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T. Temma, N. Chanover (NMSU)
We search for an appropriate method to restore WFPC1 Saturn equatorial storm images taken in 1990. As is well known, WFPC1 images suffer serious spherical aberration and therefore the choice of appropriate restoration method is crucial to do photometry or cloud morphology analysis. In our research, Maximum Entropy Method(MEM), Lucy and Wiener methods in the IRAF STSDAS package are adopted and compared mainly regarding conservation of photometric properties.
We first look at the deconvolution effect on a WFPC2 Saturn image. The brightness profiles and brightness of Saturn and its satellites(Mimas and Tethys) relative to Rhea are examined. It has become clear that the Wiener method is not desirable to restore original image information because it produces circular negative annuli around the peaks. In addition, it shows poorer contrast improvements than the other two. Though the MEM and Lucy methods exhibit quite similar sharpening and photometric effects in this analysis, the Lucy method restores more brightness from surrounding area around a point source. This results in about 2% lower relative brightness of Saturn's disk than that derived by MEM relative to Rhea. At the next stage, we undergo the following procedure. First, a noiseless model Jupiter image is constructed. Then, it is convolved with the WFPC1 point spread function, and gaussian noise is added. Finally, the artificially blurred image is deconvolved, and the result is compared with the original noiseless model image. This comparison enables us to estimate efficiency and validity of the deconvolution process.
Furthermore, we will show some preliminary radiative transfer center-limb modelling results on restored 1990 Saturn images. We present possible explanations about the difference in the cloud structures between the disturbed northern equatorial region and quiet southern equatorial region.