NOAA APT Imagery

These are my scripts for capturing NOAA automatic picture transmission (APT) imagery.

Links

• noaa-apt is the main software used for decoding images.
• wxtoimg, legacy / abandonware software used for decoding images, and I still use it to get my satellite pass schedule. A redditor has posted licensing information.
• RTL-SDR Blog's recommended dongle, this is the actual radio receiver used to turn RF signals into the .raw audio files later processed.
• RTL-SDR Blog dipole antenna kit, the antenna I'm currently using.
• Instructable for building a QFH antenna from PVC, copper, and coax, the antenna I'm currently building.

Scheduling

Generally, there can be up to 12 satellite passes per day, two each of NOAA-15, -18, and -19, in the morning and evening. Sometimes one or more of these passes will not be visible in your location. Obtain a satellite pass list for your location from wxtoimg -G (be sure to update keplers first!), and schedule the pass recording using at as exampled in scrach.txt.

Since at cannot schedule down to the second, I start my recordings at the top of the minute a satellite appears, and add two minutes to the duration. Note that passes of two satellites can overlap, so you may need to cut a recording short to free your radio for the next one.

Processing

I use .raw captures as the main source file, and process.sh will process each .raw file in a directory, deleting any .wav and .png representations and remaking them. Throughout the day I run ./process.sh /tank/archive/satellite-samples/2020-09-11 to process images for viewing.

There seems to be a bug in noaa-apt where you need to do a decode in the GUI program at least daily or locations will be entirely wrong. Open noaa-apt in GUI mode and decode a .wav file, close noaa-apt, and re-run ./process.sh.

TODO

• .raw captures are very large. Now that I have confidence in my decoding pipeline, capture.sh should convert the .raw to .wav with sox and process.sh should use the .wav as its main source file.

• Add a script for parsing either the pass list from wxtoimg -G or for building a pass list from another API.