Synthetic Aperture Random

This is the Python code behind the Twitter bot @ApertureRandom, that posts every day a new Synthetic Aperture Radar image acquired with European Space Agencies's Sentinel-1 satellites.

The images are obtained using Google Earth Engine (GEE).

Requirements

• Access to GEE (can be requested here)
• A Twitter developer account and the corresponding APP Key and APP Secret (apply here)
• Python > 3.6
• Virtualenv
• Pip

Functioning

Using Python's Schedule library, every day at a given time (default is 15:00) a new job is launched. This job retrieves all Ground Range Detected (GRD) images from GEE fulfilling the following criteria:

• Sensor: Sentinel-1
• Mode: Interferometric Wide Swath (the default mode for this satellite, for more info see the User Guide)
• Pixel resolution: 10x10m (the highest available)
• Acquisition time: not older than the last 2 days

Among the many retrieved images, the program picks one randomly. Its radiometric copol (either HH or VV) and crosspol (either HV or VH) bands are converted to RGB pseudo-colors using the following mapping:

• Red = Copol
• Green = 2 * Crosspol
• Blue = Copol / Crosspol / 100

The following information from the image is retrieved:

• Nearest city and country (using Python's reverse_geocode library
• Coordinates
• Acquisition date and time
• Orbit type (ascending or descending)
• Polarizations

Then, the image is generated, downloaded and uploaded to Twitter.

Usage

Generate a file called .env in the directory synthetic_aperture_random/ with the following structure:

APP_KEY=<APP_KEY>
APP_SECRET=<APP_SECRET>
OAUTH_TOKEN=<OAUTH_TOKEN>
OAUTH_TOKEN_SECRET=<OAUTH_TOKEN_SECRET>

and replace the values in <> with your Twitter Developer's credentials. APP_KEY and APP_SECRET can be obtained from the web. I generated the OAUTH tokens using the scripts/twitter_auth.py also provided in this repo, which requires the user to open a browser window in order to obtain an authentication pin.

You also need to authenticate your GEE account:

$ earthengine authenticate

Using a Python virtual environment

Installation:

$ virtualenv -p python3.6 _env
$ source _env/bin/activate
(env_) $ pip install -r requirements/requirements.txt

Show the help:

(env_) $ python main.py -h

Running it manually (default):

(env_) $ python main.py --manual

Leaving it running in automatic mode in a server:

$ nohup python main.py --automatic &

Using Docker

Build the image:

$ docker build -t thoyo/synthetic_aperture_random:1.0.0 .

Run it:

$ docker-compose -p twitter up -d

Check the logs:

docker logs -f twitter_synthetic_aperture_random_1

TODO

• Add unit testing
• Allow user retrieving the full resolution image (upload it to drive and provide link in status?)