STAR-3i Airborne Gravity and Geoid Mapping System

Using Interferometric Synthetic Aperture Radar (InSAR) technology, Intermap’s STAR-3i provides a new generation of digital elevation models (DEMs) and orthorectified radar image (ORRI) maps. Because the Global Positioning System (GPS) is used as the position reference for STAR-3i, the terrain data provided by STAR-3i are referenced to an ellipsoid. An accurate geoid is required to create a sea level referenced DEM. For this purpose, Intermap has developed a new airborne gravity system (AGS). It is based on the STAR-3i navigation system consisting of differential GPS (DGPS), the strapdown inertial navigational system (INS), and the STAR-3i acquisition system.One important application of long-range airborne gravimetry is regional geoid mapping. Intermap has developed the software to determine geoid undulation based on airborne gravity and other gravity data. A precise regional geoid is determined by applying downward continuation techniques to airborne gravity measurements.This paper introduces the STAR-3i airborne gravity system and the software STARGRAV for airborne gravity and geoid determination. It describes how the processing algorithm was applied to 30,000 km2 of data from Central America and Washington, DC. They were collected and processed by Intermap in 1998 and 1999 and were used to generate digital elevation, orthorectified image, and geoid products. In the paper the gravity and geoid processing results are analyzed for internal consistency at the crossover points of the lines. Further, the data are analyzed for absolute accuracy by comparison with ground gravity information. The results demonstrate that the STAR-3i AGS system can measure gravity anomalies to an accuracy of 1 – 2 mGal. The geoid determined using the STAR-3/ system has a relative accuracy of 5 – 10 centimeter (1σ) when compared with an independently determined geoid reference.