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Shuanggen Jin

Shanghai Astronomical Observatory, CAS, Center for Astro-Geodynamics Research, Faculty Member

Henan Polytechnic University, Faculty of Geomatics & Information Engineering, Faculty Member

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Shuanggen Jin is Vice-President and Professor at Henan Polytechnic University, China and Professor at Shanghai Astronomical Observatory, CAS, China. His main research areas include Satellite Navigation, Remote Sensing and Space/Planetary Exploration. He has published over 500 papers in peer-reviewed journals and proceedings, 10 patents/software copyrights and 10 books/monographs with more than 9000 citations and H-index>50. Prof. Jin has been President of International Association of Planetary Sciences (IAPS) (2015-2019), President of the International Association of CPGPS (2016-2017), Chair of IUGG Union Commission on Planetary Sciences (UCPS) (2015-2023), Editor-in-Chief of International Journal of Geosciences, Editor of Geoscience Letters, Associate Editor of IEEE Transactions on Geoscience
Phone: 86-21-34775292
Address: 80 Nandan Road, Shanghai

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Papers by Shuanggen Jin

Present-day kinematics in the Eastern Mediterranean and Caucasus from dense GPS observations

by Shuanggen Jin and Bahruz Ahadov

Physics of the Earth and Planetary Interiors, 2017

A Novel Method to Estimate Multi-GNSS Differential Code Bias without Using Ionospheric Function Model and Global Ionosphere Map

Remote Sensing

Global navigation satellite system (GNSS) differential code bias (DCB) is one of main errors in i... more Global navigation satellite system (GNSS) differential code bias (DCB) is one of main errors in ionospheric modeling and applications. Accurate estimation of multiple types of GNSS DCBs is important for GNSS positioning, navigation, and timing, as well as ionospheric modeling. In this study, a novel method of multi-GNSS DCB estimation is proposed without using an ionospheric function model and global ionosphere map (GIM), namely independent GNSS DCB estimation (IGDE). Firstly, ionospheric observations are extracted based on the geometry-free combination of dual-frequency multi-GNSS code observations. Secondly, the VTEC of the station represented by the weighted mean VTEC value of the ionospheric pierce points (IPPs) at each epoch is estimated as a parameter together with the combined receiver and satellite DCBs (RSDCBs). Last, the estimated RSDCBs are used as new observations, whose weight is calculated from estimated covariances, and thus the satellite and receiver DCBs of multi-GN...

Assessment of the Seafloor Topography Accuracy in the Emperor Seamount Chain by Ship-Based Water Depth Data and Satellite-Based Gravity Data

Sensors

The seafloor topography estimation is very important, while the bathymetry data and gravity data ... more The seafloor topography estimation is very important, while the bathymetry data and gravity data are scarce and uneven, which results in large errors in the inversion of the seafloor topography. In this paper, in order to reduce the influence of errors and improve the accuracy of seafloor inversion, the influence of different resolution data on the inversion topography in the Emperor Seamount Chain are investigated by combining ship water depth data and satellite gravity anomaly data released by SIO V29.1. Through the comparison of different resolution models, it is found that the choice of resolution affects the accuracy of the inversion terrain model. An external comparison is presented by using the international high-precision topography data and check points observations. The results show that with the increase in resolution, the fitting residuals obtained by the scale factor are optimized, and the precision of the terrain model is gradually approaching the S&S V19.1 and GEBCO-2...

Low-Latitude Ionospheric Responses and Coupling to the February 2014 Multiphase Geomagnetic Storm from GNSS, Magnetometers, and Space Weather Data

Atmosphere

The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, pa... more The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, particularly during the February 2014 multiphase geomagnetic storm. In this paper, the low-latitude ionosphere responses and their coupling mechanisms, during the February 2014 multiphase geomagnetic storm, are investigated from ground-based magnetometers and global navigation satellite system (GNSS), and space weather data. The residual disturbances between the total electron content (TEC) of the International GNSS Service (IGS) global ionospheric maps (GIMs) and empirical models are used to investigate the storm-time ionospheric responses. Three clear sudden storm commencements (SSCs) on 15, 20, and 23 February are detected, and one high speed solar wind (HSSW) event on 19 February is found with the absence of classical SSC features due to a prevalent magnetospheric convection. The IRI-2012 shows insufficient performance, with no distinction between the events and overestimating approxim...

