Procedure for obtaining SDO cutouts for an EIS data-set#
SDO cutouts (both AIA and HMI) can be obtained very quickly through the JSOC. In this article I illustrate how cutouts corresponding to a specific EIS raster can be obtained.
I consider an EIS active region observation that began at 02:30 UT on 15-Apr-2011. The raster took 62 mins to complete. We would like AIA 193 cutouts at 1 min cadence for the period 02:30 to 03:32, and HMI magnetograms at 45s cadence for the same period.
Note that Lockheed also provide a cutout service, but this is much slower than the JSOC and does not return HMI data.
Get EIS pointing and FOV size#
The wiki page Obtaining pointing information from EIS data explains how to obtain the center and FOV of an EIS raster, so you can follow the instructions there. You should get values of (xcen,ycen)=(199,305), and (fovx,fovy)=(120,160).
Get AIA 193 cutouts#
Go to the JSOC exportdata webpage
. In the 'RecordSet' box, type:
aia.lev1_euv_12s[2011.04.15_02:30/62m@1m][193]
Click on the 'Recount' button and make sure a non-zero number of Records are found.
For 'Method', choose 'url-tar' from the drop down list. You will see a new option called 'Processing' that appears. Tick the box.
Within the processing options, select 'im-patch - Extract sub-frame'. A new box appears with various input widgets, some of which will be automatically filled in.
Make sure 'Tracking' is ticked, and also tick the 'Register' option.
For the other fields, type:
LocUnits: 'arcsec from center'
T_Ref: '2011-04-15T03:01:02Z' (choose time from middle of raster)
X: 199
Y: 305
BoxUnits: pixels
Width: 300 (some contingency has been factored in here)
Height: 400 (some contingency has been factored in here)
For 'Protocol' leave it as 'FITS'. Type in your name and e-mail, and then click on 'Submit Export Request'. If you're doing this for the first time, then you will have to register. After a couple of minutes wait, click on 'Submit status request' and you should see a link to a tar file containing your data (it may take longer for large data-sets).
Note that cutouts will be rice-compressed images (there used to be an option to download uncompressed images, but this has been removed). See below for how to read compressed images quickly.
Get HMI cutouts#
Repeat the above procedure, except that in the RecordSet box you should do:
hmi.M_45s[2011.04.15_02:30/62m@45s]
For the field of view, you need to account for the difference in plate scale between AIA and HMI, so multiply by 1.2:
Width: 360
Height: 480
Reading cutout images#
A cutout image can be read with:
IDL> read_sdo, file, index, data, /use_shared_lib
The /use_shared_lib keyword is highly recommended as it greatly increases the speed at which rice-compressed images are read. It may not work on all computers though (Windows?).
Comments#
Why use pixels instead of arcsec for the FOV size?
I found erratic results when using arcsec - the HMI FOV would end up with a different size to AIA.
Why use the register option?
This performs sub-pixel interpolations so that when you make a movie from the cutouts you do not see the occasional pixel jumps that otherwise would be seen. This isn't recommended if you plan to de-spike your cutouts.
What if I want multiple AIA filters?
Instead of giving [193] in the RecordSet box, give e.g. [171,304,335].
How do I get AIA UV images?
For these you need to give 'aia.lev1_uv_24s' in the RecordSet box.
How do I get HMI 45s intensitygrams, or HMI 720s magnetograms?
In the RecordSet box, use 'hmi.Ic_45s' and 'hmi.M_720s'.
I want to respike my cutouts. Can I get spike cutouts?
The AIA de-spiking algorithm is not very good so often you will want to "respike" your images with aia_respike. This routine automatically fetches the spike file over the internet for each cutout so there's no need to download spike files for your cutouts. If you need to, however, then the RecordSet box entry is, for example:
aia.lev1_euv_12s[2011.02.10_05:00/40m@1m][193]{spike}