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Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Remote Sensing in Geology, Geomorphology and Hydrology".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 33680

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Special Issue Editors

Prof. Dr. Wenbin Shen

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Guest Editor

School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China
Interests: gravity field theory and applications; time and frequency applications; Earth rotation; the Earth’s free oscillation
Special Issues, Collections and Topics in MDPI journals

Prof. Cheinway Hwang

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Guest Editor

Department of Civil Engineering, National Chiao Tung University, Taiwan, No. 1001, University Road, Hsinchu, Taiwan
Interests: altimetry; satellite geodetic survey; statistical adjustment; satellite oceanography
Special Issues, Collections and Topics in MDPI journals

Prof. Xiaoli Ding

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Guest Editor

Hong Kong with expertise in Geodesy and Surveying, The Hong Kong Polytechnic University, Hong Kong
Interests: geodesy; geodynamics; positioning technologies (such as GPS); synthetic aperture radar (SAR) and interferometric synthetic aperture radar (InSAR); technologies for ground deformation and structural health monitoring; global change; smart city development
Special Issues, Collections and Topics in MDPI journals

Prof. Hao Ding

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Guest Editor

Department of Geophysics, School of Geodesy and Geomatics, Wuhan University, Key Lab. of Geospace Environment and Geodesy, Wuhan University, No.129 Luoyu road, Wuhan 430079, China
Interests: geophysical data analysis and explanations; time-varying gravity and Earth tides; Earth rotation

Dr. Yuanjin Pan

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Guest Editor

Department of Geophysics, School of Geodesy and Geomatics, Wuhan University, Key Lab. of Geospace Environment and Geodesy, Wuhan University, No.129 Luoyu road, Wuhan 430079, China
Interests: surface mass changes; nonlinear signals from multi-geodetic measurements; crustal deformation of Tibet; hydrological and climate changes in the Tibet and surroundings

Special Issue Information

Dear Colleagues,

We are very pleased to invite you to submit your latest research results to this Special Issue on “Geodetic and Remote Sensing Observations in Tibet, Xinjiang, and Siberia for Climate Change Studies” of the open access journal, Remote Sensing. This is the second in the series of Special Issues launched by the journal to use geodetic and remote sensing observations to study issues related to climate and environmental changes in the region covering Tibet, Xinjiang, and Siberia (TibXS). Manifestations of these changes in this region are fast glacier melts, abnormal lake level changes, steady rises of temperature, and disrupted rain patterns, among other phenomena. These changes can be detected by sensors such as satellite altimeter, GPS, GRACE and InSAR. This Special Issue welcomes papers dealing with data collection, processing, and interpretation that can lead to detecting climate and environment-related changes in Tibet, Xinjiang, and Siberia. In particular, we encourage submissions of the papers presented in the meeting “The 10th International Workshop on TibXS (Multi-Observations and Interpretations of Tibet, Xinjiang and Siberia)”, held on 10–14 August 2019, in Lugu Lake, Sichuan, China (http://main.sgg.whu.edu.cn/tibxs/tibxs2019/tibxs2019.html). Papers with novel ideas, case studies, and new scientific findings derived from multi-datasets are encouraged. Subjects dealing with time series analysis related to gravity field, climate, and environmental changes are also acceptable. Researchers working on the following subjects can contribute to this SI:

Hydrological change over river basins, lake level variation, vertical deformation, mountain glacier change, and atmospheric circulation of the Tibetan Plateau;
Geopotential and orthometric height determinations and unification of world height datum systems;
Long-term monitoring of surface processes from satellite altimeters such as ICESat, TOPEX, Jason-1, -2, and 32, ERS-1, -2, and ENVISAT and Sentinel series;
Results of satellite and terrestrial-based gravimetric observations;
Results of GNSS observations, GNSS meteorology, and ionosphere;
Regional hydrology, vertical displacement, glacier change, lake level change, and their interpretations from altimeter, GPS, monthly GRACE fields, and gravimeters;
Geophysical interpretations and consequences of gravity, GNSS, satellite altimetry, and seismic observations;
SAR and LiDAR detections of surface deformation, especially over TibXS;
Crust structure and density refinement especially in the region TibXS using multi-datasets;
Earth rotation effects related to TibXS;
Temporal gravity fields, mass migration, and strain/stress fields;
Time and frequency applications in geoscience.

