Yunzhong Shen

Tongji University

This paper forecasts global mean sea level (GMSL) changes from 2024 to 2100 using weighted singular spectrum analysis (SSA) that considers the formal errors of the previous GMSL time series. The simulation experiments are first carried out to evaluate the performance of the weighted and traditional SSA approaches for GMSL change prediction with two...

The improved SSA (ISSA) method is widely recognized for directly extracting signals from gappy time series without requiring prior interpolation. However, it is rather time consuming, particularly for long time series with large window sizes, such as Global Navigation Satellite System (GNSS) position time series. This study proposes an efficient IS...

Since 2002, the Gravity Recovery And Climate Experiment (GRACE) and its Follow-On (GRACE-FO, hereafter GRACE) missions have offered global observations of total water storage (TWS). However, the relatively short record of GRACE data poses a significant challenge for researchers to investigate the full range and long-term variability in TWS. In this...

A new dedicated coastal sea level dataset called the International Altimetry Service 2024 (IAS2024, https://doi.org/10.5281/zenodo.13208305, Peng et al., 2024c) has been presented to monitor sea level changes along the world’s coastlines. One of the reasons for generating this dataset is the quality of coastal altimeter data has been greatly improv...

This contribution introduces a Bayesian framework of fault detection, identification, and adaptation (Bayesian DIA) methods for Global Navigation Satellite System (GNSS) applications. It provides an alternative to the classical DIA approach, which allows for leveraging the prior information about faults to enhance the robustness of DIA estimators a...

First, this paper introduces a statistical model of gross errors, namely the Bernoulli–Gaussian (BG) model, which characterizes the gross error as a product of a Bernoulli variable and a Gaussian variable. The BG model offers a framework to interpret various causes of outliers through the perspective of gross errors. In addition, it unifies commonl...

High Mountain Asia (HMA) holds the largest concentration of glaciers outside the polar regions, and the melting glaciers provide freshwater for more than one billion people. Therefore, it is crucial to estimate glacier mass changes over HMA. Though GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (GRACE Follow-On) can accurately monitor...

Wavelet multiresolution analysis (MRA) is a widely used and effective method for filtering noisy time series and investigating the detailed characteristics of time series at different resolutions. However, geophysical time series often exhibit unavoidable data gaps stemming from diverse factors, impeding the straightforward implementation of ordina...

Monitoring changes in regional terrestrial water storage (TWS) and groundwater storage (GWS) is important for effectively managing water resources. Here, we investigate the TWS and GWS changes in the Yangtze River Delta using the GRACE/GRACE-FO mascon solutions, GLDAS NOAH models and in situ groundwater level changes from monitoring wells over the...

The issue of outliers has been a research focus in the field of geodesy. Based on a statistical testing method known as the w-test, data snooping along with its iterative form, iterative data snooping (IDS), is commonly used to diagnose outliers in linear models. However, in the case of multiple outliers, it may suffer from the masking and swamping...

Removing stripe noise from theGRACE (Gravity Recovery and Climate Experiment)monthly gravity fieldmodel is crucial for accurately interpreting temporal gravity variations. The conventional parameter filtering (CPF) approach expresses the signal components with a harmonic model while neglecting non-periodic and interannual signals. To address this i...

Gravity field solutions determined from the Gravity Recovery and Climate Experiment Follow‐on (GRACE‐FO) are affected by the unexpected performance degradation of one accelerometer onboard, which is circumvented by the accelerometer data transplant (ACT) technique. Three operational ACT products are presently available: JPL‐ACT and JPL‐ACH from NAS...

Understanding terrestrial water storage (TWS) changes is crucial for water management and hydrological applications. TWS changes are accurately observed by the Gravity Recovery and Climate Experiment and its Follow-On (GRACE/-FO) mission. However, the low spatial resolution limits the knowledge of water storage distribution. This study proposes a n...

The ionosphere crucially impacts on Global Navigation Satellite System (GNSS) positioning accuracy and integrity. Recently some network-based methods have shown the potential to construct a regional/global vertical total electron content (VTEC) or grid ionospheric vertical delay (GIVD) map for accuracy augmentation purposes. However, how to use the...

Regional sea level variations in the East China Sea (ECS) are estimated from multiple datasets, including satellite gravimetry, altimetry and steric datasets, and the sea level budget is investigated in terms of linear trends, annual and semiannual amplitudes and phases over the period April 2002 to December 2020 by considering the sediment factor....

