| Back | Up | Map | Glossary | Information |
First, the calibration source and the object under observation lie in separate parts of the sky. Consequently, the array is pointed at different parts of the atmosphere during calibration, then observation. Atmospheric conditions can vary considerably across the sky, affecting the incoming signals distinctly. Such directional differences typically show up as noise in the final image.
Second, it is not possible to observe the calibrator continuously as this would leave no time to observe the object of interest. However, the atmospheric conditions may fluctuate slightly while the object of study is being observed. If such fluctuations happen rapidly, the regular calibration process may not be able to correct for them adequately. Rapid atmospheric changes can add further noise to the final image.
Image of Cygnus A : Before Self-calibration
This image of Cygnus A was produced after the deconvolution process, before self-calibration
was applied. The blue and black speculations in the background represent
JPEG Image (27.5K); Credits and Copyrights
Image of Cygnus A : After Self Calibration
The image to the left was created using the same data after
self-calibration. Here the noise is much reduced. As a result, the faint trail of
the jet connecting the central galaxy to the outer lobes is revealed.
JPEG Image (12K); Credits and Copyrights
Return to Constructing an Image
Up to Insight Through Images