Height of imaging rig vs “seeing”

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DavidP
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Height of imaging rig vs “seeing”

Post by DavidP »

Hello all,
I’m in the planning stages of an observatory to be used mostly for Solar imaging. I’ve heard advice that the higher the imaging train the better in terms of local seeing from ground-based radiation and heat convection. I’d be interested to hear of different experiences with regards to this. I could see how positioning a rig 10 or 20’ high could make a difference, but 3x’ versus 5 or 6’? A SSM wouldn’t measure this would it? It seems like it measures atmospheric seeing only.


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Re: Height of imaging rig vs “seeing”

Post by christian viladrich »

Hello David,

This is an interesting question !

First thing, the SSM does measure seeing from ground level (more precisally its sensor level) to about 1500 - 2000 m high. So ground seeing is indeed measured by the SSM.

Now, the answer to your question depends on observation conditions (hour of the day, nature of the ground, humidity level of the ground, wind, etc.).

In this first example, seeing is measured at ground level (green grass, no wind) and 1 m high :
http://astrosurf.com/viladrich/astro/in ... -label.jpg
The difference is about 0.5 arsec.

In this second example (mountain site, rocky ground, no wind) the seeing is measured simultaneoulsy at 1 m and 1.5 m (using two synchronised SSM over a period of 1h, by Karine Chevalier) :
http://astrosurf.com/viladrich/astro/in ... ret-GB.png
http://astrosurf.com/viladrich/astro/in ... ing-GB.png
The difference is between 0.3 to 0.4 arsec.

This is something you can experiment by yourself at home. My suggestion would be to use two synchronised SSM. This is really worthy.

Hope this helps

Christian


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Re: Height of imaging rig vs “seeing”

Post by DavidP »

Christian.
Thank you for clarifying the SSMs ability to reflect ground level seeing.
You're data is fantastic.


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Re: Height of imaging rig vs “seeing”

Post by marktownley »

I've recently set up a pier in my garden David, and deliberately went for something 'tall', with my long refractors the objectives sit about 8' in the air, i've noticed an improvement in my seeing, when overall seeing is good!


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Re: Height of imaging rig vs “seeing”

Post by DavidP »

Do you have any pics?


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Re: Height of imaging rig vs “seeing”

Post by christian viladrich »

Interesting Mark !
I have to put on my to do list another test at home with two synchronized SSM.


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Re: Height of imaging rig vs “seeing”

Post by marktownley »

ImageP1000699 by Mark Townley, on Flickr

ImageP1000695 by Mark Townley, on Flickr


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Re: Height of imaging rig vs “seeing”

Post by DavidP »

Good job in your pier Mark


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Re: Height of imaging rig vs “seeing”

Post by Rusted »

I have some experience with my raised observatory in a very rural situation.
Fields rise gently to my east with low hedges and a few isolated trees before more distant forest starts at 1000m.
I had to go high just to see over the nearest field hedges! Which are trimmed for thickness but not height.

My 10' plywood dome is 4m high to the base ring. The mounting slightly higher.
Plywood was chosen for the dome as being thermally neutral. Or to have low thermal mass.
It certainly isn't reflective and can easily reach 130F on the inside surface! Chilling rapidly to passing cloud.
MY dome is painted sage green to match the surroundings. NOT WHITE AS IT SHOULD BE.
Domes are lovely to be in and provide shelter but have thermal issues for solar imaging.

White surfaces and materials are often thermally neutral when measured with a remote reading thermometer.
No bare metal that I have measured is cool. The only cool roofing material is white corrugated cement.

My idealised solar imaging platform would be made of wood and raised a few meters above a field of grass.
It would have an adjustable wind break of white cloth, or layers of white net, to stop wind buffeting the instruments.
The imager could be housed in a closed room off to the north or under the north side of the platform.

P1280456 rsz 600 dims.jpg
P1280456 rsz 600 dims.jpg (170.8 KiB) Viewed 91 times
P1360328 rsz 600 upright bright.JPG
P1360328 rsz 600 upright bright.JPG (120.39 KiB) Viewed 91 times


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Re: Height of imaging rig vs “seeing”

Post by EGRAY_OBSERVATORY »

An interesting project Chris and also reading through your blog too.

Thanks vm
Terry


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Re: Height of imaging rig vs “seeing”

Post by Rusted »

Thanks. I built that myself a couple of years ago and must have spent hundred of hours imaging in it.
A larger GRP dome 4.3m [14'] is [hopefully] only a month or two away from completion.
The 10' plywood dome is not sufficiently waterproof. Nor large enough for my 7" f/12 refractor + dewshield.


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Re: Height of imaging rig vs “seeing”

Post by EGRAY_OBSERVATORY »

I like it when self-designed and built projects like yours are eventually finished and up and running.

