10 November 2003 Optimizing spacecraft formations for single-pass IFSAR
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Abstract
Formation structure and relative spacecraft velocities for a multiple baseline single pass IFSAR system are investigated to optimize a composite interferometric observation over several subapertures. Two major system models are developed: (1) relative spacecraft motion, and (2) pixel height measurement variance. Analysis demonstrates that a generalized Keplerian trajectory model with an equal gravity gradient assumption provides sufficient accuracy over typical IFSAR flyby aperture lengths. A pixel height variance model is developed to address issues unique to single pass multiple baseline space-based systems. A bistatic spotlight mode IFSAR system is assumed. Bistatic operation is not necessary, but the reduced future costs of deploying high performance sensor arrays of smaller receiver spacecraft drive the development of this important technology. Modeled noises for the multiple baseline system include internal sensor noise, spatial decorrelation noise, non-parallel ground track (grid rotation) decorrelation noise, and system parameter uncertainties. With expected observation ranges in excess of 500 kilometers, large baselines are required to maximize IFSAR height sensitivity. An analysis of optimal correlation is presented that extends the work of Rodriguez & Martin (1992) to include model uncertainties. Four IFSAR formation scenarios have been investigated. The system trajectory mimics the planned flyby of the Kilauea volcano by the Air Force TechSat 21 multiple spacecraft demonstration. Supposed formations include (1) a free-fall cluster formation, (2) an optimal formation assuming adequate thrust, and (3) a free-fall flyby after optimal initial formation. Results demonstrate pixel height errors at the spotlight aim point to range from 1 to 4 meters over the several 1-second subaperture lengths, and 0.2 to 0.5 meters over the 47-second full aperture length. A fourth scenario investigates performance over a hyperbolic flyby trajectory.
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Paul J. De Rego, Paul J. De Rego, Mohammad Jamshidi, Mohammad Jamshidi, } "Optimizing spacecraft formations for single-pass IFSAR", Proc. SPIE 5151, Earth Observing Systems VIII, (10 November 2003); doi: 10.1117/12.504622; https://doi.org/10.1117/12.504622
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