Weekly Notes from the Yohkoh Soft X-Ray Telescope

(Week 23, 2002)

Science Nugget: June 7, 2002

The Yohkoh Galileo Project


Now that the operations phase of Yohkoh has drawn to a close, our energies are focused on the monumental task of archiving the data. It is our goal to provide solar data to all users, in an easy-to-access, easy-to-use format. We are inspired by Galileo Galilei: his solar observations continue to be useful today, because they provide a measure of solar activity and rotation rate from a past epoch, and because they are accessible (example sunspot drawings above).

The Team and the Task

The Yohkoh solar observatory satellite carries four science instruments: SXT, HXT, BCS, and WBS. Each of these has their own calibration issues: several past nuggets have outlined some of these for SXT in particular ([1], [2], [3], [4]). Likewise, the other instruments also require measurements of/corrections for background signals. Additionally, they require determination of appropriate data integration times: the duration of SXT image exposures is determined by the on-board computer and the camera's shutter at the time of the observation, but HXT, BCS, and WBS make continuous measurements and the data are binned into time intervals after the fact.

The task of the Galileo project then is to perform all the calibrations and instrument corrections now, so they won't need to be done ever again, and to document the whole process. In the end, we intend for any scientist (especially students) to be able to use the Yohkoh data without having to handle the ancillary data (e.g., the orbital parameters, spacecraft and camera temperatures, stray visible light "terminator" images, and dark current measurements).

Yohkoh has been an international collaboration throughout construction, launch, and operations phases, and that cooperation continues now in the archiving stage. Members of the Yohkoh team from Japan, the USA, and the UK have already begun some of the data archive chores, and continue to work together to define the data products. Corrections for stray visible light, photon scattering, and failures of the entrance filters have long been a part of the SXT software, but in the last several months we've made it a priority to finalize these corrections/calibrations. Similarly, an online catalog of HXT flare images has been developed (see last week's nugget). This will grow to include multiple images per HXT energy band, per flare, and downloadable floating-point images for your analysis.

Our final data products will be written in a "standard" format which can be read by any of a variety of software packages. Furthermore, we intend to provide uncertainty information for those who wish to produce errorbars in their analyses.


Finally, all the data will be available online, and there will be a web interface to facilitate access. At the same time, we'll redesigning some of the current web products, including YPOP (slight adjustments only), and the Yohkoh website. These nuggets will continue, but you might have noticed that we've already begun shifting the focus to observations from other solar observatories besides Yohkoh.

Galileo set a very high standard, and by taking his name for the Yohkoh data archive project we've got a lot to live up to. Our timetable is very roughly summarized below.

[Topical index] -o- [Chronological index]

June 7, 2002

David McKenzie, Alisdair Davey (mckenzie@isass1.solar.isas.ac.jp)