Evaluation of Radionavigation Systems in an Urban Environment

摘要

Extensive radionavigation data collected in New York City and vicinity from 26July to 7 August 1994 is presented. This data includes the accuracy and availability of the Global Positioning System (GPS) and LORAN and a comparison of electric (E) field (whip) and magnetic (H) field (loop) antennas at both LORAN and Differential GPS frequencies. The data includes that collected among the narrow streets and tall buildings in the Wall Street area, in the relatively more open streets and smaller buildings of the Bronx, among tall buildings but the wider space of Third Avenue, in the vicinity of the large matallic structure of the George Washington Bridge, and under a cover of foliage along the New Jersey side of the Hudson River. Initial analysis of the data shows: (1) In the deep urban canyons of Wall St. and under the elevated train tracks in the Bronx, the LORAN electric field signal is frequency highly attenuated and undetectable. The magnetic field signal is slightly attenuated but virtually always easily detectable and has repeatable phase characteristics. It may however, have very large phase shifts due to large structures making the generation of a calibrated LORAN grid and the algorithm to convert navigation data to position very difficult, (2) The availability of radionavigation fluxes can be substantially enhanced in these areas by the integration of LORAN and GPS and by the use of a precise time standard making fixes from as few as two Times of Arrival (TOA's), and (3) In heavy foliage, the availability of LORAN (either E or H field) is much higher than that of GPS.