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Standard Displacement Product

The ARIA Standard Displacement Product is a Geocoded Unwrapped Interferogram (GUNW IFG) product.

Shall target:

  • Earthquake community,
  • Volcano community,
  • Ground water community,
  • Sea-level rise and subsidence community

Shall be defined:

  • Spatial and temporal consistent, i.e. no gaps in space and time between products over a defined area of interest in ARIA
  • Processed with precise orbits for Sentinel-1
  • Geographical scope of 60°N-60°S latitude + USA
  • GIS-compatible

The product is packaged as a Netcdf4 file guided by file structure as is planned for the NISAR mission. The top-level group of the product is called “science”, which has a “grids” group containing the geo-coded datasets and a “radarMetaData” group containing specific information related to the SAR data. Within the “grids” group a distinction is made between a “data”, “imagingGeometry”, and “corrections” sub-group. The “data” group contains 2D datasets at 3’’ (~90 m) posting such as the “unwrappedPhase”, the “imagingGeometry” group contains 3D datasets posted laterally at 0.1° (~11km) such as the “incidenceAngle”, while the “corrections” group contains placeholders for potential future layers, such as for ionospheric, tropospheric, and solid earth tide corrections and where the posting is likely to vary depending on the correction. All 2D and 3D datasets are with respect to WGS84 (EPSG 4326). Detailed information on the projection information e.g. wkt is specified under the “crs*” datasets provided under the “data” and “imagingGeometry” groups. At the top-level of the product we also define a “productBoundingBox” as a GDAL compatible wkt polygon. Global attributes provide further information on the product version and citation references.

A description of the different datasets and their sampling is provided in the below, while a file structure for one of the sample products is shown in the figure at the end of this section.

"data" group

Dataset name

Description

Posting

Units

unwrappedPhase

2D Filtered unwrapped IFG geocoded

Lateral = 3’’ (~90 m)

rad

coherence

2D Coherence [0-1] from filtered IFG

unitless

connectedComponents

2D Connected component file

unitless

amplitude

2D Amplitude of IFG

watt

latitude

1D latitude sampling (center pixel)

degree

longitude

1D longitude sampling (center pixel)

degree

 

"imagingGeometry" group

Dataset name

Description

Posting

Units

incidenceAngle

3D Incidence angle grid

Lateral = 0.1° (~11km)

Vertical = -1.5, 0, 3, 9km

degree

azimuthAngle

3D azimuth angle grid

degree

lookAngle

3D look angle grid

degree

parallelBaseline

3D parallel baseline grid

meter

perpendicularBaseline

3D Perpendicular baseline grid

meter

latitudeMeta

1D latitude sampling (center pixel)

Lateral = 0.1° (~11km)

degree

longitudeMeta

1D longitude sampling (center pixel)

Lateral = 0.1° (~11km)

degree

heightMeta

1D height sampling

Vertical = -1.5, 0, 3, 9km

meter

 

"correction" group

Dataset name

Description

Posting

Units

solidEarthTide*

2D/3D solid earth tide

TBD

rad

troposphereHydrostatic*

3D Tropospheric hydrostatic delay

troposphereWet*

3D Tropospheric wet delay

ionosphere*

2D Split spectrum ionospheric delay

*Included as placeholder for potential future layers

 

"radarMetaData" group

Dataset name

Description

Units

missionID

SAR mission

N/A

productType

ARIA product type

N/A

wavelength

SAR wavelength

meter

centerFrequency

Center frequency

hertz

L1InputGranules

Reference and Secondary L1 input granules used to make product

N/A

DEM

DEM used in the processing

N/A

slantRangeStart

Slant starting range

meter

slantRangeEnd

Slant ending range

meter

slantRangeSpacing

Slant range spacing

meter

azimuthZeroDopplerStartTime

Azimuth zero Doppler start time of IFG product for the reference date

time ISO 8601

azimuthZeroDopplerEndTime

Azimuth zero Doppler end time of IFG product for the reference date

time ISO 8601

azimuthTimeInterval

Azimuth time interval

seconds

ESDthreshold

ESD coherence threshold applied in the processing, -1 refers to no ESD being applied

unitless

OrbitType

Type of orbit, which is “precise” for the UNW IFG GEO product

N/A

ISCEversion

SVN/GIT version of the ISCE software

N/A

unwrapMethod

Unwrapping method used for generating the unwrapped product

N/A

Figure 1

File structure overview of a GUNW product

 

The L2 GUNW product is generated by ARIA using the ISCE TopsApp processor. The below table provides and overview of the processing parameters.

Parameter*

Value

Additional information

Pairing Direction

Treference > Tsecondary

Reference is acquired later in time than secondary. Product sign convention: land uplift corresponds to a range decrease (negative radians).

