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Environmental and Geodetic Monitoring of the Tibetan Plateau

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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 July 2019) | Viewed by 58350

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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
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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
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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. Dr. Guoqing Zhang

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Guest Editor

Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
Interests: lake change; remote sensing; glacial lake; GLOF
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are very pleased to invite you to submit your latest research results to this Special Issue (SI) “Environmental and Geodetic Monitoring of the Tibetan Plateau” of the open access journal, Remote Sensing. The environment in the Tibet, Xinjiang and Siberia (TibXS) region is susceptible to global climate change. Recent remote sensing and geodetic observations show that lakes, glaciers, rainfalls, temperatures and other climatic parameters have undergone changes beyond model predictions. The trends of these parameters can be altered by forcings that originate from local and remote sources. Reliable predictions of the trends can only rely on observations with sufficient resolutions in space and time. In recent decades, a large volume of remote sensing and geodetic data have been made available to the scientific community that allow for detecting environment changes in the TibXS region. Typical sensors include altimeter, GPS, GRACE and SAR. This Special Issue welcomes papers dealing with observation, processing and interpretation of the remote sensing data that lead to important identifications of changes in the environment in the TibXS region. Authors who study environmental changes in the TibXS region are encouraged to submit papers to this Special Issue. In particular, we encourage submissions of the papers presented in the meeting “The 9th International Workshop on TibXS (Multi-Observations and Interpretations of Tibet, Xinjiang and Siberia)”, held from August 6–10, 2018, in Zhangye, Gansu Province, China (http://main.sgg.whu.edu.cn/tibxs/tibxs2018/tibxs2018.html). We welcome submissions that present novel approaches, case studies and new scientific findings based on multi-datasets, including various satellite sensors, especially the GRACE and altimeter data. Results on applications of time and frequency in the Tibetan Plateau are also encouraged. Researchers working on the following subjects can contribute to this SI:

Hydrological change over river basins, lake level variation, vertical deformation, mountain glacier change, 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. Dr. Guoqing Zhang
Guest Editors

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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.

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Keywords

Tibetan Plateau
geodetic observation
global environment change
time and frequency applications
Earth rotation effects
crust structure and density refinement

Published Papers (12 papers)

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Research

20 pages, 7095 KiB

Open AccessArticle

Common Mode Component and Its Potential Effect on GPS-Inferred Three-Dimensional Crustal Deformations in the Eastern Tibetan Plateau

by Yuanjin Pan, Ruizhi Chen, Hao Ding, Xinyu Xu, Gang Zheng, Wenbin Shen, YiXin Xiao and Shuya Li

Remote Sens. 2019, 11(17), 1975; https://doi.org/10.3390/rs11171975 - 22 Aug 2019

Cited by 19 | Viewed by 2928

Abstract

Surface and deep potential geophysical signals respond to the spatial redistribution of global mass variations, which may be monitored by geodetic observations. In this study, we analyze dense Global Positioning System (GPS) time series in the Eastern Tibetan Plateau using principal component analysis (PCA) and wavelet time-frequency spectra. The oscillations of interannual and residual signals are clearly identified in the common mode component (CMC) decomposed from the dense GPS time series from 2000 to 2018. The newly developed spherical harmonic coefficients of the Gravity Recovery and Climate Experiment Release-06 (GRACE RL06) are adopted to estimate the seasonal and interannual patterns in this region, revealing hydrologic and atmospheric/nontidal ocean loads. We stack the averaged elastic GRACE-derived loading displacements to identify the potential physical significance of the CMC in the GPS time series. Interannual nonlinear signals with a period of ~3 to ~4 years in the CMC (the scaled principal components from PC1 to PC3) are found to be predominantly related to hydrologic loading displacements, which respond to signals (El Niño/La Niña) of global climate change. We find an obvious signal with a period of ~6 yr on the vertical component that could be caused by mantle-inner core gravity coupling. Moreover, we evaluate the CMC’s effect on the GPS-derived velocities and confirm that removing the CMC can improve the recognition of nontectonic crustal deformation, especially on the vertical component. Furthermore, the effects of the CMC on the three-dimensional velocity and uncertainty are presented to reveal the significant crustal deformation and dynamic processes of the Eastern Tibetan Plateau. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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17 pages, 23579 KiB

