Low Cost - High Accuracy Gps Survey Receiver Design

Abstract

Abstract The NAVSTAR Global Positioning System (GPS) under development by the U. S. Department of Defense (DoD) will provide near instantaneous stationary position fixing capability in the 4-5 meter level anywhere in the world. Translocation survey processing can yield baseline accuracies in the centimeter level. By utilizing receiver technology developed under the DoD Full Scale Development program, a ruggedized, field portable, and highly accurate GPS survey receiver can be designed at cost far below lower volume specialized GPS Survey receiver designs. Introduction During the last decade significant improvements in the measurement of position over long baselineshave been made through the use of radio astrometry. These changes have come about through advances in signal measurement techniques such as precision time tagging made possible by greater oscillator stabilities and advances in measurement processing including precise location of the radio sources and parametric modelling of the atmospheric and ionospheric effects. However, the utility of these techniques has been limited by the costly equipment needed to receive the weak signals from celestial radio sources. In contrast low power signals from earth orbiting satellites can be received at comparatively much lower cost. Hence position location using satellites has achieved a much greater following. Commercial operators using Transit survey receivers number in the thousands; high accuracy receivers utilizing special translocation survey processing algorithms number in the hundreds. Accuracies in the meter range are common with multiple pass long-time averaging. GPS receivers developed under the DoD Full Scale Development (FSD) Program are expected to be less costly and more accurate than Transit receivers while providing near instantaneous position fixing capability. Translocation survey applications utilizing GPS are expected to yield baseline accuracies better than I em. Several research activities are already underway to explore the potential of GPS to verify this expected performance. While the above concepts have lowered the cost and increased the accuracy of determining baseline positions, the costs and processing latencies are still prohibitive for a significant portion of the user community. Of the two existing satellite navigation systems, "near instantaneous" processing is conceptually possible only in the GPS system. Low cost receivers for this application can be achieved only by drawing on a high volume technology base. With GPS receiver design in its infancy, the only high volume technology available is that being developed under the Full Scale Development Program mentioned above. Hence a low cost GPS translocation survey receiver would probably have to be based on this design technology. To this end the National Geodetic Survey Office of the Department of Commerce awarded a GPS Geodetic Survey Receiver, Feasibility Study to the Collins Government Avionics Division, one of two manufacturers awarded FSD contracts for a family of GPS user equipments. The study was intended to define the GPS translocation survey set requirements and to recommend the appropriate technological approach to meet these requirements at the lowest cost.