Add CDSE endpoint for data download

README.md

@@ -61,6 +61,20 @@ python -m ipykernel install --user --name topsapp_env
     ```
     The `username`/`password` pair are the appropriate Earthdata Login credentials that are used to access NASA data. This file is necessary for downloading the Sentinel-1 files, and auxiliary data. Additionally, the [`requests`](https://docs.python-requests.org/en/latest/) library automatically uses credentials stored in the `~/.netrc` for authentification when none are supplied.
 
+2. (Optional) To download Sentinel-1 SLC granules from the [Copernicus Data Space Ecosystem (CDSE)](https://dataspace.copernicus.eu/) instead of ASF, you will need CDSE credentials. These can be provided in one of two ways:
+    - Add an entry to your `~/.netrc` file:
+        ```
+        machine dataspace.copernicus.eu
+            login <cdse-username>
+            password <cdse-password>
+        ```
+    - Or set environment variables:
+        ```
+        export CDSE_USERNAME=<cdse-username>
+        export CDSE_PASSWORD=<cdse-password>
+        ```
+    A free CDSE account can be registered at [dataspace.copernicus.eu](https://dataspace.copernicus.eu/).
+
 ## Generate an ARIA-S1-GUNW
 
 Make sure you have `~/.netrc` as described above. Run the following command:
@@ -77,6 +91,19 @@ This is reflected in the [`sample_run.sh`](sample_run.sh).
 
 To be even more explicit, you can use [`tee`](https://en.wikipedia.org/wiki/Tee_(command)) to record output to both including `> >(tee -a topsapp_img.out) 2> >(tee -a topsapp_img.err >&2)`.
 
+## Generate an ARIA-S1-GUNW using CDSE for Sentinel-1 Download
+
+By default, Sentinel-1 SLC granules are downloaded from the [Alaska Satellite Facility (ASF)](https://asf.alaska.edu/). As an alternative, particularly suited for European users or those operating within the European cloud ecosystem, granules can be downloaded from the [Copernicus Data Space Ecosystem (CDSE)](https://dataspace.copernicus.eu/) by passing `--download-source cdse`. Metadata lookups and bounding box checks still use ASF, so a valid `~/.netrc` entry for `urs.earthdata.nasa.gov` remains required. Additionally, CDSE credentials must be configured as described in the *Additional setup* section above.
+
+```
+isce2_topsapp --reference-scenes S1A_IW_SLC__1SDV_20220212T222803_20220212T222830_041886_04FCA3_2B3E \
+                                 S1A_IW_SLC__1SDV_20220212T222828_20220212T222855_041886_04FCA3_A3E2  \
+              --secondary-scenes S1A_IW_SLC__1SDV_20220131T222803_20220131T222830_041711_04F690_8F5F \
+                                 S1A_IW_SLC__1SDV_20220131T222828_20220131T222855_041711_04F690_28D7  \
+              --frame-id 25502 \
+              --download-source cdse
+```
+
 ## What makes an ARIA-S1-GUNW Product *standard*?
 
 Each ARIA-S1-GUNW at the ASF that ensures that down-stream analysis by [ARIA-Tools](https://github.com/aria-tools/ARIA-tools) and [Mintpy](https://github.com/insarlab/MintPy) is done consistently and reproducibly. There are a number of exposed parameters in this plugin that we require to be set in a certain manner for a product to be considered "standard". We now discuss the standard parameters with respect to this plugin.