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STAC CARD4L SAR Extension Specification

This extension specifies how to create STAC Items that comply to the CEOS CARD4L product family specification for either

  • SAR Normalized Radar Backscatter (NRB) products in version 5.5 (PDF, Word) or
  • SAR Polarimetric Radar (POL) products in version 3.5 (PDF, Word).

The following CARD4L metadata specifications lists requirements and maps them to a proposal of XML tags. We will refer to the included XML Tags throughout this document:

  • SAR Normalized Radar Backscatter (NRB) metadata specification (XLSX)
  • SAR Polarimetric Radar (POL) metadata specification (XLSX).

Document structure: In general, the fields required in this extension are required to either meet the threshold (minimum) requirements by the CEOS CARD4L metadata specification or are required fields in STAC. Any additional optional field provided may lead to a higher percentage for the CARD4L target (desired) requirements.

The column Field Name refers to the STAC field names. The column XML Tag refers to the XML tag proposed in the CARD4L metadata specification documents. Src and Prod define whether they apply for the STAC Item of the Source and Product respectively and give the requirement number in the CARD4L documents.

  • ✓ = Applies
  • (✓) = Not mentioned in CEOS CARD4L requirements, but recommended to be added, for example for better data discovery through STAC.
  • ✗ = Does not apply

STAC Extensions: This extension makes use of a number of existing STAC extensions:

You have to read the STAC extensions in combination with this extension as this extension just provides the mapping between the STAC fields and the CARD4L requirements, but this extension doesn't give information on the data type or an actual detailed description about the fields.

Additional resources:

  • Examples

    Please note that the examples are made-up and as such are not real-world examples.

  • JSON Schemas:

    Please note that the schema gives only a first indication on whether your metadata is correctly formatted as we can't provide a full schema for validation at the moment. For example, the assets are not fully validated yet. Passing the schema also does not imply that you are CARD4L compliant!

STAC Collections

CARD4L lists a lot of requirements (and fields) that have common values across all generated STAC Items and assets. Thus, it is recommended to provide a STAC Collection for the Items and put common fields (in the STAC Item properties) into Collection summaries. While the STAC Item fields still need to be in the Item, too, you can de-duplicate links and assets by putting common links once into the STAC Collection links. Also, common assets can be just put once into the STAC Collection using the STAC extension Collection Assets. All this is still CARD4L compliant as CARD4L doesn't require all information to be in a single file.

STAC Items

CARD4L requires metadata for both source data (Src) and the product (Prod) which STAC can better deliver in two (or more) separate files. This extension assumes that at least one STAC Item for the source is available and follows this extension or at least one new STAC Item for the source data will be created following this extension. The number of source files (i.e. the number in NumberOfAcquisitions / the number of SourceAttributes tags in XML) indicate the number of source STAC Items required. See also the derived_from link relation type below. In principle, all metadata for the source data could also be provided in a (proprietary) format like XML and linked to from the product STAC Item, but this case will not be explained in-depth in this extension.

STAC Items must always be valid, but not all STAC Item requirements are covered here, only additional requirements and mappings to fulfill the CARD4L requirements are listed here:

Field Name Src Prod XML Tag Description
stac_extensions ✓ ✓ n/a REQUIRED. Must contain all extensions used. See below for details [0].
id ✓ 1.6.6 ✓ ProductID REQUIRED.
geometry ✓ 1.6.7 ✓ 1.7.6 SourceGeographicalExtent (Src), ProductGeographicalExtent (Prod) REQUIRED.
bbox ✓ 1.6.7 ✓ 1.7.5 derived from geometry (Src), ProductBoundingBox (Prod) REQUIRED. This is the WGS84 variant of the bbox. If the product is provided in another CRS, proj:bbox must provide the bounding box in the native CRS (see below).

