The images were obtained using the UIST camera/spectrograph on the United Kingdom Infrared Telescope at Mauna Kea. Each observation consisted of a series of short exposures of 0.09 seconds. Images were obtained in four different narrow band filters at wavelengths of 1.57, 1.64, 2.12 and 2.27 micrometres.
The quality of images obtained from a ground-based telescope is
limited
by turbulence in the Earth's atmosphere (known to astronomers as
"seeing").
UKIRT is situated on the 4200m summit of Mauna Kea in Hawaii, a site
renowned
for its excellent seeing. By using very short exposures we are able to
obtain even sharper images by freezing occasional instances of better
than
average seeing. The example below shows the stages in processing of a
1.64
micrometre image obtained on September 4th 2003.
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| This is the result of adding together a series of short exposures, and shows the image quality resulting from the natural long-exposure seeing at Mauna Kea. | By selecting the sharpest image or images out of the set we can freeze an instant of excellent seeing. Bad pixels on the detector array have also been cleaned out of this image. | The image has been further processed by using the technique of "unsharp masking" to enhance fine detail, and smoothing to reduce graininess. |
Another example below shows the same comparison of images for data
taken
in rather poorer seeing on Aug 16th.
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Images obtained in different filters can be combined to obtain
colour
composites. However, since Mars has usually rotated significantly
between
the time when the three filter images were obtained these may not be as
sharp as the indivdual filter images, and may have colour artifacts
such
as red and blue limbs on opposite sides of the planet.
Jeremy Bailey - 4 Novenber 2003