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Re: [Fwd: Plate Scale for Hinode/XRT]

Yeah, I got something like 1.097, if I recall correctly.


On Apr 23, 2007, at 10:42 AM, Mark Weber wrote:

> Hi,
> Kathy did some work aligning the XRT and RHESSI data, and came up  
> with a platescale of ~1.02", if I recall correctly.
> --Mark
> On Apr 23, 2007, at 8:22 AM, Leon Golub wrote:
>> Dear Ishibashi-san,
>> As far as I know, there has not been any definitive work done on  
>> the plate
>> scale question. There is, as you note, the value provided by  
>> Shimizu-san
>> from the Mercury transit, but the value we have entered so far is  
>> only a
>> placeholder pending further work and also waiting for the outcome  
>> of the
>> orbital drift analysis.
>> Regards,
>> Leon
>> Bish ishibashi wrote:
>>> Hello, I am resending the email I sent out this morning (03MDT)  
>>> since
>>> it was too long and I am told that it was rejected by the mail list.
>>> In any case, my apologies if you have somehow received twice.
>>> -------------------------------------------------------------------- 
>>> --
>>> Hello, I realize that there has got to be a better thing
>>> to think on Friday night. But it has been bothering me
>>> a bit and I would like to know what others know about the
>>> question on the proper plate scale used for Hinode/XRT.
>>> In a XRT FITS header, the keyword PLATESCL is generally
>>> set to 1.032"/pix. But is it really accurate to, say, a
>>> tenth of a percent?
>>> As many of you are aware, co-alignment of an XRT image
>>> with an image taken with another instrument is proven to
>>> be rather challenging. A chosen co-alignment method of
>>> ours is to pick a SOHO/EIT 284AA (Fe XV, logT ~ 6.3) image
>>> matching with an XRT image taken nearly at the same time,
>>> and then co-align discrete XBP features (while avoiding
>>> any major AR features) in these images spatially. While
>>> doing so, I have noted that the plate scale of 1.032"/pix
>>> does not work well. Say for instance if I am to pick one
>>> discrete feature to co-align the two images and blink them
>>> to see the result, I see decent co-alignment with the
>>> discrete feature selected for spatial correlation, whereas
>>> other discrete features on the XRT image radially move
>>> toward the selected feature. This is a classic case of an
>>> underestimated plate scale. Please see an animated gif
>>> image (plscl1032.gif) below that demonstrates this point.
>>> [the image is found at:
>>>    http://space.mit.edu/home/bish/TMP/plscl1032.gif
>>> ]
>>> So I have, via trials and errors, tuned the plate scale
>>> to identify what correlates best with an SOHO/EIT 284AA
>>> image. I should note here that the plate scale of an EIT
>>> image is known to be 2.629+/-0.001"/pix (Auchere, DeForest,
>>> and Artzner, 2000, ApJ, L529, 115). And that is what I
>>> use for my coalignment program (I do fix all FITS/WCS
>>> keywords in an EIT image according to the guideline given
>>> by the FITSIO protocol). Anyway, the derived plate scale
>>> via comparing an EIT 284AA image and an XRT (Al/Poly+Open)
>>> image is 1.0417  0.0005"/pix. The uncertainty is not
>>> based on a formal statistical error; rather it is meant
>>> to be the maximum probable inaccuracy associated with
>>> spatial correlation [1]. Please see another animated gif
>>> image for an improved co-alignment with the plate scale
>>> of 1.0417"/pix below (plscl1042.gif).
>>> [this image is found at:
>>>      http://space.mit.edu/home/bish/TMP/plscl1042.gif
>>> ]
>>> [1] the blinking method can usually tell if a discrete
>>>     feature is shifted by a quarter of a pixel. So
>>>     consider that as a total offset error accumulated
>>>     across the FOV of an image. In this example the FOV
>>>     of the XRT image used is 512x512, so the maximum
>>>     error is 1.042" * 0.25/512 ~ 0.0005"/pix.
>>> Having said all that, what is the most current value of
>>> the plate scale for Hinode/XRT? I am aware that the
>>> transit of Mercury event was used to measure a tentative
>>> plate scale of Hinode/XRT (1.056"/pix, if I recall).
>>> But I am not sure what details have been taken into
>>> account (i.e., Hinode's orbital solution, etc) to derive
>>> the value. I am not aware of the error value associated
>>> with the measurement, either.
>>> Could someone please share insights on the plate scale,
>>> please?
>>> Bish Ishibashi
>>> PS. the EIT and XRT datasets used here were taken at 0106UT
>>>     on 02-Feb-2007. I've done the same analysis on the XRT
>>>     and EIT images taken at also 0106UT on 08-Nov-2006, which
>>>     resulted in the same outcome.
>> -- 
>> ***********************************************************
>> Dr. Leon Golub; Harvard-Smithsonian Center for Astrophysics
>> 60 Garden Street, Cambridge MA 02138
>> Ph: 617 495 7177; Fax: 617 496 7577
>> e-mail: lgolub@cfa.harvard.edu
>> http://hea-www.harvard.edu/~golub/HomePage.html
>> ***********************************************************