\(γ^0_{T}\) RTC data flow

Two data flows are possible:

• with S1GammaAreaMap only γ area maps are produced,

• with S1Processor γ area maps are produced if not found, then \(γ^0_{T}\) calibrated and orthorectified files are produced.

\(γ^0_{T}\) RTC global processing

S1 Tiling processes by looping on all required S2 tiles within the time range.

For each S2 tile,

1. It downloads the necessary S1 images that intersect the S2 tile, within the specified time range, that are not already available in input data cache (all scenarios)

2. Then, it makes sure the associated γ area map exists (all scenarios),

   0. It selects a pair of input S1 images that intersect the S2 tile, it:

   1. For each input S1 image

      1. It prepares a VRT of the DEM files that intersect the S1 image,

      2. It optionally resample the DEM VRT on the footprint of the VRT,

      3. It project GEOID information on the geometry of the VRT or that resampled DEM,

      4. It sums both elevation information on the geometry of the VRT or that resampled DEM,

      5. It projects the coordinates of the input S1 image onto the geometry of the VRT or the resampled DEM,

      6. It computes the γ area map of each ground point,

      7. It orthorectifies the γ area map to the S2 tile

   2. It concatenates both files into a single γ area map for the S2 tile.

3. Then, for each polarisation (S1Processor scenario only),

   1. It calibrates with σ° LUT, cuts and orthorectifies all the S1 images onto the S2 grid,

   2. It superposes (concatenates) the orthorectified images into a single S2 tile,

   3. It normalizes the σ° orthorectified image with the γ area map.

As with the main dataflow for all other calibrations (β°, γ°, or σ°), these tasks are done in parallel in respect of all the dependencies.

\(γ^0_{T}\) RTC specific processings

Tasks for processing 33NWC and 33NWB with GammaNaughtRTC calibration – v1.2 workflow

Agglomerate DEM files in a VRT that covers S1 footprint (RTC)

Input:

All DEM files that intersect an original input S1 image

Output:

A VRT file

Function:

osgeo.gdal.BuildVRT()

StepFactory:

s1tiling.libs.otbwrappers.AgglomerateDEMOnS1

All DEM files that intersect an original input S1 image are agglomerated in a VRT file.

Note

DEM files that don’t intersect the input S1 image will not be agglomerated, and holes may appear in the resulting outer bounding box of the VRT.

Resample DEM (RTC)

Inputs:

A VRT file

Outputs:

Resampled DEM image

OTBApplication:

RigidTransformResample

StepFactory:

s1tiling.libs.otbwrappers.ResampleDEM

The DEM from the VRT are resampled by the chosen resampling factors (resample_dem_factor_x and resample_dem_factor_y).

Note

When the VRT of the inputs DEM is built, we may not have DEM information everywhere in the outer rectangular bounding box. Values may be missing.

In order for RigidTransformResample to not mess up missing DEM values, no-data values are changed to NaN values on-the-fly before the interpolations thanks to s1tiling.libs.otbwrappers.NaNifyNoData.

Project GEOID on (/resampled) DEM

Inputs:

• The resampled DEM intersecting the S1 image as reference, or the DEM VRT

• The GEOID file

Output:

None: chained in memory with Height computation

OTBApplication:

OTB Superimpose

StepFactory:

s1tiling.libs.otbwrappers.ProjectGeoidToDEM

This step projects the GEOID file on the geometry of the DEM retained (and optional resampled).

Compute full height elevation on (/resampled) DEM

Inputs:

• The resampled DEM intersecting the S1 image as reference, or the DEM VRT

• The projected GEOID on the same geometry – chained in memory from GEOID projection step

Output:

The Height projected on (resampled) DEM

OTBApplication:

OTB BandMath

StepFactory:

s1tiling.libs.otbwrappers.SumAllHeights

This step sums both DEM and GEOID information projected on the geometry of the DEM retained (and optional resampled).

Project SAR coordinates onto DEM

Inputs:

• An original input S1 image (geometry)

• The associated DEM VRT file, or a resampled version.

Output:

A SAR DEM projected file

OTBApplication:

Our patched version of DiapOTB SARDEMProjection

Note

Beware, this OTB application isn’t distributed with OTB yet. It has to be installed specifically on your machine. It will be already installed in the docker images though.

StepFactory:

s1tiling.libs.otbwrappers.SARDEMProjectionImageEstimation

This step projects the coordinates of original input S1 image in the geometry of the DEM VRT file.

Project γ area coordinates onto SAR

Inputs:

• An original input S1 image (geometry)

• The height projected on resampled DEM

• The associated SAR DEM projected file

Output:

A γ area map file on S1 geometry

OTBApplication:

SARGammaAreaImageEstimation

Note

Beware, this OTB application isn’t distributed with OTB yet. It has to be installed specifically on your machine. It will be already installed in the docker images though.

StepFactory:

s1tiling.libs.otbwrappers.SARGammaAreaImageEstimation

This step estimates the γ area coordinates on the ground in the geometry of the original input S1 image.

It uses the following parameters from the request configuration file:

• [Processing].distribute_area

• [Processing].inner_margin_ratio

• [Processing].outer_margin_ratio

• [Processing].disable_streaming.gamma_area

Orthorectification of γ area maps

Inputs:

A γ area map file in the original Sentinel-1 image geometry

Output:

The associated γ area map file orthorectified on the target MGRS Sentinel-2 tile

OTBApplication:

Orthorectification

StepFactory:

s1tiling.libs.otbwrappers.OrthoRectifyGAMMA_AREA

This steps ortho-rectifies the γ area map image file from S1 geometry to S2 grid.

It uses the following parameters from the request configuration file:

• [Processing].orthorectification_gridspacing

• [Processing].orthorectification_interpolation_method

• [Paths].dem_dir

• [Paths].geoid_file

Concatenation of γ area maps

Inputs:

A pair of γ area map files orthorectified on the target S2 tile.

Output:

The γ area map file associated to the S2 grid

OTBApplication:

Synthetize

StepFactory:

s1tiling.libs.otbwrappers.ConcatenateGAMMA_AREA

This step merges all the images of the orthorectified S1 γ area maps on a given S2 grid. As all orthorectified images are almost exclusive, they are concatenated by taking the first non-null pixel.

Application of γ area maps to σ° calibrated S2 images

Inputs:

• The γ area map file associated to the S2 grid

• A σ° calibrated, cut and orthorectified image on the S2 grid

Output:

final S2 tiles, \(γ^0_{T}\) calibrated

OTBApplication:

SARGammaAreaToGammaNaughtRTCImageEstimation

Note

Beware, this OTB application isn’t distributed with OTB yet. It has to be installed specifically on your machine. It will be already installed in the docker images though.

StepFactory:

s1tiling.libs.otbwrappers.ApplyGammaNaughtRTCCalibration

This final step applies γ area map (in S2 grid geometry) to σ° calibrated files orthorectified on the S2 grid.

It uses the following parameters from the request configuration file:

• [Processing].min_gamma_area

• [Processing].calibration_factor

• [Processing].disable_streaming.apply_gamma_area

• [Processing].nodata.RTC

γ area specific data caches

As with main dataflow, two kinds of data are cached, but only one is regularly cleaned-up by S1 Tiling. The other kind is left along as the software cannot really tell whether they could be reused later on or not.

Important

This means that you may have to regularly clean up this space.