Tagged: NOAA

Using 50 Lines of Python Code to Decode NOAA APT Weather Satellite Images

There are already many image decoders for the NOAA APT weather satellites available, with the most common and feature rich program being the abandoned freeware "WXtoIMG".

However many people may not know how simple the APT digital signal processing code is. Over on his blog post Dmitrii Eliuseev explains how only 50 lines of Python code are required to decode an image from received APT audio. Dmitrii's post shows how a Hilbert transform is used on the APT audio which is essentially the entire decoding step. This is then followed by a for loop that calculates the pixel luminosity from the decoded data, and plots it onto an image file. 

Of course the image is only grayscale (or in Dmitrii's case he decided to use greenscale), but adding false color and various other image enhancements found in advanced software like WXtoIMG are just standard image processing techniques.

Dmitrii concludes with the following:

Interesting to mention, that there are not so many operational radio communication systems in the world, the signal of which can be decoded using 20 lines of code. The NOAA satellites are about 20 years old, and when they finally will retire, the new ones will most likely be digital and format will be much more complex (the new Russian Meteor-M2 satellite is already transmitting digital data at 137 MHz). So those who want to try something simple to decode can be advised to hurry up.

[Also mentioned on Hackaday]

Simple decoding of NOAA APT satellites in Python

FAASGS: A Setup to Build a Fully Automatic Amateur and APT Weather Satellite Ground Station

Over on GitHub stdevPavelmc has released his software called FAASGS (Fully Automatic Amateur Satellite Ground Station). FAASGS is an open source program that allows RTL-SDR users to set up a satellite ground station that tunes, record and generate images for NOAA APT weather satellites, as well as records FM amateur radio satellites. The software runs on a single board computer such as a Raspberry Pi, however in the authors own setup he uses an Orange Pi Prime board. The features include:

  • Web interface to see the next passes, the recorded ones, and details for it.
  • Receive any satellite in FM mode (SSB is possible but no there is doppler control yet, so no SSB by now)
  • Record the satellite pass and keep the audio for later.
    • APT WX audio is preserved in wav format and 22050 hz of sampling (the format wximage needs to work with)
    • FM audio satellites is preserved in .mp3 mode but with high quality settings, and other tricks.
      • The spectrogram of the audio is embedded as album art (see below).
      • The pass data and receiving station are stored in the mp3 tags.
  • Automatic decode APT images from WX sats (NOAA 15, 18 and 19)
  • For the voice FM sats we craft a spectrogram and embedd the metadata of the pass on the image
FAASGS main screen showing recordings
FAASGS screen showing an FM amateur radio satellite pass

Explaining the 9A4QV V-Dipole Design for Receiving 137 MHz Weather Satellites

Back in 2017 we posted about Adam 9A4QV's simple V-Dipole antenna design which works very well for receiving NOAA and Meteor weather satellites at 137 MHz. This type of antenna is a lot easier to build compared to a QFH or turnstile, and it results in good performance if built and set up correctly. Over the years he notes that he's received a number of questions asking to clarify the design and so he's uploaded a YouTube video which explains the built and dimensions of the antenna clearly.

137 MHz WX-SAT original 9A4QV V-dipole antenna

NOAA-APT Decoder Updates: False Color, Pass Prediction and more

In the past we've posted a couple of times about the NOAA-APT decoder software as it is a worthy alternative to the now abandonware software WXtoIMG. However, it lacks certain features which makes WXtoIMG still the go to program for NOAA weather satellite decoding.

As NOAA-APT is open source it has recently seen a few new updates from another contributor, as well as the original author. These changes make it quite a bit more useful, although admittedly not perfect. Hopefully we'll see continued refinement over time. Regardless, this is still a great piece of software which is open source and multi-platform. Martin Bernardi, the original contributor writes:

Although I wasn't planning to continue working in my program, the quarantine happened so I worked on the program a little. Later, a person (Arcadie Z) added more features too, so I created a new version in case you want to add a blog post about it.

Added features since the last blog post:

- Redesigned GUI.
- Satellite prediction and map overlay (but has offsets I can't fix yet).
- False color images
- Histogram equalization (improves the contrast and brightness of images)
- Automatic image rotation depending on pass direction

In the end, the map overlay and false color does not work very well, but it is better than nothing I guess.

The NOAA-APT Decoder GUI

Microwave Humidity Sounder Decoder for the NOAA-19 Satellite Released

Back in June we posted about the release of  Zbigniew Sztanga's NOAA-HIRS-Decoder which can decode HIRS instrument data which measures the vertical temperature profile of the Earth's surface. This HIRS signal is broadcast by NOAA satellites at the same time as their APT images and the HIRS frequency is close by at 137.350 MHz. 

Recently Zbigniew has released a new decoder for the Microwave Humidity Sounder (MHS) instrument which is available on NOAA-19 only. This MHS instrument observes the Earth in the 89-190 GHz microwave band, which can be useful for measuring humidity levels. However, unlike the APT and HIRS signals which downlink data at around 137 MHz, the MHS data is broadcast in the L-band within the HRPT signal, so a motorized or tracked satellite dish will be required to receive it. Zbigniew writes:

The MHS (Microwave humidity sounder) is an instrument on NOAA-18 and NOAA-19. It replaced the older AMSU-B. It has a resolution of 90px per line and 5 channels.
 