[0] The following values for stac_extensions apply:

Value Src Prod
https://stac-extensions.github.io/card4l/v0.1.0/sar/source.json ✓ ✗
https://stac-extensions.github.io/card4l/v0.1.0/sar/product.json ✗ ✓
https://stac-extensions.github.io/file/v2.0.0/schema.json ✗ ✓
https://stac-extensions.github.io/processing/v1.1.0/schema.json ✓ ✓
https://stac-extensions.github.io/projection/v1.0.0/schema.json (✓) ✓
https://stac-extensions.github.io/raster/v1.1.0/schema.json ✗ ✓
https://stac-extensions.github.io/sar/v1.0.0/schema.json ✓ ✓
https://stac-extensions.github.io/sat/v1.0.0/schema.json ✓ (✓)
https://stac-extensions.github.io/view/v1.0.0/schema.json ✓ ✗

STAC Item Properties

CARD4L

Field Name Src Prod XML Tag Data Type Description
card4l:specification ✓ 1.4 / 1.3 ✓ 1.4 / 1.3 DocumentIdentifier / Product, attribute type (Prod) string REQUIRED. The CARD4L specification implemented, either NRB (SAR, Normalized Radar Backscatter) or POL (SAR, Polarimetric Radar).
card4l:specification_version ✓ 1.4 ✓ 1.4 DocumentIdentifier string REQUIRED. The CARD4L specification version. Currently always 5.5 for NRB and 3.5 for POL.
card4l:beam_id ✓ 1.6.4 ✗ BeamID string REQUIRED.
card4l:orbit_data_source ✓ 1.6.5 (✓) OrbitDataSource string REQUIRED for Src. For example predicted, definitive, precise or downlinked. Applies to Prod, if additional orbit correction has been applied.
card4l:orbit_mean_altitude ✓ 1.6.5 ✗ OrbitMeanAltitude number Platform (mean) altitude in meters (m).
card4l:source_processing_parameters ✓ 1.6.6 ✗ various, see below Source Processing Object Additional relevant processing parameters, e.g., Range- and Azimuth Look Bandwidth and LUT applied. If not available in machine-readable form, can also be specified in processing:lineage.
card4l:source_geometry ✓ 1.6.7 ✗ SourceDataGeometry string REQUIRED. One of slant-range or ground-range.
card4l:incidence_angle_near_range ✓ 1.6.7 ✗ IncAngleNearRange number REQUIRED. In degrees.
card4l:incidence_angle_far_range ✓ 1.6.7 ✗ IncAngleFarRange number REQUIRED. In degrees.
card4l:resolution_azimuth ✓ 1.6.7 ✗ AzimuthResolution Map<string, number> REQUIRED. The azimuth resolution per beam, in meters (m). The beam ID is the object key and the value is the resolution. See also sar:resolution_azimuth.
card4l:resolution_range ✓ 1.6.7 ✗ RangeResolution Map<string, number> REQUIRED. The range resolution per beam, in meters (m). The beam ID is the object key and the value is the resolution. See also sar:resolution_range.
card4l:noise_equivalent_intensity ✓ 1.6.9 ✗ Estimates in NoiseEquivalentIntensity Statistics Object REQUIRED. Fill the object with statistics that are available for the source data, e.g. min, max and mean. Convert each to decibel, if required.
card4l:noise_equivalent_intensity_type ✓ 1.6.9 ✗ NoiseEquivalentIntensity, attribute type string REQUIRED. One of beta0, sigma0, or gamma0.
card4l:peak_sidelobe_ratio ✓ 1.6.9 ✗ PeakSideLobeRatio number Peak sidelobe ratio (PSLR) in decibel.
