Search results for: Yunzhong Shen

Items from 1 to 20 out of 38 results

article

Inter-system and inter-frequency code biases: simultaneous estimation, daily stability and applications in multi-GNSS single-frequency precise point positioning

Nan Zang, Bofeng Li, Liangwei Nie, Yunzhong Shen

GPS Solutions > 2020 > 24 > 1 > 1-13

Both inter-system and inter-frequency code biases (ISCB and IFCB) embodied in the multi-GNSS single-frequency precise point positioning (MSFPPP) exhibit mainly as systematic errors. Comprehensive analysis of the ISCB and IFCB characteristics and proper assimilation of their impact on MSFPPP are very important. We study the simultaneous estimation of all ISCBs for GLONASS, BDS and Galileo relative...

article

Single-frequency PPP models: analytical and numerical comparison

Bofeng Li, Nan Zang, Haibo Ge, Yunzhong Shen

Journal of Geodesy > 2019 > 93 > 12 > 2499-2514

Ionosphere delay is a key factor in the single-frequency Precise Point Positioning (SFPPP). In tradition, two SFPPP models are applied, i.e., ionosphere-corrected (IC) and ionosphere-free-half (IFH) models. The ionospheric delays are directly corrected in IC model with external ionospheric products, while they are eliminated by forming the ionosphere-free combination with code and phase in IFH model...

article

A heuristic singular spectrum analysis method for suspended sediment concentration time series contaminated with multiplicative noise

Fengwei Wang, Yunzhong Shen, Qiujie Chen, Weiwei Li

Acta Geodaetica et Geophysica > 2019 > 54 > 4 > 483-497

This paper proposes a heuristic singular spectrum analysis (SSA) approach to extract signals from suspended sediment concentration (SSC) time series contaminated by multiplicative noise, in which multiplicative noise is converted to approximate additive noise by multiplying with the signal estimate of the time series. Therefore both the signal and noise components need to be recursively estimated...

article

M-estimation using unbiased median variance estimate

Ling Yang, Yunzhong Shen, Bofeng Li

Journal of Geodesy > 2019 > 93 > 6 > 911-925

This paper first proves that the traditional median variance estimate is biased when the sample number is small and then proposes an unbiased median variance estimate to calibrate for the bias of the variance estimate. The scaled median variance estimate is firstly derived, and the unbiased median variance estimate is formed with independent residuals in an adjustment model no matter whether the measurements...

article

Real-time carrier phase multipath detection based on dual-frequency C/N0 data

Zhetao Zhang, Bofeng Li, Yang Gao, Yunzhong Shen

GPS Solutions > 2019 > 23 > 1 > 1-13

Since carrier phase multipath cannot be easily captured or mitigated, especially in real-time and kinematic applications, it is necessary to assess the multipath significance. We propose a real-time multipath detection method using dual-frequency carrier-to-noise-power-density ratio (C/N0). The proposed method takes full account of the relationship between the multipath and C/N0. Specifically, when...

article

A procedure for the significance testing of unmodeled errors in GNSS observations

Bofeng Li, Zhetao Zhang, Yunzhong Shen, Ling Yang

Journal of Geodesy > 2018 > 92 > 10 > 1171-1186

It is a crucial task to establish a precise mathematical model for global navigation satellite system (GNSS) observations in precise positioning. Due to the spatiotemporal complexity of, and limited knowledge on, systematic errors in GNSS observations, some residual systematic errors would inevitably remain even after corrected with empirical model and parameterization. These residual systematic errors...

article

The influence of improper stochastic modeling of Beidou pseudoranges on system reliability

Ling Yang, Bofeng Li, Haojun Li, Chris Rizos, more

Advances in Space Research > 2017 > 60 > 12 > 2680-2690

Stochastic models are important in Global Navigation Satellite System (GNSS) estimation problems, not only for parameter estimation, or precision assessment, but also for deriving system reliability and integrity measures. China’s Beidou GNSS (BDS) has received considerable research attention, however it has mainly focused on parameter estimation challenges. In this paper the influences of the BDS...

article

Improving BeiDou precise orbit determination using observations of onboard MEO satellite receivers

Haibo Ge, Bofeng Li, Maorong Ge, Yunzhong Shen, more

Journal of Geodesy > 2017 > 91 > 12 > 1447-1460

In recent years, the precise orbit determination (POD) of the regional Chinese BeiDou Navigation Satellite System (BDS) has been a hot spot because of its special constellation consisting of five geostationary earth orbit (GEO) satellites and five inclined geosynchronous satellite orbit (IGSO) satellites besides four medium earth orbit (MEO) satellites since the end of 2012. GEO and IGSO satellites...

