SNAP Polarimetric Processing Sentinel-1

Introduction

For more information, please read the block description.

Block type: PROCESSING

This block provides a SNAP polarimetric processing workflow that is applied on SAR scenes in SAFE format. The SNAP block takes a Level 1C GRD image and generates a product ready for analysis by using a median filter for speckle filtering, creating a land-sea mask, and converting the image to a GeoTIFF format.

Supported parameters

• bbox: The bounding box to use as an AOI. Will clip to scenes that intersect with this box. Use only bbox or intersects or contains.

• intersects: A GeoJSON geometry to use as an AOI. Will clip to scenes that intersect with this geometry. Use only bbox or intersects or contains.

• contains: A GeoJSON geometry to use as an AOI. Will clip to scenes that intersect with this geometry. Use only bbox or intersects or contains.

• polarisations: Requested polarisations, either one and only one of: ["VV","VH"], ["HH", "HV"], ["VV"], ["VH"], ["HV"] or ["HH"]. The operation will fail and give a corresponding error message if the requested polarization is not avialble in the input image to SNAP.

• mask: It applies a masks for either land or sea. Use one and only one, you cannot chose both.

• tcorrection: It applies Range Doppler Terrain Correction based on a suitable Digital Elevation Model (DEM).

• clip_to_aoi: When set to true, the AOI specified via bbox, or contains, or intersect for the previous data block in the workflow will first be clipped and then processed. Please note that by default this parameter is set to false which means that the full scene will be processed.

• calibration_band: It applies calibration to provide imagery in which the pixel values can be directly related to the radar backscatter of the scene. The default option using Sigma Nought for calibration. Other available options are Beta Nought and Gamma Nought.

• speckle_filter: It applies Lee Sigma filter to remove speckle noise from the image. Please note that by default this parameter is set to true.

• linear_to_db: It converst the pixel intensity to normalised radar cross-section measured in decibel (dB) units. Please note that by default this parameter is set to true.

Example block parameters using the Sentinel-1 L1C GRD Full Scene block as data source which is processed via SNAP after clipping it to the given AOI. The processing consists here of Range Doppler Terrain correction (tcorrection set to true) and a Land mask (land set to true).

{
  "sobloo-s1-grd-fullscene:1": {
        "bbox": [
          13.358345031738283,
          52.480689337378706,
          13.395252227783203,
          52.507654123207665
        ],
        "ids": null,
        "time": "2018-01-01T00:00:00+00:00/2019-12-31T23:59:59+00:00",
        "limit": 1,
        "time_series": null,
        "orbit_direction": null,
        "acquisition_mode": null
  },
  "snap-polarimetric:1": {
  "bbox": [
          13.358345031738283,
          52.480689337378706,
          13.395252227783203,
          52.507654123207665
   ],
   "mask": null,
   "contains": null,
   "intersects": null,
   "clip_to_aoi": true,
   "tcorrection": true,
   "linear_to_db": true,
   "polarisations": [
        "VV"
  ],
  "speckle_filter": true,
  "calibration_band": [
        "sigma"
  ]
  }
}

Output format

The block outputs a GeoTIFF file. For each chosen polarization, a separate band will be generated in the output file. For instance, if both VV and VH polarizations are chosen, the output will be a single GeoTIFF with two bands, one for VV and one for VH polarization.

Download example output

You can create example output to use when testing processing blocks built to work with this data by running the block in a workflow via the console, and downloading the results in the job overview.

Capabilities

{
  "or": [
    [
      "HH",
      "HV",
      "alpha"
    ],
    [
      "VV",
      "VH",
      "alpha"
    ],
    [
      "HH",
      "alpha"
    ],
    [
      "VV",
      "alpha"
    ]
  ]
}

{
  "or": [
    "uint16",
    "float"
  ]
}