GPS-aided inertial technology and navigation-based photogrammetry for aerial mapping the San Andreas fault system

Abstract

Aerial mapping of the San Andreas Fault System can be realized more efficiently and rapidly without ground control and conventional aerotriangulation. This is achieved by the direct geopositioning of the exterior orientation of a digital imaging sensor by use of an integrated Global Positioning System (GPS) receiver and an Inertial Navigation System (INS). A crucial issue to this particular type of aerial mapping is the accuracy, scale, consistency, and speed achievable by such a system. To address these questions, an Applanix Digital Sensor System (DSS) was used to examine its potential for near realtime mapping. Large segments of vegetation along the San Andreas and Cucamonga faults near the foothills of the San Bernardino and San Gabriel Mountains were burned to the ground in the California wildfires of October-November 2003. A 175 km corridor through what once was a thickly vegetated and hidden fault surface was chosen for this study. Both faults pose a major hazard to the greater Los Angeles metropolitan area and a near real-time mapping system could provide information vital to a post-disaster response. Introduction Today there are three generally accepted methods to geoposition airborne or remotely sensed images to a local or national mapping frame of reference. The conventional method is completely dependent on well-distributed photo-identifiable geodetic ground control points and aerotriangulation. The second method combines airborne integrated GPS/INS collected data and a lesser number of ground control points with assisted aerotriangulation (Colomina, 2000). The latter method, which was chosen for this pilot study, is completely dependent on airborne GPS-aided inertial navigation systems to identify the location and orientation of each aerial image at the time of exposure. Over the years many airborne integrated GPS/INS performance tests of have been conducted (Cramer, 1999; Cramer, Stallmann, and Haala, 2000). Many of these tests were flown over flat terrain and successfully met positional accuracy standards for largescale mapping. However, tests flown over steep terrain, for the most part, have not met mapping accuracy standards at better than 1:8,000-scale (Cramer, 1999; Greening and others, 2000; Sanchez and Hothem, 2002; and Sanchez, 2004). The approach employed in this pilot study will first test a newly installed Applanix Digital Sensor System (DSS) __________________________ Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government 2.5 second cycle chip to attain an image pixel resolution of 8 – 15 cm (3 – 6 inches); and second apply carrier phase differential Global Positioning System (DGPS) postprocessing using multiple base stations of the Southern California Integrated GPS Network (Hudnut et al., 2002), to achieve a horizontal and vertical positional accuracy of less than 15 cm. A number of studies have shown significant accuracy improvements when operating in a multi-receiver configuration (Shi, 1994, Raquet, 1998, Bruton, Mostafa, and Scherzinger, 2001). Reaching these higher resolution and accuracy goals will demonstrate the potential of airborne integrated GPS/INS for the near real-time mapping of the San Andreas Fault System, thus, enabling information vital to postearthquake disaster response and damage assessment.