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Weather Satellite Station
System 4...

Up to this point we obtained reasonably clear and lengthy images. However, the images were not as sharp as we might hope and also we still had to select the frequency for a given satellite by hand.

The fourth system (see below) replaced the old receiver with a scanner-receiver from Timestep [ Timestep no longer sells sat reception equipment, Dartcom is one option] that was built especially for APT reception and works with their software for fully automatic operation.

System 1:  Image at institute
NOAA-14 image with false color enhancement. Taken with System 4.

We replaced the Icom receiver with the PROscan receiver/scanner from Timestep. It was fully compatible with the PROsat interface and program and so allowed for automatic image taking for long periods.

First setup
Our fourth system

This receiver can scan several frequencies to look not only for the NOAA satellite transmissions but also those from the Russian METEOR, OKEAN and SICH satellites. (Sweden is close enough to Russia to pick up the signals when the latter two satellites download their data.)

[Update Nov.1.08: Timestep has updated some of the following hardware/software.]

  • PROscan APT Receiver - designed specifically for APT reception, this unit can scan for transmissions from more than one satellite.
  • Preamplifier - this device is added at the antenna to boost and filter the output of the signal before it propagates through 30 meters or so of cables. It helps to improve the signal to noise ratio and get sharper pictures.
  • PROsat LC Interface - same as in System 3
  • Software:
    • PROsat for Windows - the same program environment as in System 3 can also control the PROscan receiver. One can arrange a scheduling feature such that images from selected satellites, and only when above a minumum elevation, are recorded and saved to disk automatially.

Creating Colors in a Grey World


False color image from NOAA-15 with country outlines.

The APT visible image data is in grey scale, not color. That is, a numerical value is assigned to a pixel (the smallest image element) according to it's brightness.

However, it's found that similar features tend to have similar grey values: dark areas correspond to water, medium grey to land, and light to clouds. Thus, you can assign blue, green, white to these respective areas and get a colorful image that more or less looks plausible.

More sophisticated algorithms include the IR image data to provide additional clues to what color to assign a particular area.

However, it should be clear that there is a large degree of "art" to making these color images.

For example, different "color palattes", i.e. what color is applied to what grey level, will produce significant differences in the images. Also, typically, one will apply various filters to the images to sharpen them and reduce the background noise. In what sequence the filters and colors are carried out can result in big variations.

Note that in the above image, the green areas correspond fairly well with the land areas. However, just below Great Britain we see that France has melted out into the ocean. The grey scale of a mix of clouds and water were just not sharp enough to avoid this mixup.

System 3 Satellite Station Home System 5

 

The Art of C. Sergent Lindsey
NewSpace Watch at NSG

 

 

 

 

 
 
 
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