[Loops] On the importance of background subtraction in the analysis of coronal loops observed with TRACE

[Markus J. Aschwanden]

Dear Allen,

Great idea ! Essentially you want a space AND time-dependent background.
Since a second-order approximation is probably good enough for slowly-varying
density changes, it would be sufficient to use just 3 subsequent images in time
and model the background from 
	f(x,t-dt), f(x,t), f(x,t+dt)
with second-order interpolation. Should be straightforward.
I hope some under-occupied PhD student will pick up on it!

Cheers,
Markus

On Feb 15, 2010, at 6:48 PM, Gary, Gilmer A. (MSFC-VP62) wrote:

> Markus,
> 
> A question --- has anyone tried to model "all" the loops in some manner so that the "background" variation for  a loop could be removed using time dependencies of all the individual loops (or a major set of loops)?
> 
> This would be a temporal  stereographic reconstruction and would be as arduous, but some STEREO sets might lead to interesting results. The matrix inversions might however by ill-posed and some special math might be neeeded. Anyway  a thought that was generaqted from your commmet.
> 
> Someone might  use some analytic test cases or examples might lead to some specific ideas for real observations.
> 
> Best regards,
> Allen
> 
> ________________________________________
> From: loops-bounces at solar.physics.montana.edu [loops-bounces at solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden at lmsal.com]
> Sent: Monday, February 15, 2010 5:02 PM
> To: A mailing list for scientists involved in the observation and modeling of solar loop structures
> Subject: Re: [Loops] On the importance of background subtraction in the analysis of coronal loops observed with TRACE
> 
> Sergio and Fabio,
> 
> I like to encourage you to use STEREO EUVI data, which would provide
> you the ultimate test to subtract the correct background, because you
> see a loop from two different directions and have two independent
> backgrounds. You can test the self-consistence of background subtraction,
> if you obtain the same EM of the loop from two spacecraft.
> If you look into my recent STEREO paper, you see that one can
> subtract the background with an accuracy of about 10%.
> See Fig.8 therein.
> 
> Cheers,
> Markus
> 
> Aschwanden,M.J., Nitta,N.V., Wuelser,J.P., and Lemen,J.R. 2008, The Astrophysical Journal, 680, 1477-1495
> URL1="http://www.lmsal.com/~aschwand/eprints/2008_stereo2.pdf"<http://www.lmsal.com/~aschwand/eprints/2008_stereo2.pdf>
> First 3D reconstructions of coronal loops with the STEREO A and B spacecraft: II. Electron Density and Temperature Measurements
> 
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____________________________________________
Dr. Markus J. Aschwanden
Solar & Astrophysics Laboratory
Lockheed Martin Advanced Techology Center
Org. ADBS, Bldg. 252
3251 Hanover St., Palo Alto, CA 94304, USA
Phone: 650-424-4001, FAX: 650-424-3994
URL: http://www.lmsal.com/~aschwand/
e-mail: aschwanden at lmsal.com
_______________________________________
____________________________________



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