This page (revision-7) was last changed on 07-Dec-2016 14:14 by David R Williams

This page was created on 16-May-2007 13:04 by David R Williams

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Version Date Modified Size Author Changes ... Change note
7 07-Dec-2016 14:14 3 KB David R Williams to previous
6 11-May-2010 12:39 3 KB David R Williams to previous | to last
5 16-Mar-2010 15:38 3 KB PeterYoung to previous | to last
4 19-May-2009 11:31 2 KB David R Williams to previous | to last
3 16-May-2007 13:14 2 KB David R Williams to previous | to last
2 16-May-2007 13:12 2 KB David R Williams to previous | to last
1 16-May-2007 13:04 1 KB David R Williams to last

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At line 6 changed one line
The Earth appears bigger to EIS than to the other two instruments on ''Hinode'' because of the EUV attenuation of the Earth's atmosphere (be thankful for it). So we see longer "night times" than the Orbital Event file (obev...) indicates. In fact, we have to factor in about ten minutes before the official NGT_ENTRY and the same after the NGT_EXIT in those files to take account of the period when EIS suffers the effects of the Earth's atmosphere. ''Night proper'' typically lasts about 17 minutes, but factor in the ingress and egress ("twilight" times), and the whole thing last for about 24 mins each orbit (''i.e.'', quarter of the orbit). And that's based on the first couple of days for which NGT events were predicted. These figures may evolve.
The Earth appears bigger to EIS than to the other two instruments on ''Hinode'' because of the EUV attenuation of the Earth's atmosphere (be thankful for it). So we see longer "night times" than the NGT events in the Orbital Event file (obev...) indicate. Originally, we dealt with this by factoring in about ten minutes before the official NGT_ENTRY and the same after the NGT_EXIT in those files to take account of the period when EIS suffers the effects of the Earth's atmosphere. ''Night proper'' typically lasts about 17 minutes, but factor in the ingress and egress ("twilight" times), and the whole thing lasts for about 24 mins each orbit (''i.e.'', quarter of the orbit). And that's based on the first couple of days for which NGT events were predicted. These figures may evolve with time as the orbit evolves.
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For now, I'd recommend leaving 10 minutes on either side of the NGT markers in the OBEV file if you want untainted data, or if you're dealing with data that is obviously affected by night, just steer clear of data within 10 minutes of those markers.
This year, at the request of XRT and EIS, ISAS has added in calculations of XTW, or X-ray Twilight, in addition to optical night (NGT). It's very helpful to have these extra calculations, and we are road-testing with EIS to see if the predictions do a better job than the default 10-minute buffer around NGT that we used to use.
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Since the few datasets I've looked at so far (all from the same date, from the merged telemetry) indicate that EIS twilight isn't over until about 10 minutes after NGT_EXIT, this repoint delay is not such a worry for us. The bigger worry is the length of night, including twilight, which cannot easily be calibrated out.
Since the few datasets I've looked at so far (all from the same date, from the merged telemetry) indicate that EIS twilight isn't over until about 10 minutes after NGT_EXIT, this repoint delay is not such a worry for us. The bigger worry was the length of night, including twilight, which cannot easily be calibrated out.
This page (revision-7) was last changed on 07-Dec-2016 14:14 by David R WilliamsTop