How to Coalign Images from Hinode/XRT to Those from Other Instruments

Basics of image coalignment

In order to coalign two solar images from two different observational instruments, we need to know the values listed below between the two images:

• plate scale ratio,
• roll angle difference, and
• pointing (yaw and pitch) difference

Please note that the differences of roll angles and pointings may vary with time.

The XRT Coalignment Database and the interface programs

The XRT team distributes the XRT Coalignment Database through SSWDB. The database and its IDL interface programs provide all XRT data users with the necessary information for coalignment. XRT data users can achieve coaligned results by using the database and its IDL interface programs.

The database is the results of our calibration works and being updated automatically weekly basis. You can find the details of the calibration in:

• Yoshimura and McKenzie, 2015, Solar Physics 290, 2355 (in ADS)

Since the standard data preparation software "xrt_prep.pro" uses the database in one of its correction steps, your prep'ed "index and data" should already have the corrected information for coalignment. Please be aware that the correction process for coalignment does not modify the data array, but changes the meta data stored in "index". In order to achieve the coalignment, you need some extra steps after the meta data correction. See the below section "How to achieve coalignment images".

How to achieve coaligned images

Below I put three sample programs to show how to achieve coaligned images.
(1) Quickly see the coalignment (interactively): ky_sample4.pro

Just run the program, like:

    IDL> .r ky_sample4

    IDL> .r ky_sample5

    IDL> .r ky_sample6

For further information:

• Read the above sample programs
• Read the document header in idlpro/xrt_read_coaldb.pro
• Read the coalignment section of the XRT Analysis Guide

Links