A Study of Vignetting on Images Taken with the C3 Coronagraph Aboard the SORO Satellite
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Authors
Moorman, Matthew
Issue Date
1997
Type
Thesis
Language
en_US
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Abstract
I worked at the Naval Research Lab, in Washington DC, with the solar physics
group. The solar physics group is responsible for conducting research using data from a
number of solar satellites. My project consisted of working on the correction and
measurement of vignetting present on images from an instrument on one of these
satellites. Vignetting is an optical phenomenon in which light is focused or blocked in
such a way as to wholly or partially miss a lens or imaging device. In practice this often
means some feature of the data taking instrument, such as an occulting disk or a stop,
blocks a section of the object from being recorded. This appears to us as a gradual fading
out, or darkening, of a section of the final image. In fact vignetting may become so
severe that some image sections may be blocked out entirely. This obviously causes
difficulty with image analysis, and so I was instructed to gather data about the location
and intensity of this vignetting so that it could be decided what course of action should be
taken to correct it.
My project revolved around working with images of the sun taken by the satellite.
This was made more complicated because I had to use IDL, the programming language in
which all work in the branch was done. IDL is an interactive language that is effective in
image and data manipulation. It is also an array oriented language with many
mathematical and graphical routines built into it. Since it is a language that is most often
used in astronomy, and so is probably unknown to the reader, I did not make many
specific programming references in the text. The programs that I wrote can be found in
appendix A.
The following two sections explain necessary background to the reader, such as
information about the sun and the satellite. Following this the project procedure is
explained in detail. The results of this analysis conclude the paper.
Description
v, 43 p.
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