This page (revision-27) was last changed on 26-Oct-2022 21:57 by Peter Young

This page was created on 07-Jun-2010 19:35 by PeterYoung

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26 07-Dec-2016 14:14 6 KB Peter Young to previous | to last
25 05-Apr-2011 18:14 6 KB PeterYoung to previous | to last
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EISmethods
EISmethods

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At line 1 added 2 lines
[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
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!!Pointing coordinates (getxpos, getxcen, etc.)
To get the 1D wavelength array for the window, do:
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The heliocentric coordinates for the data are given by
{{{IDL> wvl=data->getlam(iwin)
}}}
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{{{IDL> xpos=data->getxpos()
IDL> ypos=data->getypos()}}}
although bear in mind that the spectra shift in the detector-X direction during an orbit, and in the Y-direction due to the tilt of the EIS slit relative to the detector. These issues are discussed in [EIS Software Note 5|http://solarb.mssl.ucl.ac.uk/SolarB/eis_docs/eis_notes/05_WAVELENGTH_CORRECTION/eis_swnote_05.pdf] and [EIS Software Note 4|http://solarb.mssl.ucl.ac.uk/SolarB/eis_docs/eis_notes/04_SLIT_TILT/eis_swnote_04.pdf], respectively.
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XPOS gives the X-coordinate for each slit position and YPOS gives the position for each pixel in the Y direction.
!!Pointing coordinates (getxpos, getxcen, etc.)
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In addition if you want the coordinates of the center of the raster do:
The heliocentric coordinates for the center of a raster at a given wavelength, WVL, are obtained with:
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{{{IDL> xcen=data->getxcen()
IDL> ycen=data->getycen()}}}
{{{
IDL> xcen=data->getxcen(/raster)
IDL> ycen=data->getycen(wvl,/raster)
}}}
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Note that each of these is an array of same size as the number of exposures. This is because the center of the raster moves with time due to the spacecraft jitter.
More details about EIS pointing information are given on the wiki page [Obtaining pointing information from EIS data|EISPointing].
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!!Exposure times
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The exposure time for each exposure of the raster is given by
!!Time routines
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!Exposure time
The exposure time (in seconds) for each exposure of the raster is given by
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Note that the exposure times generally vary between exposures, and will not be exactly equal to the requested exposure time.
!The start and end times of an exposure
The start and end times of an exposure can be obtained through the shutter open and close times (ti1 and ti2):
{{{IDL> ti1=data->getti_1()
IDL> ti2=data->getti_2()
}}}
The units are given in TI format, which is the Hinode spacecraft time. The TI format can be converted to standard time formats using:
{{{IDL> tai=data->ti2tai(ti)
IDL> utc=data->ti2utc(ti)
IDL> sec=data->sec_from_obs_start(ti)
}}}
The last method gives the time in second since the start of the first exposure in the sequence.
NOTE: the difference between the shutter open and close times, and the exposure time returned by the getexp() method generally do not agree. The former being larger by a fraction of a second. There are various technical reasons for this including a latency between the Instrument Control Unit (ICU) communicating with the Mechanism & Heater Controller (MHC), and a delayed response time of the MHC. __Users are recommended to always use the exposure time returned by getexp().__
!Other time routines
The date of an observation can be obtained with various methods:
{{{IDL> date_obs=data->getdate_obs()
IDL> date=data->getdate()
IDL> date=data->date_obs2date(date_obs)
IDL> days=data->days_since_launch(date)
}}}
getdate_obs() gives the date in 'yyyy-mm-ddThh:mm:ss.sss' format, and getdate() in 'yyyymmdd' format. The date_obs2date converts the former to the latter format, if no date_obs is given the data object's date_obs is converted. days_since_launch() gives the number of days since launch, if no date is given then the data object's date is used.
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Any field in the fits header can also be accessed easily by using, i.e. the above can be performed by typing
{{{IDL> date_obs=hdr_obj->getinfo('DATE_OBS')
}}}
The 'GETINFO' method can also be called by the eis data object to access the fits header fields, in which case there is no need to open the eis header object, just simply write
{{{IDL> date_obs=data->getinfo('DATE_OBS')
}}}
(The data object accesses the header object associated with it and returns the header information required)
!!Intensity units
To find the units for the intensity arrays in the data object, do
{{{IDL> units=data->getunit()}}}
which returns a 3-element string array, with the first element containing the intensity units. (The other elements are empty.)
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IDL> wp=cal->warm_pixels(data,iwin)}}}
IDL> wp=cal->warm_pixels(data,iwin[0])}}}
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You can also view a 'quick and dirty' map from the data object 'd' directly via,
{{{IDL> mmap=d->mk_eis_map(195.12)}}}
This will give an intensity map computed by summing in wavelength the pixels in the spectral window.
This page (revision-27) was last changed on 26-Oct-2022 21:57 by Peter YoungTop