Open AccessArticle

An Approach to Moho Topography Recovery Using the On-Orbit GOCE Gravity Gradients and Its Applications in Tibet

by Jiakuan Wan, Chuang Xu, Zhicai Luo, Yihao Wu, Boyang Zhou and Jianguo Yan

Remote Sens. 2019, 11(13), 1567; https://doi.org/10.3390/rs11131567 - 02 Jul 2019

Cited by 7 | Viewed by 2783

Abstract

It is significant to determine the refined Moho topography for understanding the tectonic structure of the crust and upper mantle. A novel method to invert the Moho topography from the on-orbit gravity gradients is proposed in the present study. The Moho topography of Tibet is estimated by our method, which is verified by previous studies. The research results show that: (1) the deepest Moho of Tibet, approximately 70 km, is located at the western Kunlun area, where it corresponds well to that of previous publications; (2) clear Moho folds can be observed from the inverted Moho topography, whose direction presents a clockwise pattern and is in good agreement with that of Global Positioning System; (3) compared with the CRUST 1.0, our inverted Moho model has a better spatial resolution and reveals more details for tectonic structure; (4) the poor density model of the crust in Tibet may be the main reason for the differences between the obtained gravity Moho model and seismic Moho model; (5) by comparing our inverted Moho with those from previous publications, our method is correct and effective. This work provides a new method for the study of Moho topography and the interior structure of the Earth. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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17 pages, 15894 KiB

Open AccessArticle

An Improved GPS-Inferred Seasonal Terrestrial Water Storage Using Terrain-Corrected Vertical Crustal Displacements Constrained by GRACE

by Hok Sum Fok and Yongxin Liu

Remote Sens. 2019, 11(12), 1433; https://doi.org/10.3390/rs11121433 - 17 Jun 2019

Cited by 25 | Viewed by 3578

Abstract

Based on a geophysical model for elastic loading, the application potential of Global Positioning System (GPS) vertical crustal displacements for inverting terrestrial water storage has been demonstrated using the Tikhonov regularization and the Helmert variance component estimation since 2014. However, the GPS-inferred terrestrial water storage has larger resulting amplitudes than those inferred from satellite gravimetry (i.e., Gravity Recovery and Climate Experiment (GRACE)) and those simulated from hydrological models (e.g., Global Land Data Assimilation System (GLDAS)). We speculate that the enlarged amplitudes should be partly due to irregularly distributed GPS stations and the neglect of the terrain effect. Within southwest China, covering part of southeastern Tibet as a study region, a novel GPS-inferred terrestrial water storage approach is proposed via terrain-corrected GPS and supplementary vertical crustal displacements inferred from GRACE, serving as "virtual GPS stations" for constraining the inversion. Compared to the Tikhonov regularization and Helmert variance component estimation, we employ Akaike’s Bayesian Information Criterion as an inverse method to prove the effectiveness of our solution. Our results indicate that the combined application of the terrain-corrected GPS vertical crustal displacements and supplementary GRACE spatial data constraints improves the inversion accuracy of the GPS-inferred terrestrial water storage from the Helmert variance component estimation, Tikhonov regularization, and Akaike’s Bayesian Information Criterion, by 55%, 33%, and 41%, respectively, when compared to that of the GLDAS-modeled terrestrial water storage. The solution inverted with Akaike’s Bayesian Information Criterion exhibits more stability regardless of the constraint conditions, when compared to those of other inferred solutions. The best Akaike’s Bayesian Information Criterion inverted solution agrees well with the GLDAS-modeled one, with a root-mean-square error (RMSE) of 3.75 cm, equivalent to a 15.6% relative error, when compared to 39.4% obtained in previous studies. The remaining discrepancy might be due to the difference between GPS and GRACE in sensing different surface water storage components, the remaining effect of the water storage changes in rivers and reservoirs, and the internal error in the geophysical model for elastic loading. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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16 pages, 5278 KiB