Data from the instrument is present in HRPT and can be decoded with my new software. Unfortunately, only MHS on N-19 is working, because N-18's NHS is dead.
 
The instrument can be used to monitor low clouds, percipation and water vaopr in the atmosphere. I attached a sample image to the email.
 
It's available on the same repo as Aang23' HRPT decoders: https://github.com/altillimity/L-Band-Decoders/tree/master/NOAA%20MHS%20Decoder
Microwave Humidity Sounder data from NOAA-19.

John’s Windows 10 NOAA Weather Satellite Software Guide for RTL-SDR

Thank you to John First for submitting his guide all about the setup and use of the software required to receive NOAA weather satellite images on Windows 10 (pdf file) with an RTL-SDR dongle. John's guide covers the use of SDR# for receiving the signal, WXtoIMG for decoding the signal, and Orbitron for tracking the satellite and automatically tuning SDR# when a satellite is in range.

He also explains the use of the VB-Audio Virtual Cable for piping audio between SDR# and WXtoIMG, as well as the DDE Tracking and Scheduling Plugin for interfacing SDR# with Orbitron, and finally how to do NTP clock synchronization to ensure the local time is accurate.

An Excerpt from John's Guide
An Excerpt from John's Guide

A Simple Guide to Setting up a DIY NOAA Weather Satellite Ground Station

A few weeks ago we posted about Sophie Dyer and Sasha Engelmann's work in creating an artistic performance based on weather satellite reception with SDRs. More recently they have uploaded their own tutorial showing how they receive NOAA APT weather satellite images with an SDR, turnstile antenna and computer. Sasha and Sophie note that they are attempting to create visually rich guides that don't assume any prior knowledge of radio, science or engineering.

From Sasha's Twitter feed we note that they are also working on upcoming public workshops in the UK and Germany on the topic of reflections on what it means to bring an intersectional feminist ethos to satellite image decoding + weather sensing, & new creative collaborations in 2020. If you are interested in their work please follow @sashacakes and @sophiecdyer on Twitter.

Receiving NOAA weather satellites
Receiving NOAA weather satellites

Open Weather: An Artistic Performance Involving Live NOAA APT Signal Decoding for Sound Arts Festival

Just after our post a few days ago about an art project involving weather satellite reception with SDRs, we received a story submission about an artistic performance with similar weather satellite and SDR themes. The submission from Sasha Engelmann reads:

Open Work, Second Body is a live-streamed performance by designer Sophie Dyer (@sophiecdyer) [M6NYX] and geographer Sasha Engelmann (@sashacakes) [M6IOR] in collaboration with the author Daisy Hildyard. The work was performed twice during Reveil 2020, a global sound arts festival streaming sounds from listening points around the planet on the day of the International Dawn Chorus.

Open Work, Second Body asks: From the climate crisis to coronavirus: what are the tools we need to make sense of events unfolding on vastly disparate scales? Through spoken word, field recordings and live radio reception of two NOAA satellite images, the work probes the porous boundaries between our bodies, local atmospheres and weather systems.

Still image capture from livestream of Open Work, Second Body, AM performance, May 2nd 2020

Due to lockdown constraints in London, Sophie and Sasha were not able to be in the same place or to leave their apartments, so they performed the work via simultaneous streams from their respective balconies in South East and North West London. Using RTL-SDRs, Turnstile antennas, Open Broadcast Software and collaborating with two NOAA satellite passes, Sophie and Sasha shared the process of decoding NOAA satellite images with hundreds of viewers around the world, employing spoken word poetry and field recordings to complicate relationships of local and global, weather and climate, the individual and the collective. 

Recordings of the performances can be found at the links below. 

☀️Morning: https://youtu.be/-5JrxwNpJqI [performance starts at 05:25]
?️ Afternoon: https://youtu.be/h88zaCtX8cw [performance starts at 05:00]

Still image capture from livestream of Open Work, Second Body, PM performance, May 2nd 2020
Still image capture from livestream of Open Work, Second Body, PM performance, May 2nd 2020

Open Work, Second Body is part of Sophie and Sasha's larger artistic research and design project Open Weather, which employs ham radio, open data and feminist theories and approaches to build new and diverse communities around satellite image decoding and weather sensing. The Open Weather web platform will be launched in Summer 2020 and will host an archive of SDR-generated weather images, visually rich how-to guides for those with no radio and engineering experience, and material about Sophie and Sasha's collaborative artistic practice. 

For Open Work, Second Body, Sophie and Sasha would like to thank the Soundcamp Team: Grant Smith, Dawn Scarfe, Christine Bramwell, Maria Papadomanolaki and Ciara Drew. They are grateful to Daisy Hildyard for her willingness to be in conversation with them, Bill Liles NQ6Zfor technical advice, Jol Thoms for sound design, Rachel Dedman, Laure Selys and Arjuna Neuman (Radio Earth Hold) for early curatorial input, Akademie Schloss Solitude for the support of a residency, the satellites NOAA 18 and NOAA 19 and the RTL-SDR and wider ham radio community. 

http://www.sophiedyer.net

http://www.sashaengelmann.com

It's very cool to see technical hobbies like ours starting to make an impact in art and reaching a wider audience. More content and images available on Sophie's Open Weather webpage, and Sasha's Open Weather webpage

Open Weather Live Stream