Mine took a short-time to design, but a long-time (several years) to build and eventually fit-out with just about everything I will ever need for mainly Solar-viewing/imaging, but night-viewing/image capable. Actually (as far as I know) there is nothing-else to do, except any annual-maintenance (outside white-painting of the external aerated concrete block wall and cleaning/painting the sliding-roof rails (if required).

I had thought about and looked at domes etc., but I decided that I wanted a large area inside to let me even be able to sleep-in, so the sliding-roof design was my first idea.

The first thing I designed and built was actually the four-legged stand, followed by a 6'/2-metre deep and round-hole, filled with three 20'/6-metre long steel-poles into the substrate and filled with concrete c/w with the mounting-studs in place and long before any walls were in situ. That was around 2001 and between then and a couple of years ago, I was flying nearly every day, so time was limited.

Since about 2012, all the main-construction of walls, roof and motorised railway-system, as well as internal cupboards, desk and basic mains-electricity has been completed.

Last year in July, a change of computer-system from a laptop to a hi-spec computer and adding two-large-screens (one hi-res), was more or less the final part of finishing the observatory and the experience of now being able to quickly start viewing/imaging, without lots of setting-up has proven invaluable and works very well.

So it is really only in the last couple of weeks - that my observatory is now fully operational.

Much of my design-time, is actually when I'm in bed - just before falling asleep, where I seem to work-out what is best !!!

Congrats on your interesting and excellent design and construction Chris.

Regards
Terry


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Re: Height of imaging rig vs “seeing”

Post by Rusted »

Thanks Terry. :bow

Your project sounds far more sophisticated than mine.

But based on my own experience:

Don't build a plywood dome without covering it in GRP from the outset.
I spent many hundreds of monetary units on "marine quality" sealants and they all just cracked wide open in use.

Domes are very useful if you often have cold, changeable or windy weather. Or all of them together.
As soon as I see rain falling on my imaging desk I can be fully closed up in seconds.
Manually operated, bi-parting shutters are quickly opened and shut. No waiting for rain sensors and slo-motors.
The protection of the dome makes hours of sitting at low temperatures almost tolerable.
Though it does require proper clothing, gloves and footwear.

A raised platform is great fun but horribly exposed. I tried that while I was building the dome.
It required rapid-fire, tarpaulin covers for the large and sensitive instruments. Not great in windy conditions!
A platform doesn't protect the imager from the heat of the sun. While I am in constant shade in my cosy dome.
The sunlight coming through the slit is easily avoided without my having to move from my desk.

I wasted years viewing from the ground before I started getting "serious altitude sickness."
The seeing was always awful and very limited by trees and tall hedges.
The steadiness of the seeing on the sun and moon from my raised dome was often quite shocking.
Though never guaranteed. I get around that problem by imaging whenever the sun is out.
If the seeing is really awful I can get back to work on the building.

Large, hi-res, low reflection monitors are vital for monitoring momentary changes in seeing when capturing close-ups.
My ASI174 provides 3 second videos at 800x600 frame sizes. That means lots more chances for those lucky moments.
The modest frame size helps avoid etalon, sweet spot variations while still providing all the detail resolution I need.
I process as I capture. Endlessly. With all the useful software already open: SharpCap, AS!3, Imppg and PhotoFiltre.
How else was I ever going to catch up on the imagers with decades of head start over me? ;)

I sit comfortably, with my back against the north wall of the observatory. The 27" AOC monitor is hung on the massive pier in front of me.
The desk and observatory are isolated from the pier to avoid vibration.
I always wear all black clothing for imaging to avoid any reflections from the monitor spoiling my view.

The instruments and mounting cast their shadows on me and I wear peaked cap to avoid direct glare when looking around.
I can easily see the [large] telescopes in all pointing positions and monitor the intensity of the sunshine on the observatory wall.
In cloudy conditions this is useful for checking for useful short clearances. Meanwhile I can be processing or blogging or posting my latest images.
It saves my having to constantly go back to the SharpCap screen. Just to see if it is worth capturing more clouds.

I constantly change the TS binoviewer GPCs in my imaging set-up to match the seeing conditions. A 2x Barlow is almost always, complete overkill!
GPCs are far more subtle in power than Barlows. I don't need any more magnification than I already have with 150/10 and 180/12 optics.
The TS GPCs claim 1.6x, 2x and 3.4x but probably less than half that fitted onto the camera nose.

I hope somebody somewhere finds something useful. Being retired I spend literally hundreds of hours imaging.
You learn as you go along what works and what merely hinders progress.


http://fullerscopes.blogspot.dk/

Baader 160mm D-ERF, iStar 150/10 H-alpha, Baader 35nm H-a, Beloptik KG3, PST etalon, Lunt B1200S2, Assorted TS GPCs, ZWO ASI174.
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