spase://SMWG/Instrument/SDO/HMI

The SDO (Solar Dynamics Observatory) HMI
(Helioseismic and Magnetic Imager) studies the origin of solar
variability by characterizing and developing an understanding
of the sun's interior and the various components of its magnetic
activity. It extends the capabilities of the SOHO/MDI instrument
to continuous full-disk coverage at higher spatial resolution
and vector magnetograms.

HMI observes the full solar disk in the Fe I absorption line at
6173A with a resolution of 1 arc-second. HMI consists of a
refracting telescope, a polarization selector, an image
stabilization system, a narrow band tunable filter and two 4096
pixel CCD cameras with mechanical shutters and control electronics.
The continuous data rate is 55Mbits/s. Images are made in a
sequence of tuning and polarizations at a 4-second cadence for each
camera. One camera is dedicated to a 45s Doppler and line-of-sight
field sequence while the other to a 90s vector field sequence. All
of the images are downlinked for processing at the HMI/AIA Joint
Science Operations Center at Stanford University.