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This page was created on 25-Jun-2008 06:03 by David R Williams

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SbandObservingInfo
SbandObservingInfo

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[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
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An OP Period[Note 1] is the period of time during which an observing programme (''plan'') is defined. e.g. from 10:23 UT on 2008/05/02 to 11:19 UT on 2008/05/04. (The start and end of each OP period are determined by the pattern of ground-station contacts, which varies from day to day.)
An OP Period[1] is the period of time during which an observing programme (''plan'') is defined. e.g. from 10:23 UT on 2008/05/02 to 11:19 UT on 2008/05/04. (The start and end of each OP period are determined by the pattern of ground-station contacts, which varies from day to day.)
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In order to have co-ordinated observations by its three instruments, Hinode points as a whole satellite (using its AOCS[Note 6]), either tracking a point to compensate for the (differential) rotation of the Sun, or focusing on a fixed point. Either way, changes in pointing by the s/c[Note 7] take time to stabilise. After approximately 90 seconds, Hinode can track or fix on a point with better than 1" accuracy, below the spatial resolution of EIS and XRT.
In order to have co-ordinated observations by its three instruments, Hinode points as a whole satellite (using its AOCS[6]), either tracking a point to compensate for the (differential) rotation of the Sun, or focusing on a fixed point. Either way, changes in pointing by the s/c[7] take time to stabilise. After approximately 90 seconds, Hinode can track or fix on a point with better than 1" accuracy, below the spatial resolution of EIS and XRT.
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!Eclipse Season
!Eclipse Season (XTW)
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The duration of night-time is calculated for the visible band, and in the peak of eclipse season (around mid-July [Note 3]) this duration is about 20 minutes. EUV absorption (night ingress) begins about 10 minutes before the calculated entry into optical night (listed as NGT_ENTRY) and ends (night egress) in the EUV about 10 minutes after the optical band exit (NGT_EXIT). Thus, the EIS operations team recommend that you leave a __ten-minute buffer around s/c night__ in eclipse season where possible. Extended-duration observations
As of 2009, JAXA ephemeris calculations for Hinode included the calculation of nominal EUV and X-ray night (known as XTW). The duration of these is approximately 30 minutes at the peak of eclipse season (2009). This is calculated from a static model, and so doesn't take into account expansion of the ionosphere with increased solar activity, which would lengthen these obscuration periods.
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At the middle of eclipse season, clear EUV day (i.e., not including transition into or out of eclipse) lasts for approximately 60 minutes (not taking into account expansion of the ionosphere with increased solar activity).
For some more information, see the notes on [EclipseEffects].
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For some more information, see my notes on [EclipseEffects].
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On most orbits[Note 8], Hinode's orbit intercepts the South Atlantic Anomaly (SAA), a part of the geomagnetic environment where high-energy particles penetrate lower into the magnetosphere. During such passes, significantly more energetic particle hits (''cosmic rays'') are observed on the EIS detector images. These passes are calculated at the same time as other orbital events (such as Eclipse Season NGT events, when appropriate), and times vary each day. Such passes normally last approximately 15 to 20 minutes (although they can be calculated to last for as little as 30 seconds).
On most orbits[8], Hinode's orbit intercepts the South Atlantic Anomaly (SAA), a part of the geomagnetic environment where high-energy particles penetrate lower into the magnetosphere. During such passes, significantly more energetic particle hits (''cosmic rays'') are observed on the EIS detector images. These passes are calculated at the same time as other orbital events (such as Eclipse Season NGT events, when appropriate), and times vary each day. Such passes normally last approximately 15 to 20 minutes (although they can be calculated to last for as little as 30 seconds).
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There is often a substantial overlap between SAA and NGT events around the orbit. However, the phase of EUV night does not change phase in the orbit (whereas that of the SAA does). Therefore eclipses and SAA passes sometimes coincide (with night being the longer event), and sometimes do not overlap so much. However, there is almost always some overlap. (The exception to this is during the Golden Period, during which there are no SAA periods, but EUV nights continue to occur once per orbit).
There is often a substantial overlap between SAA and XTW (X-ray / EUV night) events around the orbit. However, the phase of EUV night does not change phase in the orbit in the way that that of the SAA does. Therefore nights and SAA passes sometimes coincide (with night being the longer event), and sometimes do not overlap so much. However, there is almost always some overlap. The exception to this is during the ''Golden Period'', during which there are no SAA events, but EUV nights continue to occur once per orbit.
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As a result, a some parts of the day, the less-than-complete overlap of SAA and night means that the clear window for observing in such orbits can be shorter. Taking into account the buffers (summarised below) around orbital events, the distribution of clear observing windows, calculated from a typical mid-eclipse season OBEV file, ranged from 53 to 68 minutes, with a modal value of 61 minutes.
