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20030726: Lightning Overlayed Over NOAAPort Satellite Question



Bryan,
     First I need to warn you that you are NOT supposed
to redistribute lightning data in any form. Especially not
on a public web site. I assume you are doing this only to 
demonstrate the discrepencies in the plots. If so fine. Please do not
routinely make lightning data available on your web server.
The data provider might not let us make the data freely
available to the Unidata community if it is improperly used. I'd love 
to be able to make this data freely available to any user, but the contract
that allows us to distribute the data to Universities for research
and educational purposes prohibits this. All it would take
is one recipient of the data to violate this agreement
and we could be forced to turn off this service. If you
have questions on the appropriate use of the NLDN data feel
free to ask me, or Unidata. Sorry, I suspect you are using the
data properly, but, a reminder to all sites is a good
thing since I think it would be a loss to the community
if we could not distribute this data.
     On to the issue at hand. First note that the lightning
does not move, but the clouds appear to. It appears the GOES west
view is more consistant. A couple of possibilities. 1) the clouds
are viewed from way above, their observed position relative
to the ground will depend on the altitude of the cloud and the
angle from which it is being viewed. I haven't worked out the
geometry for your case, but suspect this might explain the apparent
shift of cloud positions in your figures. 2) It is possible
this is due to a projection changing calculation, but, I suspect
this is a smaller effect. Again I haven't done calculations
so could be wrong. 

David

> Greetings fellow McIDAS users,
> 
> Question.  One of the professors here at Creighton has been using the 
> NOAAPort GOES East shot and lightning data to create a composite image 
> over Arizona.  The following links display two images, one from GOES 
> East and one from GOES West for 1845Z today with lightning data for the 
> last 30 minutes overlayed centered over KDUG.
> http://whistler.creighton.edu/products/experimental/goeseast.gif
> http://whistler.creighton.edu/products/experimental/goeswest.gif
> As you can see from the images, the lightning data on the GOES East shot 
> is significantly off from the GOES West image.  I figure there is a 
> mapping issue going on here since the GOES East shot is close to the 
> edge of its scan area, but didn't have a firm answer to give him.  
> Anyone able to shed a more technical light on this?
> 
> Bryan
> 

From address@hidden Sat Jul 26 18:58:23 2003
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David,

I agree with your first explanation: the shift is due to parallax. Note, 
how the islands & coastlines at sea level shift very little.

dave

David Knight wrote:

>Bryan,
>     First I need to warn you that you are NOT supposed
>to redistribute lightning data in any form. Especially not
>on a public web site. I assume you are doing this only to 
>demonstrate the discrepencies in the plots. If so fine. Please do not
>routinely make lightning data available on your web server.
>The data provider might not let us make the data freely
>available to the Unidata community if it is improperly used. I'd love 
>to be able to make this data freely available to any user, but the contract
>that allows us to distribute the data to Universities for research
>and educational purposes prohibits this. All it would take
>is one recipient of the data to violate this agreement
>and we could be forced to turn off this service. If you
>have questions on the appropriate use of the NLDN data feel
>free to ask me, or Unidata. Sorry, I suspect you are using the
>data properly, but, a reminder to all sites is a good
>thing since I think it would be a loss to the community
>if we could not distribute this data.
>     On to the issue at hand. First note that the lightning
>does not move, but the clouds appear to. It appears the GOES west
>view is more consistant. A couple of possibilities. 1) the clouds
>are viewed from way above, their observed position relative
>to the ground will depend on the altitude of the cloud and the
>angle from which it is being viewed. I haven't worked out the
>geometry for your case, but suspect this might explain the apparent
>shift of cloud positions in your figures. 2) It is possible
>this is due to a projection changing calculation, but, I suspect
>this is a smaller effect. Again I haven't done calculations
>so could be wrong. 
>
>David
>
>  
>
>>Greetings fellow McIDAS users,
>>
>>Question.  One of the professors here at Creighton has been using the 
>>NOAAPort GOES East shot and lightning data to create a composite image 
>>over Arizona.  The following links display two images, one from GOES 
>>East and one from GOES West for 1845Z today with lightning data for the 
>>last 30 minutes overlayed centered over KDUG.
>>http://whistler.creighton.edu/products/experimental/goeseast.gif
>>http://whistler.creighton.edu/products/experimental/goeswest.gif
>>As you can see from the images, the lightning data on the GOES East shot 
>>is significantly off from the GOES West image.  I figure there is a 
>>mapping issue going on here since the GOES East shot is close to the 
>>edge of its scan area, but didn't have a firm answer to give him.  
>>Anyone able to shed a more technical light on this?
>>
>>Bryan
>>
>>    
>>
>
>  
>