Prof. Wenbin Shen
Prof. Cheinway Hwang
Prof. Xiaoli Ding
Prof. Hao Ding
Dr. Yuanjin Pan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Tibetan Plateau
Xinjiang
Siberia
Geodetic observation
Global environment change
Time and frequency applications
Earth rotation effects
Crust structure and density refinement

Published Papers (14 papers)

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17 pages, 19626 KiB

Open AccessArticle

Strain Field Features and Three-Dimensional Crustal Deformations Constrained by Dense GRACE and GPS Measurements in NE Tibet

by Tengxu Zhang, Ziyu Shen, Lin He, Wenbin Shen and Wei Li

Remote Sens. 2022, 14(11), 2638; https://doi.org/10.3390/rs14112638 - 31 May 2022

Cited by 1 | Viewed by 1619

Abstract

The continuing impact between the Eurasia Plate and India results in the thickening and shortening of the N-S Tibetan Plateau. There has been strong tectonic movement along the boundary of the zones of deformation of the NE corner of the Tibetan plateau (NET) since the new tectonic period, with its dynamic mechanisms remaining controversial. Here, we use observations of 39 Continuous Global Positioning System (CGPS) gauges and 451 Crustal Movement Observation Network of China (CMONOC) campaign-mode stations to detect the three-dimensional deformation of the crust in the NET. Improved processing procedures are implemented to strengthen the patterns of strain throughout the NET. The principal component analysis (PCA) technique is introduced to decompose the time series into spatial eigenvectors and principal components (PCs), and the first three PCs are used to estimate and rectify common mode errors (CMEs). In addition, GRACE observations are used to detect deformation changes that account for non-tidal oceanic mass loading, hydrological loading, and surface pressure. The rectified deformation of the crust indicates the anisotropic nature of both the subsidence and uplift, and that the highest uplift rate of the Longmen Shan fault uplift reaches 7.13 ± 0.53 mm/yr. Finally, the horizontal velocity is further used to enumerate the strain rates throughout the NET. The results show that the shear band retained property in line with the strike-slip fault along the Altyn Tagh fault, the Qilian Shan faults, the Haiyuan fault, the West Qinling fault, the East Kunlun fault, and the Longmen Shan fault. In addition, the results further indicate that the whole NET shows a strong relationship with the mean principal rates of horizontal shortening strain. Extension and compression of the crust reasonably describe its sinking and uplifting. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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17 pages, 5521 KiB

Open AccessArticle

A Global Conversion Factor Model for Mapping Zenith Total Delay onto Precipitable Water

by Qingzhi Zhao, Kang Liu, Tengxu Zhang, Lin He, Ziyu Shen, Si Xiong, Yun Shi, Lichuan Chen and Weiming Liao

Remote Sens. 2022, 14(5), 1086; https://doi.org/10.3390/rs14051086 - 23 Feb 2022

Cited by 4 | Viewed by 1551

Abstract

The conversion factor is a key parameter for converting zenith wet delays (ZWD) into precipitable water vapour (PWV) with a mean value of 0.15, and the traditional method of calculating it is to model the weighted average temperature in the process of conversion factor calculation. Here, we overcome the dependence on high-precision atmospheric weighted average temperature for mapping ZWD onto PWV and build a global non-meteorological parametric model for conversion factor GΠ model by using the gridded data of global conversion factor time series from 2006 to 2013 provided by the Global Geodetic Observing System (GGOS) Atmosphere. Internal and external accuracy tests were performed using data from four times (UTC 00:00, 06:00, 12:00, and 18:00) per day throughout 2012 and 2014 as provided by the GGOS Atmosphere, and the statistical average root-mean-square (RMS) and mean absolute errors (MAE) on a global scale are 0.0031/0.0026 and 0.0030/0.0026, respectively, which only account for 1.5–2% of the conversion factor value. In addition, the observed GPS data are also used to validate the established GΠ model, and the RMS of the PWV differences between the established model and the observed meteorological data was less than 3.2 mm. The results show that the established GΠ model has a high accuracy, which can be used to calculate the PWV value where no observed meteorological parameters are available. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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24 pages, 11211 KiB