Co-/Post-seismic Ionospheric Disturbances

GNSS Atmospheric Seismology, 2019

Giant earthquakes often result in great loss of economics and lives as well as geohazards, such a... more Giant earthquakes often result in great loss of economics and lives as well as geohazards, such as tsunami and landslide. Due to the lack of measurement and theoretical understanding for the Earth’s interior, it is hard to predict the short-term earthquake’s occurrence, location, and magnitude up to now.

Summary and Prospective

GNSS Atmospheric Seismology, 2019

The worldwide seismometers could estimate rapidly the location, the magnitude and the focal mecha... more The worldwide seismometers could estimate rapidly the location, the magnitude and the focal mechanism of earthquakes, but the detailed rupture process and seismic anomalies are still difficult to be monitored precisely and understood well due to limited observations or the lack of dense near field observations.

GNSS Tropospheric Sounding

GNSS Atmospheric Seismology, 2019

The Earth’s atmosphere is a kind of inhomogeneous medium. With increase of height, atmospheric ma... more The Earth’s atmosphere is a kind of inhomogeneous medium. With increase of height, atmospheric mass decreases. When the electromagnetic wave propagates through the atmosphere, the deviation from a straight line occurs due to the variation of the air mass or density, which is called the atmospheric refraction.

Two-Mode Seismo-ionospheric Disturbances

GNSS Atmospheric Seismology, 2019

Ionospheric disturbances could be excited by various natural or artificial events from the Earth’... more Ionospheric disturbances could be excited by various natural or artificial events from the Earth’s interior to the top of the atmosphere, such as volcanoes, earthquakes, geomagnetic storms, etc (Jin et al. 2007; Jin and Park 2007; Afraimovich et al. 2010, 2013; Aoyama et al. 2016; Dautermann et al. 2009; Grawe and Makela 2016). These natural events excite acoustic resonance between the Earth’s surface and the atmosphere.

Multi-GNSS Precise Point Positioning with UWB Tightly Coupled Integration

Sensors, 2022

Global Navigation Satellite Systems (GNSSs) can provide high-precision positioning services, whic... more Global Navigation Satellite Systems (GNSSs) can provide high-precision positioning services, which can be applied to fields including navigation and positioning, autonomous driving, unmanned aerial vehicles and so on. However, GNSS signals are easily disrupted in complex environments, which results in a positioning performance with a significantly inferior accuracy and lengthier convergence time, particularly for the single GNSS system. In this paper, multi-GNSS precise point positioning (PPP) with tightly integrating ultra-wide band (UWB) technology is presented to implement fast and precise navigation and positioning. The validity of the algorithm is evaluated by a set of GNSS and UWB data. The statistics indicate that multi-GNSS/UWB integration can significantly improve positioning performance in terms of the positioning accuracy and convergence time. The improvement of the positioning performance for the GNSS/UWB tightly coupled integration mainly concerns the north and east dir...

Spatial–Temporal Variations of Total Nitrogen and Phosphorus in Poyang, Dongting and Taihu Lakes from Landsat-8 Data

Water, 2021

Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and low... more Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and lower reaches of the Yangtze River, China. In recent years, the eutrophication level of lakes has increased with the development of the social economy and caused many environmental and social problems. The concentrations of total nitrogen (TN) and total phosphorus (TP) are the key indicators of the degree of eutrophication, but the traditional ground monitoring methods are not capable of capturing such parameters in whole lakes with high spatial-temporal resolution. In this paper, empirical models are established and evaluated between the TN and TP and remote sensing spectral factors in the three lakes using Landsat 8 Operational Land Imager (OLI) satellite data and in-situ data. The results show that the inversion accuracy is higher than 75%. The TN and TP concentrations in the three lakes are inversed based on the Google Earth Engine (GEE) platform from 2014 to 2020 and their spatial-temp...

Spatio-Temporal Trends of Surface Energy Budget in Tibet from Satellite Remote Sensing Observations and Reanalysis Data

Remote Sensing, 2021

Being the highest and largest land mass of the earth, the Tibetan Plateau has a strong impact on ... more Being the highest and largest land mass of the earth, the Tibetan Plateau has a strong impact on the Asian climate especially on the Asian monsoon. With high downward solar radiation, the Tibetan Plateau is a climate sensitive region and the main water source for many rivers in South and East Asia. Although many studies have analyzed energy fluxes in the Tibetan Plateau, a long-term detailed spatio-temporal variability of all energy budget parameters is not clear for understanding the dynamics of the regional climate change. In this paper, satellite remote sensing and reanalysis data are used to quantify spatio-temporal trends of energy budget parameters, net radiation, latent heat flux, and sensible heat flux over the Tibetan Plateau from 2001 to 2019. The validity of both data sources is analyzed from in situ ground measurements of the FluxNet micrometeorological tower network, which verifies that both datasets are valid and reliable. It is found that the trend of net radiation sh...

