Dear friends let me inform you about the following preprint on Astro-PH,
http://arxiv.org/abs/1002.2121
regarding:
the importance of background subtraction in the analysis of coronal loops observed with TRACE
by Sergio Terzo and Fabio Reale, accepted for publication on A&A
Abstract In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably different. We find differences as well in the related derive filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. With the other subtraction the diagnostics are much less clear. The background subtraction is a delicate issue in the analysis of a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction from interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and of the large amount of subtracted emission in TRACE observations.
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" First 3D reconstructions of coronal loops with the STEREO A and B spacecraft: II. Electron Density and Temperature Measurements
On Feb 11, 2010, at 3:02 AM, Fabio Reale wrote:
Dear friends let me inform you about the following preprint on Astro-PH,
http://arxiv.org/abs/1002.2121
regarding:
the importance of background subtraction in the analysis of coronal loops observed with TRACE
by Sergio Terzo and Fabio Reale, accepted for publication on A&A
Abstract In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably different. We find differences as well in the related derive filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. With the other subtraction the diagnostics are much less clear. The background subtraction is a delicate issue in the analysis of a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction from interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and of the large amount of subtracted emission in TRACE observations.
<reale.vcf>_______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
____________________________________________ 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@lmsal.com _______________________________________ ____________________________________
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@solar.physics.montana.edu [loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden@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
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@solar.physics.montana.edu [loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden@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
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
____________________________________________ 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@lmsal.com _______________________________________ ____________________________________
Thank you very much, Markus we are aware of your very interesting work on the analysis of STEREO data and your suggestion is very timely and appropriate. Sergio is busy with the analysis of Hinode/XRT data at the moment, but we hope to address STEREO data as next step. Thank you again Best regards Fabio
On 02/16/2010 12:02 AM, Markus J. Aschwanden wrote:
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/%7Easchwand/eprints/2008_stereo2.pdf First 3D reconstructions of coronal loops with the STEREO A and B spacecraft: II. Electron Density and Temperature Measurements
On Feb 11, 2010, at 3:02 AM, Fabio Reale wrote:
Dear friends let me inform you about the following preprint on Astro-PH,
http://arxiv.org/abs/1002.2121
regarding:
the importance of background subtraction in the analysis of coronal loops observed with TRACE
by Sergio Terzo and Fabio Reale, accepted for publication on A&A
Abstract In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably different. We find differences as well in the related derive filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. With the other subtraction the diagnostics are much less clear. The background subtraction is a delicate issue in the analysis of a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction from interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and of the large amount of subtracted emission in TRACE observations.
<reale.vcf>_______________________________________________ Loops mailing list Loops@solar.physics.montana.edu mailto:Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
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/ http://www.lmsal.com/%7Easchwand/ e-mail: aschwanden@lmsal.com mailto:aschwanden@lmsal.com _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
loops@solar.physics.montana.edu