Tips for finding the perfect data-set#
The nature of EIS observations means that it can be quite difficult to find the data you want. For example, suppose you would like to study an active region loop and measure velocities in the Fe IX 197.86 line. How would you go about trying to find suitable data-sets?
Using eis_filter_studies#
The procedure described here starts by first narrowing down the large list of EIS rasters to those that are likely to be useful for the work. In IDL do:
IDL> s=fix_zdbase(/eis)
IDL> eis_filter_studies
The first command simply sets up the official EIS databases, and the second starts up a widget-based routine for filtering the complete set of EIS rasters to a more manageable list.
For velocity work we need to use 1" or 2" slit data and we also want to make sure that the raster covers a large range in Y to maximise the chances for obtaining good quiet Sun data (for wavelength calibration purposes). We will take a minimum raster height of 300". It is also useful to have a good range in X to make it easy to search for loop footpoints. We will use 200".
In the widget, select 'Raster type' to be 'Scanning', and 'Slit/Slot' to be 1". Also set the minimum raster height and width to be the values given above. Finally in the list of lines choose the Fe IX 197.86 line.
You will find only 3 rasters that satisfy the criteria. Switching to the 2" slit gives 6 rasters. Note down the names of each raster.
Browsing thumbnails#
The next step in finding the perfect data-set is to browse thumbnails from the 9 rasters. Go to the NRL thumbnail gallery
where you will see a long list of rasters. Scroll down the list until you find the first of the rasters you identified earlier, and click on the raster name.
You will now see a long list of html filenames. Each of the runs of the raster has two filenames: one contains thumbnail images from the Oslo archive, the other (identified by 'mssl' in the filename) contains images from the MSSL archive. The velocity maps seem to be a little better in Oslo archive so generally you should click on this file. Sometimes, however, the Oslo thumbnails may be missing in which case it's worth checking the MSSL page.
Choose the filename at the top of the list and you will see a page appear with an EIT context image, and thumbnail images (intensity, velocity and line width) from each wavelength window of the EIS raster. Clicking on any thumbnail will bring up a larger version.
To move onto the next run of the raster, click on the link in the top-left of the html window to take you to the next set of thumbnails.
By repeating this for all the rasters you can fairly quickly browse the available data-sets and find that perfect loop.
Search examples with the Oslo archive#
Searching for spectral atlas data#
A spectral atlas study is one where the entire EIS spectrum is downloaded. Such studies are valuable for studying a wide range of diagnostics and investigating atomic data issues. To find a list of all atlas studies using the Oslo archive, first go to the search page:
Type in your date range, and then look for the 'More search criteria' section. Click on the 'EIS' button. A large number of new boxes appears. Search for the box 'T_DETXW1' and type in '1024'. This tells the search tool to search for studies that have wavelength windows that are 1024 pixels wide. For the most part, only atlas studies have windows that are this wide (there may be 1 or 2 exceptions).
Unfortunately many engineering studies also take the full CCD, so a further search criterion needs to be specified. Under 'More search criteria' click on the 'Plan' button, and then search for the SCI_OBJ box. Search down the list and click on 'AR: active region'. Hold down the CTRL key (or equivalent) and also click on the 'QS: quiet sun' and 'CH: coronal hole' options. This selects all three types of solar features (all science observations must have one of these three options).
If you now do the search you will find a list of all spectral atlas studies.