ARIA Sentinel-1 GUNW Product Guide¶

This document is a guide for users of ARIA Sentinel-1 Geocoded Unwrapped (GUNW) Interferograms.

The ARIA Sentinel-1 Geocoded Unwrapped Interferogram (ARIA-S1-GUNW) product is a standardized interferometric SAR (InSAR) dataset that enables rapid analysis of surface deformation using Sentinel-1 SAR data. Produced by JPL’s ARIA project and hosted at the Alaska Satellite Facility (ASF) DAAC, it provides CF-compliant NetCDF files at 90-m pixel spacing, containing unwrapped interferometric phase measurements, imaging geometry, various correction layers, and metadata. Products are available for VV polarization only.

With over 1.1 million (and growing!) freely available products covering major fault systems, volcanic regions, and coastal zones, ARIA-S1-GUNW products facilitate scientific research and disaster response by simplifying access to centimeter-scale ground displacement measurements. Generated through an open-source, cloud-based ISCE2 TopsApp processing pipeline, these products support applications such as earthquake impact assessment, volcanic monitoring, and long-term land motion studies, with ongoing improvements enhancing their accuracy and usability.

The ARIA project also maintains the ARIA-tools software package, which is a suite of open-source tools that allows users to automate the seamless download, post-processing manipulation, aggregation, and management of ARIA-S1-GUNW products. Refer to the ARIA-tools GitHub page for a more thorough overview and installation instructions, and tutorials led by EarthScope Consortium, which demonstrate practical applications.

ARIA-S1-GUNW products are not produced globally

ARIA-S1-GUNW products are routinely produced only for specific locations, so the ASF archive may not contain products in your area of interest. See the Ordering On Demand Products section for information on ordering ARIA-S1-GUNW products for specific Sentinel-1 acquisitions.

Archived and On-Demand Products¶

While there is a large archive of ARIA-S1-GUNW products that have already been generated and are ready for download, they may not cover your area of interest. In addition, the archived products may not include the full range of temporal baseline pairings required for your analysis. If you are interested in ARIA-S1-GUNW products that are not already represented in the archive, ASF provides the ability to generate these products using specific Sentinel-1 SLC pairings.

On Demand ARIA-S1-GUNW products are generated using the same code used by the ARIA project, and have been validated to ensure that products generated On Demand and those generated by the ARIA team at JPL are fully interoperable.

Accessing Existing Products¶

You can download existing ARIA-S1-GUNW products from the Alaska Satellite Facility’s (ASF) Vertex search portal by following these steps:

Access Vertex – Go to the ASF Vertex website: https://search.asf.alaska.edu.
Search for ARIA-S1-GUNW Products – In the dataset selector, click on “ARIA S1 GUNW” to filter for these specific products. You can refine results by specifying a geographic region, date range, or other criteria using the search filters in the “filters” panel.
Preview and Select Products – Click on individual results to view metadata, including coverage area and acquisition details.
Download Data – To download, first add ARIA-S1-GUNW products to your Download Queue using the shopping cart icon next to each product, then download your selected products using the options available in the Download Queue interface.

Ordering On-Demand Products¶

If the ARIA-S1-GUNW products you need are not available in the archive, you can use ASF's On Demand platform to submit custom ARIA-S1-GUNW jobs for processing. Once processing is complete, you can access them as you would any other On-Demand products from ASF. The download links provided will be active for 14 days.

Sentinel-1C acquisitions not yet supported

ISCE2 software, which is used for processing ARIA-S1-GUNW products, does not currently support processing SLCs acquired by the newly launched Sentinel-1C platform. Until the software package is updated, users will not be able to submit ARIA-S1-GUNW jobs that include Sentinel-1C acquisitions for On-Demand processing.

ARIA Frame IDs¶

Sentinel-1 IW SLC products are not created in a way that ensures that granules for the same relative orbit and location always fully overlap over time. This results in inconsistent framing of the Sentinel-1 IW SLCs that can make it difficult to create longer series of Sentinel-1 InSAR products.

In the image below, Sentinel-1 footprints acquired over an area of interest are displayed. Over the full period of record of the mission, the SLC framing has shifted considerably, resulting in some acquisitions that hardly overlap at all.

Shifting of Sentinel-1 SLC frames over time

To address this issue, the ARIA team defined a standard set of geographic footprints, called frames, that set the geographic extent for each ARIA-S1-GUNW product. This is possible because while the Sentinel-1 IW SLC products are not consistently framed along the orbit path, the smaller burst SLCs that comprise each Sentinel-1 IW SLC product do have consistent footprints.

Each ARIA frame is defined by the extent of a specific collection of these individual burst SLCs. Each ARIA-S1-GUNW product is processed to the extent of one of these frames, which results in output products with consistent footprints through time. ARIA-S1-GUNW products containing the same bursts, and thus sharing the same geographic footprint, are said to have the same ARIA Frame ID.

To ensure that ARIA-S1-GUNW products are always created using standard footprints, the ARIA Frame ID needs to be provided along with the reference and secondary granules that cover this footprint for a given date in order to create a new ARIA-S1-GUNW product (see figure below).

