Maps, radios, Russian satellites?! A perfect combination!

In my work I do a lot of satellite image processing and analysis. But the images I use are already accessible for me here on Earth. The messy part of communication, downlinking, transmitting, and processing of the raw satellite data is handled before I even get my hands on it. This got me thinking about how that whole process works, and whether I could do it myself to some extent.

As is usually the case with neat ideas, this question lead to two things:

Firstly it showed me that I was far from the first person to try this, and in fact there is a long established community of radio enthusiasts who build ground stations, ranging from simple scrap antennas, all the way up to HAM radio experts who have thousands of dollars worth of hardware.

Secondly it led me down an enormous rabbit hole of a new world of things I don’t understand, which is always good to experience.

I’ll lay out the most basic things to understand before I go through the project, but for a really comprehensive understanding, I will link to some excellent literature on the subject (beware of the rabbit hole)

The Satellites

The quest begins with looking at satellites that broadcast their images continuously via intercept-able radio frequency. There are a few satellites that are a great start for this - namely the American NOAA 15, 17, 18, and 19, the Russian Meteor M2-2, and for a bit more of a challenge, the GOES 15,16, and 17 geostationary satellites. These are all weather satellites, so of course the resolution is not going to be the same as optical imaging satellites, and you wont see your house from the image, but what they lack in resolution they make up for in coverage. One NOAA pass can get you an image over 5,000 kilometres long, and around 3,000 wide, depending on your antenna setup. The GOES satellites take an image of one WHOLE side of the Earth!

The Hardware

The core hardware in this project is simple. First an SDR (Software Defined Radio), and secondly an antenna. I ordered a USB SDR from amazon and built my own crossed dipole antenna to the specs in this article. With surprisingly little modification the antenna picked up satellite signals clearly and reliably. The SDR acts as a radio, but connects to a digital interface to allow you to tweak all the variables that are typically un-tweakable in traditional radios. bandwidth, gain, offset, doppler compensation, and of course, recording are some of the things an SDR can do.

The Software

For controlling the SDR, I used a program called SDR#, and depending on the satellite transmission that you are intercepting, there are different recording and processing steps from SDR# onwards.

For NOAA satellites, I piped the SDR# output into a program called WXtoIMG to turn the signal into an image.

For Meteor M2-2, there is a standard decrypting, and decoding workflow that works pretty well through LRPT-Decoder (Link here)

The Process

For NOAA and Meteor satellites, you first have to know when they are going to fly overhead. These satellites are in a polar orbit, and pass overhead twice per day, but the highest pass altitude (angle above the horizon) differs between passes. Once a good pass with a high maximum altitude has been predicted, you can find a quiet radio-free area with as good South-North sky visibility as possible.

There are lots of options for tracking and planning passes. I use this one for predicting passes, and this one for tracking and mapping the satellite information during the pass.

In the SDR program, bandwidth and frequency can be set before the pass to prepare. Then, as the satellite comes over the horizon, The rhythmic pulses of the transmission should grow in clarity. Getting this signal to be completely free of static is the key to getting good images. Static in the radio frequency equates to static on the subsequent image. Below is a short recording of the sound of NOAA 19.

The quality of the intercept depends on a variety of factors, such as radio noise in the area, obstructions, antenna tuning, and the ability to compensate for the doppler shift of the transmission signal as it passes overhead.

The final step is to import the audio file of the pass into WXtoIMG and let it crunch away at decoding and converting the sound into an image. The NOAA satellites usually downlink optical, AVHRR, IR, and ADCS data which can be viewed and analyzed like any raster satellite image.

Below if a gallery of some winter shots from the NOAA satellites. In the winter (at my location anyway) we are limited to intercepting only the morning passes, as the afternoon passes are already well past sunset, and therefore we miss the optical imagery. I provided an overlay image on google earth to demonstrate the enormous coverage of a good NOAA pass. On that particular pass, we were able to receive signal for over 11 minutes, as the conditions and location were perfect. Some of the other images show the different wavelengths and modifications that can be done to the imagery after downlink.

Ill be updating the gallery as I get more good images!

Coming soon: intercepting, decoding, and projecting Meteor M2-2 and GOES!