Capability Development for a Next-Generation Solar Magnetograph, 15-9288Printer Friendly Version
Inclusive Dates: 03/01/02 - Current
Background - The sun's complex, ever-changing magnetic field gives rise to the giant, ultra-hot solar corona and affects Earth's electrical, radio, and space radiation environments. Detailed measurements of the sun's surface magnetic field are crucial to understanding how our star works, and also to predicting space weather that can cause radio and power outages and damage or destroy spacecraft. SwRI is developing a new type of magnetograph camera capable of operating at 10 to 100 times faster than current instruments, to match the needs of modern ultrahigh-resolution solar telescopes.
Measurements must be fast to avoid blurring effects from motion of the solar surface and from turbulence in Earth's atmosphere - effects that are more severe at the very high resolution used to observe fine structure on the sun. Current technology requires 15 to 30 seconds to produce a magnetogram, resulting in motion blur at resolutions better than 1 to 2 arc seconds. The research team will be able to make quantitative solar magnetograms in under 100 milliseconds, beating atmospheric blurring and preventing solar blurring at resolutions as small as 0.05 arc second (equivalent to 20 miles at the solar surface), matching the planned Advanced Technology Solar Telescope. The SwRI instrument has terrestrial applications in plasma deposition and flame-front propagation experiments.
Approach - The solar magnetic field is measured by the Zeeman splitting of spectral lines in the light emitted by the sun: in right- and left-circularly polarized light, the spectral line is slightly redder or bluer depending on the strength and direction of the magnetic field. One must measure the solar brightness as a function of three independent variables: X and Y on the image plane, and l (wavelength) of the incoming light. Current instruments use multiple exposures through a scanning narrowband filter, measuring brightness at a succession of wavelengths to determine the line-central wavelength at each separate location in the image. The team's novel stereoscopic approach eliminates the narrowband filter, collecting all needed data in a single rapid exposure, but requires significant post-processing of the image data to determine magnetic field strength. The team has developed a new technique, differential stereoscopy, which takes advantage of a geometric coincidence to extract the magnetic field information rapidly and accurately.
Accomplishments - The team has examined several processing techniques and selected differential stereoscopy as having the best combination of high-resolution, low-computational cost, and moderate robustness against noise. The team has implemented a digital model instrument and analyzed simulated solar data, and found that the model instrument operates approximately 30 times better than existing instruments in typical observing conditions.