Started SAR work

radar.md

@@ -33,6 +33,7 @@ and includes the specifications for:
 - [STAC Collections](#stac-collections)
 - [STAC Items](#stac-items)
   - [Common Metadata](#common-metadata)
+  - [Projection](#projection)
 - [Links](#links)
 - [Notes](#notes)
 
@@ -57,6 +58,19 @@ If your metadata is already compliant to this profile, you can omit the identifi
 `stac_extensions` to avoid costly regeneration of the Items. You won't get validation whether all required 
 fields are present, but this could be checked manually in the CEOS assessment/review.
 
+The following STAC extensions are relevant for this profile:
+
+| Name              | Schema URI for `stac_extensions`                                        | Required |
+| ----------------- | ----------------------------------------------------------------------- | :------: |
+| [CEOS-ARD]        | `https://stac-extensions.github.io/ceos-ard/v0.2.0/optical/schema.json` | ✓        |
+| [Processing]      | `https://stac-extensions.github.io/processing/v1.1.0/schema.json`       | ✗        |
+| [Projection]      | `https://stac-extensions.github.io/projection/v1.0.0/schema.json`       | ✓        |
+| [Raster]          | `https://stac-extensions.github.io/raster/v2.0.0/schema.json`           | ✗        |
+| [SAR]             | `https://stac-extensions.github.io/sar/v1.0.0/schema.json`              | ✓        |
+
+For details about the CEOS-ARD extension, please see the separate [CEOS-ARD extension README](README.md#fields).
+The CEOS-ARD extension fields can either be provided in the Collection or in the Items.
+
 ## STAC Collections
 
 CEOS-ARD lists a lot of requirements (and fields) that have common values across all generated STAC Items and assets.
@@ -69,22 +83,64 @@ All this is still CEOS-ARD compliant as it doesn't require all information to be
 
 ## STAC Items
 
+STAC Items must always be valid, but not all STAC Item requirements are covered here,
+only additional requirements and mappings to fulfill the CEOS-ARD requirements are listed here:
+
+| Field Name      | Req.  | Description |
+| --------------- | ----- | ----------- |
+| stac_extensions | *n/a* | **REQUIRED.** Must contain [all STAC extensions](#stac-extensions) implemented. |
+| geometry        | 1.4   | **REQUIRED.** The geometry of the acquisition. |
+| bbox            | 1.7.8 | **REQUIRED.** The bounding box of the acquisition in WGS84. |
+
+Generally, CEOS-ARD requests to provide DOIs for various resources.
+For STAC, DOIs (e.g. `10.1109/5.771073`) must be converted to URLs (e.g. `https://doi.org/10.1109/5.771073`).
+See [Resolve a DOI name](https://dx.doi.org/) for details.
+
 ### Common Metadata
 
 ...
 
+### Projection
+
+The metadata is **required** to specify the coordinate reference system (1.5) and the map projection (1.6) through
+either `proj:epsg` or one of the alternatives. The map projection is not required for ST.
+
+**Deprecation Notice:** In a future version of the version of the projection extension `proj:epsg` will be replaced by `proj:code`.
+It is recommended to provide both for now.
+
+| Field Name                            | Req.      | Description                                                  |
+| ------------------------------------- | --------- | ------------------------------------------------------------ |
+| proj:epsg / proj:wkt2 / proj:projjson | 1.7.11    | **REQUIRED**. One of the fields is required to be provided, recommended is `proj:epsg`. If there's no suitable EPSG code, set `proj:epsg` to `null` and add either `proj:wkt2` or `proj:projjson`. |
+| proj:bbox                             | 1.7.7     | **REQUIRED**. The bounding box of the acquisition in the projection defined in proj:epsg / proj:wkt2 / proj:projjson. |
+
 ## Links
 
 ...
 
 ## Notes
 
 ...
-
 [CEOS-ARD product family specifications]: <http://ceos.org/ard/>
 [Combined CEOS-ARD for Synthetic Aperture Radar, version 1.0]: <https://ceos.org/ard/files/PFS/SAR/v1.0/CEOS-ARD_PFS_Synthetic_Aperture_Radar_v1.0.pdf>
 
+[CEOS Missions Database]: <https://database.eohandbook.com/database/missiontable.aspx>
+[CEOS Instruments Database]: <https://database.eohandbook.com/database/instrumenttable.aspx>
+[CEOS Measurements Database]: <https://database.eohandbook.com/measurements/overview.aspx>
+
 [STAC]: <https://github.com/radiantearth/stac-spec>
 [Maturity Classification]: <https://github.com/radiantearth/stac-spec/tree/master/extensions/README.md#extension-maturity>
+[Common metadata]: <https://github.com/radiantearth/stac-spec/tree/v1.0.0/item-spec/common-metadata.md>
+[Media Type]: <https://github.com/radiantearth/stac-spec/blob/master/item-spec/item-spec.md#asset-media-type>
 [Collection Summaries]: <https://github.com/radiantearth/stac-spec/tree/v1.0.0/collection-spec/collection-spec.md#collection-fields>
 [Collection Assets]: <https://github.com/radiantearth/stac-spec/tree/v1.0.0/collection-spec/collection-spec.md#assets>
+
+[Accuracy]: <https://github.com/stac-extensions/accuracy>
+[Authentication]: <https://github.com/stac-extensions/authentication>
+[Classification]: <https://github.com/stac-extensions/classification>
+[CEOS-ARD]: <https://github.com/stac-extensions/ceos-ard>
+[Processing]: <https://github.com/stac-extensions/processing>
+[Projection]: <https://github.com/stac-extensions/projection>
+[Raster]: <https://github.com/stac-extensions/raster>
+[SAR]: <https://github.com/stac-extensions/sar>
+
+[UDUNITS-2]: <https://ncics.org/portfolio/other-resources/udunits2/>