The World Wide Web: Interactive Interface to Scientific Data

Volume 12, Number 1, March 1996
by Jason Mathews

The World Wide Web (WWW), originally conceived for document delivery, has evolved into a medium supporting interactive data visualization and distribution. Three WWW-based data systems, known as OMNIWeb, COHOWeb, and CDAWeb, have been developed at NSSDC and the Space Physics Data Facility (SPDF) for providing interactive access to and visualization of scientific data. A researcher can not only retrieve data but also perform interactive visualization of the data through a simple point-and-click interface.

The WWW has the technology to provide visualization and browsing of data over standardized communication protocols. WWW-based systems can be built rapidly since no resources must be directed to developing the client and server software or network protocols because of its interoperable multimedia graphical user interface and choice of several non-proprietary protocols. In addition, the hypertext feature of the WWW can be exploited to reduce development time and couple metadata (i.e., information about the data) with the system.

The NSSDC OMNIWeb data system was created in late 1994 for enhanced access to the near-Earth solar wind field and plasma data of the OMNI data set, which consists of one-hour-resolution, "near-Earth" solar wind magnetic field and plasma data, energetic proton fluxes (1-60 MeV), and geomagnetic and solar activity indices. The OMNI data set presently spans 1963-1995; the Interplanetary Monitoring Platform (IMP) 8 spacecraft is the dominant contributor since its 1973 launch. OMNIWeb introduced the enhanced capabilities of visualization, listing, subsetting, and data conversion through the WWW. Interactive visualization of the data is supported through 2-D time series plots that are dynamically generated as Graphics Interchange Format (GIF) or PostScript files using the Interactive Data Language (IDL) commercial off-the-shelf (COTS) analysis package. This visualization capability aids users in finding trends and isolating areas of interest in the data. After browsing the data users have the ability to generate screen listings or ASCII files subsetted by time span and physical parameters for further analysis.

OMNIWeb addressed the need of researchers to access a single data set with visualization and retrieval capabilities over the Web. It was designed with a generic framework in mind to support any data set conforming to the NSSDC Common Data Format (CDF) data standard. An open architecture is developed on top of this data standard, which provides a transparent machine-independent application programming interface (API) to store, manipulate, and access multidimensional data sets. Data stored in CDF are self-describing such that a CDF application can provide generic data access to any CDF data file. The access tools for listing, converting, subsetting, and plotting the CDF data were not designed for any specific CDF but to any time-ordered CDF with a minimum set of metadata attributes that describe the data to access. Furthermore, the software tools developed for OMNIWeb have been reused in another data system, COHOWeb.

The COHOWeb system was built shortly after OMNIWeb and provides similar access to the deep-space solar wind Coordinated Heliospheric Observations (COHO) data, which consist of hourly averages of solar wind plasma and magnetic field data, and spacecraft ephemeris data. Data sources include historical and on-going deep space missions such as Ulysses, Helios 1 and 2, Pioneer 10 and 11, Pioneer Venus Orbiter (Pioneer 12), and Voyager 1 and 2. Significant effort was expended by NSSDC's Natalia Papitashvili in uniformizing the multisource data, casting all magnetic field data into so-called RTN coordinates and casting all spacecraft position vectors into a common heliocentric inertial coordinate system.

COHOWeb reuses many of the ideas and the software from OMNIWeb. However, COHOWeb represents a more evolved and generalized implementation of a WWW-based data system in that multiple data sets are supported through a single interface generated dynamically from the data themselves. COHOWeb is easily expandable since data can simply be "plugged" into the system without changing the underlying software, but COHOWeb is still limited to a small collection of data sets.

CDAWeb goes one step beyond OMNIWeb and COHOWeb in providing a generic interface not tied to a single data set nor a few data sets but generated from an index of many possible data sets. Therefore, CDAWeb is extendible to large amounts of data, which are independent from the user interface. CDAWeb allows the user to select variables from CDF data files and quickly make line plots, spectrograms, radar plots, images, etc. CDAWeb uses a forms-based WWW interface with Perl Common Gateway Interface (CGI) scripts that query the data set index file (containing lists of CDFs, time ranges, variable information, etc.). The data are read into IDL using a sophisticated set of routines for handling International Solar-Terrestrial Physics (ISTP)-compliant CDFs. The selected data are then plotted in IDL according to metadata found in the CDFs that define the most appropriate plot type (e.g., spectrograms for multienergy channels). The plots are converted to GIF images and sent back in an HTML page. The pages are all created on-the-fly based on the data base and user selections.

The CDAWeb data system enables improved display and coordinated analysis of multi-instrument, multimission data bases of the kind whose analysis is critical to meeting the science objectives of the ISTP program and the InterAgency Consultative Group (IACG) Solar-Terrestrial Science Initiative. The system combines the client-server user interface technology of the World Wide Web with a powerful set of customized IDL routines to leverage the data format standards (CDF) and guidelines for implementation adopted by ISTP and the IACG. The system can be used with any collection of data granules following the extended set of ISTP/IACG standards. CDAWeb is being used both to support coordinated analysis of public and proprietary data and better functional access to specific public data such as the ISTP-precursor CDAW 9 data base that is formatted to the ISTP/IACG standards.

The following three images illustrate some of the analysis capabilities of CDAWeb, and only the first figure below (time-series plot) represents the type of plot that OMNIWeb and COHOWeb create. The spectrogram and image plots demonstrate the new capabilities of CDAWeb.

Figure 1. Time Series Plot of Data from the IMP 8 Three-Axis Magnetometer Instrument.

Figure 2. Spectrogram of Electron Differential Flux from the Energetic Particles/Los Alamos National Laboratory (LANL) Geosynchronous Investigation.

Figure 3. Image of the North Polar Cap from the Viking (Sweden) UV Auroral Imager.

OMNIWeb, COHOWeb, and CDAWeb represent various WWW-based data systems for providing interactive access to space physics data. These systems provide not only access to large amounts of science data but also allow users to perform various operations on the data. The following URLs provide access to these systems and the corresponding data:

OMNIWeb: http://nssdc.gsfc.nasa.gov/omniweb/ow.html

COHOWeb: http://nssdc.gsfc.nasa.gov/cohoweb/cw.html

CDAWeb: http://cdaweb.gsfc.nasa.gov/cdaweb/cdaw9/

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 21 Nov 1996 [EDG]