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}]
At line 32 added 7 lines
To get the 1D wavelength array for the window, do:
{{{IDL> wvl=data->getlam(iwin)
}}}
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.
At line 32 changed one line
The heliocentric coordinates for the data are given by
The heliocentric coordinates for the center of a raster at a given wavelength, WVL, are obtained with:
At line 34 changed 2 lines
{{{IDL> xpos=data->getxpos()
IDL> ypos=data->getypos()}}}
{{{
IDL> xcen=data->getxcen(/raster)
IDL> ycen=data->getycen(wvl,/raster)
}}}
At line 37 changed one line
XPOS gives the X-coordinate for each slit position and YPOS gives the position for each pixel in the Y direction. The X-coordinate given includes the jitter (in X) that was recorded by the AOCS system, the pixel position given does not, but is rather based on the ycen at exposure '0'. In case the latter is desired for exposure 'n' then the (ycen(n)-ycen(0)) should be added to ypos(n) (see below).
More details about EIS pointing information are given on the wiki page [Obtaining pointing information from EIS data|EISPointing].
At line 39 removed one line
In addition, the coordinates of the reference point used in the data object are given by
At line 41 changed 2 lines
{{{IDL> xcen=data->getxcen()
IDL> ycen=data->getycen()}}}
!!Time routines
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These points are defined to be the home position of the fine mirror in X, and the middle of the physical slit i Y. Note that this definition differs from that given in the FITS file header where XCEN and YCEN refer to the center of the raster (at the beginning of the observation). Thus, the center of the raster can be accessed by
!Exposure time
At line 46 changed 2 lines
{{{IDL> xcen=data->getinfo('XCEN')
IDL> ycen=data->getinfo('YCEN')}}}
The exposure time (in seconds) for each exposure of the raster is given by
At line 49 changed one line
or, perhaps more reliably (especially as concerns older data), by taking the average of the extreme values given by the xpos and ypos methods.
{{{IDL> exp_time=data->getexp()
}}}
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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.
Note that the exposure times generally vary between exposures, and will not be exactly equal to the requested exposure time.
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!!Exposure times
!The start and end times of an exposure
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The exposure time for each exposure of the raster is given by
The start and end times of an exposure can be obtained through the shutter open and close times (ti1 and ti2):
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{{{IDL> exp_time=data->getexp()
{{{IDL> ti1=data->getti_1()
IDL> ti2=data->getti_2()
At line 70 added 23 lines
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.
At line 112 added 20 lines
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])}}}
At line 175 added 6 lines
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