chapter

PPP augmentation with current Galileo and BeiDou constellations

Nan Zang, Bofeng Li, Yunzhong Shen

2017 Forum on Cooperative Positioning and Service (CPGPS） > 213 - 218

2017 Forum on Cooperative Positioning and Service (CPGPS）

This contribution mainly addresses PPP augmentation with current Galileo constellation. The GPS-only, GPS+Galileo, and GPS+Galileo+BDS PPP will be numerically studied with both single- and dual-frequency signals. The results show that the single-frequency GPS PPP solutions in obstructed situation can reach only meter level accuracy while GPS+Galileo and GPS+Galileo+BDS PPP solutions get 0.15m and...

article

Comparison and analysis of unmodelled errors in GPS and BeiDou signals

Zhetao Zhang, Bofeng Li, Yunzhong Shen

Geodesy and Geodynamics > 2017 > 8 > 1 > 41-48

In Global Navigation Satellite Systems (GNSS) positioning, one often tries to establish a mathematic model to capture the systematic behaviors of observations as much as possible. However, the observation residuals still exhibit, to a great extent, as (somewhat systematic) signals. Nevertheless, those systematic variations are referred to as the unmodelled errors, which are difficult to be further...

article

A noise analysis method for GNSS signals of a standalone receiver

Zhetao Zhang, Bofeng Li, Yunzhong Shen, Ling Yang

Acta Geodaetica et Geophysica > 2017 > 52 > 3 > 301-316

Extensive studies on signal noise analysis of Global Navigation Satellite Systems (GNSS) receivers are mainly based on zero and/or short baselines where a pair of receivers is required. This paper develops a new signal noise assessment method for a standalone GNSS receiver. In this new method, the time differenced geometry-free ( $$ \Delta $$ Δ GF) model is formed, where the residual ionospheric...

chapter

Equivalence of GPS Algorithms and Its Inference

Guochang Xu, Yunzhong Shen, Yuanxi Yang, Heping Sun, more

Sciences of Geodesy - I > 229-273

In the past decade of GPS research, advantages and disadvantages of the differential and un-differential GPS have been discussed in detail in many publications. First in 2002 it was algebraically pointed out that the un-differential and differential algorithms of GPS are equivalent (Xu 2002a). Various combined and uncombined methods of GPS algorithms were discussed in detail too to show the advantages...

article

An improved GRACE monthly gravity field solution by modeling the non-conservative acceleration and attitude observation errors

Qiujie Chen, Yunzhong Shen, Wu Chen, Xingfu Zhang, more

Journal of Geodesy > 2016 > 90 > 6 > 503-523

The main contribution of this study is to improve the GRACE gravity field solution by taking errors of non-conservative acceleration and attitude observations into account. Unlike previous studies, the errors of the attitude and non-conservative acceleration data, and gravity field parameters, as well as accelerometer biases are estimated by means of weighted least squares adjustment. Then we compute...

article

Tongji-GRACE01: A GRACE-only static gravity field model recovered from GRACE Level-1B data using modified short arc approach

Qiujie Chen, Yunzhong Shen, Xingfu Zhang, Wu Chen, more

Advances in Space Research > 2015 > 56 > 5 > 941-951

The modified short arc approach, where the position vector in force model are regarded as pseudo observation, is implemented in the SAtellite Gravimetry Analysis Software (SAGAS) developed by Tongji university. Based on the SAGAS platform, a static gravity field model (namely Tongji-GRACE01) complete to degree and order 160 is computed from 49months of real GRACE Level-1B data spanning the period...

article

Monthly gravity field solution from GRACE range measurements using modified short arc approach

Yunzhong Shen, Qiujie Chen, Houze Xu

Geodesy and Geodynamics > 2015 > 6 > 4 > 261-266

In this paper we present a series of monthly gravity field solutions from Gravity Recovery and Climate Experiment (GRACE) range measurements using modified short arc approach, in which the ambiguity of range measurements is eliminated via differentiating two adjacent range measurements. The data used for developing our monthly gravity field model are same as Tongji-GRACE01 model except that the range...

article

Weighted spatiotemporal filtering using principal component analysis for analyzing regional GNSS position time series

