Sentinel-1 GRD

About Sentinel-1 GRD Data

Mission Information

The Sentinel-1 imagery is provided by two polar-orbiting satellites, operating day and night performing C-band synthetic aperture radar imaging, enabling them to acquire imagery regardless of the weather. Main applications are for monitoring sea ice, oil spills, marine winds, waves & currents, land-use change, land deformation among others, and to respond to emergencies such as floods and earthquakes.

Sentinel Hub currently supports Sentinel-1 Level-1 GRD (Ground Range Detected) products only. See other Sentinel-1 products offered by ESA.

Observation Scenarios

Observation scenario defines the acquisition mode and polarization with which the Sentinel-1 will acquire data over certain area. When searching for the data the observation scenario can be helpful when selecting a combination of values of different parameters. Below is an example of observation scenario but it may vary through time depending on requirements. The full archive of observation scenarios is available.

(Source ESA)

More information:

• https://sentinel.esa.int/web/sentinel/missions/sentinel-1
• Dataset user guide

Attribution and Use

The Sentinel products are released under the license available here.

Processing Chain

The following describes the way Sentinel-1 GRD data is processed in Sentinel Hub.

1. Original or multilooked source chosen (depending on the resolution level; multilooking is done in ground range. Also see.)
2. Calibration to the chosen backscatter coefficient and thermal noise removal applied.
3. (Optional) Orthorectification using Range-Doppler terrain correction using the Mapzen DEM.

Notes:

• The orbit files used are the ones bundled in the products themselves. We find these more than sufficient for GRD use. Non-realtime products typically contain restituted orbit information.
• No speckle filtering is applied anywhere.
• The DEM, if used, is resampled using bilinear interpolation.

Accessing Sentinel-1 GRD Data

To access data you need to send a POST request to our process API. The requested data will be returned as the response to your request. Each POST request can be tailored to get you exactly the data you require. To do this requires setting various parameters which depend on the datasource you are querying. This chapter will help you understand the parameters for S1GRD data. To see examples of such requests go here, and for an overview of all API parameters see the API Reference.

Endpoint Locations

Differences in Capabilities

• Zoom out:

  • @ services.sentinel-hub.com/api/ : Zooming out will use multi-looked sources at an appropriate resolution to your viewing level. You can therefore expect high quality results at all zoom levels.
  • @ shservices.mundiwebservices.com/api/ : Zooming out will use multi-looked sources at an appropriate resolution to your viewing level. You can therefore expect high quality results at all zoom levels.
  • @ eocloud.sentinel-hub.com/v1/ : Zooming out will NOT use multi-looked sources. Zooming out is therefore more of a convenience preview as the images will be excessively noisy. If this is an issue consider using the AWS service instead.

• Backscatter coefficient:

  • @ services.sentinel-hub.com/api/ : We support gamma0, sigma0 and beta0 backscatter coefficients.
  • @ shservices.mundiwebservices.com/api/ : We support gamma0, sigma0 and beta0 backscatter coefficients.
  • @ eocloud.sentinel-hub.com/v1/ : We support gamma0 backscatter coefficient.

Data type identifier: S1GRD

Use S1GRD as the value of the input.data.type parameter in your API requests. This is mandatory and will ensure you get Sentinel-1 GRD data.

Filtering Options

This chapter will explain the input.data.dataFilter object of the S1GRD process API.

mosaickingOrder

The same as for S2L1C.

resolution (pixel spacing)

A full table of resolutions is available (here)

acquisitionMode

Sentinel-1 operates in four different acquisition modes (more).

polarization

This table contains information about the polarization two letter code used by ESA and the product's contained polarizations.

orbitDirection

timeliness

Processing Options

This chapter will explain the input.data.processing object of the S1GRD process API.

*Gamma0 and sigma0 use an ellipsoid earth model. Radiometric terrain flattening is currently not supported.

** For orthorectification we use the Mapzen DEM. The non-orthorectified products use a simple earth model as provided in the products themselves. This may be sufficient for very flat target areas and is faster to process.

Available Bands and Data

Information in this chapter is useful when defining input object in evalscript. Any string listed in the column Name can be an element of the input.bands array in your evalscript.

Units

The data values for each band in your custom script are presented in the default units as specified here. In case more than one unit is available for a given band, you may optionally set the value of input.units in your evalscript setup function to one of the options. Doing so will present data in that unit. The Source Format specifies how and with what precision the digital numbers from which the unit is derived are encoded. The Typical Range indicates what values are common for a given band and unit, however outliers can be expected.

For Sentinel-1, data values are linear power in the chosen backscattering coefficient. To specify the backscattering coefficient, set BETA0, SIGMA0_ELLIPSOID or GAMMA0_ELLIPSOID (default) as the value of input.data.processing.backCoeff in your request. The default is GAMMA0_ELLIPSOID.

Mosaicking

SIMPLE and ORBIT mosaicking types are supported.

Dataset specific constraints

• Noise: All products on both services have thermal noise reduction applied.
• Decibel units: For decibel outputs, a conversion is necessary within your evalscript, see an example here. We offer pre-defined evalscripts, which return S1GRD values in decibel units, as products in the Configuration Utility for your convenience.
• Orbit state vectors: We currently use the orbit state vectors provided in the products themselves as we find these sufficient for GRD use.

Catalog API Capabilities

To access Sentinel-1 GRD product metadata you need to send search request to our Catalog API. The requested metadata will be returned as JSON formatted response to your request. This chapter will help with understanding Sentinel 1 GRD specific parameters for search request.

Endpoint Locations

Collection identifier: sentinel-1-grd

Query extension

• sar:instrument_mode (possible values)
• sat:orbit_state (possible values)
• polarization (possible values)
• resolution (possible values)
• timeliness (possible values)

Distinct extension

• date
• sar:istrument_mode
• sat:orbit_state
• polarization

Examples

S1 GRD examples