Open AccessArticle

Present-Day Deformation of the Gyaring Co Fault Zone, Central Qinghai–Tibet Plateau, Determined Using Synthetic Aperture Radar Interferometry

by Yong Zhang, Chuanjin Liu, Wenting Zhang and Fengyun Jiang

Remote Sens. 2019, 11(9), 1118; https://doi.org/10.3390/rs11091118 - 10 May 2019

Cited by 10 | Viewed by 3822

Abstract

Because of the constant northward movement of the Indian plate and blockage of the Eurasian continent, the Qinghai–Tibet Plateau has been extruded by north–south compressive stresses since its formation. This has caused the plateau to escape eastward to form a large-scale east–west strike-slip fault and a north–south extensional tectonic system. The Karakorum–Jiali fault, a boundary fault between the Qiangtang and Lhasa terranes, plays an important role in the regional tectonic evolution of the Qinghai–Tibet Plateau. The Gyaring Co fault, in the middle of the Karakoram–Jiali fault zone, is a prominent tectonic component. There have been cases of strong earthquakes of magnitude 7 or greater in this fault, providing a strong earthquake occurrence background. However, current seismic activity is weak. Regional geodetic observation stations are sparsely distributed; thus, the slip rate of the Gyaring Co fault remains unknown. Based on interferometric synthetic aperture radar (InSAR) technology, we acquired current high-spatial resolution crustal deformation characteristics of the Gyaring Co fault zone. The InSAR-derived deformation features were highly consistent with Global Positioning System observational results, and the accuracy of the InSAR deformation fields was within 2 mm/y. According to InSAR results, the Gyaring Co fault controlled the regional crustal deformation pattern, and the difference in far-field deformation on both sides of the fault was 3–5 mm/y (parallel to the fault). The inversion results of the back-slip dislocation model indicated that the slip rate of the Gyaring Co fault was 3–6 mm/y, and the locking depth was ~20 km. A number of v-shaped conjugate strike-slip faults, formed along the Bangong–Nujiang suture zone in the central and southern parts of the -Tibet Plateau, played an important role in regional tectonic evolution. V-shaped conjugate shear fault systems include the Gyaring Co and Doma–Nima faults, and the future seismic risk cannot be ignored. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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23 pages, 8609 KiB

Open AccessArticle

Water Storage Variations in Tibet from GRACE, ICESat, and Hydrological Data

by Fang Zou, Robert Tenzer and Shuanggen Jin

Remote Sens. 2019, 11(9), 1103; https://doi.org/10.3390/rs11091103 - 09 May 2019

Cited by 24 | Viewed by 4836

Abstract

The monitoring of water storage variations is essential not only for the management of water resources, but also for a better understanding of the impact of climate change on hydrological cycle, particularly in Tibet. In this study, we estimated and analyzed changes of the total water budget on the Tibetan Plateau from the Gravity Recovery And Climate Experiment (GRACE) satellite mission over 15 years prior to 2017. To suppress overall leakage effect of GRACE monthly solutions in Tibet, we applied a forward modeling technique to reconstruct hydrological signals from GRACE data. The results reveal a considerable decrease in the total water budget at an average annual rate of −6.22 ± 1.74 Gt during the period from August 2002 to December 2016. In addition to the secular trend, seasonal variations controlled mainly by annual changes in precipitation were detected, with maxima in September and minima in December. A rising temperature on the plateau is likely a principal factor causing a continuous decline of the total water budget attributed to increase melting of mountain glaciers, permafrost, and snow cover. We also demonstrate that a substantial decrease in the total water budget due to melting of mountain glaciers was partially moderated by the increasing water storage of lakes. This is evident from results of ICESat data for selected major lakes and glaciers. The ICESat results confirm a substantial retreat of mountain glaciers and an increasing trend of major lakes. An increasing volume of lakes is mainly due to an inflow of the meltwater from glaciers and precipitation. Our estimates of the total water budget on the Tibetan Plateau are affected by a hydrological signal from neighboring regions. Probably the most significant are aliasing signals due to ground water depletion in Northwest India and decreasing precipitation in the Eastern Himalayas. Nevertheless, an integral downtrend in the total water budget on the Tibetan Plateau caused by melting of glaciers prevails over the investigated period. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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24 pages, 3249 KiB

Open AccessArticle

Upstream Remotely-Sensed Hydrological Variables and Their Standardization for Surface Runoff Reconstruction and Estimation of the Entire Mekong River Basin

