Extension Maturity Classification: Pilot
This document explains the fields of the STAC Electro-Optical (EO) Extension to a STAC Item. EO data is considered to be data that represents a snapshot of the earth for a single date and time. It could consist of multiple spectral bands in any part of the electromagnetic spectrum. Examples of EO data include sensors with visible, short-wave and mid-wave IR bands (e.g., the OLI instrument on Landsat-8), long-wave IR bands (e.g. TIRS aboard Landsat-8).
Note: This extension used to be called Earth Observation with a much broader scope (including Synthetic Aperture Radar (SAR), etc). The decision was made to limit this to what was already its natural focus, and encourage other sensors to make their own extensions. Once that happens some of these fields will evolve to higher level extensions. In the meantime other implementations are welcome to reuse the names and definitions here.
A lot of EO data will have common metadata across many Items. It is not necessary, but recommended to place common fields in STAC Collections. The exact metadata that would appear in a STAC Collection record will vary depending on the dataset.
| Field Name | Type | Description |
|---|---|---|
| eo:gsd | number | REQUIRED. Ground Sample Distance at the sensor. |
| eo:platform | string | REQUIRED. Unique name of the specific platform to which the instrument is attached. |
| eo:instrument | string | REQUIRED. Name of instrument or sensor used (e.g., MODIS, ASTER, OLI, Canon F-1). |
| eo:bands | [Band Object] | REQUIRED. This is a list of the available bands where each item is a Band Object. |
| eo:constellation | string | Name of the constellation to which the platform belongs. |
| eo:epsg | integer|null | EPSG code of the datasource, null if no EPSG code. |
| eo:cloud_cover | number | Estimate of cloud cover as a percentage (0-100) of the entire scene. If not available the field should not be provided. |
| eo:off_nadir | number | Viewing angle. The angle from the sensor between nadir (straight down) and the scene center. Measured in degrees (0-90). |
| eo:azimuth | number | Viewing azimuth angle. The angle measured from the sub-satellite point (point on the ground below the platform) between the scene center and true north. Measured clockwise from north in degrees (0-360). |
| eo:sun_azimuth | number | Sun azimuth angle. From the scene center point on the ground, this is the angle between truth north and the sun. Measured clockwise in degrees (0-360). |
| eo:sun_elevation | number | Sun elevation angle. The angle from the tangent of the scene center point to the sun. Measured from the horizon in degrees (0-90). |
eo:gsd is the nominal Ground Sample Distance for the data, as measured in meters on the ground. There are many
definitions of GSD. The value of this attribute should be related to the spatial resolution at the sensor, rather
than the pixel size of images after orthorectification, pansharpening, or scaling.
The GSD of a sensor can vary depending on off-nadir and wavelength, so it is at the discretion of the implementer
to decide which value most accurately represents the GSD. For example, Landsat8 optical and short-wave IR bands
are all 30 meters, but the panchromatic band is 15 meters. The
eo:gsd should be 30 meters in this case because that is nominal spatial resolution at the sensor. The Planet
PlanetScope Ortho Tile Product has an eo:gsd of 3.7 (or 4 if rounding), even though the pixel size of the images is
3.125. For example, one might choose for WorldView-2 the
Multispectral 20° off-nadir value of 2.07 and for WorldView-3 the Multispectral 20° off-nadir value of 1.38.
eo:platform is the unique name of the specific platform the instrument is attached to. For satellites this would
be the name of the satellite, whereas for drones this would be a unique name for the drone. Examples include
landsat-8 (Landsat-8), sentinel-2a and sentinel-2b (Sentinel-2), terra and aqua (part of NASA EOS,
carrying the MODIS instruments), mycorp-uav-034 (hypothetical drone name), and worldview02
(Maxar/DigitalGlobe WorldView-2).
eo:instrument is the name of the sensor used, although for Items which contain data from
multiple sensors this could also name multiple sensors. For example, data from the Landsat-8
platform is collected with the OLI sensor as well as the TIRS sensor, but the data is distributed
together and commonly referred to as OLI_TIRS. Examples include oli_tirs (Landsat-8), msi (Sentinel-2),
aster (Terra), and modis (Terra and Aqua).
