FORWARD FITTING ALGORITHM
The Forward-Fitting method is based on the assumption that the spatial map can be well represented by a small number of elemental source structures, each of which can be characterized by just a few parameters. Such structures might be circular, elliptical, or curved elliptical Gaussians (a loop). Such Gaussians sources can be represented by 4,6, or 7 parameters respectively.
In the Forward-Fitting algorithm, 'pixelized' maps of multiple Gaussian components are created and used to calculate a model modulation profile which is then compared to the observed modulation profile. The map iteratively evolves into a best-fit image which yields well-quantified parameters.
The Forward fit algorithm uses the Cartensian or ANNSEC coordinate system internally.
Using the Forward Fit algorithm at the command line:
Select algorithm | o->set, image_algorithm='forward' | or 'for' or 'hsi_forwardfit' |
---|---|---|
Object Class | HSI_FORWARDFIT |
|
Extract Object | ff_obj = o->get(/obj,class='hsi_forwardfit') | Extract the object used in the hsi_image object, o |
Parameter Prefix | ff, e.g. | All parameter names specific to this algorithm have this prefix |
Parameter Table | List and short description of control and info parameters specific to this algorithm |
THEORY
- Introduction into Forward-Fitting of RHESSI images - (M.J. Aschwanden, RHESSI Data Analysis Meeting, October 1999, NASA/GSFC Greenbelt MD)
- Image Reconstruction of RHESSI Data with Forward-Fitting - (M.J. Aschwanden, (GIF figures of manuscript version 1, December 1999)
- RHESSI observations of size scales of solar hard X-ray sources - (E. Schmahl, August 2002)
- Principles of Unpixelated Forward Fitting - (E. Schmahl, October 2000)
- A Forward Fitting Algorithm - (E. Schmahl, October 2000)
- Parameter-space Searches in Forward Fitting - (E. Schmahl, May 2000)
- Program Diagram for Forward Fitting - (E. Schmahl, April 2000)
- The Cash Statistic and Forward Fitting - (E. Schmahl, April 2000)
SOFTWARE TUTORIALS
- I. Standard Example - (M. J. Aschwanden, January 2002)
- II. Optimizing Initial Guess - (M. J. Aschwanden, February 2001)
- III. Number of Source Components - (M. J. Aschwanden, February 2001)
- IV. Simulation and Reconstruction of Loops - (M. J. Aschwanden, March 2001)
- V. Forward-Fits of 10 Simulated Flares - (M. J. Aschwanden, May 2001)
TEST IMAGES
- Test image comparison (BP, Clean, Fwd-fit) - (M. J. Aschwanden, PS and GIF images, January 2001)
- Test image comparison (Fwd-fit, MEM-Sato, MEM-Vis, pixon) - (E. Schmahl, February 2002)
- On the Photometric Accuracy of RHESSI Imaging and Spectroscopy - (M.J. Aschwanden, T.R.Metcalf, S.Krucker, J.Sato, A.J.Conway, G.J.Hurford, and E.J.Schmahl, 2003, Solar Physics, in press; version 2003-Oct-28) (ps-file of revised manuscript)