As a result, at many times of day, the less-than-complete overlap of SAA and night means that the clear window for observing in such orbits can be shorter. From 2009, EUV Night event were calculated for Hinode's orbit. So taking into account the buffers (summarised below) around orbital events, we can recalculate the distribution of clear observing windows from the middle of eclipse season in 2009.
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[{Image src='attach/SbandObservingInfo/Picture%202a.png'}]
The histograms below show a distribution of these windows' length over a three-day sample. There are two distinct populations (ignore the very short windows at the far left: these are due to vanishingly small SAA events that occur shortly after larger events).
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The main population follows a distribution ranging from 44 to 62 minutes, with a mode and median of around 53 minutes in length. The second population is on the far right, and corresponds to observing windows in the Golden Period where there are no SAAs, and these windows are 65 minutes long.
The sum of all this means that if you want to be of a single raster or study fitting in between eclipses, it needs to be no more than 44 minutes long (the minimum window length). However, if you are happy accepting some curtailment of the raster at one or both ends outside the Golden Period, in order to make full use of those windows that fall inside the Golden Period, then you might design a study to have maximum 65 minutes' duration. It is a gamble, obviously, because they aren't so well suited to the majority of the observing day, and cause difficulties in forecasting the telemetry that will be accumulated because images will be taken when EIS can't see the Sun.
[{Image src='attach/SbandObservingInfo/Picture 42.png'}]
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| {{{NGT_ENTRY}}} | 10 minutes before
| {{{NGT_EXIT}}} | 10 minutes after
| {{{XTW_ENTRY}}} | 2 minutes before
| {{{XTW_EXIT}}} | 2 minutes after
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__Please note__ that as of late 2008, the planning tool has a "SHOW OBEV WINDOWS" feature that factors in these buffers. This feature is shown in the screenshot below
[{Image src='attach/SbandObservingInfo/OBEV%20Windows.png'}]
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Since moving to Hinode's S-band antenna for downlinks, EIS typically can downlink something like 600 Mb[Note 2] per 24 hours. This is worked out by the total contact time at all ground-stations, in the coming OP Period, multiplied by the bandwidth to the ground[4]. Typical HOPs should be targeted to something like 250 Mb per day. __However__ , this is a rough guideline only, because the amount of telemetry that it's possible to downlink per day downlinked is quite variable, due to a number of practical factors.
Since moving to Hinode's S-band antenna for downlinks, EIS typically can downlink something like 600 Mb[2] per 24 hours. This is worked out by the total contact time at all ground-stations, in the coming OP Period, multiplied by the bandwidth to the ground[4]. Typical HOPs should be targeted to something like 250 Mb per day. __However__ , this is a rough guideline only, because the amount of telemetry that it's possible to downlink per day downlinked is quite variable, due to a number of practical factors.
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;__OP__:[Note 1|#1]''Operation Programme''
of each orbit. It lasts from late April until early September.''
;__OP__:[1|#1]''Operation Programme''
;__S-band antenna__:[4|#4] ''Hinode's secondary antenna, with a bandwidth of 262 kb/s.''
;__Eclipse Season__:[5|#5] ''The portion of the year where the sun is occluded by the Earth's atmosphere for a fraction of each orbit. It lasts from late April until early September.''
;__AOCS__:[6|#6] ''Attitude and Orbit Control System''
;__s/c__:[7|#7] ''abbreviation of'' spacecraft
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[Note 2|#2]: Remember, Mb stands for mega__bits__ (1024 × 1024 bits), as distinct from MB (for mega__bytes__). 1 MB = 8Mb.
[2|#2]: Remember, Mb stands for mega__bits__ (1024 × 1024 bits), as distinct from MB (for mega__bytes__). 1 MB = 8Mb.
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[Note 3|#3]: Is this correct? I know it's approximately true, since we start in late April, and come out of eclipse season in early September.
;__S-band antenna__:[Note 4|#4] ''Hinode's secondary antenna, with a bandwidth of 262 kb/s.''
;__Eclipse Season__:[Note 5|#5] ''The portion of the year where the sun is occluded by the Earth's atmosphere for a fraction
;__AOCS__:[Note 6|#6] ''Attitude and Orbit Control System''
;__s/c__:[Note 7|#7] ''abbreviation of'' spacecraft
[Note 8|#8]: Hinode's orbital period is 98.5 minutes
[3|#3]: Is this correct? I know it's approximately true, since we start in late April, and come out of eclipse season in early September.
[|#8]: Hinode's orbital period is 98.5 minutes
This page (revision-76) was last changed on 07-Dec-2016 14:14 by BriazWearlTop