does anyone knows if there is a way of calculating atmospheric extinction using Astap?
Taking exposures at different altitudes (90º, 50º, 30º and 20º for ex.) and comparing Star Catalog magnitudes with measured ones could be a way, but I guess Astap is already might be estimating and compensating using airmass when calculates star magnitudes. I don't know if I'm talking nonsense here, just an idea.
Regards and thank you for this wonderful piece of software!
Pablo.
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ASTAP is calculating the airmass extinction for the SQM measurement. I assume using the delta transparancy will only work if you have no light polution. That will be only the case at rare superb dark locations.
For comparing the transparancy between several nights you could theoretical compare the flux measured but again the light pollution should be constant.
There is one measurment already available and that is reporting the limiting magnitude. This value is reported if you select in tools "Magnitude (measured) annotation". This is the most practical measurement and includes transparancy. Foor good transparancy the reported magnitude will increase.
Han
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thanks for your quick answer. I did it and results seem to be reliable.
Alt Airmass LimMag
86.568 1.001 16.4
51.943 1.269 16.3
29.122 2.048 16
18.946 3.054 15.6
So I can estimate atmospheric extinction to be 0.4 mag/airmass
I wonder if would be possible to get another decimal for the Limiting magnitude parameter.
This is a test using no filter and V17 catalog . But I found that using astap with my LRGB fits, the most similar results comparing Magnitude (measured) annotation with V17 Star (database) annotation is green filter. So in order to estimate visual transparency, should this green filter be good enough or should I use a V filter? Or working with only one decimal data won't change so much?
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I'm afraid that adding an extra decimal will not add accuracy, but we can try. Here a ASTAP version (Windows executable only) modified to two decimals https://ufile.io/tn9pth7j
Ignore the tab Nova. I'm just experimenting and it is not finished or will be abandoned.
For photometry the green channel is a good substitute for a Johnson-V magnitude. If you use no filter probably the using H18 or H17 is good. The Gaia Bm (blue magnitude) band width is very similar with the sensitivity of normal sensors.
Han
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I've been doing some tests with different data and I like the method a lot. I don't know if it is as accurate as classical atmospheric extinction method but is much more simple and faster. And at least as a comparative solution, it just works.
I just realized that using Batch Processing I can just add limiting magnitude to the fits head and save a lot of time and get those extra decimals, so now it is even faster to get the data and the modification you made is not needed anymore.
I just tried that. But I don't see the point on add it to tab lights since I don't have any data in that parameter at that moment. It could be useful in Photometric tab though. But it seems that is not allowed.
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I have added the limiting magnitude to the photometry tab. It slows down the routine with about 3% which is acceptable so need for an option. So it is always calculated.
Hi,
does anyone knows if there is a way of calculating atmospheric extinction using Astap?
Taking exposures at different altitudes (90º, 50º, 30º and 20º for ex.) and comparing Star Catalog magnitudes with measured ones could be a way, but I guess Astap is already might be estimating and compensating using airmass when calculates star magnitudes. I don't know if I'm talking nonsense here, just an idea.
Regards and thank you for this wonderful piece of software!
Pablo.
Hello Pablo,
ASTAP is calculating the airmass extinction for the SQM measurement. I assume using the delta transparancy will only work if you have no light polution. That will be only the case at rare superb dark locations.
For comparing the transparancy between several nights you could theoretical compare the flux measured but again the light pollution should be constant.
There is one measurment already available and that is reporting the limiting magnitude. This value is reported if you select in tools "Magnitude (measured) annotation". This is the most practical measurement and includes transparancy. Foor good transparancy the reported magnitude will increase.
Han
Hi Han,
thanks for your quick answer. I did it and results seem to be reliable.
Alt Airmass LimMag
86.568 1.001 16.4
51.943 1.269 16.3
29.122 2.048 16
18.946 3.054 15.6
So I can estimate atmospheric extinction to be 0.4 mag/airmass
I wonder if would be possible to get another decimal for the Limiting magnitude parameter.
This is a test using no filter and V17 catalog . But I found that using astap with my LRGB fits, the most similar results comparing Magnitude (measured) annotation with V17 Star (database) annotation is green filter. So in order to estimate visual transparency, should this green filter be good enough or should I use a V filter? Or working with only one decimal data won't change so much?
Hi Pablo,
That's an interesting observation.
I'm afraid that adding an extra decimal will not add accuracy, but we can try. Here a ASTAP version (Windows executable only) modified to two decimals
https://ufile.io/tn9pth7j
Ignore the tab Nova. I'm just experimenting and it is not finished or will be abandoned.
For photometry the green channel is a good substitute for a Johnson-V magnitude. If you use no filter probably the using H18 or H17 is good. The Gaia Bm (blue magnitude) band width is very similar with the sensitivity of normal sensors.
Han
Hi Han,
I've been doing some tests with different data and I like the method a lot. I don't know if it is as accurate as classical atmospheric extinction method but is much more simple and faster. And at least as a comparative solution, it just works.
I just realized that using Batch Processing I can just add limiting magnitude to the fits head and save a lot of time and get those extra decimals, so now it is even faster to get the data and the modification you made is not needed anymore.
Thank you very much for your help
Last edit: Pablo Canedo 2022-08-01
Yes good observation. The limiting magnitude can be written with all decimals using the batch routine.
Your results looks good.
If you find a problem or have a new idea please report.
Cheers, Han
Note you can add keyword LIM_MAGN to the list in tab "lights". This make retrieval of limiting magnitude easier.
I just tried that. But I don't see the point on add it to tab lights since I don't have any data in that parameter at that moment. It could be useful in Photometric tab though. But it seems that is not allowed.
That is an interesting idea. Adding to the photometry tab is easy but should be optional if it slows down the routine.
I will have a look.
I have added the limiting magnitude to the photometry tab. It slows down the routine with about 3% which is acceptable so need for an option. So it is always calculated.
Download this development version:
https://www.hnsky.org/astap_setup.exe
Tell me if this works as expected.
Han
Yes!!! That helps a lot, thank you very much