An Approximate Graph Matching Technique for Integrity Monitoring in Integrated Intelligent Flight Deck Applications

In order to improve safety of general aviation aircrafts, NASA is exploring the role of the Integrated Intelligent Flight Deck (IIFD) within the cockpit. Among other functions, the systems provide a pilot with a perspective view of terrain using stored geo-spatial data. The safe use of the synthesized terrain at low altitudes requires some sort of integrity check of the geospatial database to alert the pilot if the synthesized terrain does not closely correspond to the physical terrain. This paper describes a terrain integrity monitor which uses a novel approach to correlate the physical terrain, derived from X-band Weather Radar (WxR) and the synthesized terrain derived from a Digital Elevation Model (DEM). The process involves representing both terrain profiles in a graph form by the extraction of shadow regions. A comparison is then made through error-correcting graph isomorphism techniques to determine the level of correlation. Initial experimental results illustrate the systems insensitivity to noise, errors and window transformation.