Weiwei Li, Yunzhong Shen, Bofeng Li

Acta Geodaetica et Geophysica > 2015 > 50 > 4 > 419-436

Principal component analysis (PCA) is a powerful tool for extracting common mode errors from the position time series of a regional station network determined by global navigation satellite system (GNSS). It is implicitly based on the assumption that a time series dataset contains temporally uniform white noise. Since the position time series of a regional station network are not uniform and could...

article

Global Earth’s gravity field solution with GRACE orbit and range measurements using modified short arc approach

Qiujie Chen, Yunzhong Shen, Xingfu Zhang, Houze Hsu, more

Acta Geodaetica et Geophysica > 2015 > 50 > 2 > 173-185

Traditionally, the Earth’s gravity field model is computed from GRACE orbit and range rate measurements, e.g., in a short arc approach where both the position and the velocity vectors are integrated from a force model. In this contribution, we use the GRACE orbit and range measurements to recover the Earth’s gravity field model, thus we only need to integrate the position vectors. We use the range...

article

Mathematical model for computing precise local tie vectors for CMONOC co-located GNSS/VLBI/SLR stations

Yunzhong Shen, Xinzhao You, Jiexian Wang, Bin Wu, more

Geodesy and Geodynamics > 2015 > 6 > 1 > 1-6

The seven co-located sites of the Crustal Movement Observation Network of China (CMONOC) in Shanghai, Wuhan, Kunming, Beijing, Xi'an, Changchun, and Urumqi are equipped with Global Navigation Satellite System (GNSS), very long baseline interferometry (VLBI), and satellite laser ranging (SLR) equipment. Co-location surveying of these sites was performed in 2012 and the accuracies of the solved tie...

article

An improved geopositioning model of QuickBird high resolution satellite imagery by compensating spatial correlated errors

Chuang Li, Yunzhong Shen, Bofeng Li, Gang Qiao, more

ISPRS Journal of Photogrammetry and Remote Sensing > 2014 > 96 > Complete > 12-19

A lot of studies have been done for correcting the systematic biases of high resolution satellite images (HRSI), which is a fundamental work in the geometric orientation and the geopositioning of HRSI. All the existing bias-corrected models eliminate the biases in the images by expressing the biases as a function of some deterministic parameters (i.e. shift, drift, or affine transformation models),...

article

GNSS ambiguity resolution with controllable failure rate for long baseline network RTK

Bofeng Li, Yunzhong Shen, Yanming Feng, Weiguang Gao, more

Journal of Geodesy > 2014 > 88 > 2 > 99-112

Many large-scale GNSS CORS networks have been deployed around the world to support various commercial and scientific applications. To make use of these networks for real-time kinematic positioning services, one of the major challenges is the ambiguity resolution (AR) over long inter-station baselines in the presence of considerable atmosphere biases. Usually, the widelane ambiguities are fixed first,...

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INFONA - science communication portal

Search results for: Yunzhong Shen

Inter-system and inter-frequency code biases: simultaneous estimation, daily stability and applications in multi-GNSS single-frequency precise point positioning

Single-frequency PPP models: analytical and numerical comparison

A heuristic singular spectrum analysis method for suspended sediment concentration time series contaminated with multiplicative noise

M-estimation using unbiased median variance estimate

Real-time carrier phase multipath detection based on dual-frequency C/N0 data

A procedure for the significance testing of unmodeled errors in GNSS observations

The influence of improper stochastic modeling of Beidou pseudoranges on system reliability

Improving BeiDou precise orbit determination using observations of onboard MEO satellite receivers

PPP augmentation with current Galileo and BeiDou constellations

Comparison and analysis of unmodelled errors in GPS and BeiDou signals

A noise analysis method for GNSS signals of a standalone receiver

Equivalence of GPS Algorithms and Its Inference

An improved GRACE monthly gravity field solution by modeling the non-conservative acceleration and attitude observation errors

Tongji-GRACE01: A GRACE-only static gravity field model recovered from GRACE Level-1B data using modified short arc approach

Monthly gravity field solution from GRACE range measurements using modified short arc approach

Weighted spatiotemporal filtering using principal component analysis for analyzing regional GNSS position time series

Global Earth’s gravity field solution with GRACE orbit and range measurements using modified short arc approach

Mathematical model for computing precise local tie vectors for CMONOC co-located GNSS/VLBI/SLR stations

An improved geopositioning model of QuickBird high resolution satellite imagery by compensating spatial correlated errors

GNSS ambiguity resolution with controllable failure rate for long baseline network RTK

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