card4l:integrated_sidelobe_ratio ✓ 1.6.9 ✗ IntegratedSideLobeRatio number Integrated sidelobe ratio (ISLR) in decibel.
card4l:noise_removal_applied (✓) ✓ 3.3 NoiseRemovalApplied boolean REQUIRED for Prod. Specifies whether noise removal has been applied (true) or not (false). If set to true, a link with relation type noise-removal is required, too.
card4l:mean_faraday_rotation_angle ✓ 1.6.11 ✗ MeanFaradayRotationAngle number In degrees.
card4l:ionosphere_indicator ✓ 1.6.12 ✗ IonosphereIndicator boolean Flag indicating whether the imagery is “significantly impacted” by the ionosphere (false - no, true – yes).
card4l:speckle_filtering ✗ ✓ 1.7.4 Filtering, FilterApplied Speckle Filter Object | null REQUIRED. Set to null if FilterApplied would be set to false. Otherwise, provide a Speckle Filter Object.
card4l:pixel_coordinate_convention ✗ ✓ 1.7.8 PixelCoordinateConvention string REQUIRED. One of center (pixel center), upper-left (pixel ULC) or lower-left (pixel LLC)
card4l:measurement_type ✗ ✓ 3.1 BackscatterMeasurement (NRB) string REQUIRED. Must be set to gamma0.
card4l:measurement_convention ✗ ✓ 3.1 BackscatterConvention (NRB) string REQUIRED. Must be set to linear amplitude, linear power (both NRB + POL) or angle (POL only).
card4l:conversion_eq ✗ ✓ 3.2 / 3.1 BackscatterConversionEq (NRB), ScalingConversionEq (POL) string REQUIRED. Indicate equation to convert from digital numbers (DN) to logarithmic decibel scale, see the CARD4L specification (3.1/3.2) for details.
card4l:relative_radiometric_accuracy ✗ ✓ 3.5 Relative in RadiometricAccuracy number Relative accuracy of the Radiometric Terrain Correction in decibel.
card4l:absolute_radiometric_accuracy ✗ ✓ 3.5 Absolute in RadiometricAccuracy number Absolute accuracy of the Radiometric Terrain Correction in decibel.
card4l:resampling_method ✗ ✓ 4.1 ResamplingMethod string The resampling method used, e.g. near, bilinear, cubic, etc. (see GDAL for more)
card4l:dem_resampling_method ✗ ✓ 4.2 DEMResamplingMethod string The resampling method used for the DEM, see above for example values.
card4l:egm_resampling_method ✗ ✓ 4.2 EGMResamplingMethod string The resampling method used for the EGM, see above for example values.
card4l:geometric_accuracy_type ✗ ✓ 4.3 type in GeoCorrAccuracy string REQUIRED. Either slant-range or gtc (Geocoded Terrain Corrected).
card4l:northern_geometric_accuracy ✗ ✓ 4.3 GeoCorrAccuracy Geometric Accuracy Object REQUIRED. An estimate of the northern or line geometric accuracy.
card4l:eastern_geometric_accuracy ✗ ✓ 4.3 GeoCorrAccuracy Geometric Accuracy Object REQUIRED. An estimate of the eastern or sample geometric accuracy.
card4l:geometric_accuracy_radial_rmse ✗ ✓ 4.3 rRMSE in GeoCorrAccuracy number Radial root mean square error (rRMSE) for output product sub-sample accuracy, in meters.
card4l:gridding_convention ✗ ✓ 4.4 GriddingConvention string REQUIRED. A brief free text description of the gridding convention used, see also the link relation type gridding-convention.

