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Constructing an Image

By intentionally making radiomaps look like photographs, astronomers can more easily discern patterns in the data collected by telescope. Before any images can be created, however, radioastronomers must process their data through a sequence of four computational steps.

1. Calibrating the Array

Calibrating an array is similar to zeroing a balance when nothing is on it. If an array is not calibrated, the data will be completely distorted, rendering it unusable. The image on the right was produced with uncalibrated data. The left-hand image was computed from calibrated data.

2. Creating a Basic Image

In this computationally-intensive step, raw data is converted into a form that can be used to produce images. After conversion, astronomers can use advanced graphics sofware to produce images. The above picture shows a rough image of the active galaxy, Cygnus A, produced at this stage. Notice all the yellow areas that tend to obscure the object's key features.

3. Deconvolution: Quieting the Noise

Deconvolution takes out the errors, which show up as yellow regions in the previous image, enabling astronomers to discern the actual shape of the object. Here the yellow regions are nearly all gone, and the lobes of gas on opposite sides of the image are now much more distinct.

4. Self-Calibration

Self-calibration fine-tunes the images even further. Notice the filaments connecting the gas lobes to the central bright spot. These become more fully visible once this last step is completed.

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NCSA. Last modified 11/13/95