Greetings,

In this memo I will try to set the stage for a productive mini-workshop on SXT image deconvolution. Please read, comment, and respond as appropriate. Under "PAST EFFORTS" I am relying on my memory so please forgive and correct me if I've gotten it wrong.

PURPOSE

To define a path toward a trustworthy and practical method of correcting SXT images for the smearing effects of the instrument point response function and scattering wings (hereafter simply termed PSF). This includes (1) an evaluation ofwhat we know about the PSF and how best to characterize it for deconvolution purposes, and (2) to discuss and compare deconvolution codes, techniques and experience.

There are many reasons to desire a robust, reliable, and speedy deconvolution code for SXT. My personal objective in organizing this meeting is the hope of coming up with a feasible way to deconvolve the PSF from our new SXT Science Composite (SSC) images in order to improve the photometric accuracy, especially of the faint corona. Others may be more interested in correction of partial frame images (PFI) in order to improve the accuracy of filter-ratio temperature analysis of flares.

We are not concerned here with super-resolution techniques, except as they may provide useful insights into the inflight point response function.

PAST EFFORTS

A number of workers, e.g., Hara and Akiyama, LaBonte, Foley and Lemen, McKenzie, have developed routines for PSF correction. The approaches vary in how they handle temperature (wavelength) dependence of the core and wings of the PSF. Several people, most recently Hara and Akiyama, have attempted to estimate the scattering through different filters from the data. A flare mode experiment has been running for some time in an attempt to better define this important parameter.

Super-resolution work, for which the experimental PSF is not required, has been done by Sylwester's group (ANDRIL), Roumeliotis, and Karovsk.

PROBLEMS

  1. We need an "adequate" temperature-independent PSF for full-frame (FFI) deconvolution. I fear that full rigor, with all of the PSF pixel-location and temperature dependence included would present an unmanageable computational deconvolution task for SSC production.
  2. For flare work with PFIs better calibration of the scattering wings is needed for the different filters. For PFIs the core of the PSF appropriate to the location of the PFI should be used. SXT_PSF.PRO provides this capability.
  3. In the case of the thicker filters, where the entrance filters provide a significant part of the entrance opacity, the scattering wings are not cylindrically symmetric -- because of increased flux onto the mirror from failed sections of the entrance filters. This pattern of assymetry changes with each entrance filter failure event. Present software does not reflect these assymmetries.
  4. Flux must be conserved and areas of low signal (negative values in the image because of statistics) must be properly handled.
  5. The experimental error must be carried through the deconvolution process.

PROVISIONAL PLAN

This workshop will follow the path of the very successful HXT image synthesis workshop. I propose that the first day of the meeting be devoted to informal presentations. The morning to PSF discussions and the afternoon to deconvolution techniques and experience. We are fortunate that Leon van Speybroeck, of AXAF experience and fame, has agreed to join us. On the second day we may break up into experiment teams to follow up, on LaBonte's computers or your laptops, ideas and arguments from the first day's work. The last 2 hours of the second day will be reserved for discussion and wrap-up.

David McKenzie and Barry LaBonte are collaborating on a workshop web site. Please send abstracts of what you plan to present or issues you plan to raise to David McKenzie for posting to this site. Especially, please list events or data sets that you are working with so that others can have a look at these before the meeting. We'll confirm the URL in a later message.

REFERENCES - PSF & scatter

[These have been moved to a separate page and expanded.]


Loren Acton,
December 7, 2000