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New Transparency Model on Astrospheric

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#1 moab360

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Posted 24 February 2018 - 03:07 PM

Hello fellow astronomers,

Today I'm happy to announce the release of an enhanced Transparency forecast on Astrospheric. Read on to learn about the new model and how to opt-in. This is one of the first updates that falls into the bucket of "the more people you tell, the better we can make the model for everyone", so please share!


overview.jpg
 

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Transparency (similar to visibility) is a measure of the amount of contrast which can be discerned as you look through the atmosphere towards your target. To view low contrast objects (nebula, galaxies, etc), one requires excellent transparency. Transparency is a measure up and out of the atmosphere, whereas visibility is generally a measure horizontally through the atmosphere.

The current Transparency model produced by Allan Rahill at the CMC is based on the amount of water vapor in the column of air above you. Generally, the higher the amount of water vapor, the worse the transparency, limiting the magnitude of stars and DSOs that can be observed. More info on this model available here.

Astrospheric's enhanced Transparency model improves upon the current water vapor based model by increasing the scale and resolution, taking elevation and surface pressure into account, taking all cloud cover into account, and increasing the sensitivity of lower level water vapor in the model. These changes look to improve the accuracy of the overall Transparency model.

Overall, this model works well because

  • Water vapor is a well forecasted variable in our atmosphere. It's crucial to other aspects of the forecast and can be validated with spectral imaging from satellites.
  • Water vapor is the primary aerosol in the North American atmosphere that impacts transparency.
    • There are certainly other factors (those who endured the forest fire burnt skies this past summer can attest), but they tend to be difficult to model by standard numerical weather models, are relatively short lived, and rely on multiple complex variables. For example, to model the impact of smoke on transparency, you need to know with high certainty variables such as particle size, wind speed at various elevations, and the total output of the fire creating the smoke (highly variable). The Aerosol Optical Depth forecast available on Astrospheric attempts to model aerosols like smoke, dust, salt, etc, but has a markedly lower resolution and accuracy.
  • The higher the elevation, the less atmosphere there is between you and what you're observing.
  • While it's possible to get great transparency at sea level, it's much more common to find a transparent sky on a mountain top.

Here are some examples of how the models are similar and different.  Note that the legends are the same

legend.png

The 30,000 mile high view
highlevelcompare.jpg

From up here, the large structures in the forecast are quite similar. This is due to the fact that the primary variable influencing the model is water vapor from the top of the atmosphere down to the floor. One difference immediately visible is that the new Transparency model produces a gradient of colors instead of a five specific colors. The legend is still the same, but now there is more data between values.


California's Central Valley
centralvalley.jpg

One area that best shows the impact of taking elevation and pressure into account is in California's Central Valley, which is nearly at sea level. The new model shows the impact of more atmosphere being taken into account at sea level versus the high elevation mountain ranges that enclose the valley floor. In general this holds true, the higher you are in the atmosphere, the better the transparency will become.

Coasts and altitude
coastpnw.jpg

The effects of elevation and pressure are visible along coast lines and mountain ranges across the continent. In general this will lead to the new model showing an overall lower forecasted transparency at low elevation vs the old model. In the example below, cloud and low elevation are leading to an overall worse transparency forecast on the east coast.  It is possible to have excellent transparency near the coast, just less likely than at higher elevation.

eastcoast.jpg

The South West
southwest.jpg

Both models (and most all humans) agree, the American Southwest is the place to be for a transparent window into our universe

A note on clouds
cloudcompare.jpg

Unlike the old transparency model, the new model takes all cloud cover into account. In the past it was possible to have excellent transparency and a thin layer of cloud cover, which was confusing. If this were a measure of horizontal transparency (visibility), then it makes sense. But, since our goal is to look out of the Earth's atmosphere, cloud cover is crucial in the forecast. In the images above you can see the new transparency model is showing a high level cirrus cloud cutting through the center.


How to view the new Transparency model
For now, the new Transparency model is opt-in, which you can do in a couple of ways

  1. If you simply want to view the differences between the two Transparency models, use the map to switch between the layers
    transparencymap.jpg

     
  2. If you want to integrate the new Transparency model into your forecast, do the following
    turnon.jpg

If you opt-in using #2 above, then you may send corrections to help improve the model over time. In fact, the more folks you know who can provide meaningful corrections to the model, the better it will become. To send a correction, simply tap the transparency icon and select a value.  You can also turn off the enhanced transparency model by selecting the transparency icon and opting out.


That's it for now, please don't hesitate to send questions and comments my way. Astrospheric is a community driven project, and while I can't always respond, I really appreciate the feedback and do read all of it.
Clear (transparent) Skies!
 


  • dswtan, Phil Cowell, psandelle and 7 others like this

#2 moab360

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Posted 01 March 2018 - 05:53 PM

Quick update- Based on observation submissions the trend appears to be that the model at lower elevations may be a bit pessimistic.  More time and data will be needed before the model can be trained though.  I should have noted in the original post that even if you agree with the current transparency forecast sending an observation is helpful for validation.

 

Looks like some very transparent skies are coming to the Southeast on Friday night into Saturday!  The seeing doesn't look great, but still good for a night of wide field astrophotography or short focal length observing smile.gif


Edited by moab360, 01 March 2018 - 05:56 PM.

  • timmbottoni likes this

#3 skywolf856

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Posted 01 March 2018 - 09:21 PM

Hi,

Can you tell me why I can't find your program on google play on my android directly, but the web connection on my PC to google play does show it?

I already have it on my Ipad no problem.



#4 moab360

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Posted 02 March 2018 - 11:11 AM

Hi,

Can you tell me why I can't find your program on google play on my android directly, but the web connection on my PC to google play does show it?

I already have it on my Ipad no problem.

It's hard to say for sure.  The requirements for Android are

  • Android 5.0 or higher
  • The device region needs to be United States or Canada

Those are the only two things that would make it not show up in the store.  Actually I think even if you were on a lower version of Android it would still show up but you wouldn't be able to install it.



#5 skywolf856

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Posted 02 March 2018 - 02:10 PM

That's it, my android version is 4.4.4.

Thanks!




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