Open AccessArticle

GRACE Data Explore Moho Change Characteristics Beneath the South America Continent near the Chile Triple Junction

by Pengchao Sun, Changsheng Guo and Dongping Wei

Remote Sens. 2022, 14(4), 924; https://doi.org/10.3390/rs14040924 - 14 Feb 2022

Cited by 1 | Viewed by 1810

Abstract

The internal and external mass migration and redistribution of the Earth system are usually accompanied by changes in the gravity field, and the Gravity Recovery and Climate Experiment (GRACE) has been proven to be able to effectively monitor and evaluate such changes. The Chile Triple Junction (CTJ) is the convergence point of the Nazca plate, the Antarctic plate and the South American plate. Subductions of different forms and rates in the north and south of the CTJ have varying degrees of impact on the surface and underground material changes of the South American plate. In this study, GRACE data are used in the estimation of the comprehensive mass changes in the South America Continent (SAC) Near the CTJ (~15° range). In addition, surface movement changes constrained by GNSS data cannot fully explain the GRACE results after deducting hydrological information, which indicates that residual signals might be attributed to mass changes beneath the crust, that is, the Moho interface deformation. After eliminating surface movement and hydrological signals from the comprehensive mass changes of GRACE, this study obtains the deep structural information and calculates the Moho changes of three significant regions with rates of −2.12 ± 0.67 cm/yr, 0.18 ± 0.19 cm/yr and −6.46 ± 1.31 cm/yr, respectively. Results have demonstrated that the subductions of the Nazca plate and the Antarctica plate have an effect on the uneven deformation of the Moho interface beneath the SAC. The Moho beneath the SAC mainly shows a deepening trend, but it is uplifted in some areas north of CTJ. On the whole, the rate of Moho changes is greater in the south than in the north. The relationship between Moho changes and surface changes also indicates that a longer timescale may be needed for maintaining isostatic balance. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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21 pages, 9055 KiB

Open AccessArticle

Factors Driving Changes in Vegetation in Mt. Qomolangma (Everest): Implications for the Management of Protected Areas

by Binghua Zhang, Yili Zhang, Zhaofeng Wang, Mingjun Ding, Linshan Liu, Lanhui Li, Shicheng Li, Qionghuan Liu, Basanta Paudel and Huamin Zhang

Remote Sens. 2021, 13(22), 4725; https://doi.org/10.3390/rs13224725 - 22 Nov 2021

Cited by 6 | Viewed by 2154

Abstract

The Mt. Qomolangma (Everest) National Nature Preserve (QNNP) is among the highest natural reserves in the world. Monitoring the spatiotemporal changes in the vegetation in this complex vertical ecosystem can provide references for decision makers to formulate and adapt strategies. Vegetation growth in the reserve and the factors driving it remains unclear, especially in the last decade. This study uses the normalized difference vegetation index (NDVI) in a linear regression model and the Breaks for Additive Seasonal and Trend (BFAST) algorithm to detect the spatiotemporal patterns of the variations in vegetation in the reserve since 2000. To identify the factors driving the variations in the NDVI, the partial correlation coefficient and multiple linear regression were used to quantify the impact of climatic factors, and the effects of time lag and time accumulation were also considered. We then calculated the NDVI variations in different zones of the reserve to examine the impact of conservation on the vegetation. The results show that in the past 19 years, the NDVI in the QNNP has exhibited a greening trend (slope = 0.0008/yr, p < 0.05), where the points reflecting the transition from browning to greening (17.61%) had a much higher ratio than those reflecting the transition from greening to browning (1.72%). Shift points were detected in 2010, following which the NDVI tendencies of all the vegetation types and the entire preserve increased. Considering the effects of time lag and time accumulation, climatic factors can explain 44.04% of the variation in vegetation. No climatic variable recorded a change around 2010. Considering the human impact, we found that vegetation in the core zone and the buffer zone had generally grown better than the vegetation in the test zone in terms of the tendency of growth, the rate of change, and the proportions of different types of variations and shifts. A policy-induced reduction in livestock after 2010 might explain the changes in vegetation in the QNNP. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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18 pages, 13398 KiB

