SOT-FG Examples

TECHNICAL NOTE: The examples in this section may rely on the user having a valid SSWIDL installation (as shown in this section) with the most recent SOT software tree installed (as shown in this section). Additionally, to access the most recent SOT catalog, users will need to have the most recent version installed (as shown in this section).

How to Identify SOT-FG Level 0 and Level 1 Data

In this example, we will identify a set of magnetogram (Stokes \(V/I\) images) for AR11158.

The first step is to find all relevant observations for the time interval of interest. We make use of the SSW routines and to access the data catalog and identify all unique observational modes that were executed during a particular time interval:

time0 = '2011-02-15T00:00:00'
time1 = '2011-02-15T12:00:00' 
modes = sot_umodes(cat, mcount=mcount, info=info)

The routine returns two variables: cat, which is the SOT catalog structure for the time range indicated, and files, which are the URLs of all SOT files found in the local database for the time range given. If the /level0 switch is set, then the URLs will correspond to the Level 0 data files, whereas if /level1 is set then the URLs will be for Level 1 data.

TIP: If the URLs still point to the Level 0 files in spite of /level1 having been set (likely because the SOT SSWDB hasn't been updated), then one can simply replace the level0 string in the URLs with level1, e.g.: idl files=str_replace(files,'level0','level1')

For the date/time period specified above, a total of 1,193 SOT Level 1 files are found in the catalog. This includes FG, SP, correlation tracker reference frames, and other images not necessarily of interest to our example. In order to winnow this down to the particular observation type, the function is used to identify all unique observation modes that were observed during the time interval. Printing the output of this function yields the following:

IDL> print,modes
       FG MG4 V/I      TF Na I 5896     1408      704
      FG (simple)       G band 4305     1728     1024
      FG (simple)      Ca II H line     1024     1024
      FG (simple)      Ca II H line     1728     1024
      FG (simple)     red cont 6684     1024     1024
      FG (simple)    blue cont 4504     1024     1024
      FG (simple)   green cont 5550     1024     1024
      FG (simple)  TF H I 6563 base      704      704
 SP IQUV 4D array             6302A      112      384

Each line in the output table contains the observation type, the wavelength of each observation type, and the dimensions of the images. The mcount keyword, on output, will list the number of catalog entries corresponding to each line in the table. Each line has unique attributes, and these can be used for downselection.

To select only those images that are Stokes \(V/I\) magnetograms, one calls again, this time using the search_array keyword. This keyword returns only those records that match the specified keyword-value pairs. For example


will return the URLs for the 131 Stokes \(V/I\) magnetograms found in the specified time interval (during which there is approximately one magnetogram every five minutes).

Downloading these files can be achieved either using a utility such as wget or curl, or by accessing any of the data portals listed in this section.