MultiRTC

A python library for creating ISCE3-based RTCs for multiple SAR data sources

Warning

This package is still in early development. Users are encouraged to not use this package in production or other critical contexts until the v1.0.0 release.

Important

All credit for this library's RTC algorithm goes to Gustavo Shiroma and the JPL OPERA and ISCE3 teams. This package merely allows others to use their algorithm with a wider set of SAR data sources. The RTC algorithm utilized by this package is described in Shiroma et al., 2023.

Dataset Support

MultiRTC allows users to create RTC products from SLC data for multiple SAR sensor platforms, and provides utilities for assessing the resulting products. All utilities can be accessed via CLI pattern multirtc SUBCOMMAND ARGS, with the primary subcommand multirtc rtc.

Below is a list of relevant SAR data sources and their support status:

Mission	File Format	Image Mode	Image Grid Type	Status
Sentinel-1	SAFE	Burst IW	Range Doppler	Supported
Sentinel-1	SAFE	Full-frame IW	Range Doppler	Unsupported
Sentinel-1	SAFE	Burst EW	Range Doppler	Unsupported
Sentinel-1	SAFE	Full-frame EW	Range Doppler	Unsupported
Capella	SICD	Spotlight	Polar	Supported*
Capella	SICD	Sliding Spotlight	Range Doppler	Supported
Capella	SICD	Stripmap	Range Doppler	Supported
Iceye	SICD	Dwell	Range Doppler	Supported
Iceye	SICD	Spotlight	Range Doppler	Supported
Iceye	SICD	Sliding Spotlight	Range Doppler	Supported
Iceye	SICD	Stripmap	Range Doppler	Supported
Iceye	SICD	Scan	Range Doppler	Supported
Umbra	SICD	Dwell	Polar	Supported*
Umbra	SICD	Spotlight	Polar	Supported*

I have done my best to accurately reflect the support status of each SAR image type, but please let me know if I have made any mistakes. Note that some commercial datasets used to use polar instead of range doppler image grids for specific images modes. This table is based on the image grid types currently being used.

*Polar image grid support is implemented via the approach detailed by Piyush Agram in his recent technical note. I have implemented his method in a fork of the main ISCE3 repo, which you can view here. The long-term plan is to merge this into the main ISCE3 repo but until that is complete, polar grid support is only available via this project's pfa-suffixed docker containers. See the running via docker section for more details.

Usage

To create an RTC, use the multirtc CLI entrypoint using the following pattern:

multirtc rtc PLATFORM SLC-GRANULE --resolution RESOLUTION --work-dir WORK-DIR

Where PLATFORM is the name of the satellite platform (currently S1, CAPELLA, ICEYE or UMBRA), SLC-GRANULE is the name of the SLC granule, RESOLUTION is the desired output resolution of the RTC image in meters, and WORK-DIR is the name of the working directory to perform processing in. Inputs such as the SLC data, DEM, and external orbit information are stored in WORK-DIR/input, while the RTC image and associated outputs are stored in WORK-DIR/output once processing is complete. SLC data that is available in the Alaska Satellite Facility's data archive (such as Sentinel-1 Burst SLCs) will be automatically downloaded to the input directory, but data not available in this archive (commercial datasets) are required to be staged in the input directory prior to processing.

Output RTC pixel values represent gamma0 power.

To create an image that is geocoded but not radiometricly corrected, use the geocoded flag instead:

multirtc geocode PLATFORM SLC-GRANULE --resolution RESOLUTION --work-dir WORK-DIR

Output geocoded pixel values represent sigma0 power.

Running via Docker

In addition to the main python interface, I've also provided an experimental docker container that contains full support for polar grid format SICD data. Encapsulating this functionality in a docker container is ncessary for now because it requires re-compiling a development version of ISCE3. The docker container can be run using a similar interface, with exception of needing to pass your EarthData credentials and the need to pass a mounted volume with an input and output directory inside:

docker run -it --rm \
    -e EARTHDATA_USERNAME=YOUR_USERNAME_HERE \
    -e EARTHDATA_PASSWORD=YOUR_PASSWORD_HERE \
    -v ~/LOCAL_PATH/PROJECT:/home/conda/PROJECT \
    ghcr.io/forrestfwilliams/multirtc:VERSION.pfa \
    rtc PLATFORM SLC-GRANULE --resolution RESOLUTION --work-dir PROJECT

The local project1 directory can be a name of your choosing and should have the structure:

PROJECT/
    |--input/
        |--input.slc (if needed)
    |--output/

If you're encountering permission denied errors when running the container, make sure that the input and output folders are owned by the same group and user IDs that the container uses (chown -R 1000:1000 ~/LOCAL_PATH/PROJECT).

