This page (revision-13) was last changed on 07-Dec-2016 14:14 by Peter Young

This page was created on 12-Nov-2009 15:08 by PeterYoung

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EISPointing
EISPointing

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At line 1 changed 3 lines
[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
!!!Obtaining pointing information from EIS data
!!!How to get the most accurate EIS pointing information
At line 15 removed 20 lines
!!Improved EIS pointing information __%%(color:red;)Update%%__
From 2014 a new EIS routine yields the spatial offset between EIS and AIA. It is called as
{{{
IDL> xy=eis_aia_offsets(date)
}}}
At present the correction needs to be applied manually to the pointing values described in the sections below. So, for example,
{{{
IDL> xcen=xcen+xy[0]
IDL> ycen=ycen+xy[1]
}}}
The EIS-AIA offsets are determined regularly by co-aligning EIS slot images with AIA images. They should lead to much-improved pointing accuracy, to the level of 5" or better. In particular, the large variations seen during the eclipse season are corrected for.
Note that the EIS-AIA offsets do not correct the short-term (orbit period) jitter of EIS, only the longer-term (~ days) pointing variation.
At line 44 changed one line
where WVL is the wavelength you are interested in. If WVL is not specified then 195.12 (the wavelength of the strong Fe XII line) is assumed. Note that the raster center in solar-Y varies with wavelength by up to 18" due to the tilt of the EIS grating relative to the detector and a spatial offset between the two CCDs.
where WVL is the wavelength you are interested in. If WVL is not specified then 256.32 (the wavelength of the He II line) is assumed. Note that the raster center in solar-Y varies with wavelength by up to 18" due to the tilt of the EIS grating relative to the detector and a spatial offset between the two CCDs.
At line 48 changed one line
''Why is this an approximate pointing?'' Rasters can take several minutes to several hours to complete and, during this time, the Sun is rotating opposite to the raster direction. This has the consequence that the field-of-view in X is effectively reduced. For observations at disk center the reduction will be 10" per hour of observation. An additional factor is that each individual exposure is affected by satellite and instrument jitter, which may have a systematic trend over the course of the raster although this will affect the raster field of view by a few arcseconds at most.
''Why is this an approximate pointing?'' Rasters can take several minutes to several hours to complete and, during this time, the Sun is rotating opposite to the raster direction. This has the consequence that the field-of-view in X is effectively reduced. For observations at disk center the reduction will be 10" per hour of observation. An additional factor is that each individual exposure is affected by satellite and instrument jitter, which may have a systematic trend over the course of the raster although this effect will affect the raster field of view by a few arcseconds at most.
At line 50 removed one line
!!Field of view
At line 52 removed 24 lines
The field of view (FOV) of an EIS raster can be obtained by doing:
{{{
IDL> fovx=data->getfovx()
IDL> fovy=data->getfovy()
}}}
or by reading the values from the FITS header via
{{{
IDL> fovx=data->getinfo('FOVX')
IDL> fovy=data->getinfo('FOVY')
}}}
so if you want to overplot a box on an AIA image (for example) to show the EIS FOV for a raster, you can do:
{{{
IDL> x0=xcen-fovx/2
IDL> x1=xcen+fovx/2
IDL> y0=ycen-fovy/2
IDL> y1=ycen+fovy/2
IDL> oplot,[x0,x1,x1,x0,x0],[y0,y0,y1,y1,y0]
}}}
This page (revision-13) was last changed on 07-Dec-2016 14:14 by Peter YoungTop