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Unformatted text preview: GPS/IMU Error Analysis for Airborne SAR Remote Sensing L.J. Harcke, R.M. Ueberschaer, J.W. Sinko, and J.M. Strus SRI International BIOGRAPHY Leif J. Harcke joined SRI International in 2004 as a senior research engineer in the area of imaging radar systems en- gineering. He received the B.S. and M.Eng. degrees from Cornell University and the Ph.D. degree from Stanford University, all in the field of electrical engineering. Before joining SRI he was a member of the technical staff at the Jet Propulsion Laboratory. Ronald M. Ueberschaer is a senior research engineer at SRI in the area of radar signal processing. He joined SRI in 1984 after receiving the B.S. degree in physics from Georgia Institute of Technology. James W. Sinko, a principal engineer at SRI, received the B.S. degree in engineering science and the M.S. degree in electrical engineering from Stanford University, and the Ph.D. degree in electrical engineering from the University of Rochester. Dr. Sinko has worked with radar and aircraft systems at SRI since 1967. For the last 13 years, he has been working with precision GPS for military and civil applications. Joseph M. Strus is a systems analyst at SRI, where he has worked on precision navigation applications since 2001. His interests are GPS, GPS/INS, and estimation theory, and he holds several GPS-related patents. He received the B.S. and Ph.D. degrees in mathematics from the University of Illinois at Urbana-Champaign. Before coming to SRI he was a GPS systems engineer in the Government Systems Division of Rockwell Collins. 1 ABSTRACT We report on simulated integration of a tactical grade in- ertial measurement unit (IMU) with a differential GPS re- ceiver for airborne real-time synthetic aperture radar (SAR) imaging at ultra high frequencies (UHF or P-band). Ten scenarios were investigated for cases simulating character- istics of both differential GPS and IMU errors. Types of errors included 3-D Gaussian position error, Markov ran- dom walk errors, simple track offset biases, ramp offsets, and step-function biases. We confirm previous results that positioning errors affect SAR image formation through an increase in peak and/or integrated sidelobe errors, while bi- ases due to satellite outages and/or IMU integration error affect geolocation accuracy. We conclude that the wave- length is long enough at UHF radar frequencies to enable a tactical grade IMU to be substituted for the navigation grade IMU typically employed in higher frequency mi- crowave SAR systems. 2 INTRODUCTION In the airborne remote sensing environment, accurate flight track recovery is critical to several parts of the SAR imag- ing process (Curlander and McDonough, 1991; Carrara et al. , 1995). Tracking errors affect image formation as the aircraft flies along the synthetic aperture, as well as geocod- ing or referencing of the resultant SAR image to an ab- solute coordinate frame for mapping. For the image for- mation problem, an airborne UHF SAR requires accurate...
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- Spring '11