Merge pull request #5 from Terradue/main

feat: resolves #4

Author: emmanuelmathot

README.md

@@ -36,6 +36,7 @@ The fields in the table below can be used in these parts of STAC documents:
 | product:type                | string | The product type.                                            |
 | product:timeliness          | string | The average expected timeliness of the product as an [ISO 8601 Duration](https://en.wikipedia.org/wiki/ISO_8601#Durations). |
 | product:timeliness_category | string | A proprietary category identifier for the timeliness of the product. |
+| product:acquisition_type    | string | The acquisition type of the product.                         |
 
 > \[!IMPORTANT]  
 > `product:timeliness` is REQUIRED if `product:timeliness_category` is provided.
@@ -49,6 +50,28 @@ Some extensions may specify more specific rules for this field.
 
 This field superceedes the `sar:product_type` field.
 
+#### product:acquisition_type
+
+The product acquisition type describes the purpose of the acquisition.
+It is similar to the `acquisitionType` field from the 
+[OGC® Earth Observation Metadata profile of Observations & Measurements , Table 5](https://docs.ogc.org/is/10-157r4/10-157r4.html#24):
+
+> Used to distinguish at a high level the appropriateness of the acquisition for "general" use,
+> whether the product is a nominal acquisition, special calibration product or other.
+
+Admitted values are:
+- `nominal`
+- `calibration`
+- `other`
+
+Sentinel-2 [Annex A (page 90)](https://sentinel.esa.int/documents/247904/2047089/Sentinel-2_Cal-Val_Phase-E2.) provides the calibration sites so some
+acquisitions over those areas will be acquired for calibration purposes.
+The `product:acquisition_type` field brings is the possibility to "flag" products as `nominal`, `calibration`
+or `other` (not `nominal`, not `calibration`).
+
+[Sentinel-1](https://sentinels.copernicus.eu/web/sentinel/-/copernicus-sentinel-1-calibration-campaign-on-going-in-europe) provides few acquisitions
+in given dates and orbits that were acquired in a different mode. Those products would have `calibration`.
+
 #### Timeliness
 
 Below you can find an example that shows how the timeliness fields could be used.

examples/collection.json

@@ -39,6 +39,9 @@
     ],
     "product:timeliness_category": [
       "NRT"
+    ],
+    "product:acquisition_type": [
+      "calibration"
     ]
   },
   "links": [

examples/item.json

@@ -16,7 +16,8 @@
     ],
     "product:type": "GRD",
     "product:timeliness": "PT3H",
-    "product:timeliness_category": "NRT"
+    "product:timeliness_category": "NRT",
+    "product:acquisition_type": "nominal"
   },
   "geometry": {
     "type": "Polygon",

json-schema/schema.json

@@ -119,6 +119,9 @@
         },
         "product:timeliness_category": {
           "$ref": "#/definitions/product:timeliness_category"
+        },
+        "product:acquisition_type": {
+          "$ref": "#/definitions/product:acquisition_type"
         }
       },
       "patternProperties": {
@@ -137,6 +140,10 @@
     "product:timeliness_category": {
       "type": "string"
     },
+    "product:acquisition_type": {
+      "type": "string",
+      "enum": [ "nominal", "calibration", "other" ]
+    },
     "json_schema": {
       "$comment": "JSON Schema",
       "type": "object"