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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At line 1 changed one line
When Hinode goes into eclipse, the pointing mode changes from gyros-plus-UltraFineSunSensors to gyro only (because it can't see the Sun any more!). In this case, there was prediceted to be a drift in the pointing. This gets corrected some time after Hinode comes out of night.
[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
!!!Eclipse Effects
At line 3 changed one line
In the one case i've looked at where a mode change occurs (from gyro to gyro+ufss), the repoint takes of order 15 seconds. This was taken from the shift seen in 20070509_074627, a HH---N03 raster, with nominal 5 second cadence (more like 6-and-a-bit). This repoint happened between 07:53:27.275 (expo start time, admittedly) and 07:53:47.117 (expo start time). The corresponding NGT_EXIT happened at 07:45:30, so there is just over 8 minutes until the repoint due to mode switch. 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.
!!What happens when Hinode goes into and comes out of night
At line 5 changed one line
Nights typically last 16 to 17 minutes in the EUV (no transmission), with the total time that obscuration effects happen (either twilight or true night) clocking up 23 to 24 minutes per orbit (or a quarter of one orbit). That's now, too. It'll be interesting to see how serious it gets in the deepest part of eclipse season.
!1. There is ''Hinode night'' and ''Hinode twilight''!
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.
At line 7 changed one line
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 just steering 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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!2. Pointing mode
When ''Hinode'' goes into "eclipse", the pointing mode changes from gyros-plus-UltraFineSunSensors to gyro only (because it can't see the Sun any more!). In this case, there was prediceted to be a drift in the pointing. This gets corrected some time after Hinode comes out of night.
In the __one__ case I've looked at where a mode change occurs (from gyro to gyro+ufss), the repoint takes of order 15 seconds. This was taken from the shift seen in eis_l0_20070509_074627.fits, a HH---N03 raster, with nominal 5-second cadence (more like 6-and-a-bit). This repoint happened between 07:53:27.275 (expo start time, admittedly) and 07:53:47.117 (expo start time). The corresponding NGT_EXIT happened at 07:45:30, so there is just over 8 minutes until the repoint due to mode switch.
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.
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!3. How much time is available for observing during eclipse season?
The eclipses have their maximum duration around 20 June each year. The EIS CO is provided with the times for "X-ray twilight" each orbit and, for 20 June 2009, the duration of XRT twilight was 30 minutes. The guideline for EIS COs is to schedule the next observation no less than 2 minutes after exiting XRT twilight. (N.B. This is now factored into the planning tool buffers which allow observing windows to be calculated).
There is also often minimal overlap with SAA passes, though, which also curtail the useful observing time. There is more information at [SbandObservingInfo] on this, but the minimum useful duration is as small as 44 minutes, and as large as 62 minutes outside the SAA-free "Golden Period", and 65 minutes during the Golden period.
See [the discussion on this|SbandObservingInfo] for more details.
This page (revision-7) was last changed on 07-Dec-2016 14:14 by David R WilliamsTop