Frame vs granule geographic footprint

ARIA Frame ID Maps¶

The ARIA project provides geojson files indicating the extent of each ARIA Frame ID. These files can be downloaded and used for reference. You may find it helpful to extract the polygon for a specific frame from the geojson and use the Import AOI functionality in Vertex to search for Sentinel-1 acquisitions over that frame.

There are different ARIA Frame ID maps for the ascending and descending orbit directions. Make sure that you are using the appropriate geojson file.

Search for Sentinel-1 SLC Acquisition Dates for an ARIA Frame ID¶

The ARIA processing code takes a list of reference and secondary Sentinel-1 IW SLC granules as input, but it can be tricky to find all of the necessary granules for a given ARIA Frame ID. To ensure that there is full coverage over the desired ARIA Frame, users will just pass the ARIA Frame ID and the dates of the desired primary and secondary passes over that frame into the On-Demand job specification rather than assembling lists of primary and secondary SLCs.

To find suitable primary and secondary acquisition dates to use for a specific ARIA Frame ID, use a Geographic Search for Sentinel-1 SLC IW products in Vertex, setting the Area of Interest to the desired ARIA Frame ID, as delineated in the ARIA Frame ID maps.

Applying appropriate filters to the Geographic Search will help ensure that you find results that match the desired ARIA Frame ID:

Area of Interest: use the extent of the desired ARIA Frame from the reference geojson, or drop a point in the middle of the ARIA Frame location
Start Date / End Date: restrict the date range as desired
File type: L1 Single Look Complex (SLC)
Beam Mode: IW
Polarization: select both VV+VH and VV (HH ARIA S1 GUNW products are not supported)
- Note that only the VV polarization will be processed, but this will include VV SLCs acquired in both dual-pol and single-pol modes in the search results
Direction: match the orbit direction of the ARIA Frame ID reference geojson used to select the desired ARIA Frame (or reference the dir attribute from the ARIA Frame ID geojson file)
Subtype: select both SA and SB (ARIA S1 GUNW products from Sentinel-1C acquisitions are not currently supported)
Path Start / Path End: path of the desired ARIA Frame (path attribute from the ARIA Frame ID geojson file)

Select an acquisition that intersects the ARIA Frame ID for a date you want to include in your InSAR pair, then use the Baseline or SBAS tool to find an appropriate date to pair with it.

Common area covered by the selected reference and secondary scenes must cover at least 90% of the ARIA Frame. If the SLCs available for the submitted dates do not meet this coverage constraint, the job will fail to process.

Submit On-Demand ARIA-S1-GUNW Jobs¶

On Demand support not currently available in Vertex for ARIA-S1-GUNW products

On-demand ARIA S1 GUNW products cannot currently be submitted directly from Vertex, but we plan to make this feature available in the second half of 2025.

Vertex is still very useful for selecting Sentinel-1 SLC acquisition dates to submit for processing, but once you identify reference and secondary dates for the desired ARIA Frame ID, you will need to submit the job for processing using the HyP3 Python SDK or HyP3 API.

On-Demand ARIA-S1-GUNW jobs can be submitted using the ARIA_S1_GUNW job type via the HyP3 API, or via the HyP3 Python SDK using the submit_aria_s1_gunw_job method of the HyP3 class.

Unlike ASF's other On-Demand InSAR workflows, customizable processing options (multilooking, filter strength, etc.) are not available for ARIA-S1-GUNW jobs.

To submit an ARIA_S1_GUNW job, all you need is:

the ARIA Frame ID number
the reference date, which is the more recent pass over the ARIA Frame
the secondary date, which is the earlier pass over the ARIA Frame

The dates must be in YYYY-MM-DD format.

Reference and Secondary Dates¶

ARIA S1 GUNW products use the SLCs from the more recent pass as reference, while secondary scenes are from the earlier pass in the date pair. When submitting a job using the HyP3 API or SDK, the date passed as the reference date must be more recent than the secondary date. If they are in the opposite order, an error will be raised.

Note that this order is opposite of the other On-Demand InSAR products available from ASF. Both the InSAR GAMMA products and the Burst InSAR products use the earlier acquisition as reference, and the more recent acquisition as secondary. This means that the ARIA unwrapped interferograms have the opposite sign from the unwrapped interferograms generated by the other ASF On-Demand InSAR workflows. In the ARIA S1 GUNW products, negative phase differences indicate movement away from the sensor and positive phase differences indicate movement towards the sensor.

Product Packaging¶

Naming convention¶

The ARIA-S1-GUNW product names contain detailed information about their acquisition and processing, as illustrated in the figure below.

GUNW naming convention includes:

Satellite orientation. A for ascending or D for descending
Satellite look direction. L for left-looking or R for right-looking
Satellite track number (3-digit number)
Reference and secondary acquisition dates (YYYYMMDD)
Center time of reference scene(s) in UTC (HHMMSS)
Longitude and latitude in whole degrees
Unique product hash
Standard product version

GUNW naming scheme

Product Elements¶

The product is packaged as a NetCDF4 file, with its top-level group named science. Within the science group, there is a grids group, which is further divided into three subgroups: data, imagingGeometry, and corrections.