Note that the following fields are aligned with the CARD4L Optical extension:

  • card4l:specification
  • card4l:specification_version
  • card4l:northern_geometric_accuracy
  • card4l:eastern_geometric_accuracy
  • card4l:geometric_accuracy_radial_rmse
Statistics Object
Field Name Type Description
mean number mean value of all the pixels in the band
minimum number minimum value of the pixels in the band
maximum number maximum value of the pixels in the band
... number Additional statistics (see below)

The three properties above are the fields for mean, min and max. values. You can choose to provide other fields depending on what is available for your source data. Nevertheless, you have to provide at least one property in the Statistics Object.

Speckle Filter Object

The following fields are all specified in CARD4L requirement 1.7.4. It is required to add all speckle filter parameters to this object.

Field Name Data Type XML Tag Description
type string FilterType REQUIRED.
window_size_col integer WindowSizeCol
window_size_line integer WindowSizeLine
... ... OtherParameters Add all speckle filter parameters.
Source Processing Object

Additional relevant processing parameters, e.g., Range- and Azimuth Look Bandwidth and LUT applied. If not available in machine-readable form, can also be specified in processing:lineage. The following fields are all suggested in CARD4L requirement 1.6.6. None of the fields is required.

Field Name Data Type XML Tag Description
lut_applied string lutApplied
range_look_bandwidth Map<string, number> RangeLookBandwidth Range Look Bandwidth per beam, in Gigahertz (GHz). The beam ID is the object key and the value is the bandwidth.
azimuth_look_bandwidth Map<string, number> AzimuthLookBandwidth Azimuth Look Bandwidth per beam, in Gigahertz (GHz). The beam ID is the object key and the value is the bandwidth.
... ... n/a Add all source data processing parameters.
Geometric Accuracy Object
Field Name Data Type XML Tag Description
bias number NothernBias / LineBias / EasternBias / SampleBias [1] REQUIRED. Bias, in meters.
stddev number NothernSTDev / LineSTDev / EasternSTDev / SampleSTDev [1] REQUIRED. Standard deviation, in meters.

[1] Depending on the type given in card4l:geometric_accuracy_type different specifications are referred to:

  • gtc: Mirrors Northern... and Eastern... XML tags
  • slant-range: Mirrors Line... and Sample... XML tags

Common Metadata

Field Name Src Prod XML Tag Description
license ✓ 1.3 ✓ 1.3 Product, attribute Copyright Recommended to be specified in a STAC Collection.
datetime ✓ ✓ n/a REQUIRED. Recommended to set to the central timestamp between start_datetime and end_datetime.
start_datetime ✓ 1.6.3 ✓ 1.5 FirstAcquistionDate (Prod), StartTime (Src) REQUIRED. Start time of the first acquisition.
end_datetime ✓ 1.6.3 ✓ 1.5 LastAcquistitionDate (Prod), EndTime (Src) REQUIRED. End time of the last acquisition.
instruments ✓ 1.6.2 (✓) Instrument REQUIRED for Src. Check STAC for potential values, example: c-sar for Sentinel-1
constellation ✓ 1.6.2 (✓) n/a Constellation name in lower-case. Only if part of a constellation, e.g. sentinel-1 for Sentinel 1A and 1B. Can often be derived from platform.
platform ✓ 1.6.2 (✓) Satellite REQUIRED for Src. Platform name in lower-case. Use a specific name such as sentinel-1a if part of constellation. MUST NOT duplicate constellation.
gsd ✗ ✓ 1.7.3 ProductColumnSpacing / ProductRowSpacing REQUIRED. Convert to meters, if required. Currently, there's no way to express separate ground sample distances for x and y.

Processing

Field Name Src Prod XML Tag Description
processing:facility ✓ 1.6.6 ✓ 1.7.1 ProcessingFacility REQUIRED. The name of the facility that produced the data.
processing:level ✓ 1.6.6 ✓ 1.7.1 n/a REQUIRED. See here for suggested processing levels.
processing:software ✓ 1.6.6 ✓ 1.7.1 SoftwareVersion REQUIRED. A dictionary with software name/version number for key/value describing one or more softwares that produced the data.
processing:lineage ✓ ✓ n/a A human-readable description of the full processing workflow and parameters, e.g. algorithms and corrections applied.
processing:expression ✓ ✓ n/a A machine-readable description of the full processing workflow and parameters, e.g. a Dask graph, an openEO process or a SNAP graph. Alternatively, you can also link to a processing chain with the relation type processing-expression (see below).

Projection

Field Name Src Prod XML Tag Description
proj:epsg (✓) ✓ 1.7.9 CoordinateReferenceSystem REQUIRED for Prod. EPSG code as integer or null if there is no suitable EPSG code.
proj:wkt2 / proj:projjson (✓) ✓ 1.7.9 CoordinateReferenceSystem REQUIRED for Prod. Either WKT2 or PROJJSON needs to be given in addition to the EPSG code. It is also allowed to give both.
proj:bbox (✓) ✓ 1.7.5 ProductBoundingBox REQUIRED for Prod if the native CRS is not WGS84. This is the bounding box in the native CRS of the product. Can be omitted if the native CRS is WGS84.
proj:shape ✗ ✓ 1.7.7 NumberLines, NumberPixelsPerLine REQUIRED for Prod. Number of pixels in Y and X directions for the default grid. See comment below**.
proj:transform ✗ (✓) n/a Recommended to include the affine transformation coefficients for the default grid. See comment below [2].