Open AccessArticle

The Interannual Fluctuations in Mass Changes and Hydrological Elasticity on the Tibetan Plateau from Geodetic Measurements

by Meilin He, Wenbin Shen, Jiashuang Jiao and Yuanjin Pan

Remote Sens. 2021, 13(21), 4277; https://doi.org/10.3390/rs13214277 - 24 Oct 2021

Cited by 3 | Viewed by 1726

Abstract

The mass balance of water storage on the Tibetan Plateau (TP) is a complex dynamic system that has responded to recent global warming due to the special regional characteristics and geographical environment on the TP. In this study, we present global positioning system (GPS), gravity recovery and climate experiment (GRACE) and follow-on (FO) observations obtained during the 2002–2020 period to identify hydrological changes on the TP. The spatial long-term trends in the GRACE/GRACE-FO data show continuous glacier mass losses around the Himalayas and accumulated mass on the inner TP due to the increased water mass in lakes. The singular spectrum analysis (SSA) was applied for interpolation of the data gap with GRACE/GRACE-FO. We evaluated the correlation between the vertical displacements obtained from 214 continuous GPS stations and GRACE/GRACE-FO-modeled water mass loads and found a high correlation, with spatial variabilities associated with the seasonal terrestrial water storage (TWS) pattern. The common-mode component obtained from continuous GPS coordinates was decomposed using principal component analysis (PCA) and presented different periodic signals related to interannual fluctuations in hydrology and the dynamics of the inner Earth. Moreover, the various characteristics of precipitation and temperature revealed similar interannual fluctuations to those of the El Niño/Southern Oscillation. We conclude that the GPS-inferred interannual fluctuations and the corresponding GRACE/GRACE-FO-modeled hydrological loads reflect climate responses. These findings shed light on the complex role of the spatiotemporal climate and water mass balance on the TP since the beginning of the 21st century. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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17 pages, 10313 KiB

Open AccessArticle

Geometric Evolution of the Chongce Glacier during 1970–2020, Detected by Multi-Source Satellite Observations

by Yongling Sun, Lin Liu, Yuanyuan Pei and Kai Wang

Remote Sens. 2021, 13(18), 3759; https://doi.org/10.3390/rs13183759 - 19 Sep 2021

Viewed by 2067

Abstract

Glacier surge, which causes a quick movement of ice mass from high to low elevation, is closely associated to the glacial hazards of debris flows and glacial lake outburst floods. Over the West Kunlun Shan, surge events have been detected for some glaciers, however, the characteristics (e.g., the active phase) of the identified surge-type glaciers are not fully understood due to the paucity of long-term observations of glacier changes. In this study, we investigated the geometric evolution of the Chongce Glacier (a surge-type glacier) over the past five decades. Glacier elevation changes were observed by comparing topographic data from different times. Surface velocity and terminus position were derived using a cross-correlation algorithm and band ratio method, respectively. A decreasing rate of glacier surface thinning was found for the Chongce Glacier during the studied period. Glacier elevation changes of −0.46 ± 0.12, −0.12 ± 0.05, and 0.27 ± 0.11 m yr⁻¹ were estimated for the periods of 1970–2000, 2000–2012, and 2012–2018, respectively. Moreover, this glacier experienced obvious surface lowering over the terminus zone and clear surface thickening over the upper zone during 1970–2000, and the opposite during 2000–2018. Surface velocity of the Chongce Glacier was less than 300 m yr⁻¹ in 1990–1993, and then quickly increased to more than 1000 m yr⁻¹ between 1994 and 1998, and dropped to less than 50 m yr⁻¹ in 1999–2020. Over the past five decades, the Chongce Glacier generally experienced a slight retreat, except for a terminus advance from 1995 to 1999. According to the spatial pattern of glacier elevation changes in 1970–2000 and the long-term changes of glacier velocity and terminus position, the recent surge event at the Chongce Glacier likely initiated in winter 1993 and terminated in winter 1998. Furthermore, the start date, end date, and duration of the active phase indicate that the detected surge event was likely triggered by a thermal mechanism. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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19 pages, 4415 KiB

