On Sep 23, 2010, at 8:43 AM, Harry Warren wrote:
Markus,
I thought that your papers on the early STEREO data indicated that background subtraction was reasonably well understood. You obtained similar intensities from the two different vantage points.
Dear Harry, Good point, with STEREO we have a double-check of the background, which gives us more confidence on background definition methods. However I find a high sensitivity of the DEM width on the background definition using 6 coronal AIA filters. With 3 filters from STEREO it is easier in a more restricted temperature range.
Also, you've stressed the importance of computing the cross-correlation of the emission at different temperatures. Considering only highly correlated data removes many spurious broad DEM results.
In principle, yes, but I there are more near-cospatial loops in 6 AIA filters than in 3 filter data from TRACE or STEREO.
I think that the most significant problem is our bias toward bright loops that we can measure easily. They might not be representative.
I fully agree with this bias. On the other side, bright loops have a higher probability of multi-strand structuring, so finding near-isothermal bright loops is even a stronger argument than near-isothermal week strands. Cheers, Markus
Finally, a quick comment on the paper. I was expecting to see some Monte Carlo simulations and least-square fits to the resulting data. Isn't the real question how many lines and what level of uncertainty do we need to determine the emission measure.
Best wishes,
Harry
On 9/23/10 10:20 AM, "Markus J. Aschwanden" aschwanden@lmsal.com wrote:
Friends,
I'm glad to see that the EM loci method is put on a more quantitative basis, especially in relationship to Gaussian DEM functions with variable temperature spread. While the two methods can now being used interchangably thanks to this recent nice study of Landi and Klimchuk, the biggest diagnostic problem for coronal loops is (in my view) still the proper background subtraction. Every contaminations from background fluxes introduces always a bias towards broader multi-thermal DEMs. This problem is even worse for AIA data, because more filters involve more confusion.
Looking forward to a patented background subtraction technique.
Cheers, Markus
-- // --------------------------------------------------------------------- // Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren // ---------------------------------------------------------------------
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 _______________________________________ ____________________________________