Introduction

After stumbling upon the online communities around software defined radio (mainly the RTL-SDR Blog and the RTL-SDR subreddit), I discovered it was possible to receive high resolution, full disk images of the Earth from NOAA’s GOES satellites using cheap and simple (relative to most other satcom systems) hardware setup. Since I’m located in the Northeastern United States, I’ve got a pretty good view of GOES-16, so I decided to see if I could actually manage to set up a receiver.

Hardware

Based on a few guides I found online (see Notes below), I determined that I needed the following hardware:

  1. Raspberry Pi 3B+.

    Raspberry Pi with RTL-SDR
    Raspberry Pi setup with RTL-SDR
  2. An RTL-SDR software defined radio dongle.

    RTL-SDR v3 and accessories
    RTL-SDR v3 and accessories
  3. An LNA (low noise amplifier) and SAW filter design for the frequency GOES uses (around 1.7 GHz). I used the SAWbird+ GOES Barebones from Nooelec.
  4. A 2.4 GHz parabolic grid antenna modified for 1.7 GHz.

    2.4 GHz Wifi Antenna Modified for GOES 16 HRIT Reception (at 1694.1 MHz)
    2.4 GHz Wifi Antenna Modified for GOES 16 HRIT Reception (at 1694.1 MHz)
  5. Various RF adapters and coaxial cables needed to connect everything together (depends on specific setup, see Notes).

Software

To setup the software side of things, I followed lxe’s guide, summarized below.

Prep your Raspberry Pi and install necessary drivers and software.

0. Get your Raspberry Pi ready

  • Download Raspbian Lite Image and Etcher
  • Use Etcher to write the image to the SD card.
  • Mount the SD card as a volume on your machine.
  • Follow this procedure to configure WiFi and SSH.
  • Plug the card into your Raspberry Pi and turn it on.
  • Find the IP address of the Raspberry Pi using your gateway/router administrative interface.

Now you can SSH into your Raspberry PI as pi with a default password raspberry.

1. Get everything up to date

From now on all commands should be run on the Raspberry Pi.

sudo apt update
sudo apt dist-upgrade

# reboot the device
sudo reboot

2. Install dependencies

# get the packages necessary to build and run goestools
sudo apt install git build-essential cmake libusb-1.0 libopencv-dev libproj-dev

3. Install librtlsdr

Grab the latest librtlsdr source, compile it, and install the shared libraries/includes.

# download, compile, and install librtlsdr
git clone https://github.com/steve-m/librtlsdr.git
cd librtlsdr
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr -DINSTALL_UDEV_RULES=ON ..
sudo make -j2 install

# load udev rules and blacklist the DVB driver shipped with the OS
sudo cp ../rtl-sdr.rules /etc/udev/rules.d/
sudo ldconfig
echo 'blacklist dvb_usb_rtl28xxu' | sudo tee --append /etc/modprobe.d/blacklist-dvb_usb_rtl28xxu.conf

# reboot the device
sudo reoboot

4. Test your the RTL-SDR dongle

rtl_test 

You should see something like this:

Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001
...

If it hangs, just press crtl-c to exit. It doesn’t have to finish.

If there are errors, or if the device is not recognized:

  • Reinstall the driver from Step 3
  • Ensure the dongle is secured in the USB port
  • Remove all USB hubs and plug in into the Pi directly
  • Make sure you power your Raspberry Pi with at least a 2.5A power supply
  • Check the device using lsusb command. You should see ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 or something of the like listed there. If not, try the previous steps.
  • Run dmesg and check for errors such as error -71 related to the USB device. This may mean that your RTL-SDR receiver might be broken. This happened to me, so I ordered another one, which ran fine.

5. Install goestools

git clone https://github.com/pietern/goestools.git
cd goestools
git submodule init
git submodule update --recursive
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr ..

# this will take a while on a raspberry pi
sudo make -j2 install 

6. Create goesrecv.conf config

cat <<EOF > ~/goesrecv.conf
[demodulator]
mode = "hrit"
source = "rtlsdr"

[rtlsdr]
frequency = 1694100000
sample_rate = 2400000
gain = 5
bias_tee = false

[costas]
max_deviation = 200e3

[decoder.packet_publisher]
bind = "tcp://0.0.0.0:5004"
send_buffer = 1048576

[monitor]
statsd_address = "udp4://localhost:8125"
EOF

If you’re using a NooElec SmarTee dongle with an always-on bias tee, or if you’re powering your SAWBird through the micro USB port, set bias_tee = false under [rtlsdr].

