Data Preprocessing And Analysis Of High-Precision Microwave Ranging System For Low-Low Satellite-to-Satellite Tracking Gravity Satellite

The gravity field of the Earth is a fundamental physical field that governs the spatial distribution and temporal evolution of the planet’s internal and surface mass.For scientific research,geographic mapping,and military defense,the high-precision and high-spatial-temporal-resolution gravity field of the earth is of crucial importance.Ground detection,aerial detection,and satellite detection are the three primary methods for detecting the Earth’s gravitational field.The characteristics of satellite gravimetry are global coverage and real-time update.Since the turn of the century,it has been at the forefront of international and domestic scientific investigation.Low-low satellite-to-satellite tracking（LLSST）gravity satellites mission accounts for high precision and high temporal and spatial resolution,providing essential and significant scientific data for key fields related to the national welfare and livelihoods of human,including earth science,hydrology,glaciology,seismology,oceanography,and atmospheric science.Microwave inter-satellite ranging system is the important scientific payload for LLSST gravity satellites.It provides data for global gravity field inversion by measuring the inter-satellite distance change resulting from the temporal and spatial changes of the Earth’s gravity field.Using GRACE Follow-On（GFO）mission as an example,this paper focuses on the working principles,measurement mechanisms,and noise distribution of the pivotal KBR microwave ranging system for the LLSST mission.The article discusses the data preprocessing,in-orbit calibration,and analysis methods of the KBR ranging system.In-orbit calibration is an important step in data preprocessing,which provides input for compensating attitude coupling noise in microwave ranging signals.The article first discusses the data preprocessing algorithm,which uses the dual one-way ranging mode combined with dual-frequency ranging signals to efficiently suppress the carrier frequency instability noise in data preprocessing.It eliminates ionospheric interference and completes key steps such as time tag correction,time alignment,anti-aliasing filtering,and necessary steps such as time-of-flight correction and phase center correction.Secondly,the article discusses the in-orbit calibration algorithm,and based on the GFO satellite KBR antenna phase center in-orbit calibration maneuver strategy,analyzes the spectral characteristics of the ranging signal changes caused by the maneuver.It introduces the double-difference linear combination method to eliminate multipath noise associated with attitude changes during the maneuver.It proposes a three-step method parameter estimation algorithm for estimating actual maneuver parameters,multipath noise,and phase center correction based on the difference between the actual maneuver and the nominal setting.The main research results of this article are:（1）the microwave ranging data product in this article and the residual of the official GFO mission data in the effective signal frequency band of the Earth’s gravity field are lower than 1×10^-9 m Hz^-0.5,far lower than the noise level of the payload and the design requirements of the microwave ranging system,which meets the accuracy requirements of Earth’s gravity field inversion;（2）Using GFO’s high-precision laser inter-satellite distance as a reference and comparing the residual of GFO and this article’s calibration results with the same laser inter-satellite distance,this article validates the effectiveness of the in-orbit calibration algorithm and the correctness of the in-orbit calibration results.The calibration results of this article are more effective in compensating for the attitude coupling noise in microwave ranging signals.This paper can provide relevant technical accumulation and reference for the data preprocessing and calibration of the microwave ranging system of China’s LLSST satellite mission,as well as the theoretical technical foundation for the intersatellite ranging system of the space gravitational wave detection mission.