Open AccessArticle

Retracking Cryosat-2 Data in SARIn and LRM Modes for Plateau Lakes: A Case Study for Tibetan and Dianchi Lakes

by Xiaoli Deng, Ren-Bin Wang, Fukai Peng, Yong Yang and Nan-Ming Mo

Remote Sens. 2021, 13(6), 1078; https://doi.org/10.3390/rs13061078 - 12 Mar 2021

Cited by 5 | Viewed by 2016

Abstract

This paper estimates lake level variations over two small and adjacent lakes in the Tibetan plateau (TP), namely Gemang Co and Zhangnai Co, as well as the inland Dianchi Lake in China using CryoSat-2 SARIn-mode and LRM 20-Hz waveforms over the period of 2011–2018. Different retrackers and a dedicated data editing procedure have been used to process CryoSat-2 data for determining the lake level time series. The lake level estimations are indirectly validated against those from Jason-2 in TP and from in situ data in Dianchi Lake, both showing good agreement with strong correlation coefficients >0.74. The results of this paper suggest that the official ICE retracker for LRM data and APD-PPT retracker for SARIn-mode waveforms are the most appropriate retrackers over Dianchi Lake and TP lakes, respectively. The trend estimates of the time series derived by both retrackers are 61.0 ± 10.8 mm/yr for Gemang Co and Zhangnai Co in TP, and 30.9 ± 64.9 mm/yr for Dianchi Lake, indicating that the lake levels over three lakes were continuously rising over the study period. The results of this study show that CryoSat-2 SARIn-mode data can be used for monitoring many small lakes that have not been measured by other altimetry missions in TP. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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20 pages, 13077 KiB

Open AccessArticle

Simulation of the Dynamic Water Storage and Its Gravitational Effect in the Head Region of Three Gorges Reservoir Using Imageries of Gaofen-1

by Xian Ma, Linsong Wang, Chao Chen, Jinsong Du and Shida Sun

Remote Sens. 2020, 12(20), 3353; https://doi.org/10.3390/rs12203353 - 14 Oct 2020

Cited by 4 | Viewed by 1771

Abstract

The construction of a high-resolution dynamic water storage model, driven by the mass load of the huge water storage of the Three Gorges Reservoir (TGR), is the necessary basic data for accurately simulating changes in the geophysical field, e.g., gravity, crustal deformation, and stress. However, previously established models cannot meet the needs of accurately simulating the impoundment effects of TGR, because these models were simplified and approximated and did not consider the variation of river boundaries caused by water level changes. In this study, we combined high-resolution Gaofen-1 (GF-1) satellite imageries and real-time water level in front of the dam and extracted 31 river boundaries of the head region of TGR between the lowest (145 m) and the highest (175 m) impoundment stages based on the Normalized Differential Water Index (NDWI) and threshold segmentation from Otsu method. Developed dynamic water storage model based on higher-resolution GF-1 data can show the true river boundary changes more exactly, especially in local areas. Compared to the previous approximate models, the model that we constructed accurately depicts the boundary distribution information of the different impoundment stages. Moreover, we simulated TGR-induced gravitational effects based on the high-precision forward modeling of the dynamic water storage model (i.e., considering changes of dynamic water area and water level). The theoretical modelled results are consistent with in situ gravity measurements with the difference mainly within 10 μGal. Our results indicate that water storage variations of TGR mainly affect the gravity field response within 1000 m of the reservoir bank with its maximum amplitude up to several hundred μGal. The dynamic water storage and its simulation results of gravitational effects can effectively eliminate the impact of surface water load driven by the TGR under human control and greatly improve the signal-to-noise ratio of regional gravity observational data. Thus, this work will be beneficial in the application of geophysical and geodetic monitoring aimed to comprehensively track the local and regional geological structural stability, e.g., artificial reservoir induced earthquake and landslide. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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24 pages, 8991 KiB