Undifferenced Kinematic Precise Orbit Determination of Swarm and GRACE-FO Satellites from GNSS Observations

Sensors, 2022

Low Earth Orbit (LEO) satellites can be used for remote sensing and gravity field recovery, while... more Low Earth Orbit (LEO) satellites can be used for remote sensing and gravity field recovery, while precise orbit determination (POD) is vital for LEO satellite applications. However, there are some systematic errors when using the LEO satellite orbits released by different agencies in multi-satellite-based applications, e.g., Swarm and Gravity Recovery and Climate Experiment-Follow-On (GRACE-FO), as different GNSS precise orbit and clock products are used as well as processing strategies and software. In this paper, we performed undifferenced kinematic PODs for Swarm and GRACE-FO satellites simultaneously over a total of 14 days by using consistent International Global Navigation Satellite System (GNSS) Service (IGS) precise orbit and clock products. The processing strategy based on an undifferenced ionosphere-free combination and a least squares method was applied for Swarm and GRACE-FO satellites. Furthermore, the quality control for the kinematic orbits was adopted to mitigate abr...

Long-Term Variations of Plasmaspheric Total Electron Content from Topside GPS Observations on LEO Satellites

Remote Sensing, 2021

The plasmasphere is located above the ionosphere with low-energy plasma, which is an important co... more The plasmasphere is located above the ionosphere with low-energy plasma, which is an important component of the solar-terrestrial space environment. As the link between the ionosphere and the magnetosphere, the plasmasphere plays an important role in the coupling process. Therefore, it is of great significance to study the electron content variation of the plasmasphere for the solar-terrestrial space environment. Nowadays, the topside global positioning system (GPS) observations on Low Earth Orbit (LEO) satellites provide a unique opportunity to estimate and study variations in the plasmasphere. In this paper, the plasmaspheric total electron content (PTEC) is estimated, and its long-term variations are studied from topside GPS observations onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The PTEC in the daytime is higher than that in the nighttime, with the peak between 14:00 and 17:00 in the magnetic local time, while the minimum value ...

Variation Characteristics of Multi-Channel Differential Code Biases from New BDS-3 Signal Observations

Remote Sensing, 2022

A multi-frequency Global Navigation Satellite System (GNSS) provides greater opportunities for po... more A multi-frequency Global Navigation Satellite System (GNSS) provides greater opportunities for positioning and navigation applications, particularly the BeiDou Global Navigation Satellite System (BDS-3) satellites. However, multi-frequency signals import more pseudorange channels, which introduce more multi-channel Differential Code Biases (DCBs). The satellite and receiver DCBs from the new BDS-3 signals are not clear. In this study, 9 DCB types of the new BDS-3 signals from 30-days Multi-GNSS Experiment (MGEX) observations are estimated and investigated. Compared with the DCB values provided by the Chinese Academy of Science (CAS) products, the mean bias and root mean squares (RMS) error of new BDS-3 satellite DCBs are within ±0.20 and 0.30 ns, respectively. The satellite DCBs are mostly within ±0.40 ns with respect to the product of the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The four sets of constructed closure errors and their mean values are within ±0.30 ns and ±0.15 ...

phase observations: A simulation study

The detection and repair of the cycle slip or gross error is a key step for high precision global... more The detection and repair of the cycle slip or gross error is a key step for high precision global positioning system (GPS) carrier phase navigation and positioning due to interruption or unlocking of GPS signal. A number of methods have been developed to detect and repair cycle slips in the last two decades through cycle slip linear combinations of available GPS observations, but such approaches are subject to the changing GPS sampling and complex algorithms. Furthermore, the small cycle slip and gross error cannot be completely repaired or detected if the sampling is quite longer under some special observation conditions, such as Real Time Kinematic (RTK) positioning. With the development of the GPS modernization or Galileo system with three frequencies signals, it may be able to better detect and repair the cycle slip and gross error in the future. In this paper, the cycle slip and gross error of GPS carrier phase data are detected and repaired by using a new combination of the simulated multi-frequency GPS carrier phase data in different conditions. Results show that various real-time cycle slips are completely repaired with a gross error of up to 0.2 cycles.

