초록 ▼

A method and a system are disclosed for measuring the baseline vector b between a pair of survey marks on the ground by radio interferometry using radio signals broadcast from the earth orbiting satellites of the NAVSTAR Global Positioning System (GPS), the radio signals broadcast by the satellites

A method and a system are disclosed for measuring the baseline vector b between a pair of survey marks on the ground by radio interferometry using radio signals broadcast from the earth orbiting satellites of the NAVSTAR Global Positioning System (GPS), the radio signals broadcast by the satellites being double-sideband modulated with their carriers suppressed. An antenna is positioned at each survey mark. The signals received by one antenna during a predetermined time span are separated into upper and lower sideband components. These separate components are filtered, converted to digital form, and then multiplied together. Their product is analyzed digitally by means of correlation with quadrature outputs of a local oscillator to determine the power, and the phase relative to that local oscillator, of the carrier wave that is implicit in the double-sideband signal being received from each satellite. Differences in Doppler shift are utilized to distinguish the carriers of different satellites. The signals received at the same time by the other antenna are processed in the same manner. Thus, the powers and carrier phases of the signals from a plurality of satellites are measured simultaneously and numerical data representing the measurement results are obtained at each survey mark. The measurements are performed in real time at each mark without reference to signals that are received at any other place and without knowledge of any of the coded signals that modulate the GPS carriers. The data from the measurements performed simultaneously but independently at the two survey marks, once per second for a predetermined time span, are then processed together to determine the baseline vector that extends from one mark to the other. Two methods of processing are disclosed. In either method, an “ambiguity function”, is computed which is a function of the measurement data and of a trial value b of the baseline vector. The vector space of b is systematically searched to find the unique value of b that maximizes the computed function. This value of b is taken to be the desired determination of b. By using signals from a plurality of five satellites and a time span of about 5000 seconds, a baseline vector determination can be obtained by the method of the present invention with an accuracy of about 5 millimeters in each coordinate for a baseline length of about 100 meters.

대표청구항 ▼

The method of deriving position related data, related to signals modulated by mutually orthogonal codes, from overlapping spread spectrum signals transmitted concurrently with the same frequencies by each of a plurality of satellites, the data being derived independently of externally derived knowle

The method of deriving position related data, related to signals modulated by mutually orthogonal codes, from overlapping spread spectrum signals transmitted concurrently with the same frequencies by each of a plurality of satellites, the data being derived independently of externally derived knowledge of the information content of the related modulating codes, comprising: receiving from the satellites a first composite of the overlapping spread spectrum signals with an upward looking, omnidirectional antenna positioned at a first mark; reconstructing the first composite of spread spectrum signals to form a second composite simultaneously including a plurality of reconstructed components related to the code modulated signals implicit in the signals received from the satellites; and applying predictions of the frequency histories of the signals from the satellites to the second composite to derive said position related data therefrom.