- Title: Electro-Optical
- Identifier: https://stac-extensions.github.io/eo/v1.1.0/schema.json
- Field Name Prefix: eo
- Scope: Item, Collection
- Extension Maturity Classification: Stable
- Owner: @matthewhanson
- History: Prior to March 30, 2021
This document explains the fields of the Electro-Optical (EO) Extension to the SpatioTemporal Asset Catalog (STAC) specification.
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).
It is strongly recommended to use Instrument Fields with the EO extension, to provide information about the platform (satellite, aerial, etc) used to capture the images.
For defining view geometry of data, it is strongly recommended to use the view extension.
- Examples:
- JSON Schema
- Changelog
| Field Name | Type | Description |
|---|---|---|
| eo:bands | [Band Object] | An array of available bands where each object is a Band Object. If given, requires at least one band. |
| eo:cloud_cover | number | Estimate of cloud cover, in % |
| eo:snow_cover | number | Estimate of snow and ice cover, in % |
The eo:bands array is used to describe the available spectral
bands in an Asset. This enables clients to read
the file and understand which band is 'red' and which is 'nir' (near infrared) so that it can perform an
NDVI operation, for example. Each Asset should specify
its own band object. If the individual bands are repeated in different assets they should all use the same values and
include the optional name field to enable clients to easily combine and summarize the bands.
The eo:bands array may optionally be used in the Item Properties to summarize the available bands in the assets. This should
be a 'union' of all the possible bands represented in assets. It should be considered merely informative - clients should rely
on the eo:bands of each asset. An Item is only allowed to use eo:bands in its Properties if it has at least one asset with
a defined bands array.
NOTE: In STAC versions 0.9.x and prior, eo:bands could only be used by an Asset putting the Band Object definitions in
an Item Properties and referencing these via array index. 1.0.0-beta.1 introduced the current behavior.
Estimate of cloud cover as a percentage (0-100) of the entire scene. If not available, the field should not be provided. Generally, this value should be used in Item Properties rather than Item Assets, as an Item from an electro-optical source is a single snapshot of the Earth, so the cloud cover value would apply to all assets.
Estimate of snow and ice covered surfaces as a percentage (0-100) of the entire scene. If not available, the field should not be provided. Generally, this value should be used in Item Properties rather than Item Assets, as an Item from an electro-optical source is a single snapshot of the Earth, so the snow cover value would apply to all assets.
| Field Name | Type | Description |
|---|---|---|
| name | string | The name of the band (e.g., "B01", "B8", "band2", "red"). |
| 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 0.29 syntax MAY be used for rich text representation. |
| 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). |
| solar_illumination | number | The solar illumination of the band, as measured at half the maximum transmission, in W/m2/micrometers. |
At least one of the fields must be specified.
This is typically the name the data provider uses for the band. It should be treated like an 'id', to identify that a particular band used in several assets represents the same band (all the other fields should be the same as well). It is also recommended that clients use this name for display, potentially in conjunction with the common name.
These fields are a common way to approximately describe a spectral band. In most cases even these numbers are not as useful as the
common_name that should be supplied with the spectral bands, where they exist. For non-standard bands (such as with hyperspectral sensors)
the wavelength fields indicate where the band is.
Another common way to define a spectral band with a minimum and maximum wavelength, where outside these bounds the transmission is 0%, and non-zero inside the bounds (e.g., 80%). The maximum transmission of a band is not captured in any of these metrics, nor is it important in most cases.
However, spectral transmission for a filter does not go from 0% to a constant max value (e.g., 80%) then back to 0%. Such a filter is referred to as a "top-hat" filter due to it's shape, but does not exist in reality. Thus, the minimum and maximum wavelengths are typically selected to be the point at which transmission drops below some threshold, and this threshold is often half of the maximum transmission. Thus if a filter's maximum transmission is 80%, the min and max thresholds would be the points where the transmission drops below 40%.
The center_wavelength of a band is the midpoint between the min and max wavelengths:
center_wavelength = (min_wavelength + max_wavelength) / 2The full_width_half_max (FWHM) is the difference between the min and max wavelengths,
thus representing the width of the band at half it's maximum transmission.
full_width_half_max = max_wavelength - min_wavelengthFor example, if we were given a band described as (0.4um - 0.5um) the center_wavelength would be 0.45um
and the full_width_half_max would be 0.1um.
In some cases the full transmission profile is needed, such as when harmonizing between two sensor modalities. It is recommended that the full spectral profile be included as a link or an asset (preferably at the Collection level).
In satellite-based remote sensing applications, the calibration of the sensor recorded top-of-atmosphere reflectance to radiance, or vice-versa, is carried out using a reference spectral solar irradiance value. It depends of the extra-terrestrial solar irradiance (e.g. [Thuillier et al., 2003]) at a specific spectral wavelength, of the illumination conditions during the calibration data acquisition (through platform navigation and attitude), of the instrument viewing geometry on the diffuser panel. The value in this field is the mean value representing the solar illumination in W/m2/micrometers at a specific level (e.g. Top of Atmosphere) for the asset. For instance, this value is used for optical calibration of an asset (e.g. ESUN(b) value in OTB optical calibration application)
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 allowed common names 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 | NAIP |
|---|---|---|---|---|---|---|
| coastal | 0.40 - 0.45 | 1 | 1 | |||
| blue | 0.45 - 0.50 | 1 | 2 | 2 | 3 | 3 |
| green | 0.50 - 0.60 | 2 | 3 | 3 | 4 | 2 |
| red | 0.60 - 0.70 | 3 | 4 | 4 | 1 | 1 |
| yellow | 0.58 - 0.62 | |||||
| pan | 0.50 - 0.70 | 8 (L7 only) | 8 | |||
| rededge | 0.70 - 0.79 | 5, 6, 7 | ||||
| nir | 0.75 - 1.00 | 4 | 8 | 2 | 4 | |
| 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.
One of the emerging best practices is to use Asset Roles to provide clients with more information about the assets in an item. The following list includes a shared vocabulary for some common EO assets. This list should not be considered definitive, and implementors are welcome to use other asset roles. If consensus and tooling consolidates around these role names then they will be specified in the future as more standard than just 'best practices'.
| Role Name | Description |
|---|---|
| reflectance | An asset the provides reflectance values, instead of just radiance. |
| temperature | An asset that provides actual temperature measurements. |
| saturation | Points to a file that indicates where pixels in the input spectral bands are saturated. |
| cloud | Points to a file that indicates whether a pixel is assessed as being cloud |
| cloud-shadow | Points to a file that indicates whether a pixel is assessed as being cloud shadow. |
All contributions are subject to the STAC Specification Code of Conduct. For contributions, please follow the STAC specification contributing guide Instructions for running tests are copied here for convenience.
The same checks that run as checks on PR's are part of the repository and can be run locally to verify that changes are valid.
To run tests locally, you'll need npm, which is a standard part of any node.js installation.
First you'll need to install everything with npm once. Just navigate to the root of this repository and on your command line run:
npm installThen to check markdown formatting and test the examples against the JSON schema, you can run:
npm testThis will spit out the same texts that you see online, and you can then go and fix your markdown or examples.
If the tests reveal formatting problems with the examples, you can fix them with:
npm run format-examples