High-Frequency Noise in the Gravity Recovery and Climate Experiment Intersatellite Ranging System

The Gravity Recovery and Climate Experiment mission consists of two satellites flying in tandem with a high-precision intersatellite range measurement system. The range measurements are collected continuously and are used to make accurate determinations of the Earth's gravity field at monthly intervals. The changes in the monthly models (i.e., the temporal variations in the gravity field) are manifestations of the global mass change between the Earth's atmosphere, ocean, and land systems. The primary focus of the study was twofold: 1) to understand the characteristics and sources of the high-frequency noise, in the range of 0.02-0.1 Hz, in the dual one-way ranging, and 2) to explore methods for mitigating the effect of the noise. Based on the mathematical model of the dual one-way ranging observation, the Allan variance was computed from the K-band range measurements to establish an upper bound for the frequency instability of the ultrastable oscillators and its contribution to the high-frequency noise. Because the residuals of the time derivative of the dual one-way ranging are dominated by the high-frequency noise, they were also examined to evaluate the contributions of various other factors such as the system noise from the microwave receiver and the antenna offset correction noise. The results indicate that the system noise is the dominant source of the excessive high-frequency noise. As one method of mitigation for the ongoing mission, a tighter bandwidth filter for the dual one-way ranging was investigated.