GNSS-based tracking of fixed or slow-moving structures
A multi-antenna GNSS system and method provide earth-referenced GNSS heading and position solutions. The system and method compensate for partial blocking of the antennas by using a known attitude or orientation of the structure, which can be determined by an orientation device or with GNSS measurements. Multiple receiver units can optionally be provided and can share a common clock signal for processing multiple GNSS signals in unison. The system can optionally be installed on fixed or slow-moving structures, such as dams and marine vessels, and on mobile structures such as terrestrial vehicles and aircraft.
1. A GNSS-based method of tracking relative movement of a fixed or slow-moving structure, which method comprises the steps of:
providing a master receiver unit with a master GNSS receiver having a first clock, a master RF transmitter, and a master processor;
providing a master GNSS antenna connected to said master receiver;
providing a slave receiver unit with a slave GNSS receiver having a second clock, a slave RF receiver, a slave processor, and a temperature sensor connected to a thermocouple;
providing a slave antenna array comprising multiple slave GNSS antennas, each selectively connected to said slave receiver via an antenna switch control;
controlling the antenna switch control by the master processor;
mounting said slave GNSS antennas on the structure at fixed locations relative to each other and said structure to define distance and geometry constraints, wherein separating the antennas by a distance greater than a carrier phase wavelength of the GNSS signals, and at least a portion of the slave GNSS antennas being blocked by said structure from at least a portion of the satellites in the GNSS constellation;
synchronizing the first and second clocks;
receiving GNSS signals at each of the master GNSS antenna and the slave GNSS antennas and respectively measuring carrier phase observations therefrom, wherein at least one slave antenna receives signals from only a portion of the in-view satellites due to the structure blocking its view;
transmitting master receiver unit carrier phase observations using the master RF transmitter;
receiving said master receiver unit carrier phase observations using the slave RF receiver;
determining in the slave processor the relative locations and relative ambiguities of the multiple slave GNSS antennas using the measured carrier phase observations and the received said master receiver unit carrier phase observations;
time-tagging and storing the relative locations, relative ambiguities, and carrier phase observations;
forming single or double difference equations and solving for global ambiguities using the relative antenna locations and relative ambiguities;
compensating for ambient temperature at the slave antennas based on the temperature sensor;
measuring said GNSS signals at respective antennas at intervals corresponding to the orbital cycles of said satellites and the Earth's rotation and averaging the measured GNSS signals to reduce or eliminate multipath contributions;
computing and storing in the slave processor a position and an attitude solution for said structure at a plurality of spaced points in time; and
comparing the position and attitude solution at first and second spaced points in time to provide an output representing a movement of the structure.
2. The method of claim 1 wherein the slave processor is programmed with a temperature look-up table to compensate for ambient temperature with input from said temperature sensor.