Remote Sensing Systems for Ocean: A Review (Part 2: Active Systems)

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2022

As discussed in the previous part of this review paper, Remote Sensing (RS) creates unprecedented... more As discussed in the previous part of this review paper, Remote Sensing (RS) creates unprecedented opportunities by providing a variety of systems with different characteristics to study and monitor oceans. Part 1 of this review paper was dedicated to reviewing passive RS systems and their main applications in the ocean. Here, in part 2, seven active RS systems, including scatterometers, altimeters, gravimeters, Synthetic Aperture Radar (SAR), Light Detection and Ranging (LiDAR), Sound Navigation and Ranging (SONAR), High-Frequency (HF) radars are comprehensively reviewed. For consistency, this part is structured similarly to part 1. The aforementioned systems, along with their characteristics and primary applications, are introduced in separate sections. This review paper provides useful information to all students and researchers who are interested in the oceanographic applications of active RS systems.

Nitrogen and climate change

Groundwater storage is an important parameter in water resource management, land-surface processe... more Groundwater storage is an important parameter in water resource management, land-surface processes and hydrological cycle. However, the traditional instruments are very difficult tomonitor global groundwater storage variations due to high cost and strong labor intensity. In this paper, the global total terrestrial water storage (TWS) is derived from approximately 10 years of monthly geopotential coefficients from GRACE observations (2002 August–2012 April), and the groundwater storage is then obtained by subtracting the surface water, soil moisture, snow, ice and canopy water from the hydrological models GLDAS (Global Land Data Assimilation System) and WGHM (WaterGAP Global Hydrology Model). The seasonal, secular and acceleration variations of global groundwater storage are investigated from about 10 years of monthly groundwater time series. Annual and semiannual amplitudes of GRACE–WGHM and GRACE–GLDAS are almost similar, while WGHM ground-water results are much smaller. The larger...

GPS TOOLBOX M_DCB: Matlab code for estimating GNSS satellite and receiver differential

Global navigation satellite systems (GNSS) have been widely used to monitor variations in the ear... more Global navigation satellite systems (GNSS) have been widely used to monitor variations in the earth’s ionosphere by estimating total electron content (TEC) using dual-frequency observations. Differential code biases (DCBs) are one of the important error sources in estimating precise TEC from GNSS data. The International GNSS Service (IGS) Analysis Centers have routinely provided DCB estimates for GNSS satellites and IGS ground receivers, but the DCBs for regional and local network receivers are not provided. Furthermore, the DCB values of GNSS satellites or receivers are assumed to be constant over 1 day or 1 month, which is not always the case. We describe Matlab code to estimate GNSS satellite and receiver DCBs for time intervals from hours to days; the software is called M_DCB. The DCBs of GNSS satellites and ground receivers are tested and evaluated using data from the IGS GNSS network. The estimates from M_DCB show good agreement with the IGS Analysis Centers with a mean differ...

Remote Sensing Systems for Ocean: A Review (Part 1: Passive Systems)

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2022

Reliable, accurate, and timely information about oceans is important for many applications, inclu... more Reliable, accurate, and timely information about oceans is important for many applications, including water resource management, hydrological cycle monitoring, environmental studies, agricultural and ecosystem health applications, economy, and the overall health of the environment. In this regard, remote sensing (RS) systems offer exceptional advantages for mapping and monitoring various oceanographic parameters with acceptable temporal and spatial resolutions over the oceans and coastal areas. So far, different methods have been developed to study oceans using various RS systems. This urges the necessity of having review studies that comprehensively discuss various RS systems, including passive and active sensors, and their advantages and limitations for ocean applications. In this article, the goal is to review most RS systems and approaches that have been worked on marine applications. This review paper is divided into two parts. Part 1 is dedicated to the passive RS systems for ocean studies. As such, four primary passive systems, including optical, thermal infrared radiometers, microwave radiometers, and Global Navigation Satellite Systems, are comprehensively discussed. Additionally, this article summarizes the main passive RS sensors and satellites, which have been utilized for different oceanographic applications. Finally, various oceanographic parameters, which can be retrieved from the data acquired by passive RS systems, along with the corresponding methods, are discussed.

Water Quality Variability and Related Factors along the Yangtze River Using Landsat-8

Remote Sensing, 2021

Chlorophyll-a (Chl-a), total nitrogen (TN), and total phosphorus (TP) are important indicators to... more Chlorophyll-a (Chl-a), total nitrogen (TN), and total phosphorus (TP) are important indicators to evaluate water environmental quality. Monitoring water quality and its variability can help control water pollution. However, traditional monitoring techniques of water quality are time-consuming and laborious, and can mostly conduct with sample point-to-point at the edge of lakes and rivers. In this study, an empirical (regression-based) model is proposed to retrieve Chl-a, TN, and TP concentrations in the Yangtze River by Landsat-8 images from 2014 to 2020. The spatial-temporal distribution and variability of water quality in the whole Yangtze River are analyzed in detail. Furthermore, the driving forces of water quality variations are explored. The results show that the mean absolute percentage error (MAPE) of the water quality parameters are 25.88%, 4.3%, and 8.37% for Chl-a, TN, and TP concentrations, respectively, and the root mean square errors (RMSE) are 0.475 μg/L, 0.110 mg/L, ...