Open AccessArticle

Recent Climate Change Feedbacks to Greenland Ice Sheet Mass Changes from GRACE

by Fang Zou, Robert Tenzer, Hok Sum Fok and Janet E. Nichol

Remote Sens. 2020, 12(19), 3250; https://doi.org/10.3390/rs12193250 - 06 Oct 2020

Cited by 7 | Viewed by 2703

Abstract

Although a significant effort has been dedicated to studying changes in the mass budget of the Greenland Ice Sheet (GrIS), mechanisms behind these changes are not yet fully understood. In this study, we address this issue by investigating the link between climate controls and mass changes of the GrIS between August 2002 and June 2017. We estimate the GrIS mass changes based on averaging the Gravity Recovery and Climate Experiment (GRACE) monthly gravity field solutions from four processing data centers. We then investigate the possible impact of different climate variables on the GrIS mass changes using the North Atlantic Oscillation (NAO), temperature, precipitation, and the 700 hPa wind retrieved from the ERA-5 reanalysis. Results indicate a decrease of −267.77 ± 32.67 Gt/yr in the total mass of the GrIS over the 16-year period. By quantifying the relationship between climate controls and mass changes, we observe that mass changes in different parts of Greenland have varying sensitivity to climate controls. The NAO mainly controls mass changes in west Greenland, where the summertime NAO modulations have a greater impact on the summer mass loss than the wintertime NAO modulations have on the winter mass gain. The GrIS mass changes are correlated spatially with summer temperature, especially in southwest Greenland. Mass balance changes in northwest Greenland are mostly affected by wind anomalies. These new findings based on wind anomalies indicate that the summer atmospheric circulation anomalies control surface temperature and snow precipitation and consequently affect mass changes in different parts of Greenland. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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23 pages, 5767 KiB

Open AccessArticle

Quantitative Evaluation of Spatial and Temporal Variation of Soil Salinization Risk Using GIS-Based Geostatistical Method

by Zheng Wang, Fei Zhang, Xianlong Zhang, Ngai Weng Chan, Hsiang-te Kung, Xiaohong Zhou and Yishan Wang

Remote Sens. 2020, 12(15), 2405; https://doi.org/10.3390/rs12152405 - 27 Jul 2020

Cited by 17 | Viewed by 2868

Abstract

Soil salinization is one of the environmental threats affecting the sustainable development of arid oases in the northwest of China. Thus, it is necessary to assess the risk of soil salinity and analyze spatial and temporal changes. The objective of this paper is to develop a temporal and spatial soil salinity risk assessment method based on an integrated scoring method by combining the advantages of remote sensing and GIS technology. Based on correlation coefficient analysis to determine the weights of risk evaluation factors, a comprehensive scoring system for the risk of salinity in the dry and wet seasons was constructed for the Ebinur Lake Wetland National Nature Reserve (ELWNNR), and the risk of spatial variation of soil salinity in the study area was analyzed in the dry and wet seasons. The results show the following: (1) The risk of soil salinity during the wet season is mainly influenced by the plant senescence reflectance index (PSRI), deep soil water content (D_wat), and the effect of shallow soil salinity (SH_sal). The risk of soil salinity during the dry season is mainly influenced by shallow soil salinity (SH_sal), land use and land cover change (LUCC), and deep soil moisture content (D_wat). (2) The wet season was found to have a high risk of salinization, which is mainly characterized by moderate, high, and very high risks. However, in the dry season, the risk of salinity is mainly characterized by low and moderate risk of salinity. (3) In the ELWNNR, as the wet season changes to dry season (from May to August), moderate-risk area in the wet season easily shifts to low risk and risk-free, and the area of high risk in the wet season easily shifts to moderate risk. In general, the overall change in salinity risk of the ELWNNR showed a significant relationship with changes in lake water volume, indicating that changes in water volume play an important role in the risk of soil salinity occurrence. Ideally, the quantitative analysis of salinity risk proposed in this study, which takes into account temporal and spatial variations, can help decision makers to propose more targeted soil management options. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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15 pages, 2516 KiB

