---
title: noaa-apt image decoder
layout: landing
---

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					<img src="images/index_sidebar.jpg" alt="Example image"/>
					Example image of Europe, the quality of the images depend mostly on
					the antenna. Credit: JKamue
				</section>
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					<img src="images/index_sidebar_2.jpg" alt="Example image"/>
					Another image with a map overlay drawn over it.
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				<h2>Receive and decode images from weather satellites</h2>
				<span class="byline">Free (GPLv3) NOAA APT decoder, available
					for GNU/Linux, Windows, Raspberry Pi 2+ and OSX</span>
			</header>

			<p>
				<em>noaa-apt</em> takes a recorded WAV file and decodes the image. As an
				example,
				<a href="{{ site.baseurl }}/examples/argentina.wav"> this is a WAV file I recorded using GQRX</a>
				using a RTL-SDR and a double cross antenna.
				When loading that file on <em>noaa-apt</em>, you get as a result
				<a href="{{ site.baseurl }}/examples/argentina.png">this image</a>.
			</p>

			<h3>Why?</h3>

			<p>
				NOAA satellite reception is fun, cheap and relatively easy. You can buy
				a <a href="https://osmocom.org/projects/rtl-sdr/wiki/Rtl-sdr">RTL-SDR</a>
				for less than 30USD, it looks like a USB drive but it has a connector
				for antennas. Using SDR software like <em>GQRX</em> and <em>SDR#</em>
				you can receive FM signals, for example broadcast FM (around 100MHz) or
				better, receive APT signals from NOAA satellites (around 137MHz) and
				then decode them with <em>noaa-apt</em>.
			</p>

			<p>
				I made
				<em>noaa-apt</em> because <em>WXtoIMG</em>, the most popular decoding
				software, it's propietary and
				<a href="https://www.rtl-sdr.com/notice-wxtoimg-website-down/">no longer maintained</a>,
				but you can get old recovered versions from an
				<a href="https://wxtoimgrestored.xyz/">unofficial website</a>. Also, the
				<a href="{{ site.baseurl }}/guide.html#wxtoimg-guide">
					steps required to decode WAV files on it
				</a>
				are not that obvious.
			</p>

			<p>
				There are lots of really good
				<a href="{{ site.baseurl }}/alternatives.html">Alternatives</a>, but all
				of them require compilation, Python or don't provide graphical user
				interfaces. So I wanted to create an easy to use alternative for Windows
				users, being useful to advanced GNU/Linux users doing some kind of
				automation too.
			</p>

			<h3>Disadvantages</h3>

			<p>
				<em>WXtoIMG</em> has better false-color and image overlays, also has
				features <em>noaa-apt</em> does not have (like live decoding). Anyways,
				the quality of the black and white image should be the same in both
				programs.
			</p>

			<p>
				If you get some kind of error or bad result open a Issue or send me an
				email. Also I'm not a native english speaker so please let me know where
				I made mistakes. Both the code and the website is on the
				<a href="https://github.com/martinber/noaa-apt">GitHub repository</a>.
			</p>

			<h3>Screenshot</h3>

			<img src="images/gui.png" alt="GUI"/>

			<h3>About NOAA images</h3>

			<ul>
				<li>
					NOAA satellites are transmitting images 24/7, and the image you
					receive is a real-time image of your location. The transmission is
					free to be received by anyone with an antenna, and there is no
					<em>official</em> decoder or receiver.
				</li>

				<li>
					NOAA <strong>images are black and white</strong>. When you see a color
					image it means it was colorized by some program, this is called
					<em>false color</em>.
				</li>

				<li>
					NOAA <strong>images do not have map lines</strong> (divisions between
					countries, states, or coastlines). When you see images with lines, it
					means that they used noaa-apt or WXtoImg to draw them according to a
					map and calculations about the position of the satellite when the
					image was taken.
				</li>

				<li>
					The <strong>images are upside down 50% of the time</strong>, that's
					because the satellites sometimes go from south to north and sometimes
					fron north to south. noaa-apt and WXtoImg can calculate the orbit of
					the satellite and rotate the image accordingly.
				</li>

				<li>
					Images look <strong>much better on daylight</strong>, the satellites
					also send infrared images at night but I recommend receiving passes
					when the sun is high in the sky,
				</li>
			</ul>

			<h3>Features</h3>

			<ul>
				<li>Decode raw images from WAV files.</li>
				<li>Add map overlays with countries, states, provinces and lakes.</li>
				<li>Simple false color</li>
				<li>Really easy to use (at least easier than other decoders).</li>
				<li>Histogram equalization.</li>
				<li>You can disable syncing and export every step of the decoding
					process, useful for corrupted recordings.</li>
				<li>Telemetry band reading.</li>
				<li>Resample WAV files preserving modification timestamps.</li>
				<li>Modify timestamps of files.</li>
				<li>Edit filter parameters from a configuration file.</li>
				<li>Rotate the output image, in case of ascending (South to North) passes.</li>
			</ul>

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