Dataset/] style out fill:#acc8ff,stroke:#333,color:#282828,stroke-width:2px out --> o1[/magnitude for each subswath and each polarization/] style o1 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px out --> o2[/metadata/] style o2 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px out --> o3[/overview/] style o3 fill:#acc8ff,stroke:#87afff,color:#282828,stroke-width:2px end

This diagram represents the application of the SAR-Calib processor workflow applied for Sentinel-1 SLC Datasets. More details about this systematic processor can be found here.

Note

The calibration of Sentinel-1 SLC products has the objective to offer the following assets:

an overview asset derived from geocoded Sigma Nought to be used only for visualization in the map,
magnitude and metadata assets required for InSAR processing when drag and dropping a SLC dataset into an on-demand processor (e.g. COIN).

Warning

Being magnitude assets not geocoded, the only asset offered in a Sentinel-1 SLC dataset which is visible in the map is the overview one.

Output

The output is a Sentinel-1 SLC or GRD Calibrated Dataset represented by a STAC item GeoJSON² including:

magnitude assets for each subswath and at each polarization and metadata (only for SLC dataset),
sigma nought (dB) single-band assets at each polarization (only for GRD dataset),
and overview assets (single-pol overviews and dual- or full-pol band composites).

All single band and overview assets are given at full resolution and in COG format.

The assets magnitude-vv-iw1, magnitude-vv-iw2, magnitude-vv-iw3, magnitude-vh-iw1, magnitude-vh-iw2, magnitude-vh-iw3 contained in a calibrated Sentinel-1 IW SLC dataset cannot be visualized in the map and cannot be used as single band for drag and drop into processing services.

Sigma nought products are Float32 single-band assets in COG format, one for each polarization (e.g. s0_db_c_vv which refers to the common band name for sigma nought in dB from C-band SAR in VV polarization).

Visual products are given as 8-bit multi-band assets in COG format (e.g. overview-vv which refers to visual product at full resolution derived from sigma nought in dB from C-band SAR in VV polarization). A default overview product at low resolution is also derived for product preview when EULA is not signed by the user.

Note

In a Sentinel-1 SLC dataset only an overview asset is given. It represents a full resolution visual product in grayscale derived from sigma nought in dB from C-band SAR in VV polarization.

Below is given an example of assets included in the STAC item of a Sentinel-1 GRD HR IW VV/VH Calibrated Dataset derived in the ESA Charter Mapper for the Charter Activation 784.

  "assets": {
    "s0_db_c_vh": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "data",
        "sigma0",
        "visual"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/s0_db_c_vh.tif",
      "sar:polarizations": [
        "VH"
      ],
      "raster:bands": [
        {
          "spatial_resolution": 20,
          "statistics": {
            "minimum": "-55.574871063232",
            "maximum": "26.465213775635",
            "mean": "-12.625484901143",
            "stddev": "9.7783755895775",
            "valid_percent": "100"
          },
      "file:size": 479204279
    },
    "overview-vh": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "composite",
        "sigma0",
        "visual"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/overview-vh.tif",
      "sar:polarizations": [
        "VH"
      ],
      "file:size": 91087524
    },
    "s0_db_c_vv": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "data",
        "sigma0",
        "visual"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/s0_db_c_vv.tif",
      "sar:polarizations": [
        "VV"
      ],
      "raster:bands": [
        {
          "spatial_resolution": 20,
          "statistics": {
            "minimum": "-53.406005859375",
            "maximum": "32.925624847412",
            "mean": "-8.4565923958473",
            "stddev": "7.6702384773274",
            "valid_percent": "100"
          },
        }
      ],
      "file:size": 493054941
    },
    "overview-vv": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "composite",
        "sigma0",
        "visual"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/overview-vv.tif",
      "sar:polarizations": [
        "VV"
      ],
      "file:size": 95496514
    },
    "overview-dual": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "composite",
        "decibel",
        "sigma0",
        "visual"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/overview-dual.tif",
        }
      ],
      "file:size": 199984634
    },
    "overview-vv-low-res": {
      "type": "image/tiff; application=geotiff",
      "roles": [
        "composite",
        "overview"
      ],
      "href": "https://.../S1A_IW_GRDH_1SDV_20221011T112901_20221011T112926_045394_056D8C_1BE7-calibrated/overview-vv-low-res.tif",
        }
      ],
      "file:size": 12526152
    }
  }

ESA, Sentinel Online, Sentinel-1 Mission Guide. Available at: sentinel.esa.int ↩
ESA Science Toolbox Exploitation Platform, SNAP Toolbox available at https://step.esa.int. ↩↩
SNAPISTA, SNAP GPT Python wrapper documentation available at https://snap-contrib.github.io/snapista/. ↩