Estimating the Effects of JPEG Compression and Radiation on the Accuracy of Vector Magnetic Fields Measurements for Solar-B

Details Estimating the Effects of JPEG Compression and Radiation on the Accuracy of Vector Magnetic Fields Measurements for Solar-B Estimating the Effects of JPEG Compression and Radiation on the Accuracy of Vector Magnetic Fields Measurements for Solar-B

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh52a0471l&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH52A-0471

Computer Science

Performance

7524 Magnetic Fields, 7529 Photosphere, 7594 Instruments And Techniques

Scientific paper

The Japanese Solar-B satellite, currently scheduled for launch in September 2005, includes a spectro-polarimeter (SP) to precisely measure the full Stokes polarization vector (I,Q,U,V) in the Fe I lines at 6302Å. These will be processed to produce vector magnetograms of the solar surface using algorithms based on those for the Advanced Stokes Polarimeter (ASP) as described in Skumanich, et al, 1997, ApJ Suppl 110. Accumulations of the raw images into time averaged I,Q,U,V images will be done on board and the results will be 12 bit JPEG compressed to make the best use of the available telemetry. Hence a single radiation hit in a raw image affects the entire time average at that point. Also, radiation spikes affect JPEG compression performance. Because of concerns about these effects, we simulated them separately and in combination using ASP data and radiation level measurements from the TRACE satellite. Like TRACE, Solar-B will fly in a high inclination, sun synchronous orbit and be exposed to radiation from the polar radiation belts as well as the SAA. Since the SP detector will be better shielded than that on TRACE, we hope that these will be an over estimate of the effects. The results from the simulations are very encouraging. We find that for active region magnetic fields we can use JPEG to compress the data volume by more than a factor of 10 without compromising the accuracy of the inferred magnetic field vector. The radiation in the polar regions has little effect and even the much stronger SAA radiation causes average perturbations that are less than the formal errors for sunspot fields and about twice the formal errors for plage fields. However, very weak field measurements will benefit from less lossy compression and periods of low radiation. Of course, the very strong radiation hits always produce artifacts. Compression performance is affected only slightly so it will not be necessary to avoid observations in the SAA because of excessive telemetry usage. This work was supported by NASA contract NAS8-01002.

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