receiving weather images from the NOAA satellites using software defined radio (SDR)

My experiences with amateur radio satellites.

You can use the heavens above site or n2yo to see what satellites are passing you and when.

Here is a collection of the satellite that I have decoded transmissions from.

NOAA Weather Satellites

The NOAAx satellites are weather satellites that broadcast a satellite image over VHF using the APT (Autmatic Picture Transmission) protocol They were commisioned by the National Oceanic and Atmospheric Administration

The two that often orbit over me are the NOAA-15 and the NOAA-19.

Finding out when its passing

for that you can use the heavens above site or the Look4Sat android app.

example view for the NOAA 19 satellite on heavens-above.com

The start and end times are when the satellite is passing and the altitude and azimuth are the angle and direction respectively. a 90° azimuth is directly over your head. you can use this information to help you orient yourself when you try to record the signal.

recording the signal

I used my baofeng uv5r to listen in on the frequency specified in the Look4Sat android app (137.62MHz in my case)

I recorded the audio using my cellphone. (I recorded a video but audio only would probably work better)

The longer and clearer recording you can get the better the final image will be.

I then stripped the audio from the video using ffmpeg

ffmpeg -i video.mp4 -c:v copy -vn audio.wav

using wxtoimg

If you are on windows you can use wxtoimg to decode your audio into a satellite image

wxtoimg is abandonware and getting hold of a copy can be a bit tricky with all the reposted copies available. I used this link to get my installer.

The software is old enough that the windows version should work without issues in wine on linux but there is better software available on linux.

The audio then needs to be mixed down to mono and resampled at 11025Hz to match the requirements for wxtoimg

the audio then needs to be saved as a .wav file.

This can be done using Audacity

note: if you have ffmpeg installed audacity may be able to automatically extract the audio from a video file on import
GIF showing the processing of the audio preparing it for wxtoimg in audacity

the audio can then be imported into wxtoimg and it will be automatically processed into an image

using noaa-apt

get noaa-apt here

results

My first attempt went quite poorly

My first attempt at getting a sattelite image from one of the NOAA weather sattelites using my Baofeng uv5r

On my second attempt i was able to see some border informaiton and part of an image on the left

My second attempt at getting a sattelite image from one of the NOAA weather sattelites using my Baofeng uv5r

but after giving it few more shots and taking a much longer recording I was able to decode a pretty decent image.

The best result I got from the baofeng (false color) The best result I got from the baofeng (raw+IR)

Here is a false color image and the raw+infrared image (you can make out some clouds as well as the west side of Africa)

The boafeng doesn't really have enough bandwidth to get a full quality image and it's really easy to accidentally move and mess up the signal (which you can see in the vertical lines)

I still haven't managed to get my SDR working for this. (I think i might need a different antenna) but it should provide much better image quality.

tips

  1. try to get as long a recording as possible without too many interferences.
  2. recording the direct audio out from the headphone out into some kind of audio interface may provide cleaner recordings
  3. using a better antenna could also help

I will be trying this again with an antenna and an SDR which should provide higher bandwidth (and thus more data) for a better quality image.

references