Mike Simmons wrote:
On Fri, 3 Dec 2004 19:02:23 +0000 (UTC), Pierre Vandevenne
wrote:

I have a very basic understanding of digital signal processing at the
mathematical level and what is achieved in terms of resolution is
apparently beyond what can be achieved iin the frameworkd of my limited
understanding.

I would appreciate immensely if someone specialized in signal processing
could explain how this works.

....snip...

And if this actually works, my next question will be, "why did those nasa
guy put their scope in space"?

There are larger telescopes on Earth and with adaptive optics and other
techniques they can record finer resolution than the telescopes in space.
But the ones in space don't have weather or daytime, aren't limited to a
small area of the field for the best resolution, don't require good seeing
for diffraction-limited observing like AO systems do, don't have skyglow
from the atmosphere (I suppose imaging through the gegenschein is
limitingg) and many other factors that make it harder to do these things
from Earth. They can take longer exposures and not have to take multiple
exposures and stack and combine the images (maybe something similar is
still done?). The information arriving at the telescope in space hasn't
been spread around to where you have to go chasing it and putting it back
in order.

There is still interesting processing to do on space images. One certainly
does want to combine multiple images - if nothing else, to reject false
structures from cosmic-ray impacts in the detectors. This is why
individual Hubble image exposures almost never go above half an orbit
even when something is visible longer - the amount of image compromised
starts to become too large. Standard procedure is to combine two with
rejection of wild pixels that are high in one; and for critical
applications more. As was done on the Deep Fields, there is also
a gain to be had from multiple observations slightly offset from
one another, sincethe cameras had to incororate compromises between
pixel sampling and field of view. This technique, "drizzling",
regains a bit of the resolution lost by undersampling the PSF core.
And, incidentally, gives images which look just beautiful when magnified
to the level of original pixels.

So some things are still the same all over...

Bill Keel