eo:constellation is the name of a logical collection one or more platforms that have similar payloads and have
their orbits arranged in a way to increase the temporal resolution of acquisitions of data with similar geometric and
radiometric characteristics. This field allows users to search for related data sets without needing to specify which
specific platform the data came from, for example, from either of the Sentinel-2 satellites. Examples include landsat-8
(Landsat-8, a constellation consisting of a single platform), sentinel-2 (Sentinel-2),
rapideye (operated by Planet Labs), and modis (NASA EOS satellites Aqua and Terra). In the case of modis, this
is technically referring to a pair of sensors on two different satellites, whose data is combined into a series of
related products. Additionally, the Aqua satellite is technically part of the A-Train constellation and Terra is not
part of a constellation, but these combine to form the logical collection referred to as MODIS.
eo:epsg - A Coordinate Reference System (CRS) is the native reference system (sometimes called a 'projection') used by the data, and can usually be referenced using an EPSG code. If the data does not have a CRS, such as in the case of non-rectified imagery with Ground Control Points, eo:epsg should be set to null. It should also be set to null if a CRS exists, but for which there is no valid EPSG code.
| Field Name | Type | Description |
|---|---|---|
| name | string | The name of the band (e.g., "B01", "B02", "B1", "B5", "QA"). |
| common_name | string | The name commonly used to refer to the band to make it easier to search for bands across instruments. See the list of accepted common names. |
| description | string | Description to fully explain the band. CommonMark 0.28 syntax MAY be used for rich text representation. |
| gsd | number | Ground Sample Distance, the nominal distance between pixel centers available, in meters. Defaults to eo:gsd if not provided. |
| accuracy | number | The expected error between the measured location and the true location of a pixel, in meters on the ground. |
| center_wavelength | number | The center wavelength of the band, in micrometers (μm). |
| full_width_half_max | number | Full width at half maximum (FWHM). The width of the band, as measured at half the maximum transmission, in micrometers (μm). |
eo:gsd is the Ground Sample Distance, measured in meters on the ground. This value is the nominal distance between
pixel centers for the data.
Since GSD can vary across a scene depending on projection, this should be the average or most
commonly used GSD in the center of the image. For instance, Landsat8 optical and short-wave IR bands are 30 meters
and the panchromatic band is 15 meters. The Planet PlanetScope Ortho Tile Product has a band gsd of 3.125 (3 if
rounding), which is different from the eo:gsd of 3.7 (4 if rounding).
full_width_half_max (FWHM) is a common way to describe the size of a spectral band. It is the width, in micrometers (μm), of the bandpass measured at a half of the maximum transmission. Thus, if the maximum transmission of the bandpass was 80%, the FWHM is measured as the width of the bandpass at 40% transmission.
The band's common_name is the name that is commonly used to refer to that band's spectral properties. The table below shows the common name based on the average band range for the band numbers of several popular instruments.
| Common Name | Band Range (μm) | Landsat 5/7 | Landsat 8 | Sentinel 2 | MODIS |
|---|---|---|---|---|---|
| coastal | 0.40 - 0.45 | 1 | 1 | ||
| blue | 0.45 - 0.50 | 1 | 2 | 2 | 3 |
| green | 0.50 - 0.60 | 2 | 3 | 3 | 4 |
| red | 0.60 - 0.70 | 3 | 4 | 4 | 1 |
| yellow | 0.58 - 0.62 | ||||
| pan | 0.50 - 0.70 | 8 (L7 only) | 8 | ||
| rededge | 0.70 - 0.75 | ||||
| nir | 0.75 - 1.00 | 4 | 8 | 2 | |
| nir08 | 0.75 - 0.90 | 5 | 8a | ||
| nir09 | 0.85 - 1.05 | 9 | |||
| cirrus | 1.35 - 1.40 | 9 | 10 | 26 | |
| swir16 | 1.55 - 1.75 | 5 | 6 | 11 | 6 |
| swir22 | 2.10 - 2.30 | 7 | 7 | 12 | 7 |
| lwir | 10.5 - 12.5 | 6 | |||
| lwir11 | 10.5 - 11.5 | 10 | 31 | ||
| lwir12 | 11.5 - 12.5 | 11 | 32 |
The difference between the nir, nir08, and nir09 bands are that the nir band is a wider band that covers most of the spectral range of 0.75μm to 1.0μm. nir08 and nir09 are narrow bands centered 0.85μm and 0.95μm respectively. The same goes for the difference between lwir, lwir11 and lwir12.
