In order to control the accuracy, it is necessary to clearly understand several key points that affect the accuracy of the GPS locator. The gps car tracker measurement error can be divided into three parts according to its source: the error of the GPS signal itself, including the orbit error (ephemeris error) and the SA error, which affect the transmission error of the GPS signal, including the sunlight pressure, the ionospheric delay, Cycle slip caused by tropospheric delay, multipath propagation and other causes of cargo affected by it. The errors of GPS receivers mainly include clock error, inter-channel deviation, phase-locked loop delay, code tracking loop deviation, antenna phase center deviation and so on.
The design of the gps car tracker network is very flexible. The following issues should be noted: 1 Except for special needs, the general GPS baseline length difference is not too large, so that the GPS measurement accuracy is evenly distributed; 2 GPS networks should not have an open website structure, and should form closed loops and sub-loops; (3) Should Try to eliminate the effects of multipath, prevent GPS signals from being reflected to the GPS antenna through other objects, avoid strong reflections on the ground, and avoid strong reflection environments.
The static GPS side of the control network adopts carrier phase measurement, which is usually set as a straight line point. Observe GPS satellites synchronously with the pending point to obtain the carrier phase observation value, thereby obtaining the coordinate of the pending point or the coordinate value between two points, that is, baseline measurement . Short baseline measurement can eliminate the influence of SA. The dynamic measurement method to solve the impact of SA is real-time differential positioning, that is, set a reference point on a known coordinate point, remove the error correction value through the reference station, and transmit it to the navigation positioning mobile station in real time through the data link, thereby eliminating the SA and the two stations. The influence of various common errors improves the navigation and positioning accuracy of the mobile station. The navigation software and integrated navigation system are processed by filtering and other processing, so that the difference in navigation positioning accuracy reaches sub-meter level when the distance is about 100 km, and when it is 1500 km long, the gap is very far from the meter level.
The disturbance of sunlight pressure on the satellite affects the satellite's orbit and is the most important source of error in precise orbit determination. The existing solar light correction models include: standard light intensity correction model, multi-element light scattering model and ROCK 4 light scattering perturbation model. The accuracy of these models is basically the same and can meet the requirements of 1 m orbit determination. In recent years, people have proposed methods of adding random process parameters or using first-order trigonometric polynomials to approximate long-term non-modeling of long orbits, which can obtain more ideal results, and even meet the zero requirement. 1≤0. 2m accuracy
The ionosphere causes the code signal propagation delay, which is related to the electron density along the line of sight of the satellite and the user receiver. The average vertical delay value can reach about 3m at night, about 15m during the day, and 9m and 45m at low elevation angles, and it will increase during abnormal periods. In order to reduce the loss of positioning accuracy caused by the ionospheric delay, a dual-frequency receiver is used to collect gps car tracker data in the long reference measurement and perform real-time delay correction on the ionosphere to obtain better results. For the user's single-frequency receiver, although the mathematical model can be used for correction, the residual error is still very large. By raising the height of the satellite to this angle, impact can also be reduced.
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