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InSAR Extension Specification

This document explains the InSAR Extension to the SpatioTemporal Asset Catalog (STAC) specification.

Interferometric synthetic aperture radar, abbreviated InSAR (or deprecated IfSAR), is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation, using differences in the phase of the waves returning to the satellite or aircraft. The technique can potentially measure millimetre-scale changes in deformation over spans of days to years. It has applications for geophysical monitoring of natural hazards, for example earthquakes, volcanoes and landslides, and in structural engineering, in particular monitoring of subsidence and structural stability.

The extension is primarly intented to describe products of InSAR processing, typically interferograms and related products.

Item Properties

Field Name Type Description
insar:perpendicular_baseline number The distance between two acquisition spots perpendicular to the satellite viewing direction
insar:temporal_baseline number The time period between the reference and secondary acquisitions
insar:height_of_ambiguity number This height of ambiguity is the 2 π interferometric phase cycle scaled with the perpendicular baseline between both satellites. The smaller the height of ambiguity is, the lower is the influence of errors caused by the instrument or the different decorrelation effects.
insar:reference_datetime string Date of reference acquisition, in UTC. It is formatted according to RFC 3339, section 5.6.
insar:secondary_datetime string Date of secondary acquisition, in UTC. It is formatted according to RFC 3339, section 5.6.
insar:processing_dem string String representing the Digital Elevation Model used for processing the input data. A list is proposed in the DEMs section
insar:geocoding_dem string String representing the Digital Elevation Model used for geocoding the product. A list is proposed in the DEMs section

Best Practices

Core and other extensions fields

It is higly recommended to use the following fields to describe the InSAR product:

Field name InSAR usage
date_time Center Time of the product, in UTC. (Here the date is not significant)
sar:instrument_mode REQUIRED. The name of the sensor acquisition mode that is used
sar:polarizations Any combination of polarizations of the input products.
sar:looks_range Number of range looks, which is the number of groups of signal samples (looks) perpendicular to the flight path
sar:looks_azimuth Number of azimuth looks, which is the number of groups of signal samples (looks) parallel to the flight path.
sar:observation_direction Antenna pointing direction relative to the flight trajectory of the satellite, either left or right.
sar:pixel_spacing_range The range pixel spacing, which is the distance between adjacent pixels perpendicular to the flight path, in meters (m).
sar:pixel_spacing_azimuth The azimuth pixel spacing, which is the distance between adjacent pixels parallel to the flight path, in meters (m)
sar:resolution_range The range resolution, which is the maximum ability to distinguish two adjacent targets perpendicular to the flight path, in meters (m).
sar:resolution_azimuth The azimuth resolution, which is the maximum ability to distinguish two adjacent targets parallel to the flight path, in meters (m).
processing:level L3 level is recommended since InSAR is a composite product.
processing:lineage Describe InSAR specific technique. For instance, Geocoded Unwrapped Interferogram TOPSAR
processing:software Software used for InSAR processing. For instance {"ESA SNAP Toolbox": "8.0"}, {"SNAPHU": "1.4.2"}
proj:epsg EPSG code of the projection of the product
sat:orbit_state ascending or descending
sat:relative_orbit relative orbit (track) of the input datasets
sci:publications DOI of publications citing the data
view:azimuth The azimuth angle of the center of the product.
view:incidence_angle The incidence angle of the center of the product.

Assets roles

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 InSAR 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
coherence 2D Coherence [0-1] from filtered interferogram
phase 2D Filtered wrapped interferogram geocoded in radians
unwrapped_phase 2D Filtered unwrapped interferogram geocoded in radians
los_displacement 2D Displacement in the satellite line of sight (LOS)
amplitude 2D Amplitude of interferogram in Watt

Combined with "standard" asset roles data, overview, visual and metadata, specific related assets can be included.

Digital Elevation Models (DEMs)

The DEM are named to commonly used datasets. The table below shows the common DEM dataset name based. This list should not be considered definitive, and implementors are welcome to use other DEM names.

DEM Name Description Spatial Resolution
SRTM1 Shuttle Radar Topography Mission 1 arcsecond (~30m)
SRTM3 Shuttle Radar Topography Mission 3 arcseconds (~90m)
SRTM30 Shuttle Radar Topography Mission 30 arcseconds (~1km)
COP-DEM_EEA-10 Copernicus DEM - European states (EEA39) including all islands of those countries plus French Overseas 10m
COP-DEM_GLO30 Copernicus DEM - Global Coverage 30m
COP-DEM_GLO90 Copernicus DEM - Global Coverage 90m
GTOPO30 USGS Global Terrain Elevation Data (30m) 30m

Relation types

The following types should be used as applicable rel types in the Link Object.

Type Description
reference This link points to the reference input product STAC Item
secondary This link points to the secondary input product STAC Item

Links roles

It is possible to use Links Roles to provide clients with more information about the linked item in an item or a collection. The following list includes a shared vocabulary for InSAR 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
event Item is related to an event (e.g. earthquake, volcano eruption)
coesismic Item is related to a coesismic event or data results (e.g. interferogram)
post Item is related to a post event or data results (e.g. interferogram)
pre Item is related to a pre event or data results (e.g. interferogram)

Contributing

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.

Running tests

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 install

Then to check markdown formatting and test the examples against the JSON schema, you can run:

npm test

This 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