Ok, so in my last post I showed that I was able to receive an image from a weather satellite using only a cheap handheld radio and my phone. You’re probably asking yourself how, right?

Well, that’s what this series is all about! First, let’s build a basic knowledge framework and then we’ll dive into the nitty gritty details.

Meet the Satellites

There are all kinds of satellites orbiting Earth at different altitudes and in different types of orbits. But, for this series, we are going to focus specifically on weather satellites in Low Earth Orbit (LEO). What is Low Earth Orbit, you ask? Well, I’ll explain that in more detail later. For now, let’s just focus on the satellites. Just know that satellites in LEO are easier to “talk to” than the ones in higher orbits.

Currently, there are 5 weather satellites in LEO that transmit signals you can pick up with fairly simple equipment.

• NOAA (National Oceanic and Atmospheric Administration) operates three of them.
• Roscosmos (the Russian space agency) operates the other two.

Different Satellites, Different Signals

Each of these satellites transmits different types of data using different formats and frequencies. Some of these formats require specialized equipment like satellite dishes, but NOAA satellites have one special format called APT that makes them easy for hobbyists to receive:

A Fax Machine in Space

The APT (Automatic Picture Transmission) format is literally like a fax machine in space.

Fax machines work by scanning a document line by line and transmitting it line by line over analog phone lines to the machine at the other end. APT works the same way, except instead of scanning a piece of paper, the satellite is scanning Earth’s surface as it flies overhead. Then, it transmits that data line by line back to Earth.

Of course, there isn’t a long phone line stretching into space! Instead, NOAA satellites broadcast this data using radio waves in the 137Mhz range. This frequency is not too far from broadcast FM radio, which means you don’t need fancy equipment to receive it. A basic radio and some free software are enough to turn that signal into an image.

Here’s what it sounds like!

How Good is the Image Quality?

APT isn’t the highest-resolution format these satellites use, but it’s still pretty impressive for what it is. Here’s how it compares to higher-quality transmissions:

• APT: ~2.5 mi/pixel (4 km/pixel) – clear enough for tracking large-scale weather systems like hurricanes and storm fronts.
• HRPT: ~0.6 mi/pixel (1 km/pixel) – offers sharper, more detailed images, but requires specialized equipment like satellite dishes.

So, while APT isn’t sharp enough to spot individual buildings, it’s perfect for tracking large-scale weather patterns like hurricanes, storms, and cloud cover.

The results speak for themselves!

The above was captured using a more sophisticated technique than the one I alluded to in my previous post. But it’s still easy and cheap.

Is This Legal? Why Isn’t It Encrypted?

Great question! The short answer: it’s 100% legal, and it’s designed to be open.

There are two big reasons why this data isn’t encrypted:

1. It’s not a spy satellite.
   • • Unlike military satellites, these weather satellites aren’t zooming in on people or vehicles.
   • • As we saw earlier, APT images have a resolution of 2.5 mi/pixel (4 km/pixel), so they can track weather systems, not individuals.
2. It’s designed for public access.
   • • Agencies like NOAA and Roscosmos want this data to be available to meteorologists, researchers, and even everyday people.
   • • This is especially useful in remote areas (like the back-country of Alaska), where weather conditions can be life-threatening.
   • • Even if you don’t have TV or internet, a simple radio and a laptop can let you see live satellite images at least twice a day.

Because of these reasons, encryption would go against the whole point of making weather data widely accessible.

Let’s Sum Up

What’s Next?

Now that we understand what these satellites are and why they’re easy to receive, let’s get into how to actually pick up their signals.

In future posts, we will cover:

• 
What kind of radio and antenna you need

• How to track the satellites so you know when they’re overhead

• The software that turns those weird radio sounds into actual images

Stay tuned! (See what I did there? )