Present-day kinematics in the Eastern Mediterranean and Caucasus from dense GPS observations

by Shuanggen Jin and Bahruz Ahadov

Physics of the Earth and Planetary Interiors, 2017

A Novel Method to Estimate Multi-GNSS Differential Code Bias without Using Ionospheric Function Model and Global Ionosphere Map

Remote Sensing

Global navigation satellite system (GNSS) differential code bias (DCB) is one of main errors in i... more Global navigation satellite system (GNSS) differential code bias (DCB) is one of main errors in ionospheric modeling and applications. Accurate estimation of multiple types of GNSS DCBs is important for GNSS positioning, navigation, and timing, as well as ionospheric modeling. In this study, a novel method of multi-GNSS DCB estimation is proposed without using an ionospheric function model and global ionosphere map (GIM), namely independent GNSS DCB estimation (IGDE). Firstly, ionospheric observations are extracted based on the geometry-free combination of dual-frequency multi-GNSS code observations. Secondly, the VTEC of the station represented by the weighted mean VTEC value of the ionospheric pierce points (IPPs) at each epoch is estimated as a parameter together with the combined receiver and satellite DCBs (RSDCBs). Last, the estimated RSDCBs are used as new observations, whose weight is calculated from estimated covariances, and thus the satellite and receiver DCBs of multi-GN...

Assessment of the Seafloor Topography Accuracy in the Emperor Seamount Chain by Ship-Based Water Depth Data and Satellite-Based Gravity Data

Sensors

The seafloor topography estimation is very important, while the bathymetry data and gravity data ... more The seafloor topography estimation is very important, while the bathymetry data and gravity data are scarce and uneven, which results in large errors in the inversion of the seafloor topography. In this paper, in order to reduce the influence of errors and improve the accuracy of seafloor inversion, the influence of different resolution data on the inversion topography in the Emperor Seamount Chain are investigated by combining ship water depth data and satellite gravity anomaly data released by SIO V29.1. Through the comparison of different resolution models, it is found that the choice of resolution affects the accuracy of the inversion terrain model. An external comparison is presented by using the international high-precision topography data and check points observations. The results show that with the increase in resolution, the fitting residuals obtained by the scale factor are optimized, and the precision of the terrain model is gradually approaching the S&S V19.1 and GEBCO-2...

Low-Latitude Ionospheric Responses and Coupling to the February 2014 Multiphase Geomagnetic Storm from GNSS, Magnetometers, and Space Weather Data

Atmosphere

The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, pa... more The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, particularly during the February 2014 multiphase geomagnetic storm. In this paper, the low-latitude ionosphere responses and their coupling mechanisms, during the February 2014 multiphase geomagnetic storm, are investigated from ground-based magnetometers and global navigation satellite system (GNSS), and space weather data. The residual disturbances between the total electron content (TEC) of the International GNSS Service (IGS) global ionospheric maps (GIMs) and empirical models are used to investigate the storm-time ionospheric responses. Three clear sudden storm commencements (SSCs) on 15, 20, and 23 February are detected, and one high speed solar wind (HSSW) event on 19 February is found with the absence of classical SSC features due to a prevalent magnetospheric convection. The IRI-2012 shows insufficient performance, with no distinction between the events and overestimating approxim...

Co-/Post-seismic Ionospheric Disturbances

GNSS Atmospheric Seismology, 2019

Giant earthquakes often result in great loss of economics and lives as well as geohazards, such a... more Giant earthquakes often result in great loss of economics and lives as well as geohazards, such as tsunami and landslide. Due to the lack of measurement and theoretical understanding for the Earth’s interior, it is hard to predict the short-term earthquake’s occurrence, location, and magnitude up to now.

Summary and Prospective

GNSS Atmospheric Seismology, 2019

The worldwide seismometers could estimate rapidly the location, the magnitude and the focal mecha... more The worldwide seismometers could estimate rapidly the location, the magnitude and the focal mechanism of earthquakes, but the detailed rupture process and seismic anomalies are still difficult to be monitored precisely and understood well due to limited observations or the lack of dense near field observations.