Despite the increasing accuracies of GRACE/GRACE-FO gravity field models through worldwide endeavors, the temporal aliasing effect caused by the imperfect background models used in gravity field modelling is still a crucial factor that degrades the quality of gravity field solutions. Since the important role of temporal resolution of atmospheric de...

The Yangtze River Basin (YRB), home to around 400 million people, boasts of abundant water resources and significant spatial heterogeneity. Revealing the driving factors of water storage changes in YRB is essential for effective water resource management and sustainable development. In this study, we assess the drivers of total water storage (TWS)...

Accurate error covariance is crucial for post-processing GRACE gravity field solutions in terms of Spherical Harmonic Coefficients (SHCs). Unfortunately, most GRACE SHC products only provide formal errors of SHCs due to the large storage requirements of covariance matrices. A covariance matrix can be decomposed into a diagonal matrix and an orthogo...

Satellite Gravity Gradiometry (SGG) data play an important role in modeling static gravity fields, particularly considering the decrease in orbital altitude from 259.5 to 229.0 km during the final 15 months of the Gravity field and steady-state Ocean Circulation Explorer (GOCE). However, there is limited discussion regarding the contribution of dec...

In geodesy, Tikhonov regularization and truncated singular value decomposition (TSVD) are commonly used to derive a well-defined solution for ill-conditioned observation equations. However, as single-parameter regularization methods, they may face some limitations in application due to their lack of flexibility. In this contribution, a kind of mult...

The issue of dealing with outliers has been a research focus in the field of geodesy. Based on the statistical testing method known as the w-test, data snooping along with its iterative form, iterative data snooping (IDS), is commonly used to diagnose outliers in linear models. However, in the case of multiple outliers, these methods may suffer fro...

The issue of outliers has been a research focus in the field of geodesy. Based on a statistical testing method known as the w-test, data snooping along with its iterative form, iterative data snooping (IDS), is commonly used to diagnose outliers in linear models. However, in the case of multiple outliers, it may suffer from the masking and swamping...

The Greenland Ice Sheet (GrIS), Antarctic Ice Sheet (AIS), and global Mountain Glaciers (MGs) are highly susceptible to climate change and exert a significant influence on the global mean sea level (GMSL). To extend the record of global ice mass change and qualify corresponding contribution to GMSL, we conducted a comprehensive investigation into t...

The mass anomaly time series, derived from the monthly time-variable gravity fields of the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO), contain various deterministic signals such as long-term trends, annual and semi-annual signals. Singular spectrum analysis (SSA) is a data-driven method that effectively dec...

The Antarctic Ice Sheet (AIS) is susceptible to global climate change, and its mass loss has been 92 ± 18 Gt/yr between 1992 and 2020. Given the current intensive global warming, we investigate the AIS mass changes from January 2003 to December 2022, using the newly released satellite gravimetry and atmospheric datasets. The results show that the c...

As the main contributor to global sea-level rise, the Greenland Ice Sheet (GrIS) has undergone significant mass change over the last two decades. The satellite mission of GRACE (Gravity Recovery And Climate Experiment) and its follow-on mission (GRACE-FO) provide accurate observations but low spatial resolution. In contrast, satellite altimetry pro...

During gravity field modeling, the conventional acceleration approach rarely incorporates KBR inter-satellite range rate data from the GRACE mission. To propose an improved acceleration method, this study introduces initial orbital position and velocity vectors to be estimated along with a combination of Cowell, KSG, and Adams integrators. In addit...

Investigating the global sea level budget is essential to quantify the total sea level change (altimetry) and its components, including the steric sea level change and the ocean mass change (gravity), where the latter is mainly attributed to four mass-driven components (Greenland, Antarctica, glaciers and land water storage). In this study, a 24-ye...

High quality Interferometric Synthetic Aperture Radar (InSAR) interferograms are essential for determining surface deformation from InSAR time series. However, InSAR interferograms are usually polluted by spatially correlated errors (SCEs), especially the unmodelled atmospheric phase delays. To mitigate spatially correlated errors and improve the q...

The detection, identification, and adaptation method based on data snooping (DIA-datasnooping) is commonly used to deal with outliers in the Gauss–Markov model. However, the application of DIA-datasnooping might be limited in case of multiple outliers. In this contribution, the Maximum a posteriori (MAP) estimate is applied to the DIA framework, an...

