GPS L2P(Y)信号在GNSS-IR技术中的特殊误差源及改正方法

Special Error Sources and Correction Methods for GPS L2P(Y)Signals in GNSS-IR Technology

全球导航卫星系统干涉反射测量(global navigation satellite system interferometric reflectometry,GNSS-IR)技术只基于传统测量型接收机便可完成对站点周围环境的遥感,具有成本低、自动化程度高、全天候、连续监测、框架固定等优势。然而,其中的全球定位系统(global positioning system,GPS)L2P信号表现出一类特殊的GNSS-IR误差,在对信噪比(signal-to-noise ratio,SNR)的频谱分析中存在“双峰”现象,从而导致GNSS-IR反演误差。目前,对于该误差源的成因认识不清晰,也没有相应的改正策略,使得GPS L2P信号应用受限。因此,对GPS L2P信号“双峰”误差的成因进行分析,并提出了对应的改正策略。首先,选择位于海洋或水库边的4个站点,利用不同的跟踪方式捕获了站点的L2P信号;然后,根据不同L2P跟踪方式的SNR数据的频谱表现,分析了不同跟踪方式下的“双峰”误差对水位/潮位反演结果的影响;最后,提出了一种“双峰”误差改正策略并进行了相应的误差改正实验。结果表明,所提误差改正策略可以较好地改正L2P“双峰”误差,增加GPS L2P信号的GNSS-IR水位/潮位反演可用性。

Objectives:With the advancement of global navigation satellite systems(GNSS),GNSS remote sensing technology has been undergoing steady expansion.GNSS interferometric reflectometry(GNSS-IR)has emerged as an integral part of this domain,which allows for remote sensing of the surrounding environment using traditional geodetic receivers.It offers several advantages,including cost-effectiveness,high levels of automation,all-weather operability,continuous monitoring capabilities,and stable frameworks.However,a distinct type of error associated with global positioning system(GPS)L2P signal has been observed.In spectral analysis,this error exhibits a“bimodal”behavior and subsequently contributes to inaccuracies in GNSS-IR retrievals.Presently,the underlying causes of this error source remain unclear,and there are no corresponding correction strategies available.This limitation constrains the utilization of GPS L2P signal within GNSS-IR applications.Given the widespread deployment of dual-frequency GPS tracking stations worldwide,optimizing the utilization of GPS L2P signal has the potential to enhance the performance of these tracking stations in GNSS-IR applications.Hence,this study aims to analyze the origins of the“bimodal”error in GPS L2P signal within the context of GNSS-IR technology and proposes corresponding correction strategies.Methods:First,the Lomb-Scargle periodogram(LSP)method is used to analyze the spectrum of signal-to-noise ratio(SNR)arcs of the L2P signal,and the phenomenon of“double peaks”in LSPs is observed.According to the tracking mode of L2P,the mathematical relationship between the frequencies of the double peaks should be related to the ratio of L1 wavelength and L2 wavelength.Then,the bimodal error in L2P inversion is corrected according to this mathematical relation.Results:The analysis draws upon data from four stations situated in proximity to distinct aquatic environments.It investigates the spectral characteristics of SNR data under different L2P tracking modes and find the bimodal errors linked to various tracking modes influenced on water level/tide inversions.A bimodal error correction strategy is introduced.The results conclusively demonstrate that the proposed error correction strategy effectively mitigates L2P bimodal errors,thereby enhancing the utility of GPS L2P signals in GNSS-IR water level/tide retrievals.No matter which tracing mode is adopted,the LSP diagram of L2P(Y)signals has the phenomenon of“double peaks”.This phenomenon leads to some inversion values not related to L2P signal,but to L1 signal.However,under different tracking modes,the influence of bimodal error is different.Under half-code tracking mode,the SNR arcs of L2P signal are seriously polluted by L1 signal;while under the non-code tracking mode,the SNR arcs of L2P signal are mildly polluted by L1 signal.Conclusions:The proposed correction strategy can effectively correct the bimodal error of L2P(Y)signals.Especially in the half-code tracking mode,this method makes the inversion result of L2P(Y)signals from unusable to usable.