by Linghao Zhou, Hok Sum Fok, Zhongtian Ma and Qiang Chen

Remote Sens. 2019, 11(9), 1064; https://doi.org/10.3390/rs11091064 - 05 May 2019

Cited by 12 | Viewed by 3414

Abstract

River water discharge (WD) is an essential component when monitoring a regional hydrological cycle. It is expressed in terms of surface runoff (R) when a unit of river basin surface area is considered. To compensate for the decreasing number of hydrological stations, remotely-sensed WD estimation has been widely promoted over the past two decades, due to its global coverage. Previously, remotely-sensed WD was reconstructed either by correlating nearby remotely-sensed surface responses (e.g., indices and hydraulic variables) with ground-based WD observations or by applying water balance formulations, in terms of R, over an entire river basin, assisted by hydrological modeling data. In contrast, the feasibility of using remotely-sensed hydrological variables (RSHVs) and their standardized forms together with water balance representations (WBR) obtained from the river upstream to reconstruct estuarine R for an entire basin, has been rarely investigated. Therefore, our study aimed to construct a correlative relationship between the estuarine observed R and the upstream, spatially averaged RSHVs, together with their standardized forms and WBR, for the Mekong River basin, using estuarine R reconstructions, at a monthly temporal scale. We found that the reconstructed R derived from the upstream, spatially averaged RSHVs agreed well with the observed R, which was also comparable to that calculated using traditional remote sensing data (RSD). Better performance was achieved using spatially averaged, standardized RSHVs, which should be potentially attributable to spatially integrated information and the ability to partly bypass systematic biases by both human (e.g., dam operation) and environmental effects in a standardized form. Comparison of the R reconstructed using the upstream, spatially averaged, standardized RSHVs with that reconstructed from the traditional RSD, against the observed R, revealed a Pearson correlation coefficient (PCC) above 0.91 and below 0.81, a root-mean-squares error (RMSE) below 6.1 mm and above 8.5 mm, and a Nash–Sutcliffe model efficiency coefficient (NSE) above 0.823 and below 0.657, respectively. In terms of the standardized water balance representation (SWBR), the reconstructed R yielded the best performance, with a PCC above 0.92, an RMSE below 5.9 mm, and an NSE above 0.838. External assessment demonstrated similar results. This finding indicated that the standardized RSHVs, in particular its water balance representations, could lead to further improvement in estuarine R reconstructions for river basins affected by various systematic influences. Comparison between hydrological stations at the Mekong River Delta entrance and near the estuary mouth revealed tidally-induced backwater effects on the estimated R, with an RMSE difference of 4–5 mm (equivalent to 9–11% relative error). Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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18 pages, 4290 KiB

Open AccessArticle

Robust, Long-term Lake Level Change from Multiple Satellite Altimeters in Tibet: Observing the Rapid Rise of Ngangzi Co over a New Wetland

by Haihong Wang, Yonghai Chu, Zhengkai Huang, Cheinway Hwang and Nengfang Chao

Remote Sens. 2019, 11(5), 558; https://doi.org/10.3390/rs11050558 - 07 Mar 2019

Cited by 31 | Viewed by 3978

Abstract

Satellite altimetry has been successfully applied to monitoring water level variation of global lakes. However, it is still difficult to retrieve accurate and continuous observations for most Tibetan lakes, due to their high altitude and rough terrain. Aiming to generate long-term and accurate lake level time series for the Tibetan lakes using multi-altimeters, we present a robust strategy including atmosphere delay corrections, waveform retracking, outlier removal and inter-satellite bias adjustment. Apparent biases in dry troposphere corrections from different altimeter products are found, and such correctios must be recalculated using the same surface pressure model. A parameter is defined to evaluate the performance of the retracking algorithm. The ICE retracker outperforms the 20% and 50% threshold retrackers in the case of Ngangzi Co, where a new wetland has been established. A two-step algorithm is proposed for outlier removal. Two methods are adopted to estimate inter-satellite bias for different cases of with and without overlap. Finally, a 25-year-long lake level time series of Ngangzi Co are constructed using the TOPEX/Poseidon-family altimeter data from October 1992 to December 2017, resulting in an accuracy of ~17 cm for TOPEX/Poseidon and ~10 cm for Jason-1/2/3. The accuracy of retrieved lake levels is on the order of decimeter. Because of no gauge data available, ICESat and SARAL data with the accuracy better than 7 cm are used for validation. A correlation more than 0.9 can be observed between the mean lake levels from TOPEX/Poseidon-family satellites, ICESat and SARAL. Compared to the previous studies and other available altimeter-derived lake level databases, our result is the most robust and has resulted in the maximum number of continuous samples. The time series indicates that the lake level of Ngangzi Co increased by ~8 m over 1998–2017 and changed with different rates in the past 25 years (-0.39 m/yr in 1992–1997, 1.03 m/yr in 1998–2002 and 0.32 m/yr in 2003–2014). These findings will enhance the understanding of water budget and the effect of climate change. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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25 pages, 10192 KiB