Open AccessArticle

Water Balance Standardization Approach for Reconstructing Runoff Using GPS at the Basin Upstream

by Hok Sum Fok, Linghao Zhou, Yongxin Liu, Robert Tenzer, Zhongtian Ma and Fang Zou

Remote Sens. 2020, 12(11), 1767; https://doi.org/10.3390/rs12111767 - 30 May 2020

Cited by 3 | Viewed by 1949

Abstract

While in-situ estuarine discharge has been correlated and reconstructed well with localized remotely-sensed data and hydraulic variables since the 1990s, its correlation and reconstruction using averaged GPS-inferred water storage from satellite gravimetry (i.e., GRACE) at the basin upstream based on the water balance standardization (WBS) approach remains unexplored. This study aims to illustrate the WBS approach for reconstructing monthly estuarine discharge (in the form of runoff (R)) at Mekong River Delta, by correlating the averaged GPS-inferred water storage from GRACE of the upstream Mekong Basin with the in-situ R at the Mekong River Delta estuary. The resulting R based on GPS-inferred water storage is comparable to that inferred from GRACE, regardless of in-situ stations within Mekong River Delta being used for the R reconstruction. The resulting R from the WBS approach with GPS water storage converted by GRACE mascon solution attains the lowest normalized root-mean-square error of 0.066, and the highest Pearson correlation coefficient of 0.974 and Nash-Sutcliffe efficiency of 0.950. Regardless of using either GPS-inferred or GRACE-inferred water storage, the WBS approach shows an increase of 1–4% in accuracy when compared to those reconstructed from remotely-sensed water balance variables. An external assessment also exhibits similar accuracies when examining the R estimated at another station location. By comparing the reconstructed and estimated Rs between the entrance and the estuary mouth, a relative error of 1–4% is found, which accounts for the remaining effect of tidal backwater on the estimated R. Additional errors might be caused by the accumulated errors from the proposed approach, the unknown signals in the remotely-sensed water balance variables, and the variable time shift across different years between the Mekong Basin at the upstream and the estuary at the downstream. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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25 pages, 28420 KiB

Open AccessArticle

Quantitative Evaluation of Environmental Loading Induced Displacement Products for Correcting GNSS Time Series in CMONOC

by Chenfeng Li, Shengxiang Huang, Qiang Chen, Tonie van Dam, Hok Sum Fok, Qian Zhao, Weiwei Wu and Xinpeng Wang

