GDM-OPT-ETQ: Multiple Pairwise Image Correlation of OPTical images for EarThQuake analysis¶

Select input data¶

The Geobrowser offers multiple ways to search a large variety of EO-based dataset and the user should refer to the Geobrowser section for a general introduction. For this tutorial we will use a data package which is accessible through the “Data Packages” tab on the upper left of the screen. If you type “Ridgecrest” into the search box you should be able to find a data package named “Ridgecrest_2019_S2_2im”. Alternatively you can access the `Ridgecrest data package`_ directly by clicking on the link: .. Ridgecrest datapackage: https://geohazards-tep.eu/t2api/share?url=https%3A%2F%2Fgeohazards-tep.eu%2Ft2api%2Fdata%2Fpackage%2Fsearch%3Fid%3DRidgecrest_2019_S2_2im

Click on the data package, hold Shift and Drag and Drop all four products in the Sentinel-2 products field in the service panel on the right:

Set the processing parameters¶

There are 16 processing parameters that can be adjusted. A short explanation of the parameter is provided when hovering over the parameter fields.

• DEM: Defines the Digital Elevation Model used for filtering the displacement fields. The Merit [6] and the COP-DEM_GLO-30 [7] are available to GEP users. The default DEM is the Merit DEM.
• Sentinel-2 band: Defines the Sentinel-2 band for matching. The option B04 is recommended since the red band is also used for band to band co-registration by the ESA Sentinel-2 production center.
• Split date: Is an optional parameter of the form “yyyy-MM-dd” which will split the time series into two subsets. Pairs will only be formed among members of different subsets. This is particularly interesting in the case of quantifying co-seismic displacement. The default value is left empty.
• Minimum matching range: Defines the minimum matching range for creating the image pairs. The matching range is expressed in acquisitions so if a minimum range is set to 1, all the images (N) will be paired with at least the next image in time (N+1). The default value is set to 1.
• Maximum matching range: Defines the maximum matching range for creating the image pairs. The matching range is expressed in acquisitions so if a maximum range is set to 2, all the images (N) will be paired with at most the next second image in time (N+2). The default value is set to 5.
• Matching direction: Define the time direction for the matching. If Forward is selected, the pairs are only created in the time direction. If Forward+Backward is selected, the pairs will be created in both directions (i.e. time and reverse time direction). The default value is set to Forward.

• Window size: Controls the size of the template used for matching. It controls the neighborhood around the central pixel. The minimum value is 1 (3x3 pixels) and the maximum value is 7 (15x15 pixels). The default value is 3 (7x7 pixels). A smaller window size allow better reconstructing small scale variations but can lead to more noise. Vice versa, larger window sizes lead to greater robustness against noise but smooth small scale details. For large scale motion such as co-seismic slip, we recommend to use large window sizes.
• Decorrelation threshold: Discards the matches with a correlation coefficient below a value expressed in the range [0,1]. The default value is 0.2.
• Spatial matching range: Defines the search range in pixel for finding matches based on the template. The actual search range is computed from this parameter as round(Spatial matching range/0.8)+2. The parameter has to be adjusted according to the maximum expected displacement taking into account possible coregistration biases of the input images.
• Regularization parameter: Similar to the window size, controls the smoothness of the expected motion field. Increasing the regularization parameter puts greater emphasis on a smooth motion field where neighboring pixels will have similar displacement values. For large scale features such as co-seismic displacement, large value lead to smoother and less noisy results. The default value is 0.3.
• Use a direction for regularization: By default the regularization is isotropic but the user can choose a direction for the regularization meaning the displacement field will constrain a smooth gradient in this direction.
• Direction of the fault plane / Teta0: Direction for the regularization, in the case of strike-slip earthquake and if the a priori known, it is recommended to chose the direction of the fault (with East Teta0=0).
• Snow mask: If set to True, the areas of the images covered by snow are masked. The default value is set to True.
• Cloud mask: If set to True, the areas of the images covered by clouds are masked. The default value is set to True.
• Slope mask range minimum: The pixels located on terrain slopes with a slope angle larger than the value set with the parameter are filtered out in the products. By default, the parameter is set to 80, so pixels located on slopes with angle larger than 80 degrees are filtered.
• Slope mask range maximum: The pixels located on terrain slopes with a slope angle smaller than the value set with the parameter are filtered out in the products. By default, the parameter is set to 90 degrees, so pixels located on slopes with angle between Slope mask range minimum and 90 degrees are filtered.
• Apply correction and filtering: If set to True, the geometric corrections (as described in [3] )and the filtering (as described in [4]) are applied. They are highly recommended for any use case and are applied by default.
• Apply correction and filtering: If set to True, the jitter undulation observed in Sentinel-2 images are filtered out [8]. This correction is recommended for displacement fields with large spatial wavelength like co-seismic displacemnet fields. By default, the paratemeter is True and the correction is applied.

Run the job¶

• You are good to go. Click on the button Run Job at the bottom of the right panel.

• Once the job has finished, click on the Show results button to obtain a list of products for visualization.

Disclaimer¶

The GDM-OPT services are scientific softwares provided at the best CNRS/ForM@Ter (EOST/A2S) knowledge according to state-of-the-art image matching algorithms. No warranty is provided on the processors and results of the services. CNRS/ForM@Ter (EOST/A2S) is not responsible for any software inaccuracies, bugs, errors and misuse. Generated results have a defined accuracy according to the relevant scientific publications available in the literature. Result accuracy is estimated on a statistical basis. Provided results are not validated by CNRS/ForM@Ter and, indeed, it is user responsibility to validate them. CNRS/ForM@Ter is not responsible for the use, quality, accuracy and interpretation of results and products that are generated by using the processors and services provided within the platform. CNRS/ForM@Ter is not responsible for the use, quality, accuracy and interpretation of third party results, products and services derived from the use of the processors and services. CNRS/ForM@Ter is not responsible of possible outages of the provided services. CNRS/ForM@Ter is not responsible of any kind of third party loss derived from service outage, result inaccuracies, software errors of the provided services and products. The maintenance, update and user support are provided by EOST/A2S free of charge and at best effort. EOST/A2S is not responsible for any consequence derived from delays on replies to user requests or support inaccuracies.

• CNRS: Centre National de la Recherche Scientifique / French National Research Council
• ForM@Ter: Pôle Terre Solide / Solid Earth Centre
• EOST: Ecole et Observatoire des Sciences de la Terre / School and Observatory of Earth Sciences
• A2S: Application de Surveillance par Satellite / Application Satellite Survey