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Session 122 - The Sun.
Oral session, Thursday, January 18
Salon del Rey South, Hilton
The LASCO C1 coronagraph was designed to examine the fine structure of the solar corona in the region from 1.1R_ødot to 3R_ødot. Even though the diffraction limit of the telescope is \approx 3\arcsec, the nominal resolution is set by the CCD pixels (5.6\arcsec\/). A pixel size of 1.5\arcsec\/ or smaller is needed in order to obtain diffraction limited observations (according to the Nyquist criterium). Therefore, the resulting images are undersampled by a factor of approximately 4. Some of this lost resolution can be recovered by acquiring successive observations using sub-pixel displacements of the steerable primary mirror incorporated into the LASCO/C1 design (``Dynamic Imaging'').
The spatial resolution of the LASCO/C1 coronagraph can be enhanced by combining or co-adding multiple observations separated by fractions of a pixel. We have identified several methods for constructing sub-pixel estimates, evaluated the performance of simple co-addition techniques, and developed an improved algorithm for obtaining fractional pixel restorations. Simulations were used to test this algorithm and to explore its limitations. In this presentation, we describe the algorithm and the results of these simulations. The results show that the resolution of the C1 coronagraph can be enhanced, even in the presence of significant noise and modest differences between successive observations.