GNSS Tropospheric Sounding

GNSS Atmospheric Seismology, 2019

The Earth’s atmosphere is a kind of inhomogeneous medium. With increase of height, atmospheric ma... more The Earth’s atmosphere is a kind of inhomogeneous medium. With increase of height, atmospheric mass decreases. When the electromagnetic wave propagates through the atmosphere, the deviation from a straight line occurs due to the variation of the air mass or density, which is called the atmospheric refraction.

Two-Mode Seismo-ionospheric Disturbances

GNSS Atmospheric Seismology, 2019

Ionospheric disturbances could be excited by various natural or artificial events from the Earth’... more Ionospheric disturbances could be excited by various natural or artificial events from the Earth’s interior to the top of the atmosphere, such as volcanoes, earthquakes, geomagnetic storms, etc (Jin et al. 2007; Jin and Park 2007; Afraimovich et al. 2010, 2013; Aoyama et al. 2016; Dautermann et al. 2009; Grawe and Makela 2016). These natural events excite acoustic resonance between the Earth’s surface and the atmosphere.

Multi-GNSS Precise Point Positioning with UWB Tightly Coupled Integration

Sensors, 2022

Global Navigation Satellite Systems (GNSSs) can provide high-precision positioning services, whic... more Global Navigation Satellite Systems (GNSSs) can provide high-precision positioning services, which can be applied to fields including navigation and positioning, autonomous driving, unmanned aerial vehicles and so on. However, GNSS signals are easily disrupted in complex environments, which results in a positioning performance with a significantly inferior accuracy and lengthier convergence time, particularly for the single GNSS system. In this paper, multi-GNSS precise point positioning (PPP) with tightly integrating ultra-wide band (UWB) technology is presented to implement fast and precise navigation and positioning. The validity of the algorithm is evaluated by a set of GNSS and UWB data. The statistics indicate that multi-GNSS/UWB integration can significantly improve positioning performance in terms of the positioning accuracy and convergence time. The improvement of the positioning performance for the GNSS/UWB tightly coupled integration mainly concerns the north and east dir...

Spatial–Temporal Variations of Total Nitrogen and Phosphorus in Poyang, Dongting and Taihu Lakes from Landsat-8 Data

Water, 2021

Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and low... more Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and lower reaches of the Yangtze River, China. In recent years, the eutrophication level of lakes has increased with the development of the social economy and caused many environmental and social problems. The concentrations of total nitrogen (TN) and total phosphorus (TP) are the key indicators of the degree of eutrophication, but the traditional ground monitoring methods are not capable of capturing such parameters in whole lakes with high spatial-temporal resolution. In this paper, empirical models are established and evaluated between the TN and TP and remote sensing spectral factors in the three lakes using Landsat 8 Operational Land Imager (OLI) satellite data and in-situ data. The results show that the inversion accuracy is higher than 75%. The TN and TP concentrations in the three lakes are inversed based on the Google Earth Engine (GEE) platform from 2014 to 2020 and their spatial-temp...

Spatio-Temporal Trends of Surface Energy Budget in Tibet from Satellite Remote Sensing Observations and Reanalysis Data

Remote Sensing, 2021

Being the highest and largest land mass of the earth, the Tibetan Plateau has a strong impact on ... more Being the highest and largest land mass of the earth, the Tibetan Plateau has a strong impact on the Asian climate especially on the Asian monsoon. With high downward solar radiation, the Tibetan Plateau is a climate sensitive region and the main water source for many rivers in South and East Asia. Although many studies have analyzed energy fluxes in the Tibetan Plateau, a long-term detailed spatio-temporal variability of all energy budget parameters is not clear for understanding the dynamics of the regional climate change. In this paper, satellite remote sensing and reanalysis data are used to quantify spatio-temporal trends of energy budget parameters, net radiation, latent heat flux, and sensible heat flux over the Tibetan Plateau from 2001 to 2019. The validity of both data sources is analyzed from in situ ground measurements of the FluxNet micrometeorological tower network, which verifies that both datasets are valid and reliable. It is found that the trend of net radiation sh...

