SXT Pointing Update
Dear Yohkoh investigators,
David McKenzie asked a clarifying question about the impact of the
pointing update. The question and my response may be of interest to
some of you, so I am distributing it (attached below).
For those of you interested in the detailed implementation of the
change, we will not change the actual database, but incorporate the
change in the Yohkoh software that reads the database. The effect
for the user is the same.
Jean-Pierre Wuelser
----------------------------------------------------------------------
Hi David,
> > We plan to update (improve) the pointing of the whole database between
> > Friday and Saturday January 23/24 1998. This change may have impact
> > for people who compare SXT images aligned before the change with images
> > aligned after the change (e.g., with SXT_PREP).
>
> Just so I understand, this does not affect me if I only compare 1993
> images to other 1993 images, or 1998 images to other 1998 images.
> Correct?
It does NOT affect you if you only compare 1993 images to other 1993
images that were sxt_prep'd either ALL BEFORE January 23/24 1998, or
ALL AFTER 23/24 1998.
It WOULD affect you if you compared 1993 images that were sxt_prep'd
BEFORE January 23/24 1998 with 1993 images that were sxt_prep'd AFTER
January 23/24 1998. There would be a 1 - 2 arcsecond N-S jump in the
alignment between the two sets (if you used some sort of registration
in sxt_prep).
Same reasoning applies to January 1998 data, except that the N-S jump
in the latter case could be up to 4 arcseconds.
Only the updated database will give you the best possible image alignment
in terms of solar coordinates, or alignment with groundbased data.
Best wishes,
Jean-Pierre
Return to help page