spase://SMWG/Instrument/Ground/MaunaLoaSO/MK4

The Mark-III instrument was the third generation white
light K-coronameter instrument at MLSO, and it operated from 4 February,
1980, through 30 September, 1999. The field of view of the Mark-III
K-Coronameter (Mk3) was 1.122 to 2.44 solar radii (as measured from sun
center). The sun's corona was scanned by a linear array detection system
which is rotated in solar position angle about the center of the solar disk.
It took about three minutes to acquire one coronal image.
The Mark-III K-Coronameter data are scaled such that 104.4 pixels
corresponds to one solar radius. Spatial sampling is 10 arcseconds
radially by 0.5 degrees in azimuth. All data are rotated so that solar
north is oriented straight up; solar north is known to within three degrees.
Daily averaged images and mass ejection images from the K-Coronameter have
instrumental `vignetting' left in the data to offset the coronal radial
density gradient, allowing for better viewing of the corona. Calibrated
images in units of polarization brightness (pB) are available and may be
requested via the E-mail address listed above.
The Mark-IV K-coronameter, was constructed by HAO in collaboration with
Rhodes College (Memphis, Tennessee). It has been in operation since
October, 1998, at MLSO.
The Mark-IV K-coronameter replaces its predecessor, the Mark-III and
features a high speed liquid crystal polarization modulator, a low noise
CCD line array detector, and an achromatic polarizing beam splitter to
measure Stokes I, Q, and U. Mark-IV produces polarization brightness maps
of the lower corona in white light (700 to 900nm) from about 1.14 to 2.86
solar radii at a 3-minute cadence. Its plate scale is 5.95"/pixel, with
data accuracy of approximately %15 and a noise level of approximately
4x10-9 B/Bsun.
The Mark-IV instrument is a significant improvement over its predecessor
in the following ways: lower system noise due to an improved detector and
associated electronics, better sky noise rejection due to improved
polarization optics and faster polarization modulation rate, higher
spatial resolution, and a wider field of view.
These improvements result in higher quality polarization-brightness
images which may be taken over a greater range of sky conditions than
was heretofore possible.
For information about the Mk4 K-Coronameter calibration technique, see
Elmore et al. (199?).