The data group contains 2D datasets at a resolution of 3 arc-seconds (~90 m).
The imagingGeometry group includes 3D datasets posted laterally at 0.1-degree intervals (~11 km).
The corrections group provides ionospheric and solid Earth corrections, and if a weather model is available, the corresponding tropospheric correction layer (HRRR/reference/troposphereWet) will be included here.

All 2D and 3D datasets are in the EPSG:4326 projection.

The output netCDF file will include the layers listed in the table below.

Group	Dataset Name	Description	Units
data	amplitude	2D Amplitude of IFG	watt
	coherence	2D Coherence [0-1] from filtered IFG	unitless
	connectedComponents	2D Connected component file	unitless
	unfilteredCoherence	2D Coherence [0-1] from unfiltered IFG	unitless
	unwrappedPhase	2D Filtered unwrapped IFG geocoded	rad
corrections	ionosphere	2D Split spectrum ionospheric delay	rad
	ionosphereBurstRamps	Digital elevation model	rad
	reference/solidEarthTide	2D/3D solid earth tide for reference granule	rad
	secondary/solidEarthTide	2D/3D solid earth tide for secondary granule	rad
	HRRR/reference/troposphereWet	2D/3D wet troposphere for reference granule	rad
	HRRR/secondary/troposphereWet	2D/3D wet troposphere for secondary granule	rad
	HRRR/reference/troposphereHydrostatic	2D/3D hydrostatic troposphere for reference granule	rad
	HRRR/secondary/troposphereHydrostatic	2D/3D hydrostatic troposphere for secondary granule	rad
imagingGeometry	azimuthAngle	3D azimuth angle grid	degree
	incidenceAngle	3D Incidence angle grid	degree
	lookAngle	3D look angle grid	degree
	parallelBaseline	3D parallel baseline grid	meter
	perpendicularBaseline	3D perpendicular baseline grid	meter

Ionospheric Correction Layer¶

Although the ionospheric effects for C-band SAR are only about one-sixteenth of those at L-band, the measurement accuracy of Sentinel-1 C-band SAR data can still be degraded by long-wavelength ionospheric signals. Utilizing the range-split spectrum methodology available within ISCE2, ARIA-S1-GUNW products include an ionospheric correction layer packaged as a differential field between the secondary and reference input data, which can be directly subtracted from the unwrappedPhase field.

Solid Earth Tides Correction Layers¶

Solid Earth tides (SET) are periodic deformations of the Earth's crust caused by gravitational forces from the Moon and Sun, resulting in surface displacements of up to several centimeters. Correcting for SET in InSAR is crucial to prevent these predictable, cyclic motions from being misinterpreted as real ground deformation. ARIA-S1-GUNW products include an SET correction layer for both the reference and secondary input data that are created using the PySolid python package.

Tropospheric Delay Correction Layers¶

Tropospheric delay correction is essential for many InSAR applications because atmospheric variations in temperature, pressure, and humidity can distort phase measurements, mimicking ground deformation and reducing accuracy. ARIA-S1-GUNW products for both the continental U.S. and Alaska also contain a tropospheric delay correction layer that is produced via the Raytracing Atmospheric Delay Estimation for RADAR (RAiDER) Python package.

RAiDER uses the NOAA High-Resolution Rapid Refresh weather model to calculate the tropospheric delay correction at a spatial resolution of approximately 3 km. If the HRRR weather model is not available for a location of interest, (i.e. outside of the continental U.S. and Alaska) the tropospheric delay correction layer will not be included in the ARIA-S1-GUNW product. The wet and hydrostatic tropospheric delay correction are provided for both the reference and secondary input data.

Data Access¶

Refer to the Downloads page for more information on viewing and downloading ARIA S1 GUNW On Demand products in Vertex or programmatically. Once processing is complete, download links for On Demand products are valid for 14 days.

References¶

Bekaert, David, et al. "The ARIA-S1-GUNW: The ARIA Sentinel-1 Geocoded Unwrapped Phase Product for Open InSAR Science and Disaster Response." IGARSS 2023-2023 IEEE International Geoscience and Remote Sensing Symposium. IEEE (2023).

Buzzanga, Brett, et al. "Toward sustained monitoring of subsidence at the coast using InSAR and GPS: An application in Hampton Roads, Virginia." Geophysical Research Letters 47.18 (2020): e2020GL090013.

Liang, Cunren, et al. "Ionospheric correction of InSAR time series analysis of C-band Sentinel-1 TOPS data." IEEE Transactions on Geoscience and Remote Sensing 57.9 (2019): 6755-6773.

Yunjun, Zhang, et al. "Range geolocation accuracy of C-/L-band SAR and its implications for operational stack coregistration." IEEE Transactions on Geoscience and Remote Sensing 60 (2022): 1-19.