If you’re using RTL-SDR.com dongle, set bias_tee = true to power the SAWBird board.

7. Roughly point your antenna at the satellite

Find where the GOES-16 or GOES-17 satellites are in the sky at your location using agsattrack.com.

Note the azimuth and elevation.

Use an actual real compass to point your dish at the azimuth. I’ve been using the iPhone phone compass, which has a 20-30 degree error, rendering it practically useless.

Adjust your dish angle according to the elevation.

8. Run goesrecv and perform fine antenna adjustments

goesrecv -v -i 1 -c ~/goesrecv.conf

This will show output every second that looks something like this:

...
2018-09-15T21:52:03Z [monitor] gain:  8.44, freq: -2121.4, omega: 2.589, vit(avg):  2400, rs(sum):  0, packets: 0, drops:  55

The vit(avg) stat shows the average viterbi error rate over 1 second interval (if running with -i 1).

If there’s no signal, the vit value should be over 2000. When signal is stronger it should decrease.

This should help you point the antenna correctly. Slightly rotate the dish right or left and note whether the vit errors are increasing or decreasing.

Once you’re at the local error minimum, perform the same process to find the minimum error rate while slightly adjusting the vertical angle.

When the vit errors are at their lowest, you’ve pointed the antenna. Double check the antenna position again with a compass to make sure you’re pointed at the intended satellite; GOES-17 and GOES-16 are only about 15 degrees from each other in the sky.

9. Restart goesrecv and play around with the config parameters.

If your vit errors are under 400, and you’re observing no packet drops, you’re all set!

If the average errors are at around 1500-1800, try the following:

  • Terminate and restart goesrecv. This should allow it to readjust the gain and frequency offset to get a better read on the signal.

  • Cool the Raspberry Pi and the RTL-SDR dongle. I’ve noticed that temperature might significantly affect reception quality.

  • Play around with goesrecv.conf parameters. Try adjusting the gain and sample_rate. For the NooElec XTR or other E4000 tuners, you might need to set your gain to 10 or below.

Once you decreased the error rates, but your vit is still over 400, try making very slight adjustments to the antenna again.

10. Process packets into images

While goesrecv is running, in a separate session, run:

goesproc -c /usr/share/goestools/goesproc-goesr.conf -m packet  --subscribe tcp://127.0.0.1:5004

Once goesproc receives enough packets, it will start writing images and text to the locations described in /usr/share/goestools/goesproc-goesr.conf.

Writing: ./goes16/m2/ch13/2018-09-15/GOES16_M2_CH13_20180915T231750Z.jpg
Writing: ./goes16/m2/ch13_enhanced/2018-09-15/GOES16_M2_CH13_enhanced_20180915T231750Z.jpg
Writing: ./goes16/m2/ch02/2018-09-15/GOES16_M2_CH02_20180915T231750Z.jpg
Writing: ./goes16/m2/fc/2018-09-15/GOES16_M2_FC_20180915T231750Z.jpg
Writing: ./goes16/m1/ch07/2018-09-15/GOES16_M1_CH07_20180915T231820Z.jpg
...
goesrecv and goeslrit running on my laptop
goesrecv and goeslrit running on my laptop.

Results

Here are some of the images I was able to get off of GOES-16:

Full disk, false color image of Earth from GOES 16.
Full disk, false color image from GOES16 (false color provided by goesproc).
Cropped false color image of Earth from GOES 16.
Same image as above, but cropped to show full resolution.
GOES 16 Channel 7 Enhanced GOES 16 Channel 8 Enhanced GOES 16 Channel 9 Enhanced GOES 16 Channel 13 Enhanced GOES 16 Channel 14 Enhanced GOES 16 Channel 15 Enhanced
Some more full disk images from GOES16, enhanced by goesproc.

Next Steps

While this was a great proof-of-concept prooving to myself that it’s possible to get a downlink from GOES-16 using off-the-shelf parts, there’s a lot more that could be done with this concept.

  • Automate the ground station to provide images and weather data 24/7.
  • Waterproof electronics enclosure so the ground station can stay outside indefinitely.
  • Solar power system so the ground station can be placed anywhere with sufficient sun.

Notes

This wouldn’t have been possible without the work of a lot of others before me. Some of the most usefull resources I found about this subject are:

  • Pieter Noordhuis’ goestools and his guide for setting up A minimal LRIT/HRIT receiver
  • This guide that goes into a little more detail about how to use goestools.
  • Additionally the RTL-SDR Blog is a wealth of knowledge about anything to do with this type of software defined radio.