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feat: Add SAR swath information
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‎README.md

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## Item Properties or Asset Fields
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| Field Name | Type | Description |
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| --------------------------- | --------- | ------------------------------------------------------------ |
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| sar:instrument_mode | string | **REQUIRED.** The name of the sensor acquisition mode that is commonly used. This should be the short name, if available. For example, `WV` for "Wave mode" of Sentinel-1 and Envisat ASAR satellites. |
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| sar:frequency_band | string | **REQUIRED.** The common name for the frequency band to make it easier to search for bands across instruments. See section "Common Frequency Band Names" for a list of accepted names. |
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| sar:center_frequency | number | The center frequency of the instrument, in gigahertz (GHz). |
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| sar:polarizations | \[string] | **REQUIRED.** Any combination of polarizations. |
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| sar:product_type | string | ***DEPRECATED** in favor of [`product:type`](https://github.com/stac-extensions/product).* The product type, for example `SSC`, `MGD`, or `SGC` |
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| sar:resolution_range | number | The range resolution, which is the maximum ability to distinguish two adjacent targets perpendicular to the flight path, in meters (m). |
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| sar:resolution_azimuth | number | The azimuth resolution, which is the maximum ability to distinguish two adjacent targets parallel to the flight path, in meters (m). |
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| sar:pixel_spacing_range | number | The range pixel spacing, which is the distance between adjacent pixels perpendicular to the flight path, in meters (m). Strongly RECOMMENDED to be specified for products of type `GRD`. |
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| sar:pixel_spacing_azimuth | number | The azimuth pixel spacing, which is the distance between adjacent pixels parallel to the flight path, in meters (m). Strongly RECOMMENDED to be specified for products of type `GRD`. |
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| sar:looks_range | number | Number of range looks, which is the number of groups of signal samples (looks) perpendicular to the flight path. |
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| sar:looks_azimuth | number | Number of azimuth looks, which is the number of groups of signal samples (looks) parallel to the flight path. |
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| sar:looks_equivalent_number | number | The equivalent number of looks (ENL). |
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| sar:observation_direction | string | Antenna pointing direction relative to the flight trajectory of the satellite, either `left` or `right`. |
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| Field Name | Type | Description |
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| --------------------------- | -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
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| sar:instrument_mode | string | **REQUIRED.** The name of the sensor acquisition mode that is commonly used. This should be the short name, if available. For example, `WV` for "Wave mode" of Sentinel-1 and Envisat ASAR satellites. |
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| sar:frequency_band | string | **REQUIRED.** The common name for the frequency band to make it easier to search for bands across instruments. See section "Common Frequency Band Names" for a list of accepted names. |
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| sar:center_frequency | number | The center frequency of the instrument, in gigahertz (GHz). |
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| sar:polarizations | \[string] | **REQUIRED.** Any combination of polarizations. |
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| sar:product_type | string | ***DEPRECATED** in favor of [`product:type`](https://github.com/stac-extensions/product).* The product type, for example `SSC`, `MGD`, or `SGC` |
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| sar:resolution_range | number | The range resolution, which is the maximum ability to distinguish two adjacent targets perpendicular to the flight path, in meters (m). |
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| sar:resolution_azimuth | number | The azimuth resolution, which is the maximum ability to distinguish two adjacent targets parallel to the flight path, in meters (m). |
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| sar:pixel_spacing_range | number | The range pixel spacing, which is the distance between adjacent pixels perpendicular to the flight path, in meters (m). Strongly RECOMMENDED to be specified for products of type `GRD`. |
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| sar:pixel_spacing_azimuth | number | The azimuth pixel spacing, which is the distance between adjacent pixels parallel to the flight path, in meters (m). Strongly RECOMMENDED to be specified for products of type `GRD`. |
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| sar:looks_range | number | Number of range looks, which is the number of groups of signal samples (looks) perpendicular to the flight path. |
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| sar:looks_azimuth | number | Number of azimuth looks, which is the number of groups of signal samples (looks) parallel to the flight path. |
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| sar:looks_equivalent_number | number | The equivalent number of looks (ENL). |
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| sar:observation_direction | string | Antenna pointing direction relative to the flight trajectory of the satellite, either `left` or `right`. |
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| sar:swath | \[Beam Object] | Composition of the swath of the SAR acquisition. |
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**Note:** In this specification *range* values are meant to be measured perpendicular to the flight path and *azimuth* values
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are meant to be measured parallel to the flight path.
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**Important:** In the `properties` of a STAC Item `sar:polarizations` must be a set with unique elements.
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In assets `sar:polarizations` can contain duplicate elements and, if possible, the polarizations must appear in the same order as in the file.
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### Beam Object
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The `sar:swath` field is an array of objects that describe the composition of the swath of the SAR acquisition.
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According to the instrument mode defined in `sar:instrument_mode`, the `sar:swath` is composed of one or more beams.
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| Field Name | Type | Description |
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| -------------- | --------------------- | -------------------------------------------------------------------------------------- |
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| id | string | **REQUIRED.** The unique identifier of the beam. It can be the subswath identifier |
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| relative_burst | number | Identification number that uniquely identifies a burst cycle within each repeat cycle. |
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| polarizations | \[string] | Any combination of polarizations. |
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| view:* | View extension fields | Additional fields from the [View extension](https://github.com/stac-extensions/view) |
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> \[!NOTE]
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> If the value of a field repeats for all beams, it is recommended to include it only in the first beam.
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Example of a `sar:swath` field:
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```json
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"sar:swath": [
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{
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"id": "IW1",
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"relative_burst": 541,
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"polarizations": ["VV", "VH"],
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"view:incident_angle": 32.0
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},
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{
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"id": "IW2",
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"view:incident_angle": 34.0
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},
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{