Undifferenced Kinematic Precise Orbit Determination of Swarm and GRACE-FO Satellites from GNSS Observations

Sensors, 2022

Low Earth Orbit (LEO) satellites can be used for remote sensing and gravity field recovery, while... more Low Earth Orbit (LEO) satellites can be used for remote sensing and gravity field recovery, while precise orbit determination (POD) is vital for LEO satellite applications. However, there are some systematic errors when using the LEO satellite orbits released by different agencies in multi-satellite-based applications, e.g., Swarm and Gravity Recovery and Climate Experiment-Follow-On (GRACE-FO), as different GNSS precise orbit and clock products are used as well as processing strategies and software. In this paper, we performed undifferenced kinematic PODs for Swarm and GRACE-FO satellites simultaneously over a total of 14 days by using consistent International Global Navigation Satellite System (GNSS) Service (IGS) precise orbit and clock products. The processing strategy based on an undifferenced ionosphere-free combination and a least squares method was applied for Swarm and GRACE-FO satellites. Furthermore, the quality control for the kinematic orbits was adopted to mitigate abr...

Long-Term Variations of Plasmaspheric Total Electron Content from Topside GPS Observations on LEO Satellites

Remote Sensing, 2021

The plasmasphere is located above the ionosphere with low-energy plasma, which is an important co... more The plasmasphere is located above the ionosphere with low-energy plasma, which is an important component of the solar-terrestrial space environment. As the link between the ionosphere and the magnetosphere, the plasmasphere plays an important role in the coupling process. Therefore, it is of great significance to study the electron content variation of the plasmasphere for the solar-terrestrial space environment. Nowadays, the topside global positioning system (GPS) observations on Low Earth Orbit (LEO) satellites provide a unique opportunity to estimate and study variations in the plasmasphere. In this paper, the plasmaspheric total electron content (PTEC) is estimated, and its long-term variations are studied from topside GPS observations onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The PTEC in the daytime is higher than that in the nighttime, with the peak between 14:00 and 17:00 in the magnetic local time, while the minimum value ...

Variation Characteristics of Multi-Channel Differential Code Biases from New BDS-3 Signal Observations

Remote Sensing, 2022

A multi-frequency Global Navigation Satellite System (GNSS) provides greater opportunities for po... more A multi-frequency Global Navigation Satellite System (GNSS) provides greater opportunities for positioning and navigation applications, particularly the BeiDou Global Navigation Satellite System (BDS-3) satellites. However, multi-frequency signals import more pseudorange channels, which introduce more multi-channel Differential Code Biases (DCBs). The satellite and receiver DCBs from the new BDS-3 signals are not clear. In this study, 9 DCB types of the new BDS-3 signals from 30-days Multi-GNSS Experiment (MGEX) observations are estimated and investigated. Compared with the DCB values provided by the Chinese Academy of Science (CAS) products, the mean bias and root mean squares (RMS) error of new BDS-3 satellite DCBs are within ±0.20 and 0.30 ns, respectively. The satellite DCBs are mostly within ±0.40 ns with respect to the product of the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The four sets of constructed closure errors and their mean values are within ±0.30 ns and ±0.15 ...

phase observations: A simulation study

The detection and repair of the cycle slip or gross error is a key step for high precision global... more The detection and repair of the cycle slip or gross error is a key step for high precision global positioning system (GPS) carrier phase navigation and positioning due to interruption or unlocking of GPS signal. A number of methods have been developed to detect and repair cycle slips in the last two decades through cycle slip linear combinations of available GPS observations, but such approaches are subject to the changing GPS sampling and complex algorithms. Furthermore, the small cycle slip and gross error cannot be completely repaired or detected if the sampling is quite longer under some special observation conditions, such as Real Time Kinematic (RTK) positioning. With the development of the GPS modernization or Galileo system with three frequencies signals, it may be able to better detect and repair the cycle slip and gross error in the future. In this paper, the cycle slip and gross error of GPS carrier phase data are detected and repaired by using a new combination of the simulated multi-frequency GPS carrier phase data in different conditions. Results show that various real-time cycle slips are completely repaired with a gross error of up to 0.2 cycles.

Remote Sensing Systems for Ocean: A Review (Part 2: Active Systems)

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2022

As discussed in the previous part of this review paper, Remote Sensing (RS) creates unprecedented... more As discussed in the previous part of this review paper, Remote Sensing (RS) creates unprecedented opportunities by providing a variety of systems with different characteristics to study and monitor oceans. Part 1 of this review paper was dedicated to reviewing passive RS systems and their main applications in the ocean. Here, in part 2, seven active RS systems, including scatterometers, altimeters, gravimeters, Synthetic Aperture Radar (SAR), Light Detection and Ranging (LiDAR), Sound Navigation and Ranging (SONAR), High-Frequency (HF) radars are comprehensively reviewed. For consistency, this part is structured similarly to part 1. The aforementioned systems, along with their characteristics and primary applications, are introduced in separate sections. This review paper provides useful information to all students and researchers who are interested in the oceanographic applications of active RS systems.