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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David,<br>
<br>
I agree with your first explanation: the shift is due to parallax.
Note, how the islands &amp; coastlines at sea level shift very little.<br>
<br>
dave<br>
<br>
David Knight wrote:<br>
<blockquote type="cite"
 cite="address@hidden">
  <pre wrap="">Bryan,
     First I need to warn you that you are NOT supposed
to redistribute lightning data in any form. Especially not
on a public web site. I assume you are doing this only to 
demonstrate the discrepencies in the plots. If so fine. Please do not
routinely make lightning data available on your web server.
The data provider might not let us make the data freely
available to the Unidata community if it is improperly used. I'd love 
to be able to make this data freely available to any user, but the contract
that allows us to distribute the data to Universities for research
and educational purposes prohibits this. All it would take
is one recipient of the data to violate this agreement
and we could be forced to turn off this service. If you
have questions on the appropriate use of the NLDN data feel
free to ask me, or Unidata. Sorry, I suspect you are using the
data properly, but, a reminder to all sites is a good
thing since I think it would be a loss to the community
if we could not distribute this data.
     On to the issue at hand. First note that the lightning
does not move, but the clouds appear to. It appears the GOES west
view is more consistant. A couple of possibilities. 1) the clouds
are viewed from way above, their observed position relative
to the ground will depend on the altitude of the cloud and the
angle from which it is being viewed. I haven't worked out the
geometry for your case, but suspect this might explain the apparent
shift of cloud positions in your figures. 2) It is possible
this is due to a projection changing calculation, but, I suspect
this is a smaller effect. Again I haven't done calculations
so could be wrong. 

David

  </pre>
  <blockquote type="cite">
    <pre wrap="">Greetings fellow McIDAS users,

Question.  One of the professors here at Creighton has been using the 
NOAAPort GOES East shot and lightning data to create a composite image 
over Arizona.  The following links display two images, one from GOES 
East and one from GOES West for 1845Z today with lightning data for the 
last 30 minutes overlayed centered over KDUG.
<a class="moz-txt-link-freetext" 
href="http://whistler.creighton.edu/products/experimental/goeseast.gif";>http://whistler.creighton.edu/products/experimental/goeseast.gif</a>
<a class="moz-txt-link-freetext" 
href="http://whistler.creighton.edu/products/experimental/goeswest.gif";>http://whistler.creighton.edu/products/experimental/goeswest.gif</a>
As you can see from the images, the lightning data on the GOES East shot 
is significantly off from the GOES West image.  I figure there is a 
mapping issue going on here since the GOES East shot is close to the 
edge of its scan area, but didn't have a firm answer to give him.  
Anyone able to shed a more technical light on this?

Bryan

    </pre>
  </blockquote>
  <pre wrap=""><!---->
  </pre>
</blockquote>
</body>
</html>

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From address@hidden Sat Jul 26 20:11:50 2003
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Date: Sat, 26 Jul 2003 21:13:42 -0500
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David, everyone,

First off, thanks for responding on a Saturday.  See my 
comments/questions below:

David Knight wrote:

>Bryan,
>     First I need to warn you that you are NOT supposed
>to redistribute lightning data 
>
<snip>

Thanks for the reminder and yes, the current lightning data, with the 
exception of these two files, is limited to the university only.  Should 
I remove the two satellite shots?  In the future, though, is there a 
proper way to do this?  The image sizes would have meant over a full meg 
in an email, something I would not like to send out as attachments.  Or, 
would instructions on how to reproduce the problem suffice?

>     On to the issue at hand. First note that the lightning
>does not move, but the clouds appear to. It appears the GOES west
>view is more consistant. A couple of possibilities. 1) the clouds
>are viewed from way above, their observed position relative
>to the ground will depend on the altitude of the cloud and the
>angle from which it is being viewed. I haven't worked out the
>geometry for your case, but suspect this might explain the apparent
>shift of cloud positions in your figures. 2) It is possible
>this is due to a projection changing calculation, but, I suspect
>this is a smaller effect. Again I haven't done calculations
>so could be wrong. 
>
I agree with your first answer.  Is there a way to correct this?  I 
doubt it, but figure that I could at least ask the question.

>
>David
>  
>


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