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"id": "IW3",
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"view:incident_angle": 36.0
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}
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]
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```
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### Common Frequency Band Names
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The `sar:frequency_band` is the name that is commonly used to refer to that band's spectral
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properties. The table below shows the common name based on the wavelength and frequency ranges for several SAR satellites.
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| Common Name | Wavelength Range (cm) | Frequency Range (GHz) | Satellites |
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| ----------- | --------------------- | --------------------- | ---------- |
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| P | 30 - 120 | 0.25 - 1 | |
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| L | 15 - 30 | 1 - 2 | ALOS, JERS, NISAR, SOACOM |
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| S | 7.5 - 15 | 2 - 4 | HJ-1C |
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| C | 3.8 - 7.5 | 4 - 8 | EnviSat, ERS, Radarsat, Risat-1, Sentinel-1 |
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| Common Name | Wavelength Range (cm) | Frequency Range (GHz) | Satellites |
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| ----------- | --------------------- | --------------------- | -------------------------------------------------- |
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| P | 30 - 120 | 0.25 - 1 | |
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| L | 15 - 30 | 1 - 2 | ALOS, JERS, NISAR, SOACOM |
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| S | 7.5 - 15 | 2 - 4 | HJ-1C |
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| C | 3.8 - 7.5 | 4 - 8 | EnviSat, ERS, Radarsat, Risat-1, Sentinel-1 |
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| X | 2.4 - 3.8 | 8 - 12.5 | Cosmo-SkyMed, TerraSAR-X, TanDEM-X, PAZ, KOMPSat-5 |
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| Ku | 1.7 - 2.4 | 12.5 - 18 | |
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| K | 1.1 - 1.7 | 18 - 26.5 | |
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| Ka | 0.75 - 1.1 | 26.5 - 40 | |
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| Ku | 1.7 - 2.4 | 12.5 - 18 | |
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| K | 1.1 - 1.7 | 18 - 26.5 | |
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| Ka | 0.75 - 1.1 | 26.5 - 40 | |
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### Product type
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The product type for SAR data defines the type of processed data contained in the assets.
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A list of suggestions for [`product:type`](https://github.com/stac-extensions/product) include:
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| product:type | Type | Description |
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| ------------ | --------- | ----------- |
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| SSC | complex | Single-look Slant-range Complex image (standard SLC) |
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| MGD | amplitude | Multilooked Ground-range Detected image |
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| GRD | amplitude | Multilooked Ground-range Detected image (used by Sentinel-1) |
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| GEC | amplitude | Geocoded Ellipsoid Corrected image |
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| GTC | amplitude | Geocoded Terrain Corrected image |
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| RTC | amplitude | Geocoded Radiometrically Terrain Corrected image |
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| SGC | complex | Single-look Ground projected Complex image |
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| product:type | Type | Description |
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| ------------ | --------- | --------------------------------------------------------------- |
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| SSC | complex | Single-look Slant-range Complex image (standard SLC) |
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| MGD | amplitude | Multilooked Ground-range Detected image |
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| GRD | amplitude | Multilooked Ground-range Detected image (used by Sentinel-1) |
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| GEC | amplitude | Geocoded Ellipsoid Corrected image |
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| GTC | amplitude | Geocoded Terrain Corrected image |
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| RTC | amplitude | Geocoded Radiometrically Terrain Corrected image |
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| SGC | complex | Single-look Ground projected Complex image |
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| SLC | complex | Single-look Ground projected Complex image (used by Sentinel-1) |
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This can vary by data provider, who all may use slightly different names.
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This list should not be considered definitive, and implementors are welcome to use other asset roles. If consensus and tooling consolidates around
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these role names then they will be specified in the future as more standard than just 'best practices'.
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| Role Name | Description |
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| --------- | ---------------------------------------------------------------------- |
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| local-incidence-angle | Points to the local incidence angle file. |
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| ellipsoid-incidence-angle | Points to the ellipsoid incidence angle file. |
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| noise-power | Points to the noise power file. |
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| amplitude | Points to the intensity file with focused SAR data that has been ground range detected (e.g. GRD). |
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| magnitude | Points to the intensity file where data are represented as complex numbers containing amplitude and phase information (e.g SLC). |
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| sigma0 | Points to the radar backscatter file where data is referenced in ground surface. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| beta0 | Points to the radar backscatter file where data is referenced in the slant range plane and is radiometrically calibrated. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| gamma0 | Points to the radar backscatter file where data is referenced in the plane perpendicular to the line of sight. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| date-offset | Points to the date-offset file. |
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| covmat | Points to the Points to the Normalized Polarimetric Radar Covariance Matrix (CovMat) file. |
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| prd | Points to the Polarimetric Radar Decomposition (PRD) file. |
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| Role Name | Description |
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| ------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| local-incidence-angle | Points to the local incidence angle file. |
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| ellipsoid-incidence-angle | Points to the ellipsoid incidence angle file. |
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| noise-power | Points to the noise power file. |
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| amplitude | Points to the intensity file with focused SAR data that has been ground range detected (e.g. GRD). |
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| magnitude | Points to the intensity file where data are represented as complex numbers containing amplitude and phase information (e.g SLC). |
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| sigma0 | Points to the radar backscatter file where data is referenced in ground surface. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| beta0 | Points to the radar backscatter file where data is referenced in the slant range plane and is radiometrically calibrated. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| gamma0 | Points to the radar backscatter file where data is referenced in the plane perpendicular to the line of sight. It is often derived from an `amplitude` or a `magnitude` role asset. |
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| date-offset | Points to the date-offset file. |
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| covmat | Points to the Points to the Normalized Polarimetric Radar Covariance Matrix (CovMat) file. |
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| prd | Points to the Polarimetric Radar Decomposition (PRD) file. |
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## Contributing
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‎examples/sentinel-1.json

