Downloading and decoding NOAA APT images with rtl-sdr

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drew
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Downloading and decoding NOAA APT images with rtl-sdr

Postby drew » Wed Jul 21, 2021 8:59 pm

So back in late March I posted about those European RF nerds that were decoding video from SpaceX launches as the video feed was in the clear. That post can be found here.

https://forum.ausrocketry.com/viewtopic.php?f=4&t=6667

Obviously SpaceX has now encrypted that feed but safe to say I was pretty blown away by the fact that a rtl-sdr and wifi antenna could be used to hand track a rocket booster in real time. And given that there's no reason why you can't do this with other satellites, right?

Pretty quickly I realised that there's a community of folks around the world downlinking from satellites with rtl-sdrs and appropriate antennas. Many, MANY moons ago (a decade at least) when I didn't have a family and had a reasonably large discretionary budget and bought my 5 element portable Arrow yagi for 70cm I also bought an Arrow satellite antenna. This is a dual band yagi designed for ISS comms; it has a 7 element 70cm yagi and then a 3 element 2m yagi. I connect it up to my AirSpy Mini which I hang off an old laptop of mine running Debian 10. I use Look4Sat on Android to both plan for and point my yagi during passes. I've started with NOAA Automatic Picture Transmission (APT) images. I record a .wav file with gqrx to get the data in a format that I can then decode.

Here are a couple from my backyard.
Image

Image

These images are black and white and fairly low res (4 sq km per pixel) but it's still quite fun. All of these were at night so they're infrared. So the left hand image is long-wave infrared and the right is mid-wave infrared.

Last week we went up north for vacation; here's a better (longer) pass taken from Geraldton. I'm not 100% certain but I believe all the weird artefacts in the image are due to RF interference in Geraldton as we were staying basically down town. I've never had that swirling occur before or since. Interesting though.

Image

Then further north at Hamelin Pool/Shark Bay I was able to get some other passes.

Image

Here's what an APT analog transmission looks like in gqrx.

Image

Moving forward I'm going to attempt to caputure some Russian Meteor M2 passes. These are transmitted with Low Resolution Picture Transmission (LRPT) which is color and higher resolution (1 sq km per pixel). These transmissions are digital (QPSK) and are much more involved in terms of recording and decoding. I'll keep you all updated on my progress. Below is a screenshot of gqrx showing a Meteor M2 pass which leads me to believe my yagi will work for this sort of work as I can clearly see the signal.

Image
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 26,850ft - L935 - THUNDA 2019
Max V - 3,004 ft/s, ~Mach 2.67 - L935 - THUNDA 2019

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OverTheTop
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Re: Downloading and decoding NOAA APT images with rtl-sdr

Postby OverTheTop » Thu Jul 22, 2021 9:00 am

Nice work Drew! :)
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drew
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Re: Downloading and decoding NOAA APT images with rtl-sdr

Postby drew » Thu Jul 22, 2021 11:35 am

Thanks OTT! I hope you're well...
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 26,850ft - L935 - THUNDA 2019
Max V - 3,004 ft/s, ~Mach 2.67 - L935 - THUNDA 2019

User avatar
OverTheTop
It's only money...
It's only money...
Posts: 2989
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Location: Melbourne, Australia

Re: Downloading and decoding NOAA APT images with rtl-sdr

Postby OverTheTop » Thu Jul 22, 2021 1:49 pm

Thanks Drew. All well down here. Not too much covid in our area. I get vaccinated in about 4 weeks. Stay safe over there too.

BTW, I love how the software allows visualisation of the data these days. There are some brilliant tools for SDR. Not like the good old days where the tools were all hardware :) . I remember doing a lot of theory in my engineering degree relating to SDR but the processing power back then made it impractical for all but the military. Nowadays it is within everyone's reach.
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"Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

drew
Southern fried goodness
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Posts: 1092
Joined: Sat Aug 01, 2009 10:20 pm
Location: Perth

Re: Downloading and decoding NOAA APT images with rtl-sdr

Postby drew » Thu Jul 22, 2021 2:32 pm

Thanks mate. Trying to be as safe as possible over here. I got my second pfizer jab on Monday so in a week I should be in the clear so to speak. Well, at least until we get the Delta booster in 2022.

And yes, the capabilities of sdrs are pretty off the charts these days!
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 26,850ft - L935 - THUNDA 2019
Max V - 3,004 ft/s, ~Mach 2.67 - L935 - THUNDA 2019

drew
Southern fried goodness
Southern fried goodness
Posts: 1092
Joined: Sat Aug 01, 2009 10:20 pm
Location: Perth

Re: Downloading and decoding NOAA APT images with rtl-sdr

Postby drew » Mon Jul 26, 2021 7:03 pm

I was able to catch NOAA-18 this morning at ~10am. Below is the visible (black and white) image from the pass.

Image
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 26,850ft - L935 - THUNDA 2019
Max V - 3,004 ft/s, ~Mach 2.67 - L935 - THUNDA 2019


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