Asset definitions that contain band data should reference the band index. Each asset should provide a eo:bands property that is an array of 0 based indexes to the correct Band Objects.
Item Asset Object fields
| Field Name | Type | Description |
|---|---|---|
| eo:bands | [number] | Lists the band names available in the asset. |
See example-landsat8.json for a full example.
{
"stac_version": "0.8.0",
"stac_extensions": ["eo"],
"id": "LC08_L1TP_107018_20181001_20181001_01_RT",
"type": "Feature",
...
"properties": {
...
"eo:bands": [
{
"name": "B1",
"common_name": "coastal",
"gsd": 30,
"center_wavelength": 0.44,
"full_width_half_max": 0.02
},
{
"name": "B2",
"common_name": "blue",
"gsd": 30,
"center_wavelength": 0.48,
"full_width_half_max": 0.06
},
{
"name": "B3",
"common_name": "green",
"gsd": 30,
"center_wavelength": 0.56,
"full_width_half_max": 0.06
},
...
]
},
"assets": {
"B1": {
"href": "https://landsat-pds.s3.amazonaws.com/c1/L8/107/018/LC08_L1TP_107018_20181001_20181001_01_RT/LC08_L1TP_107018_20181001_20181001_01_RT_B1.TIF",
"type": "image/tiff; application=geotiff",
"eo:bands": [0],
"title": "Band 1 (coastal)"
},
"B2": {
"href": "https://landsat-pds.s3.amazonaws.com/c1/L8/107/018/LC08_L1TP_107018_20181001_20181001_01_RT/LC08_L1TP_107018_20181001_20181001_01_RT_B2.TIF",
"type": "image/tiff; application=geotiff",
"eo:bands": [1],
"title": "Band 2 (blue)"
},
"B3": {
"href": "https://landsat-pds.s3.amazonaws.com/c1/L8/107/018/LC08_L1TP_107018_20181001_20181001_01_RT/LC08_L1TP_107018_20181001_20181001_01_RT_B3.TIF",
"type": "image/tiff; application=geotiff",
"eo:bands": [2],
"title": "Band 3 (green)"
},
...
}
}
Planet example:
{
"stac_version": "0.8.0",
"stac_extensions": ["eo"],
"id": "20171110_121030_1013",
"type": "Feature",
...
"properties": {
...
"eo:bands": [
{
"full_width_half_max": 0.08,
"center_wavelength": 0.63,
"common_name": "red"
},
{
"full_width_half_max": 0.09,
"center_wavelength": 0.545,
"common_name": "green"
},
{
"full_width_half_max": 0.06,
"center_wavelength": 0.485,
"common_name": "blue"
},
{
"full_width_half_max": 0.08,
"center_wavelength": 0.82,
"common_name": "nir"
}
]
},
"assets": {
"analytic": {
"href": "https://api.planet.com/data/v1/assets/eyJpIjogIjIwMTcxMTEwXzEyMTAxMF8xMDEzIiwgImMiOiAiUFNTY2VuZTRCYW5kIiwgInQiOiAiYW5hbHl0aWMiLCAiY3QiOiAiaXRlbS10eXBlIn0",
"title": "PSScene4Band GeoTIFF (COG)",
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"eo:bands": [0,1,2,3]
}
}
}
A number of implementations listed on STAC Implementations page are making use of the core EO properties, including the SpaceNet, CBERS, sat-api and Planet implementations. This is not marked as more mature because the eo:bands portion is still being fleshed out.
The extensions page gives an overview about related extensions.