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"sar:looks_equivalent_number": 2.7,
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"sar:frequency_band": "C",
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"sar:center_frequency": 5.405,
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"sar:swath": [
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{
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"id": "EW",
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"polarizations": [
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"HH"
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],
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"view:incident_angle": 40.1
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}
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],
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"product:type": "GRD"
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},
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"geometry": {

‎json-schema/schema.json

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"type": "array",
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"minItems": 1,
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"items": {
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"type": "string",
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"enum": [
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"HH",
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"VV",
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"HV",
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"VH"
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]
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"$ref": "#/definitions/polarizations"
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}
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},
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"sar:product_type": {
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"left",
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"right"
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]
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},
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"sar:swath": {
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"title": "Swath",
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"type": "array",
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"items": {
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"$ref": "#/definitions/beam"
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}
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}
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},
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"patternProperties": {
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}
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},
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"additionalProperties": false
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},
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"beam": {
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"anyOf": [
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{
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"type": "object",
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"properties": {
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"id": {
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"title": "Beam identification",
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"type": "string",
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"minLength": 1
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},
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"relative_burst": {
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"title": "Relative burst identificator",
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"type": "integer",
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"minimum": 0
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},
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"polarizations": {
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"title": "Polarizations",
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"type": "array",
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"minItems": 1,
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"items": {
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"$ref": "#/definitions/polarizations"
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}
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}
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},
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"additionalProperties": true
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},
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{
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"$ref": "https://stac-extensions.github.io/view/v1.0.0/schema.json#/definitions/fields",
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"additionalProperties": true
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},
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{
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"required": [
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"id"
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]
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}
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]
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},
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"polarizations": {
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"type": "string",
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"enum": [
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"HH",
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"VV",
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"HV",
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"VH"
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]
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}
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}
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}
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}

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