Open AccessArticle

Assessing the Glacier Boundaries in the Qinghai-Tibetan Plateau of China by Multi-Temporal Coherence Estimation with Sentinel-1A InSAR

by Yueling Shi, Guoxiang Liu, Xiaowen Wang, Qiao Liu, Rui Zhang and Hongguo Jia

Remote Sens. 2019, 11(4), 392; https://doi.org/10.3390/rs11040392 - 15 Feb 2019

Cited by 6 | Viewed by 3633

Abstract

The sensitivity of synthetic aperture radar (SAR) coherence has been applied in delineating the boundaries of alpine glaciers because it is nearly unaffected by cloud coverage and can collect data day and night. However, very limited work with application of SAR data has been performed for the alpine glaciers in the Qinghai-Tibetan Plateau (QTP) of China. In this study, we attempted to investigate the change of coherence level in alpine glacier zone and access the glacier boundaries in the QTP using time series of Sentinel-1A SAR images. The DaDongkemadi Glacier (DDG) in the central QTP was selected as the study area with land cover mainly classified into wet snow, ice, river outwash and soil land. We utilized 45 Sentinel-1A C-band SAR images collected during October of 2014 through January of 2018 over the DDG to generate time series of interferometric coherence maps, and to further extract the DDG boundaries. Based on the spatiotemporal analysis of coherence values in the selected sampling areas, we first determined the threshold as 0.7 for distinguishing among different ground targets and then extracted the DDG boundaries through threshold-based segmentation and edge detection. The validation was performed by comparing the DDG boundaries extracted from the coherence maps with those extracted from the Sentinel-2B optical image. The testing results show that the wet snow and ice present a relatively low level of coherence (about 0.5), while the river outwash and the soil land present a higher level of coherence (0.8–1.0). It was found that the coherence maps spanning between June and September (i.e., the glacier ablation period) are the most suitable for identifying the snow- and ice-covered areas. When compared with the boundary detected using optical image, the mean value of Jaccard similarity coefficient for the total areas within the DDG boundaries derived from the coherence maps selected around July, August and September reached up to 0.9010. In contrast, the mean value from the coherence maps selected around December was relatively lower (0.8862). However, the coherence maps around December were the most suitable for distinguishing the ice from the river outwash around the DDG terminus, as the river outwash areas could hardly be differentiated from the ice-covered areas from June through September. The correlation analysis performed by using the meteorological data (i.e., air temperature and precipitation records) suggests that the air temperature and precipitation have a more significant influence on the coherence level of the ice and river outwash than the wet snow and soil land. The proposed method, applied efficiently in this study, shows the potential of multi-temporal coherence estimation from the Sentinel-1A mission to access the boundaries of alpine glaciers on a larger scale in the QTP. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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17 pages, 3565 KiB

Open AccessArticle

Locking Status and Earthquake Potential Hazard along the Middle-South Xianshuihe Fault

by Rumeng Guo, Yong Zheng, Wen Tian, Jianqiao Xu and Wenting Zhang

Remote Sens. 2018, 10(12), 2048; https://doi.org/10.3390/rs10122048 - 17 Dec 2018

Cited by 22 | Viewed by 3874

Abstract

By combining the seismogenic environment, seismic recurrence periods of strong historical earthquakes, precise locations of small–moderate earthquakes, and Coulomb stress changes of moderate–strong earthquakes, we analyze the potential locking status of a seismically quiet segment of Xianshuihe fault between Daofu County and Kangding City (SDK). The interseismic surface velocities between 1999 and 2017 are obtained from updated global positioning system (GPS) observations in this region. After removing the post-seismic relaxation effect caused by the 2008 M_w 7.9 Wenchuan earthquake that occurred around the fault segment, the observed velocities reveal a pronounced symmetric slip pattern along the SDK trace. The far field slip rate is 7.8 ± 0.4 mm/a, and the fault SDK is confirmed to be in an interseismic silent phase. The optimal locking depth is estimated at 7 km, which is perfectly distributed on the upper edge of the relocated hypocenters. A moment deficit analysis shows cumulative seismic moment between 1955 and 2018, corresponding to an M_w 6.6 event. Finally, based on a viscoelastic deformation model, we find that moderate–strong earthquakes in the surrounding area increase the Coulomb stress level by up to 2 bars on the SDK, significantly enhancing the future seismic potential. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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18 pages, 7328 KiB