This contribution introduces a statistical model of gross errors, which is called the Bernoulli-Gaussian (BG) model, where the gross error consists of the product of a Bernoulli variable and a Gaussian variable. First, with the BG model, different causes of outliers can be interpreted from the perspective of gross errors. As well, the commonly used...

The singular spectrum analysis (SSA) is a powerful tool to de-noise the geodetic time series and extract geophysical signals of interest. However, when missing data exists in geodetic time series, the ordinary SSA cannot be directly used to process them. Moreover, the heterogeneous properties of the geodetic time series are usually not considered i...

It is critical to understand the mechanisms and impacts of global climate change in cryosphere and polar environment. Here we describe the design and progress of the remote sensing products we have developed to monitor these changes. We obtain datasets by combining multi-sensor remote sensing systems with field validation systems, and then develop...

Groundwater overdraft in North China (NC) has posed adverse threats to sustainable development due to the reduction of freshwater availability. To comprehensively clarify the groundwater change and formulate reasonable control strategies, groundwater storage anomaly (GWSA) is investigated using the high-resolution time-variable gravity field model...

To enrich the understanding of the dynamic evolution of the water resources in North China, terrestrial water storage anomalies (TWSA) from January 2003 to June 2017 are derived using the new GRACE time-variable gravity field model Tongji-GraceCom. Additionally, the spatiotemporal characteristics of terrestrial water fluxes (TWF) at multiple time s...

To increase data availability and accuracy in the coastal zone, especially in the last 5 km to the coast, we present a SCMR (Seamless Combination of Multiple Retrackers) processing strategy to combine sea surface height (SSH) estimates from waveform retrackers of SGDR MLE4, ALES, WLS3 and MB4 for Jason-3 and Saral missions, and of SAMOSA and SAMOSA...

A 24-year global mean barystatic sea level change from January 1993 to December 2016 is derived by the joint use of Tongji-LEO2021 and Tongji-Grace2018 monthly gravity field solutions, with which the global sea level budget is investigated together with altimetry, steric and four mass elements (glaciers, Greenland, Antarctica and land water storage...

Study region: Pearl River Basin (PRB) has a tropical to subtropical climate in China. Study focus: An unprecedented extreme flood broke out in PRB during 2014-2016 super El Niño period. We construct the water storage deficit index (WSDI) to quantify this extreme flood event. The principal component analysis approach is used to analyze the WSDI in P...

Tropospheric delay is one of the main error sources that should be considered in global navigation satellite system (GNSS) positioning and integrity monitoring. Usually, it is first corrected by an empirical tropospheric zenith total delay (ZTD) model and an elevation-dependent mapping function during the preprocessing procedure, and then, the resi...

The mass loss of the Antarctic Ice Sheet (AIS) is an important contributor to global sea-level rise in response to the warming ocean and atmospheric temperatures as well as the changes in current systems and precipitation patterns. In this study, a regional mascon method is developed to squeeze more mass change signals, in which the pseudo-observat...

When ordinary principal component analysis (PCA) is employed to analyze the position time series of a regional GNSS station network, the GNSS time series are assumed to be homogeneous, and the missing data in the time series must be restored beforehand. To directly process incomplete and heterogeneous GNSS position time series, we develop the exten...

Since few time‐variable gravity field models were developed before the Gravity Recovery and Climate Experiment (GRACE) era, one normally estimates the global mean ocean mass (GMOM) changes by summing the mass contributions. In this study, new monthly gravity field models named Tongji‐LEO2021 developed from Early Low Earth Orbit (LEO) satellites' ob...

The gravity field recovery from GRACE (Gravity Recovery and Climate Experiment) mission data are contaminated by both observation noise and dynamic force errors, especially the temporal aliasing errors. To reduce their influence, four approaches are widely adopted, namely the estimation of empirical accelerations (ACC approach), the estimation of K...

Accurate estimates of global sea-level change from the observations of Altimetry, Argo and Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) are of great value for investigating the global sea�level budget. In this study, we analyzed the global sea-level change over the period from January 2005 to December 2019 by consi...

Accurate estimates of global sea-level change from the observations of Altimetry, Argo and Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) are of great value for investigating the global sea-level budget. In this study, we analyzed the global sea-level change over the period from January 2005 to December 2019 by consi...

