Request for Changes-82: Sentinel1 IW SLC deburst filter

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Status

Summary

This RFC provide a new filter and application to perform deburst of Sentinel1 IW SLC products.

Rationale

IW is the routine acquisition mode mostly used for Sentinel1. For this mode, SLC images are composed of several bursts, separated by black lines. Burst are overlapping in azimuth time (and thus in lines), which means that the last lines of a burst correspond to the first lines of next bursts (see [1] for details). Bursts lines are synchronized in azimuth time. This image construction makes the processing of off-the-shelf IW product difficult. If ossimSarSensorModel can handle bursts perfectly, the inverse sensor model is discontinuous which may cause artifacts during orthorectification resampling. Other neighborhood based processing techniques such as speckle filtering will also react poorly near bursts limits. The implemented deburst operation consists in removing black and burst overlapping lines so as to get a continuous, regularly azimuth time sampled image. Sensor model parameters are updated accordingly, which means that ortho-rectification can still be performed after deburst (and it is actually advised to do it that way). The RFC comes with a deburst filter working for S1 IW products, as well as the app to use the filter.

[1] https://sentinel.esa.int/documents/247904/685163/Sentinel-1_User_Handbook (p.53)

Implementation details

Classes and files

ThirdParty/OssimPlugins

The ossimSarSensorModel has been updated with a deburst method. This method performs the deburst of metadata and return the line ranges to keep in the deburst image. Two static methods for coordinate conversion between deburst and original images have also been added.

The ossimSentinel1Model saveState method has been updated to re-export the deburst parameters (single burst).

Adapters/OSSIMAdapters

The otb::SarSensorModelAdapter has been created so as to give access to specific methods of ossimSarSensorModel' while hiding OSSIM includes.

Filtering/SAR

A new module called Filtering/SAR has been created. It contains a single new filter called otb::SarDeburstImageFilter which implements the deburst operation based on calls to the adapter.

Applications

A new SARDeburst application has been created in Applications/AppSARCalibration. The application is very simple, since deburst has no parameters.

Tests

ossimSentinel1Model test code has been updated to perform deburst and check sensor model precision with respect to GCPs with the deburst model. Filter and application also have a test with a S1 extract.

Documentation

New classes, methods and applications have been documented.

Additional notes

This is only proven to work with S1 IW products for now, even if the deburst method is in ossimSarSensorModel, which means it could possibly handle other sensors with a similar mode.

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