Use GIMP to process satellite images

Satellite photos are familiar, their underlying technology less so. Mike Bedford reveals how to process their spectacular images.

- Mike Bedford

Photographs of the Earth taken from space are a P part of everyday life, appearing on TV and newspaper weather reports. This state of affairs dates back little more than 60 years, though, to when TIROS-1, the first weather satellite, was launched. How things have changed in the intervening period. By the end of April last year, 971 satellites were in orbit for the purpose of Earth observation. And unlike the early days, these satellites aren't just operated by governmental organisations: several commercial enterprises now supply photography of the Earth's surface. But publicly owned satellites are still important.

If you want to learn about the technology, the good news is that these satellites have the undeniable advantage of free access to raw data. We saw this in LXF273 when we looked at how to receive data from America's NOAA Weather satellites and display that data as a map. The NOAA satellites are great for amateur experimentation because they orbit at a low altitude. This means they can easily be received using simple equipment, even though we took the approach of receiving the signal through a WebSDR, an online software-defined radio.

On the reverse side of the coin, NOAA satellites transmit just two black and white images: usually one in the visible spectrum and the other in the near-infrared. Therefore the scope for producing coloured images even false colour - is severely limited. So, here we're investigating a different class of satellites that enables us to produce spectacular colour images, with plenty of scope for choosing between true colour and the many different false colour alternatives.

Introducing Landsat