Temporal Baseline

N/A

As large as to meet minimal pairing in time

Perpendicular Baseline

N/A

Not considered

Temporal Minimal Match

2

Ensure acquisition date is used at least two times as a reference for different IFG pairings

Orbit type

Precise orbits

Degraded orbit quality is not allowed

Azimuth Looks

7

Corresponds to an azimuth posting of 14.5 m*7 = ~101 m

Range Looks

19

Corresponds to a slant range posting of 5 m*19 = ~95 m

Processing DEM

SRTM and NED

Use of 30m SRTM for world and 30m NED for USA

Geocoding DEM

SRTM and NED

Use of 90m SRTM for world and 90m NED for USA

Enhanced Spectral Diversity Threshold

0.8-0.5

Default is 0.8. If coherence is too low and ESD fails, threshold is relaxed in steps of 0.05 until 0.5 is reached, after which processing is done using orbit information only.

Overview of the processing parameters. *Other processing parameters correspond to ISCE topsApp defaults.

Spatial and temporal connectivity

The spatial extend of an individual GUNW product is that of a Sentinel-1 frame. During the interferogram formation one of the two acquisition dates (either the “reference” or “secondary”) will consist out of a single ESA sentinel-1 product, which is referred to as “spatial reference”, while the other acquisition date will use as many ESA sentinel-1 products it needs to cover the “spatial reference” over the ARIA AOI completely.

We explicitly avoid SLC stitching of ESA Sentinel-1 products originating from a different Instrument Processing Facility (IPF). The acquisition date with multiple IPF versions is to be used as “spatial reference”. Note that the derived GUNW products can still be stitched along-track and thus no impact is expected for the spatial connectivity. In case both acquisition dates have multiple IPF versions, the interferogram pairing combination is skipped, and a next available interferogram combination is attempted. This procedure is repeated until the temporal minimal match criteria is met.

Figure 2

Example of interferogram pairing of a “Reference” with a “Secondary” acquisition with a minimal match criterion set to 2. Following the spatial coverage and IPF pairing rules only the acquisitions made on 20150408 and 20150327 are considered valid for “Secondary”. As the IPF is changing for the “Secondary” acquisition on 20150408, while that of the “Reference” is consistent, the frame definition of the “Secondary” will be used as “spatial reference” for the 20150502-20150408 interferogram, leading to 4 standard products for this pairing. As the IPF is consistent for both the “Reference” and “Secondary” acquisition made on 20150327, the frame definition of the “Reference” will be used as “spatial reference” for the 20150502-20150327 interferogram, leading to 3 standard products for this pairing.

 

Sensor-DatasetName-A/D-L/R-tracknumber-mode-YYYYMMDD_YYYYMMDD-HHMMSS-XXYYYN/S_XXYYYN/S-PP/RP/PR/RR-systemTag-versionTag.nc

Example:
S1-GUNW-A-R-035-tops-20170206_20170107-020845-42995N_41129N-PP-a63b-v2_0_0.nc

Parameter

Description

Sensor

Satellite name (string):
e.g. S1, CSK, ALOS2, ALOS

DatasetName

Dataset name of the product (string):
e.g. GUNW, GUNW_COSESIMIC

A/D

Satellite orientation (char):
A for Ascending, D for descending

L/R

Satellite look direction (char):
L for left looking, R for right looking

tracknumber

Satellite track (3-digit number):
e.g. 078

mode

Acquisition mode (string):
e.g. tops, stripmap, spotlight, scansar

YYYYMMDD-YYYYMMDD

Reference and secondary acquisition date (YYYYMMDD):
e.g. 20161201_20170101

HHMMSS

Center time of product in UTC (HHMMSS):
e.g. 063021

XXYYYN/S-XXYYYN/S

Decimal latitude of western edge of the south and north most IFG corner (5-digit number with 3 significant digits):
e.g. 01000S_01000N

PP/RP/PR/RR

Precise (P) or restituted (R) orbit precision for respectively reference and secondary acquisition.

systemTag

data system product tag (unique hash for product)

versionTag

standard product version tag

The product version tag captures if changes have been made to the standard product processing workflow. Changes are summarized below. Note that the product version tag is different from the global attribute “version” variable in the NETCDF file which captures changes in the standard product data structure.

Product Version Tag

Description

2.0.0

Initial release of standard product

2.0.1

Update to use NED over US for processing and geocoding

 

Unwrapping Errors

 

Unwrapping is not trivial. GUNW products are provided as is, with no warranties that the products are correctly unwrapped. It is the user responsibility to apply masking and correct for unwrapping errors that might be present.
Both the “coherence” and “connectedComponent” layers included within the GUNW products act as quality markers for the unwrapping. The “connectedComponent” layer is an output from the unwrapping method which provides more information on the confidence of the unwrapping. Most often unwrapping errors observed within the products occur in regions with low coherence, i.e. connected component 0, or between disconnected regions, i.e. different connected components.
Best practice is to mask out water bodies as well as connected component zero. In addition, it is recommended to inspect if there are multiple connected components left and correct the unwrapped phase where needed.