SOHO Scientists Take a “Quick Look” at the Sun with IDL Software

The European Space Agency, in conjunction with NASA, launched the SOHO (Solar and Heliospheric Observatory) project on December 2, 1995. The twelve instruments aboard SOHO provide the first long term, uninterrupted view of the Sun. Data gathered from SOHO is used to study the internal structure of the Sun, its extensive outer atmosphere, and the origin of the solar wind—the stream of highly ionized gas that blows continuously outward through the solar system.

The Coronal Diagnostic Spectrometer (CDS) is one of the instruments aboard SOHO. The gratings and optics of the CDS instrument contain irregularities. The very large amounts of data gathered from it must be quickly and accurately processed to remove the oddities and inconsistencies in the data.

XCFIT_BLOCK is a generalized, expandable “component fitting system” (CFIT) for planning observations for some of the SOHO instruments. It reads images (FITS files) from SOHO and other spacecraft, as well as ground-based instruments.

Stein Vidar Hagfors Haugan, the European Space Agency’s Science Operations Coordinator for SOHO, uses IDL tocharacterize the peculiarities of the CDS and “clean” the data derived from it. “Without this process, the irregularities might easily be taken as ‘interesting solar physics features’,” corrupting any scientific analysis, according to Haugan.

To this end, Haugan has developed several “quick-look” applications with IDL to process and display data from the CDS to the user in a quick and easy manner. Haugan works primarily with FITS files, from a number of different SOHO instruments, everything from single-sensor time series to four-dimensional data sets from spatial scans by spectrometers (wavelength, x, y, time). “It’s really the ‘whole package’ that makes IDL unique,” according to Haugan. “The interactivity, the relative ease of making a graphical front-end, the object orientation features, and the possibility of expanding the language using Dynamically Loaded Modules (DLMs) are all features in IDL that are valuable for my applications.”

Haugan believes IDL “has been instrumental in creating some very powerful, easy-to-use applications,” and estimates that it has dramatically reduced his development time by “a factor somewhere between 5 and 10.” “The applications I’ve created to analyze the CDS data are enormously more interactive and flexible than they would have been using C or another programming language. There are so many applications I wouldn’t have dreamed of making in the first place if it hadn’t been for IDL.”

An analysis tool used to fit emission line profiles to data sets from spectrometers—developed by Haugan for the CDS instrument—but general enough to be used for any kind of similar data sets. The processing engine can also be used in batch mode to process very large data sets (long series of repeated observations).