vzi Velocity Image with Hankel Geometry
mzi Modulation Image with Hankel Geometry
izi Intensity Image with Hankel Geometry
vzi, mzi and izi are solar disk images generated from velocity, modulation, and intensity calibrated images, respectively, which have been further processed through the GEOMPIPE subsystem of the VMICAL pipeline.
These images have undergone a flat-fielding of the intensity band and a more accurate geometry calculation. The geometry calculation is done in two steps. First, the limb points are found using a Laplacian-based edge detector, and fit with a 5 parameter ellipse (x and y center, major and minor axis lengths, and position angle). Then the routine described by Toner & Jeffries (1993) is used to obtain an improved estimate for the image size. This latter routine also provides an estimate for the azimuthally averaged Modulation Transfer Function (mtf), which is the modulus of the Fourier transform of the observational Point Spread Finction.
See Toner, C. G., & Jeffries, S. M., 1993, ApJ, 415, 852. Since the publication of this paper, the limb darkening equation has been modified to be a function of Legendre polynomials in (2cos(theta)-1). This function has better orthogonality properties than the simple cos(theta) expansion used previously.
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