Modeling and Geometry Design for PseudoliteAugmented Airborne DGPS

摘要

Carrier phase DGPS systems have been increasingly usedin airborne surveying. However, the accuracy andavailability of GPS positioning cannot meet the stringentrequirements of large-scale photogrammetry. Groundbasedpseudolites can strengthen the measurementgeometry for airborne GPS systems, and improveambiguity resolution. As a result, positioning accuracy andreliability can be improved, especially in the verticalcomponent.In order to effectively augment DGPS aided airbornesurveying with pseudolites, carrier phase measurements ofpseudolites need to be employed in the positioningprocess. However, due to the comparatively smallseparations between pseudolites and receivers, somechallenging issues have to be investigated, such asgeometry design, nonlinearity, tropospheric delay andpseudolite location errors.Geometry design is extremely important for pseudoliteaugmented GPS positioning system. Optimally locatedpseudolite and reference receiver can significantlyimprove the geometric strength of positioning solutionsand thus reduce the effects of nonlinearity and pseudolitelocation error. The optimal locations of pseudolite andreference receiver are proposed based on analyzing theseissues and the simulation results in airborne surveyingscenarios.Nonlinearity is a challenging issue in pseudoliteaugmented DGPS. The nonlinear geometry bias in