Output Layers

MultiRTC outputs one main RTC image and seven metadata images as GeoTIFFs. All layers follow the naming schema {FILEID}_{DATASET}.tif, with the main RTC image omiting the _{DATASET} component. The layers are as follows:

• FILEID.tif: The radiometric and terrain corrected backscatter data in gamma0 radiometry.
• FILEID_incidence_angle.tif: The angle between the LOS vector and the ellipsoid normal at the target.
• FILEID_interpolated_dem.tif: The DEM used of calculating layover/shadow.
• FILEID_local_incidence_angle.tif: The angle between the LOS vector and terrain normal vector at the target.
• FILEID_mask.tif: The layover/shadow mask. 0 is no shadow or shadow, 1 is shadow, 2 is layover and 3 is layover and shadow.
• FILEID_number_of_looks.tif: The number of radar samples used to compute each output image pixel.
• FILEID_rtc_anf_gamma0_to_beta0.tif: The conversion values needed to normalize the gamma0 backscatter to beta0.
• FILEID_rtc_anf_gamma0_to_sigma0.tif: The conversion values needed to normalize the gamma0 backscatter to sigma0.

More information on the metadata images can be found in the OPERA RTC Static Product guide on the OPERA RTC Product website.

All metadata images other than FILEID_mask.tif, and FILEID_number_of_looks.tif are omitted for geocode-only products.

DEM options

Currently, only the NISAR DEM can be automatically downloaded and it is the default DEM option. This is a global height above the WGS84 ellipsoid DEM sourced from the COP-30 DEM.

MultiRTC also supports custom DEMs via the use of the --dem option. For example:

multirtc rtc PLATFORM SLC-GRANULE --dem DEM-PATH --resolution RESOLUTION --work-dir WORK-DIR

We recommend using OpenTopography to locate high-resolution DEMs for your area of interest. Note that custom DEM must meet three criteria to be used for processing:

1. The DEM must fully cover the spatial extent of your input SLC granule.
2. The DEM must be in the EPSG:4326 (lat/lon) spatial projection.
3. The height values of the DEM must represent the height above the WGS84 ellipsoid.

The prepdem subroutine can be used to reformat an existing DEM to meet the final two requirements:

multirtc prepdem INPUT-DEM-PATH OUTPUT-DEM-PATH VERTICAL-DATUM

Where VERTICAL-DATUM is the vertical datum of your input DEM. Currently the WGS84, EGM2008, and NAD88 (over the United States) datums are supported.

If the low resolution of the available DEM options is causing radiometry issues, try using the geocode workflow instead of rtc.

Calibration & Validation Subcommands

Warning

This submodule currently only support Umbra SICD data! Reach out if you would like to see this submodule expanded to other datasets.

MultiRTC includes three calibration and validation (cal/val) subcommands for assessing the geometric and radiometric quality of SAR products. These tools are useful for analyzing geolocation, co-registration, and impulse response performance.

ale Absolute Location Error

Quantifies the geolocation accuracy of a SAR image by comparing known corner reflectors at the Rosamond, California site with their positions in the geocoded image.

Usage:

multirtc ale FILEPATH DATE AZMANGLE PROJECT --basedir BASEDIR

See multirtc ale --help for descriptions of each argument.

rle Relative Location Error

Measures the relative alignment of overlapping geocoded SAR images by measuring the offsets between each 1024x1024 pixel chunk of the images.

Usage:

multirtc rle REFPATH SECPATH PROJECT --basedir BASEDIR

See multirtc rle --help for descriptions of each argument.

pt Point Target Analysis

Evaluates the impulse response of corner reflector at the Rosamond, California site in the SAR image, including resolution, peak to side-lobe ratio (PSLR), and integrated side-lobe ratio (ISLR).

Usage:

multirtc pt FILEPATH DATE AZMANGLE PROJECT --basedir BASEDIR

See multirtc pt --help for descriptions of each argument.

When will support for [insert SAR provider here] products be added?

We're currently working on this package on a "best effort" basis with no specific timeline for any particular dataset. We would love to add support for every SAR dataset ASAP, but we only have so much time to devote to this package. If you want a particular dataset to be prioritized there are several things you can do:

• Open an issue requesting support for your dataset and encourage others to like or comment on it.
• Provides links to example datasets over the Rosamond, California corner reflector site (Lat/Lon 34.799,-118.095) for performing cal/val.
• Reach out to us about funding the development required to add your dataset.

Developer Setup

1. Ensure that conda is installed on your system (we recommend using mambaforge to reduce setup times).
2. Download a local version of the multirtc repository (git clone https://github.com/forrestfwilliams/multirtc.git)
3. In the base directory for this project call mamba env create -f environment.yml to create your Python environment, then activate it (mamba activate multirtc)
4. Finally, install a development version of the package (python -m pip install -e .)

To run all commands in sequence use:

git clone https://github.com/forrestfwilliams/multirtc.git
cd multirtc
mamba env create -f environment.yml
mamba activate multirtc
python -m pip install -e .

License

MultiRTC is licensed under the BSD-3-Clause license. See the LICENSE file for more details.

Code of conduct

We strive to create a welcoming and inclusive community for all contributors to this project. As such, all contributors to this project are expected to adhere to our code of conduct.

Please see CODE_OF_CONDUCT.md for the full code of conduct text.

Contributing

Contributions to this project plugin are welcome! If you would like to contribute, please submit a pull request on the GitHub repository.

Contact Us

Want to talk about this project? We would love to hear from you!

Found a bug? Want to request a feature? open an issue