Copernicus-STAC-API : Sentinel-1-Workflow

This workflow automates the retrieval and processing of Sentinel-1 SAR imagery from the Copernicus DataSpace. It uses Keycloak for secure authentication to download products via the OData API and converts the TIFF files of HH and HV polarizations into NetCDF format. The workflow simplifies access to satellite data for scientific analysis.

Sentinel-1 SAR Data Workflow using Copernicus APIs

This repository provides a Python-based workflow for downloading, processing, and converting Sentinel-1 SAR imagery from the Copernicus DataSpace into NetCDF format. The workflow integrates with the Copernicus DataSpace APIs using Keycloak authentication for secure access and utilizes various Python libraries like requests, rasterio, and xarray for data handling.

Keycloak Authentication

The workflow begins by obtaining an authentication token from the Keycloak OAuth2 API. This token is necessary for secure access to the Sentinel-1 product download API.

The function get_keycloak sends a POST request to the Keycloak server, providing the username and password to obtain an OAuth2 token. This token is used for all subsequent API requests to ensure authenticated access.

Downloading Sentinel-1 Products

Once authenticated, the workflow downloads Sentinel-1 products using the OData API. After retrieving the authentication token, the product download link is constructed using the product ID, which is obtained from the API metadata.

Workflow:

• Keycloak Authentication: First, the get_keycloak function is called to retrieve the token for secure authorization.
• Constructing the Download URL: The product ID is used to build the download URL for accessing the product ZIP file from the OData API.
• Downloading the Product: The product is downloaded by passing the authentication token via an HTTP GET request and saved locally for further processing.

Unzipping and Converting to NetCDF

After downloading the .zip files containing Sentinel-1 data, the .tiff files representing the HH and HV polarization channels are extracted and processed. These TIFF files are then converted to NetCDF format using the Python libraries rasterio and xarray.

Steps:

• Unzipping the Data: The .zip archive is extracted, and the .tiff files within the measurement folder are located, specifically those related to HH and HV polarizations.
• Converting to NetCDF: The .tiff images are read using rasterio, transformed into an xarray.DataArray, and appended to a new or existing NetCDF file for each product.

API Overview

1. Keycloak API for Authentication:

• URL: https://identity.dataspace.copernicus.eu/auth/realms/CDSE/protocol/openid-connect/token
• Method: POST
• Purpose: To authenticate and obtain an OAuth2 token for accessing Copernicus DataSpace APIs.

2. OData API for Product Download:

• URL Template: https://zipper.dataspace.copernicus.eu/odata/v1/Products({product_id})/$value
• Method: GET
• Purpose: Download Sentinel-1 SAR products by their unique product ID.

3. STAC API for Metadata Search (Implied):

• Purpose: Search for Sentinel-1 SAR imagery based on certain filters like bounding box, time range, and polarization type.

The STAC API is used for finding the Sentinel-1 products that match specific search criteria, which helps to locate product IDs used for downloading the data.

Summary

This workflow automates the process of downloading and converting Sentinel-1 SAR imagery from the Copernicus DataSpace into a manageable format (NetCDF). It leverages secure authentication via the Keycloak API and processes large satellite imagery efficiently by transforming the raw .tiff images into NetCDF format for further scientific analysis.