Remote Sens. 2020, 12(4), 594; https://doi.org/10.3390/rs12040594 - 11 Feb 2020

Cited by 18 | Viewed by 3557

Abstract

Mass redistribution within the Earth system deforms the surface elastically. Loading theory allows us to predict loading induced displacement anywhere on the Earth’s surface using environmental loading models, e.g., Global Land Data Assimilation System. In addition, different publicly available loading products are available. However, there are differences among those products and the differences among the combinations of loading models cannot be ignored when precisions of better than 1 cm are required. Many scholars have applied these loading corrections to Global Navigation Satellite System (GNSS) time series from mainland China without considering or discussing the differences between the available models. Evaluating the effects of different loading products over this region is of paramount importance for accurately removing the loading signal. In this study, we investigate the performance of these different publicly available loading products on the scatter of GNSS time series from the Crustal Movement Observation Network of China. We concentrate on five different continental water storage loading models, six different non-tidal atmospheric loading models, and five different non-tidal oceanic loading models. We also investigate all the different combinations of loading products. The results show that the difference in RMS reduction can reach 20% in the vertical component depending on the loading correction applied. We then discuss the performance of different loading combinations and their effects on the noise characteristics of GNSS height time series and horizontal velocities. The results show that the loading products from NASA may be the best choice for corrections in mainland China. This conclusion could serve as an important reference for loading products users in this region. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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18 pages, 3604 KiB

Open AccessArticle

Recent Accelerating Glacier Mass Loss of the Geladandong Mountain, Inner Tibetan Plateau, Estimated from ZiYuan-3 and TanDEM-X Measurements

by Lin Liu, Liming Jiang, Zhimin Zhang, Hansheng Wang and Xiaoli Ding

Remote Sens. 2020, 12(3), 472; https://doi.org/10.3390/rs12030472 - 02 Feb 2020

Cited by 17 | Viewed by 3007

Abstract

The headwaters of many Asian rivers are at mountain glaciers of the Tibetan Plateau. Glacier melt-water is a non-negligible contributor of river runoff, especially for a drought year. However, the observation of mass glacier changes was scarce in recent years. Here, we estimated the recent glacier mass change of the Geladandong mountain, by differencing the digital elevation models (DEMs) produced from ZiYuan-3 images and TanDEM-X data. Moreover, we compared the SRTM-C DEM with TanDEM-X DEMs to retrieve glacier mass balances since 2000. The annual mass loss rates of −0.11 ± 0.03 and −0.47 ± 0.09 m w.e. yr⁻¹ were derived in 2000–2012 and 2012−2018, respectively. This result revealed an accelerating rate of negative glacier mass changes during recent years, which is mainly caused by the significant increase of mass loss over non-surge glaciers, rather than surge-type glaciers, which held a slight increase of mass loss. In addition, we found a pronounced discrepancy of glacier mass change between non-surge and surge-type glaciers during 2012−2018, and suggested that this difference may be caused by the heterogeneous responses of surge-type glaciers to climate variations, because of the different timing and type of surge events. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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12 pages, 796 KiB

Open AccessLetter

Drift of the Earth’s Principal Axes of Inertia from GRACE and Satellite Laser Ranging Data

by José M. Ferrándiz, Sadegh Modiri, Santiago Belda, Mikhail Barkin, Mathis Bloßfeld, Robert Heinkelmann and Harald Schuh

Remote Sens. 2020, 12(2), 314; https://doi.org/10.3390/rs12020314 - 18 Jan 2020

Cited by 1 | Viewed by 3477

Abstract

The location of the Earth’s principal axes of inertia is a foundation for all the theories and solutions of its rotation, and thus has a broad effect on many fields, including astronomy, geodesy, and satellite-based positioning and navigation systems. That location is determined by the second-degree Stokes coefficients of the geopotential. Accurate solutions for those coefficients were limited to the stationary case for many years, but the situation improved with the accomplishment of Gravity Recovery and Climate Experiment (GRACE), and nowadays several solutions for the time-varying geopotential have been derived based on gravity and satellite laser ranging data, with time resolutions reaching one month or one week. Although those solutions are already accurate enough to compute the evolution of the Earth’s axes of inertia along more than a decade, such an analysis has never been performed. In this paper, we present the first analysis of this problem, taking advantage of previous analytical derivations to simplify the computations and the estimation of the uncertainty of solutions. The results are rather striking, since the axes of inertia do not move around some mean position fixed to a given terrestrial reference frame in this period, but drift away from their initial location in a slow but clear and not negligible manner. Full article

(This article belongs to the Special Issue Geodetic and Remote Sensing Observations in Tibet, Xinjiang and Siberia for Climate and Environment Change Studies)

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