Level 2A STAC product
This document describes the Level 1C product JSON (.json) file. The product file contains metadata and references to files that make up a product.
The Level 1C product file complies with STAC specification. STAC is a standardised way to expose collections of spatial temporal data. For more information about STAC specification, refer to The STAC Specification.
Sample file
Sample : LANDSAT-9_OLI_20220804T083603_20220804T083634_L2A_R1C1_product.json
STAC extensions
The FarEarth product file makes use of STAC extensions. The list of STAC extensions used in FarEarth is shown below.
- Projection Extension Specification (proj)
- Electro-Optical Extension Specification (eo)
- View Geometry Extension Specification (view)
Assets
Each FarEarth product consists of a product file and a set of asset files.
- The product file describes the product at high-level and lists asset files
- Each asset file has a type and at least one role associated with it
- The role describes the information and intended use of the file
- The type describes the file format
Product files may also contain high-level metadata used to index the product in the FarEarth Catalogue.
Asset Roles
| Role | Asset description |
|---|---|
atmospheric | Optional data product produced with the atmospheric information |
data | Image data |
metadata | Metadata about the product |
quality | Information about the quality of the product |
thumbnail | Overview / preview image of the product |
angles | Information about the viewing and solar angles |
gverify | Information on the geometric verification of the product |
aux | Additional files required by the product |
Properties
The Level 2A product JSON has a properties section with details about the product.
FarEarth-specific properties have been grouped into categories below.
FarEarth Catalogue properties
Properties can be used to specify or find products in the FarEarth Catalogue.
| Property | Description |
|---|---|
subscriptionId | The ID of the FarEarth subscription that owns the product |
orderId | The unique ID for the order for the product. An example is AAAA-1001 |
dataset | FarEarth products can be placed into a dataset, which is a subset of the FarEarth Catalogue |
correlationId | An ID that is shared for all FarEarth products. It is derived from the FarEarth product with the correlation ID, or was used to derive the FarEarth product. It is recommended that this ID is unique |
sceneCol | If an interval is subdivided into multiple scenes, this property will reflect the column number of the scene. Column numbers start at 1 from the left, across the track of the satellite |
sceneRow | If an interval is subdivided into multiple scenes, this property will reflect the row number of the scene. Row numbers start at 1, along the track of the satellite |
FarEarth quality properties
The properties are specific to FarEarth and provide information on the geometric quality of a FarEarth product.
| Property | Description |
|---|---|
processingBaseline | Version of the processing algorithm used |
orthomodel | Orthorectification model used during processing. See orthorectification |
fe:qaGeo:ce95 | Circular Error with a 95 % probability. It is a metric used to quantify the geometric accuracy of a product, calculated as an average of all the CE95 errors calculated for each band |
fe:qaGeo:gsdX | Minimum ground sampling distance of all the images in the product, in horizontal direction |
fe:qaGeo:gsdY | This is the minimum ground sampling distance of all the images in the product, in the vertical direction |
bandAlignmentModel | The orthorectification model used to align the sensor bands of the product |
offNadirMode | Whether the image has been captured off-nadir. Options are NADIR, ALONG_TRACK or ACROSS_TRACK |
Orthorectification
The orthorectification type is either systematic or precision.
Systematic orthorectification
Systematic orthorectification uses calibration coefficients, NavAtt data, and rough reference data such as the mean height above ellipsoid for the image.
Precision orthorectification
Precision orthorectification uses tiepoints and reference data to refine the geolocation of the image to higher accuracies. Individual pixels of the Digital Elevation Model (DEM) are used to determine precisely where the pixel is.