Nitrogen and climate change

Groundwater storage is an important parameter in water resource management, land-surface processe... more Groundwater storage is an important parameter in water resource management, land-surface processes and hydrological cycle. However, the traditional instruments are very difficult tomonitor global groundwater storage variations due to high cost and strong labor intensity. In this paper, the global total terrestrial water storage (TWS) is derived from approximately 10 years of monthly geopotential coefficients from GRACE observations (2002 August–2012 April), and the groundwater storage is then obtained by subtracting the surface water, soil moisture, snow, ice and canopy water from the hydrological models GLDAS (Global Land Data Assimilation System) and WGHM (WaterGAP Global Hydrology Model). The seasonal, secular and acceleration variations of global groundwater storage are investigated from about 10 years of monthly groundwater time series. Annual and semiannual amplitudes of GRACE–WGHM and GRACE–GLDAS are almost similar, while WGHM ground-water results are much smaller. The larger...

GPS TOOLBOX M_DCB: Matlab code for estimating GNSS satellite and receiver differential

Global navigation satellite systems (GNSS) have been widely used to monitor variations in the ear... more Global navigation satellite systems (GNSS) have been widely used to monitor variations in the earth’s ionosphere by estimating total electron content (TEC) using dual-frequency observations. Differential code biases (DCBs) are one of the important error sources in estimating precise TEC from GNSS data. The International GNSS Service (IGS) Analysis Centers have routinely provided DCB estimates for GNSS satellites and IGS ground receivers, but the DCBs for regional and local network receivers are not provided. Furthermore, the DCB values of GNSS satellites or receivers are assumed to be constant over 1 day or 1 month, which is not always the case. We describe Matlab code to estimate GNSS satellite and receiver DCBs for time intervals from hours to days; the software is called M_DCB. The DCBs of GNSS satellites and ground receivers are tested and evaluated using data from the IGS GNSS network. The estimates from M_DCB show good agreement with the IGS Analysis Centers with a mean differ...

Remote Sensing Systems for Ocean: A Review (Part 1: Passive Systems)

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2022

Reliable, accurate, and timely information about oceans is important for many applications, inclu... more Reliable, accurate, and timely information about oceans is important for many applications, including water resource management, hydrological cycle monitoring, environmental studies, agricultural and ecosystem health applications, economy, and the overall health of the environment. In this regard, remote sensing (RS) systems offer exceptional advantages for mapping and monitoring various oceanographic parameters with acceptable temporal and spatial resolutions over the oceans and coastal areas. So far, different methods have been developed to study oceans using various RS systems. This urges the necessity of having review studies that comprehensively discuss various RS systems, including passive and active sensors, and their advantages and limitations for ocean applications. In this article, the goal is to review most RS systems and approaches that have been worked on marine applications. This review paper is divided into two parts. Part 1 is dedicated to the passive RS systems for ocean studies. As such, four primary passive systems, including optical, thermal infrared radiometers, microwave radiometers, and Global Navigation Satellite Systems, are comprehensively discussed. Additionally, this article summarizes the main passive RS sensors and satellites, which have been utilized for different oceanographic applications. Finally, various oceanographic parameters, which can be retrieved from the data acquired by passive RS systems, along with the corresponding methods, are discussed.

Water Quality Variability and Related Factors along the Yangtze River Using Landsat-8

Remote Sensing, 2021

Chlorophyll-a (Chl-a), total nitrogen (TN), and total phosphorus (TP) are important indicators to... more Chlorophyll-a (Chl-a), total nitrogen (TN), and total phosphorus (TP) are important indicators to evaluate water environmental quality. Monitoring water quality and its variability can help control water pollution. However, traditional monitoring techniques of water quality are time-consuming and laborious, and can mostly conduct with sample point-to-point at the edge of lakes and rivers. In this study, an empirical (regression-based) model is proposed to retrieve Chl-a, TN, and TP concentrations in the Yangtze River by Landsat-8 images from 2014 to 2020. The spatial-temporal distribution and variability of water quality in the whole Yangtze River are analyzed in detail. Furthermore, the driving forces of water quality variations are explored. The results show that the mean absolute percentage error (MAPE) of the water quality parameters are 25.88%, 4.3%, and 8.37% for Chl-a, TN, and TP concentrations, respectively, and the root mean square errors (RMSE) are 0.475 μg/L, 0.110 mg/L, ...