[2] Values are assumed to apply to all Assets of an Item. If this is not the case, these fields should be specified at the Item Asset level instead.

SAR

Field Name Src Prod XML Tag Description
sar:instrument_mode ✓ 1.6.4 (✓) ObservationMode REQUIRED for Src.
sar:frequency_band ✓ 1.6.4 (✓) RadarBand REQUIRED for Src.
sar:center_frequency ✓ 1.6.4 ✗ RadarCenterFrequency REQUIRED. In Gigahertz (GHz).
sar:polarizations ✓ 1.6.4 (✓) Polarizations REQUIRED for Src.
sar:product_type ✓ 1.6.6 ✓ 3.1 ProductLevel (Src), Measurements, attribute type (Prod, POL only) REQUIRED. Src: Find suitable product type in the SAR extension. Prod: NRB for Normalized Radar Backscatter products, COVMAT for Normalized Radar Covariance Matrix products or PRD for Polarimetric Radar Decomposition products.
sar:observation_direction ✓ 1.6.4 ✗ AntennaPointing REQUIRED. Lower-case
sar:looks_azimuth ✓ 1.6.6 ✗ AzimuthNumberOfLooks REQUIRED.
sar:looks_range ✓ 1.6.6 ✗ RangeNumberOfLooks REQUIRED.
sar:pixel_spacing_azimuth ✓ 1.6.7 ✗ AzimuthPixelSpacing REQUIRED. In meters (m).
sar:pixel_spacing_range ✓ 1.6.7 ✗ RangePixelSpacing REQUIRED. In meters (m).
sar:resolution_azimuth ✓ 1.6.7 ✗ AzimuthResolution REQUIRED. The maximum ability to distinguish two adjacent targets parallel to the flight path, which is the lowest value of card4l:resolution_azimuth, in meters (m).
sar:resolution_range ✓ 1.6.7 ✗ RangeResolution REQUIRED. The maximum ability to distinguish two adjacent targets perpendicular to the flight path, which is the lowest value of card4l:resolution_range, in meters (m).
sar:looks_equivalent_number ✓ 1.6.9 ✗ EquivalentNumberOfLooks

Satellite

Field Name Src Prod XML Tag Description
sat:orbit_state ✓ 1.6.5 (✓) PassDirection REQUIRED for Src. Lower-case
sat:relative_orbit ✓ (✓) n/a
sat:absolute_orbit ✓ (✓) n/a

View

Field Name Src Prod XML Tag Description
view:azimuth ✓ 1.6.5 ✗ PlatformHeading In degrees. STAC uses the range 0 to 360°, so if you use the range -180 - 180, you need to add +180 for conversion.
view:incidence_angle ✓ 1.6.5 ✗ n/a In degrees. Center between card4l:incidence_angle_near_range and card4l:incidence_angle_far_range. This is the sensor incidence angle. For per-pixel incidence angles, refer to the asset with the role local-incidence-angle.

STAC Item Links

All CARD4L compliant STAC Catalog are required to make intensive use of STAC link relation types such as root, parent, child, item and collection, which then covers explicit requirements such as 1.6.1 and 1.7.1 (e.g. SourceDataRepository and RepositoryURL) through STAC links.

