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Session 15 - Interplanetary, Instrumentation.
Oral session, Monday, June 30
Ballroom A, Chair: Victor Pizzo

[15.03] New Digital Magnetograph at Big Bear Solar Observatory

H. Wang (NJIT), C. Denker (BBSO), T. Spirock (NJIT), S. Yang (NJIT), P. Goode (New Digital MNJIT)

A new magnetograph system has been installed and tested at Big Bear Solar Observatory. The system uses part of BBSO's existing VMG system: a quarter wave plate, a Ferro-Electric Liquid Crystal to switch polarizations, and a 0.25A bandpass Zeiss filter tuned at CaI 6103A. A 256 by 256 12-bit Dalsa camera is used as the detector and as the driver to switch the liquid crystal. The data rate of the camera is 90 frames/s. The camera is interfaced by a Pentium-166 with a Mutech imaging board for data acquisition and analyses. The computer has 128mb of ram, up to 700 live images can be stored in the memory for a quick post-exposure image processing (image selection and alignment). We have improved the sensitivity and spatial resolution significantly over the old BBSO VMG system for the following reasons: new digital image data is in 12 bits while the video signal is below 8 bits. Polarizations weaker than 1% can not be detected by a single pair subtraction in the video system. The digital system can detect a polarization signal below 0.1% by a single pair subtraction. (2) Data rate of the digital system is 90 frames/s, that of the video system is 30 frames/s. So the time difference between two polarizations is reduced in the new system. Under good seeing conditions, the data rate of 90 frames/s ensures that the wavefront distortions are "frozen" and approximately the same for the left and right circular polarized image pairs. (3) Magnetograms are constructed after image selection and alignment. The same system has potential for further imaging processing, e.g. image de-stretch, and speckle interferometry. Preliminary results will be presented at the meeting.


Program listing for Monday