Hi Jon,

I just looked at your web site.

In regards to seeing:

The weather balloon reduction needs a few adjustments.
Look up "Dewan optical turbulence"

You will need to adjust the optical turbulence as a function of altitude
by the density of air to compute the refractive index.

The wind shear effect goes as the square of the wind gradient.
you also need an outer scale, the depth of the optically significant
turbulence.

I have been looking at this for a few years as well and have recently
come back from an observing run where I used a SCIDAR to measure the
altitude profile of the seeing while also measuring the image quality
from one second exposures.

It seems as if most of the seeing came from the layers near the ground.
we had an approaching front at the time and the upper wind were over 100
mph. The upper seeing was only about 10% or less of the lower layers (
within 3000 feet) and the telescope combined.

The upper layers appeared to have larger time scales compared to the
lower layers. The near ground layers had the smallest time scales and
largest amplitude.

The seeing varied over the 4 day run from 2.5 arc seconds down to 0.45
arc seconds.

It looks like the near ground layer and telescope enclosure have the
greatest amplitude.

Dan

Ps The Images being discussed in this thread are the results of the
image processing and do not represent the actual reference image.

even with adaptive optics people have "over reconstructed" images
as the system PSF is unstable and reconstruction tends to magnify
these errors.






Jon wrote:
Jon,

I'm not sure you followed the links and read what said there. It's a
little beyond a simple good/bad binary logic.
You can quantify the probability of getting good frames based strictly
on your seeing values (not estimated but MEASURED) and scope size .
If you don't have the means to measure your seeing , something like a
DIMM
setup, I don't see how you could make any judgment .
Most amateurs do not measure seeing and are not even aware that it
could be measured .
If you measured your seeing and the relationship between your seeing
and your scope size should produce N good frames over a period of time
and it produced none, AND you measured your telescope as an instrument
in the configuration you were using for imaging AND it was diffraction
limited, THEN please write a paper and publish the results . You might
be discovering a new mathematical model for atmospheric turbulence .
Until then, I'm not with you or Roland but with Kolmogorov .

best regards,
matt tudor


Matt, I admit I only glanced at the links. I took a closer look at the
simple webpage. I am getting in deep water here, but if I understand it
correctly, the equation shown above the graph gives the probability of
getting a diffraction limited frame for a given seeing and telescope
aperture. How was this equation arrived at? Empirical data/ theoretical
modelling/both? I assume the idea is that over (short) time there is
variation around the mean value of seeing, i.e. multiple seeing
measurements would show a certain distribution with variation around a
mean, and one tail of the distribution will correspond to the better than
average seeing.

In my opinion (not supported by DIMM, but subjective seeing asessments
based on the Pickering scale), the shape of the distribution can vary
greatly between nights. Especially when there is a strong jet stream above,
there is little variation around the mean, and I think on those nights
there will not be any really good frames however long one captures. Making
the exposures short will not overcome the problem; the "fast" seeing means
a constantly blurred image.

On a side note, I have looked a bit into the possibility of making DIMM
measurements with a web camera. The main obstacle is the software; I have
some DIMM software, but it is not compatible with any web cameras.

On my webpage http://home.no.net/jonbent/Sky.html#Anchor-Seein-40104
I have made an attempt to correlate my seeing estimates to meteorological
conditions. I freely admit I have no theoretical background in either
meteorology or astronomy, so my speculations may seem naive. If you have
any comments or corrections please contact me.
Jon Kristoffersen