Relation Type Src Prod XML Tag Description
card4l-document ✓ ✓ 1.4 DocumentIdentifier REQUIRED. Instead of the document identifier, provide URLs to the Word (media type: application/vnd.openxmlformats-officedocument.wordprocessingml.document) and PDF (media type: application/pdf) document.
derived_from ✗ ✓ 1.6 n/a REQUIRED. Points back to the source's STAC Item, which must comply to the Src requirements. May be multiple items, if the product is derived from multiple acquisitions. The number of acquisitions (NumberOfAcquisitions) is the number of links with this relation type.
about (✓) (✓) n/a URL to other documentation, e.g. algorithms used in the generation process.
related ✗ ✓ 1.7.2 AncillaryData URL to the sources of ancillary or auxiliary data used in the generation process. Excludes DEMs, which use the relation elevation-model instead.
access ✓ 1.6.1 ✓ 1.7.1 n/a URL to data access information.
satellite ✓ 1.6.2 ✗ SatelliteReference URL to the relevant CEOS Missions, Instruments and Measurements Database record.
state-vectors ✓ 1.6.5 ✗ StateVector URL to an orbit data file containing at least 5 state vectors.
sensor-calibration ✓ 1.6.8 ✗ SensorCalibration URL to the sensor calibration parameters.
pol-cal-matrices ✓ 1.6.10 ✗ PolCalMatrices URL to the complex-valued polarimetric distortion matrices with the channel imbalance and the cross-talk applied for the polarimetric calibration.
referenced-faraday-rotation ✓ 1.6.11 ✗ ReferenceFaradayRotation URL to the method or paper used to derive the estimate for the mean Faraday rotation angle.
noise-removal ✗ ✓ 3.3 NRAlgorithm REQUIRED if noise removal has been applied. URL to the noise removal algorithm details.
radiometric-terrain-correction ✗ ✓ 3.4 RTCAlgorithm REQUIRED. URL to the Radiometric Terrain Correction algorithm details.
radiometric-accuracy ✗ ✓ 3.5 RadAccuracyReference URL describing the radiometric uncertainty of the product.
geometric-correction ✗ ✓ 4.1 GeoCorrAlgorithm URL to the Geometric Correction algorithm details.
elevation-model or surface-model ✗ ✓ 4.2 DEMReference REQUIRED. URL to the Digital Elevation Model (DEM) or Digital Surface Model (DSM) used for Geometric Terrain Correction. Preferably URLs to a STAC Item with additional metadata such as the line-spacing, column-spacing, horizontal and vertical accuracy.
earth-gravitational-model ✗ ✓ 4.2 EGMReference REQUIRED. URL to the Earth Gravitational Model (EGM) used for Geometric Correction. Preferably URLs to a STAC Item with additional metadata for the EGM (see above).
geometric-accuracy ✗ ✓ 4.3 GeometricCorrAccuracy URL to documentation of estimate of absolute localization error.
gridding-convention ✗ ✓ 4.4 GriddingConvention URL that describes the gridding convention used.
processing-expression ✓ 1.6.6 ✓ 1.7.1 / 4.1 / ... n/a A processing chain (or script) that describes how the data has been processed.

Note: CARD4L XML files also allow DOIs to be given instead of URLs. DOIs must be converted to URLs for STAC!

STAC Item Assets

Whether the metadata are provided in a single record relevant to all pixels, or separately for each pixel, is at the discretion of the data provider.

The role names specify the values to be used in the Asset's roles. Each of the assets can either be exposed individually or grouped together in any form. In the latter case the role names can simply be merged to a set of unique role names. Roles can also be combined for a single file. The italic role names could be used as the asset's key.

All additional properties are required, except the properties in italic.

