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Building a Weather Satellite Station
Introduction...

 


A typical raw image output
from NOAA-15 showing both the visible and IR images.

You can build your very own ground station for receiving satellite images, amateur radio satellite downlinks, Space Station ham radio broadcasts, and more. A basic system using your PC can be put together for a few hundred US dollars.


Tracking satellites and receiving their broadcasts is great fun and also brings a wonderful sense of interaction with the spacecraft flying above us.

Remember, no amateur radio license is required for receive-only stations.

See the main Radio page for more information about the different kinds of satellite broadcasts that you can scan. In particular, the HearSat site has lots of info on satellite radio scanning.

Here I concentrate on receiving broadcasts from weather satellites. And also, I focus primarily on receiving images from low altitude, polar orbiting satellites. However, System 5 will briefly discuss reception of geostationary weather sat images.

Note: While we used the Icom receiver and TimeStep components, there are many other hardware and software options to choose from. Follow the links on the Radio page to shop around for the components right for you..

 

Background

I worked for several years as a visiting scientist at the Manne Siegbahn Institute in Sweden. During my final year there, my group leader, Prof. Thomas Lindblad decided to work on a nano-satellite project.

He asked me to help him develop a basic satellite ground station to gain some experience with satellite communications and also as a possible source of educational projects suitable for undergraduate and high school students.

Here I present an introduction to weather satellite reception and review a sequence of 5 systems that we put together going from a cheap, basic system, using freeware and PC sound cards, to a more expensive, elaborate system with commercial software and components. (Even the cost of the later, however, is well within the range of many home entertainment centers.)

Note: We got lots of assistance from space radio experts Bruce Lockhart and Henry Bervenmark. Also, Sven Grahn, of the Swedish Space Corporation and a long-time space radio enthusiast, gave us some useful tips.

LEO vs GEO

Weather satellites can generally be categorized as Low Earth Orbiters (LEO) and Geostationary Orbiters (GEO). The LEO satellites typically follow an orbit of a few hundred to a couple of thousand kiliometers in altitude.

The GEO satellites orbit at around 40,000km above the equator where they move at the same angular speed as the rotation of the earth and so appear to be suspended above a given point on the equator.

The GEO satellites get a view of most of a hemisphere of the earth and can monitor the weather of that region over time.

The LEO satellites, on the other hand, constantly move relative to the earth's surface so cannot monitor a given area continously. But they are closer and so can obtain sharper pictures than the GEO satellites.

The LEO weather satellites also orbit from pole to pole. This allows them to pass over most areas on earth at least once within a given time.

NOAA Polar Orbiters

The US National Oceanographic and Atmospheric Administration (NOAA) operates both GEO and LEO polar satellites. Here we concentrate primarily on the polar orbiters.

The NOAA polar satellites orbit at 850km and pass within view of all areas on earth at least twice day. The satellite carries a number of instruments including cameras for both visible and Infrared light.

The cameras scan back and forth at right angles to the ground path, like a broom sweeping side-to-side as you walk forward, taking picture strips that cover an area 3000km wide. The satellite thus makes a continuous picture as if it was a tape reeling out from an endless roll.

The image, however, is not recorded on the satellite. Each image strip is immediately broadcast to the ground at a frequency just above 137MHz. The satellite will be in range for up to 12min as the satellite passes from horizon to horizon.

The broadcast uses the APT (Automatic Picture Transmission) analog format for the imagery. (A digital format - High Resolution Picture Transmission (HRPT ) signal is also transmitted but it is more difficult to receive and decode and we did not try to receive it in this project. )

Currently, there are 6 operational NOAA polar orbiters but usually only two or three have the APT activated at a given time. (In this report, only images from NOAA-14 and NOAA-15 were received.) See NOAA satellite Status.

The Russian METEOR series of satellites also broadcast with the APT format. In addition, the remote sensing SICH and OKEAN radar satellites occasionally broadcast images but only over Russia (scanners in nearby countries have picked up some of these images.)

Procedure for APT Reception

To obtain the LEO weather sat images, the following basic steps are required:

  • Track the desired satellite to find when it will appear and how long it will be in view (i.e. how high in elevation it will rise). (See NASA's online
    J-Track
    program for an example of NOAA satellite tracking.)

  • Tune the receiver to the right frequency, e.g. 137.620MHz for NOAA-14 and 137.500 for NOAA-15 and pick off the AM signal that carries the image data. The 2400Hz AM subcarrier signal will produce a distinctive "tick-tock" sound from the speakers.

  • Receive the signal for as much of the satellite pass as possible.

  • Decode the signal into the image (Depending on the system, this is done in real-time or the signal is saved to file that is decoded later.)

Find more links to introductory info about weather satellite reception see the main Space Radio page.


Note: There are many other options to the particular hardware and software components that we chose for our systems. Explore the weathersat links to find the system that is best for you.


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