aptdec

apt decoder satellite

Jon Beniston 3141493ae6 Rename apt_getsample to apt_getsamples, as it gets more than one sample.		vor 3 Jahren
.github	Add release windows build	vor 4 Jahren
cmake	Add action for windows debug	vor 4 Jahren
palettes	Add improved N19 HRPT palette, remove the older bad ones	vor 4 Jahren
src	Rename apt_getsample to apt_getsamples, as it gets more than one sample.	vor 3 Jahren
util	Fix img2pal.py and improve error messages	vor 4 Jahren
.gitignore	Windows build now working properly	vor 4 Jahren
CMakeLists.txt	Rename library so lib isn't repeated on Linux	vor 3 Jahren
CONTRIBUTING.md	Add contributing guidelines, subject to change	vor 4 Jahren
LICENSE	I don't really know what happened, but I can think of these off the top of my head	vor 5 Jahren
Makefile	Add notice about deprecation of the makefile (and fix it)	vor 4 Jahren
README.md	Add support for building a shared library (libaptdec).	vor 3 Jahren
build_windows.bat	Return to src root	vor 3 Jahren
build_windows.sh	Add support for building a shared library (libaptdec).	vor 3 Jahren
textlogo.png	A few changes here and there.	vor 5 Jahren

README.md

Introduction

Aptdec is a FOSS program that decodes images transmitted by NOAA weather satellites. These satellites transmit constantly (among other things) medium resolution (4km/px) images of the earth over a analog mode called APT. These transmissions can easily be received with a cheap SDR and simple antenna. Then the transmission can be decoded in narrow FM mode.

Aptdec can turn the audio recordings into PNG images and generate images such as:

Raw image: both channels with full telemetry included
Individual channel: one of the channels form the image
Temperature image: a temperature compensated image derived from the IR channel
Palleted image: a image where the color is derived from a palette (false color, etc)
MCIR: a false color that uses a underlay map for color

The input audio format can be anything supported by libsndfile (although only tested with WAV and FLAC). Sample rate doesn’t matter, although lower samples rates will process faster.

Quick start

sudo apt install cmake git gcc libsndfile-dev libpng-dev
git clone https://github.com/Xerbo/aptdec.git && cd aptdec
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make

Using the Makefile with GNU automake is now deprecated and will be removed soon.

Examples

To create an image from gqrx_20200527_115730_137914960.wav (output filename will be gqrx_20200527_115730_137914960-r.png)

./aptdec gqrx_20200527_115730_137914960.wav

To manually set the output filename

./aptdec -o image.png gqrx_20200527_115730_137914960.wav

Decode all WAV files in the current directory and put them in images

mkdir images && ./aptdec -d images *.wav

Apply a denoise filter (see Post-Processing Effects for a full list of post-processing effects)

./aptdec -e d gqrx_20200527_115730_137914960.wav

Create a temperature compensated image for NOAA 18

./aptdec -i t -s 18 gqrx_20200527_115730_137914960.wav

Apply a falsecolor palette

./aptdec -i p -p palettes/WXtoImg-N18-HVC.png gqrx_20200527_115730_137914960.wav

Usage

Arguments

-i [r|a|b|t|m|p] Output type (stackable)
-e [t|h|l|d|p|f] Effects (stackable)
-o <path>        Output filename
-d <path>        Destination directory
-s (15-19)       Satellite number
-m <path>        Path to WXtoImg map
-p <path>        Path to palette
-r               Realtime decode
-g               Gamma adjustment (1.0 = off)
-k               Map offset (in px, default: 0)

Image output types

r: Raw Image
a: Channel A
b: Channel B
t: Temperature
m: MCIR (Map Color InfraRed)
p: Palleted

Post-Processing Effects

t: Crop telemetry (only effects raw image)
h: Histogram equalise
l: Linear equalise
d: Denoise
p: Precipitation overlay
f: Flip image (for northbound passes)
c: Crop noise from ends of image

Realtime decoding

Aptdec even supports decoding in realtime. The following decodes the audio coming from the audio device pulseaudio alsa_output.pci-0000_00_1b.0.analog-stereo

mkfifo /tmp/aptaudio
aptdec -r /tmp/aptaudio
sox -t pulseaudio alsa_output.pci-0000_00_1b.0.analog-stereo.monitor -c 1 -t wav /tmp/aptaudio

To stop the decode and calibrate the image simply kill the sox process.

Palette formatting

Palettes are just simple PNG images, 256x256px in size with 24bit RGB color. The X axis represents the value of Channel A and the Y axis the value of Channel B.

Compiling with cmake

Thanks to the help of Aang23 aptdec is moving towards cmake + cpack for builds.

To use cmake to build instead of GNU automake:

mkdir build && cd build
cmake ..
make

You can cross build for Windows from Linux with the build_windows.sh script, you will need the following:

sudo apt install wget cmake make mingw-w64 git unzip

To build natively on Windows using MSVC, you will also need: git, ninja and cmake. Then run:

.\build_windows.bat

If you just wish to build libaptdec on Windows, libpng and libsndfile aren’t needed.

License

See LICENSE