Research on GPS/BDS Single Point Velocity Measurement Considering Direction Constraints

High precision velocity measurement is an important function of Global Navigation Satellite System, which is widely used in transportation, high-dynamic positioning, aeronautical gravity, geophysics and other fields. The GNSS velocity measurement model based on Doppler observations can achieve centimeter-level high-precision velocity measurement. The measurement quantity in this model is instantaneous velocity, which is not affected by the motion state. However, due to the influence of noise, the accuracy of Doppler range rate measurement is mostly cm/s level and is influenced by the geometric structure of satellites. With the development of GNSS and increase of satellites number, the accuracy of multi-system velocity measurement is further improved. In velocity measurement, information such as direction of velocity may be obtained from map information of road or orbit. Herein such constraint information in GNSS speed measurement system can improve the accuracy of velocity measurement, especially in areas with poor observation environment such as high occlusion. Static experiments show that under good observation environment, the accuracy of eastward velocity can be improved by 30% and northward velocity by 35% considering plane direction constraints of velocity. In high occlusion area, the accuracy of eastward velocity can be improved by 52% and northward velocity by 43% considering the plane direction constraints of velocity.