RTL-SDR: Photography from Satellites in Orbit

An image from NOAA 18 on June 11th

Now that I've successfully applied my RTL-SDR device toward aircraft tracking and digital radio reception, my next challenge was tuning in signals from space, like Jeff Goldblum's charcter in Independence Day. As sophisticated as this sounds to someone unfamiliar with radio, and electromagnetic signals, receiving and sending data to and from space is a pretty mundane thing these days. Use GPS on your phone or in the car? You're connected to a machine floating in space. And, satellite television services have been around for decades. But, I wanted to put my RTL-SDR device and rooftop antenna to use taking advantage of some weather satellites that pass over every populated country on earth at least once per day sending real-time pictures down to anyone who'd like to view them. In a way, I would be using government weather satellites from the United States and Russia to take very, very long-range selfies.    

NOAA 19 before its launch

These satellites, the NOAA 15, 18 and 19 (from the US) and the Meteor M2 3 and 4 (from Russia) are very similar in purpose and function, and orbit at similar distances about 500 miles above Earth. They circle around the globe (sorry flat-Earthers) on a north-south path crossing the north and south poles while the earth spins below them. That way, they're able to pass over and see most parts of the earth below during a given time window -think of painting a sculpture in an up-and-down motion as it spins on a pottery wheel. As the satellites orbit, they continually take photos and measurements, and transmit them back to earth at specific frequencies (137.62 MHz for NOAA 15 and 137.9 MHz for Meteor M2-3, for example). These frequencies are just below the VHF frequencies used for HAM radio in the United States, and can be heard with an SDR device, and a lot of store-bought radios for CB, HAM and other uses. But, you'll need software to de-modulate the APT transmission, otherwise it will simply sound like static or clicking to the naked ear.  

In spite of having an antenna, an SDR receiver and some software experience with air-band radio, and ADS-B airline tracking radio, reaching a satellite proved to be fairly difficult. For one, the satellites are always moving, and you can only retrieve their signal during a ten to fifteen-minute window while they pass sufficiently overhead. Secondly, the software used for amateurs like me to locate, track and decode the satellites' signals are always changing and often out-of-date, as many of these programs are created and supported by amateur enthusiasts, and not large institutions.

NOAA 19 on Satellite Tracker

My previously helpful guidebook, The Hobbyist's Guide to the RTL-SDR proved to be out-of-date with many of its recommendations for software. I tried all of the suggested ways of connecting to NOAA (National Oceanic & Atmospheric Agency) satellites as well as the Meteor M2 (Russian Space Agency, Roscosmos) satellites in the chapter on low earth orbit (LEO) satellites, and while helpful in explaining the general process, it gave some applications and programs that simply do not work well anymore. Certain PC satellite trackers, for example, no longer seemed to provide accurate tracking for my location, and SDR++ (a great software defined radio receiver) had no way to decode the satellite's modulated signals into valuable data or images. I ended up spending a lot of time recording audible fuzz, to demodulate it into visible TV snow, or listening for a satellite that wasn't there.

I finally found some reliable software by browsing the r/RTLSDR Subreddit, a surprisingly active and supportive community of digital radio enthusiasts with a wellspring of info on satellite communication. It was clear, Satdump was the go-to free application for tracking, hearing and demodulating satellite radio signals. Where my book was offering various programs to do each part of the process, Satdump does all three for a variety of different satellites and LEO objects, including the NOAA and Meteor M2 Satellites. Additionally, I used the Satellite Tracker app on my iPhone to track satellites, verify their actual position and path with Satdump, and find out when I needed to be at my computer to record the downlink. 

My initial set-up

I had my first success when I finally timed a NOAA 15 satellite pass correctly, and started recording the correct radio frequency (137.62 MHz) on Satdump when the satellite came into range. De-modulating a signal is a little difficult for a lay-person, but a Redditor had suggested I listen for "ticking" over the airwaves as the satellite passes. Sure enough, once NOAA 15 popped up in the tracking window as a little red dot, I heard a tick-tick-tick, like an old clock, as the mass of chaotic static in the de-modulator widow started to move together in unison. I was synced with the Satellite! Satdump would start downloading images and data from NOAA 15 onto my desktop. I was using a little handheld antenna indoors, and the satellite's pass was not perfectly overhead. It was just a convenient time for me to run to my computer and set-up, so the first pictures were not great. There was a lot of fuzz where my downlink faded, due to a small antenna with poor reception indoors, but what did come out was unmistakable: swirling clouds and storms over the eastern US and Canada, with the Great Lakes visible. It looks like the Satellite had been well to the east of my receiving range when I caught its signal, but it was clearly a photo of Earth from above!

My rooftop UHF/VHF antenna

Since then, I got a Daiwa coaxial switch for my rooftop antenna, so I could use it for both the RTL-SDR and HAM radio transceiver. Plus, learned a bit more about Satdump's tuning and de-modulating options. Now I'm not only pulling visual images, but data sets with land/sea temperature and precipitation info as well. Plus, I had the opportunity to wait for some very close satellite passes overhead where the signal was the best for the longest period of time. 

Having downloaded numerous images from each of the current NOAA satellites, my next challenge is connecting to the Russian Meteor M2 satellites. There are are only two of them, and one has been either been offline or not functioning for some time. But, I did manage to get a partial image from Meteor M2-3 as of June 11th, 2024 using Satdump, RTL-SDR and my HAM antenna. It's just a mater of waiting for M2-3 to pass-over at closer range. Other challenges will be to build some new antennas specific to this type of satellite communication, as my current set-up is optimized for terrestrial amateur radio, which is likely the cause of some of the static in my images.  

Stay tuned to Cubicalruins.com for an in-depth tutorial on using Satdump to demodulate and image APT signals, as well as updates on connecting to the new generation of NOAA GOES satellites, which are a whopping 22,000 miles away from Earth. Who knows, maybe we can prepare you to save the world one day. 

Image from NOAA 15

Image from NOAA 15 with borders and shorelines colored for reference

A raw NOAA 15 image super-imposed over a flat map of Earth for reference