Role Name(s) Src Prod XML Tag Additional properties Description
card4l, metadata ✗ ✓ 2.1 n/a type Points to a metadata XML file that follows the CARD4L metadata specification. Media type: application/xml
data-mask, metadata ✗ ✓ 2.2 DataMask type, raster:bands (with values [see notes], nodata, data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape REQUIRED. Points to the data mask file.
contributing-area, metadata ✗ ✓ 2.3 LocalContributingArea type, raster:bands (with unit, data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape Points to the normalized scattering area file.
local-incidence-angle, metadata ✗ ✓ 2.4 LocalIncAngle type, raster:bands (with unit, data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape REQUIRED. Points to the DEM-based local incidence angle file. unit is usually degree.
ellipsoid-incidence-angle, metadata ✗ ✓ 2.5 EllipsoidIncAngle type, raster:bands (with unit, data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape, card4l:ellipsoidal_height unit is usually degree.
noise-power, card4l, metadata ✗ ✓ 2.6 NoisePower type, raster:bands (with unit, data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape REQUIRED if noise removal was applied. unit is usually NESZ or NEBZ.
gamma-sigma-ratio, metadata ✗ ✓ 2.7 GammaToSigmaRatio type, raster:bands (with data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape
(acquisition-id or date-offset), metadata ✗ ✓ 2.8 AcquisitionIDImage type, raster:bands (with data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape REQUIRED for multi-source products only. Acquisition ID or acquisition date for each pixel is identified (see 2.8 for details).
(elevation-model or surface-model or earth-gravitational-model), metadata ✗ ✓ 2.9 PerPixelDEM type, raster:bands (with data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape Per-pixel DEM/DSM/EGM as used in product generation.
backscatter, data ✗ ✓ 3.1 (NRB) BackscatterMeasurementData type, created, sar:polarizations, raster:bands (with data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape, card4l:border_pixels REQUIRED for NRB. Points to the backscatter measurements for the polarizations specified in sar:polarizations.
(covmat and/or prd), data ✗ ✓ 3.1 (POL) Measurements type, created, sar:polarizations (CovMat only), raster:bands (with data_type and bits_per_sample), file:byte_order, file:header_size, proj:transform, proj:shape, card4l:border_pixels REQUIRED for POL. Points to the Normalized Polarimetric Radar Covariance Matrix (CovMat) or the Polarimetric Radar Decomposition (PRD)

Additional Asset Properties

The following table lists properties that may occur in the assets. The list doesn't specify which fields apply to which asset and it also doesn't specify which fields are required. For those details please refer to the "Additional properties" column in the table above.

Field Name Src Prod XML Tag Data Type Description
type (✓) ✓ DataFormat string The media type of the file format.
created ✓ 1.6.6 ✓ 1.7.1 ProcessingDate (Src), ProcessingTime (Prod) string The time of the processing is specified via the created property of the asset as specified in the STAC Common metadata.
sar:polarizations (✓) ✓ n/a [string] The polarization(s) of the asset.
file:header_size ✗ ✓ 1.7.7 HeaderSize integer File header size in bytes (required if applicable to the file format).
file:byte_order ✗ ✓ ByteOrder string One of big-endian or little-endian
raster:bands ✗ ✓ see below [Raster Band Object] Bands with at least the required fields for the corresponding asset role (see above and below).
card4l:ellipsoidal_height ✗ ✓ EllipsoidalHeight number Indicate which ellipsoidal (mean) height was used, in meters.
card4l:border_pixels ✗ ✓ 1.7.7 NumBorderPixels integer Number of border pixels (required only if applicable).
proj:shape ✗ ✓ 1.7.7 NumberLines, NumberPixelsPerLine [integer] The shape of the asset. See comment below [3].
proj:transform ✗ (✓) n/a [number] The affine transformation coefficients for the default grid. See comment below*.

[3] proj:shape and proj:transform only need to be specified at the Item Asset level if the values vary between Assets. Specify in Item properties otherwise. See also comment in Projection.

raster:bands
Field Name Src Prod XML Tag Data Type Description
data_type ✗ ✓ DataType string One of the Data Types.
unit ✗ ✓ SampleType string The unit of the values in the asset, preferably compliant to UDUNITS-2 units (singular).
bits_per_sample ✗ ✓ BitsPerSample integer Actual number of bits per sample (e.g., 8, 16, 32, ...)
values ✗ ✓ 2.2 ValidData and InvalidData in BitValues [Mapping Object] Specify value(s) for valid and invalid data separately. [4]
nodata ✗ ✓ 2.2 NoData in BitValues [any] Value(s) for no-data.

[4] raster:bands[*].values is not standardized yet in STAC, this could change to file:values or something different with a similar structure in the future.