Real-Time Kinematic Network of Tehran, from Design to Application

Following the request of the Tehran municipality and in order to provide the spatial information required in their various projects, a real-time kinematic network has been designed for Tehran. Based on the existing measures such as the dilution of precision at the network point positions, two different designs have been proposed. A minimum number of six GNSS stations are used in both of the proposed designs. In contrary to the first design (Design 1), the second design (Design 2) provides a better coverage within the city. The impact of the distance dependent errors within the proposed designs as well as the other existing measures has been analyzed for selecting the optimum design. The GNSS almanac as well as the IGS GIM and meteorological data obtained from the existing synoptic stations within and next to the city are used for this purpose. Totally, only the effect of tropospheric refraction suggests the second design as the optimum one in this project. GNSS measurements made at this network point positions are used to verify the measures used through the design process. Two testing approaches have been used to check the efficiency of the designed network in real-time applications. In the first approach and within the city of Tehran point positions are determined independently using kinematic as well as static positioning techniques. Different correction estimation and dissemination algorithms including FKP, MAX and i-MAX techniques have been applied for this purpose. In the second approach, the central and northern reference stations of the network, separately plays the role of a rover receiver (test point) while it is not contributing in computing the network corrections. Repeatability, accuracy and precision of these points’ positions have been analyzed. Result of this verification analysis acknowledges the applied method to design the TNRTK. Accuracy of 1 to 3 cm is achieved in the coordinate components within the network area. However, the accuracy of the point positions outside of the network area, especially height components, is not fulfilling the presupposed accuracy of an NRTK due to the tropospheric effects.