VITMO: A Case Study in Virtual Observatories as Data Portals and Development of Web Services as Search Tools

Virtual Observatories are more than data portals that span multiple missions and data sets. They need to provide a system that is useable by a broad swath of people with different backgrounds. The great promise of Virtual Observatories is the ability to perform complex search operations on a large variety of different data sets. This allows the researcher to isolate and select the relevant measurements for their topic of study. The Virtual ITM Observatory (VITMO) is unique in having many diverse datasets that cover a large temporal and spatial range that present a unique search problem. VITMO provides many methods by which the user can search for and select data of interest including restricting selections based on geophysical conditions (solar wind speed, Kp, etc) as well as finding those datasets that overlap in time and/or space. We are developing a series of light-weight web services that will provide a new data search capability for VITMO and other VxOs. The services will consist of a database of spacecraft ephemerides and instrument fields of view; an overlap calculator to find times when the fields of view of different instruments intersect; and a magnetic field line tracing service that will map in situ and ground based measurements to the equatorial plane in magnetic coordinates for a number of field models and geophysical conditions. Each service on their own provides a useful new capability for virtual observatories; operating together they will provide a powerful new search tool. The ephemerides service is being built using the Navigation and Ancillary Information Facility (NAIF) SPICE toolkit (http://naif.jpl.nasa.gov/naif/index.html) allowing them to be extended to support any Earth orbiting satellite with the addition of the appropriate SPICE kernels or two-line element sets (TLE). An instrument kernel (IK) file will be used to describe the observational geometry of the instrument (e.g., Field-of-view size, shape, and orientation). The overlap calculator uses techniques borrowed from computer graphics to identify overlapping measurements in space and time. The calculator will allow a user defined uncertainty to be selected to allow 'near misses' to be found. The magnetic field tracing service will feature a database of pre-calculated field line tracings of ground stations but will also allow dynamic tracing of arbitrary coordinates. These services will allow the non-specialist user of VITMO to select data that they were previously unable to locate, opening up analysis opportunities beyond the instrument teams and making it much easier for future students who come into the field.