Solar Scintillation Monitor + trigger

[bokemon]

Yes, I know there is a seeing monitor. But it would also be nice if Sharpcap could do "solar scintillation" mode, where all it does it capture the total integrated intensity from a camera sensor, and then runs whatever low-pass / high-pass algorithm on that intensity to derive seeing in arc-seconds. I'd like to use this feature in two ways:
1) just literally get a camera sensor (no lens, but maybe a ND filter) and point it at the sun to get a seeing value. I would take this setup and test out various locations, time of day, etc without having to set up my telescope. The utility here is the "absolute value" of seeing in arc seconds that holds across all different setups, locations, times, etc.
2) Fire up two instances of sharpcap, and have this trigger the capture instead of Seeing Monitor. My understanding is that seeing monitor, via using contrast, is a more spatially and temporally local measurement.

[admin]

Hi,

I must admit that I have never quite understood how this sort of technique would measure the quality of seeing, which doesn't bode well for any attempts to implement it!

cheers,

Robin

[Jean-Francois]

Hello Robin,

The intensity of the sun illumination is varying like the night stars scintillation.

Here an example few days ago. It is a star in Orion. The funny is the small vertical line. It is several geostationary satellites.
The star line is not homogenous illuminated. The spot is moving on the detector and the intensity is varying.

Star_scintillation.png (36.27 KiB) Viewed 3725 times

It is the same with the sun disc illuminating and a detector (normally a photodiode).
So more continuous intensity means low turbulence.

Bokemon, if you are reading my other messages, then you will find a script that does fast what you want (at least the beginning)..


Regards,
Jean-Francois

[bokemon]

I learned about this from looking at a few DIY SSM guides, but:
They pretty much take a signal from a photodiode (not focused on anything) and just measure the low pass (average) and high pass component of the signal. Then out of nowhere is a magic formula that is seeing (arc-sec)= (prefactor) x (rms variation) / (average intensity). The DIY project is largely about soldering the analog circuit together, then programming an Arduino.
One thing to watch out for is (I suppose?) a rolling shutter effect where the time of reading the first sensor line of pixels is not the same as the last line. OK, maybe just read a small group of pixels then?

[admin]

Hi,

OK, so essentially the physics behind it is microlensing by the atmospheric turbulence causes the brightness of illumination to change at a given point, and the time variation of that is related to the seeing (more turbulence, more frequent changes in the optical structure of the atmosphere, more variation, I guess).

It might be possible to do the same with a small camera (guide cam, etc) and software processing in SharpCap. No sun here today, so I can't test whether I can get the exposure low enough not to saturate when pointing the sensor (no lens) towards the sun. I supposed that even if it doesn't go low enough, a pinhole illumination or neutral filter could be used.

The biggest issue is that SharpCap is designed quite firmly around operating one camera at a time - changing things so that one camera can be used for scintillation measurement and another for capture would require a fairly substantial re-work of one part of the code On the other hand, it's a code change that I've thought would need to happen at some point anyway, so not out of the question.

cheers,

Robin

[Jean-Francois]

Hello Robin,

Bokemon mentions to use 2 instances of SharpCap (each instance with one camera).
The question is now how to trig the capture in one instance from the other instance ... all from a script.

Jean-Francois

[admin]

Oh well, in that case... easy... Someone's writing a web server... viewtopic.php?p=39426#p39426



cheers,

Robin