Study region North China (NC) is an important social and economic center in China. Study focus NC is suffering from obvious land deformation. The vertical time series of 20 Global Positioning System (GPS) stations are explored to determine the seasonal driving sources and hydrological-induced displacement trends together with the mass loading mode...

https://meetingorganizer.copernicus.org/EGU22/EGU22-1604.html

In this contribution, we estimate the global mean mass sea-level (GMMSL) rise spanning January 1993 to December 2016 by using the Tongji-Grace2018 and Tongji-LEO2021 monthly gravity field solutions. In the post-processing, Tongji-Grace2018 and Tongji-Leo2021 solutions are filtered with P4M6 decorrelation plus Gauss 300km filtering, Tongji-Leo2021 s...

The terrestrial water storage change (TWSC) from January 2003 to December 2016 over the HongLiu River region (HLRR) is derived from the CSR-RL06 and Tongji-Grace2018 time-variable gravity field models. In addition, the major influencing factors of the regional TWSC are quantified via the water balance equations using precipitation, evapotranspirati...

North China (NC) is faced groundwater shortage in the past decades. To understand the characteristics of Groundwater Storage (GWS) change in NC, GWS Anomaly (GWSA) is analyzed by using Independent Component Analysis (ICA) with the high-resolution time-variable gravity field model Tongji-RegGrace2019 and hydrological models. According to the spatiot...

Efficient Variance Component Estimation (VCE) is significant to optimal data combination in large-scale least-squares problems as those encountered in satellite geodesy, where millions of observations are jointly processed to estimate a huge number of unknown parameters. In this paper, an efficient VCE algorithm with rigorous trace calculation is p...

The ill-posed models are widely encountered in various inversions of geodesy and remote sensing. The regularization approaches can significantly stabilize the solution to ill-posed models since the high-frequency noise is effectively suppressed. Although the famous Tikhonov regularization and truncated singular value decomposition (TSVD) regulariza...

The global sea-level budget is studied using the GRACE (Gravity Recovery and Climate Experiment) solutions, Satellite Altimetry and Argo observations based on the updated budget equation. When the global ocean mass change is estimated with the updated Tongji-Grace2018 solution, the misclosure of the global sea-level budget can be reduced by 0.11 ~...

Before the gravity solutions from the observations of Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) satellite missions are used to estimate the Global Ocean Mass Change (GOMC), spatial filtering method must be applied due to the strong noise over the oceans, different filtering methods will cause different signal le...

The global sea-level budget is theoretically closed between the Gravity Recovery and Climate Experiment (GRACE) solution, Satellite Altimetry and Argo observations. Five GRACE solutions (CSR RL06, GFZ RL06, JPL RL06, ITSG-Grace2018 and Tongji-grace2018) are used to estimate the Global Mean Ocean Mass (GMOM) change and demonstrate the sea-level budg...

GRACE Spherical Harmonics (SH) solutions are usually provided together with the corresponding formal errors, however, all Multichannel Singular Spectrum Analysis (MSSA) approaches neglect the formal errors of SH coefficients in processing the GRACE time series. In this contribution, we propose a weighted MSSA to directly process the incomplete time...

Climate change has led to increased droughts and floods over mainland Australia, resulting in water scarcity, excessive surplus and socioeconomic losses. Therefore, it is of great significance to comprehensively evaluate droughts and floods from the meteorological and hydrological perspective. Firstly, we determine the Standard Precipitation and Ev...

In recent years, many droughts have happened over mainland Australia, especially the two severe prolonged droughts, from 2006 to 2009 and 2018 to 2020, resulting in serious water scarcity. Therefore, using the Total Storage Deficit Index (TSDI) from the Gravity Recovery and Climate Experiment (GRACE), we analyzed the two severe prolonged droughts f...

Independent component analysis (ICA) is one of the most effective approaches in extracting independent signals from a global navigation satellite system (GNSS) regional station network. However, ICA requires the involved time series to be complete, thereby the missing data of incomplete time series should be interpolated beforehand. In this contrib...

We recompute the 26-year weekly Geocenter Motion (GCM) time series from 1994 to 2020 through the network shift approach using Satellite Laser Ranging (SLR) observations to LAGEOS1/2. Then the Singular Spectrum Analysis (SSA) is applied for the first time to separate and investigate the geophysical signals from the GCM time series. The Principal Com...

We recompute the 26-year weekly Geocenter Motion (GCM) time series from 1994 to 2020 through the network shift approach using Satellite Laser Ranging (SLR) observations to LAGEOS1/2. Then the Singular Spectrum Analysis (SSA) is applied for the first time to separate and investigate the geophysical signals from the GCM time series. The Principal Com...