Open AccessArticle

Assessment and Correction of the PERSIANN-CDR Product in the Yarlung Zangbo River Basin, China

by Jiangtao Liu, Zongxue Xu, Junrui Bai, Dingzhi Peng and Meifang Ren

Remote Sens. 2018, 10(12), 2031; https://doi.org/10.3390/rs10122031 - 13 Dec 2018

Cited by 19 | Viewed by 3678

Abstract

Satellite products can provide spatiotemporal data on precipitation in ungauged basins. It is essential and meaningful to assess and correct these products. In this study, the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) product was evaluated and corrected using the successive correction method. A simple hydrological model was driven by the corrected PERSIANN-CDR data. The results showed that the accuracy of the original PERSIANN-CDR data was low on a daily scale, and the accuracy decreased gradually from the east to the west of the basin. With one correction step, the accuracy of the corrected PERSIANN-CDR data was significantly higher than that of the initial data. The correlation coefficient increased from 0.58 to 0.73, and the probability of detection (POD) value of the corrected product was 18.2% higher than the original product. The temporal-spatial resolution influenced the performance of the satellite product. As the resolution became coarser, the correlation coefficient between the corrected PERSIANN-CDR data and the gauged data gradually became lower. The Identification of unit Hydrographs and Component flows from Rainfall, Evapotranspiration, and Streamflow (IHACRES) model could be satisfactorily applied in the Lhasa River basin with corrected PERSIANN-CDR data. The successive correction method was an effective way to correct the bias of the PERSIANN-CDR product. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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14 pages, 4183 KiB

Open AccessArticle

Improvement of Downward Continuation Values of Airborne Gravity Data in Taiwan

by Qilong Zhao, Xinyu Xu, Rene Forsberg and Gabriel Strykowski

Remote Sens. 2018, 10(12), 1951; https://doi.org/10.3390/rs10121951 - 04 Dec 2018

Cited by 9 | Viewed by 3999

Abstract

An airborne gravity survey was carried out to fill gaps in the gravity data for the mountainous areas of Taiwan. However, the downward continuation error of airborne gravity data is a major issue, especially in regions with complex terrain, such as Taiwan. The root mean square (RMS) of the difference between the downward continuation values and land gravity was approximately 20 mGal. To improve the results of downward continuation we investigated the inverse Poisson’s integral, the semi-parametric method combined with regularization (SPR) and the least-squares collocation (LSC) in this paper. The numerically simulated experiments are conducted in the Tibetan Plateau, which is also a mountainous area. The results show that as a valuable supplement to the inverse Poisson’s integral, the SPR is a useful approach to estimate systematic errors and to suppress random errors. While the LSC approach generates the best results in the Tibetan Plateau in terms of the RMS of the downward continuation errors. Thus, the LSC approach with a terrain correction (TC) is applied to the downward continuation of real airborne gravity data in Taiwan. The statistical results show that the RMS of the differences between the downward continuation values and land gravity data reduced to 11.7 mGal, which shows that an improvement of 40% is obtained. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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19 pages, 7183 KiB

Open AccessArticle

Glacial Lakes in the Nepal Himalaya: Inventory and Decadal Dynamics (1977–2017)

by Nitesh Khadka, Guoqing Zhang and Sudeep Thakuri

Remote Sens. 2018, 10(12), 1913; https://doi.org/10.3390/rs10121913 - 29 Nov 2018

Cited by 59 | Viewed by 17119

Abstract

Himalayan glaciers, in general, are shrinking and glacial lakes are evolving and growing rapidly in number and size as a result of climate change. This study presents the latest remote sensing-based inventory (2017) of glacial lakes (size ≥0.0036 km²) across the Nepal Himalaya using optical satellite data. Furthermore, this study traces the decadal glacial lake dynamics from 1977 to 2017 in the Nepal Himalaya. The decadal mapping of glacial lakes (both glacial-fed and nonglacial-fed) across the Nepal Himalaya reveals an increase in the number and area of lakes from 1977 to 2017, with 606 (55.53 ± 16.52 km²), 1137 (64.56 ± 11.64 km²), 1228 (68.87 ± 12.18 km²), 1489 (74.2 ± 14.22 km²), and 1541 (80.95 ± 15.25 km²) glacial lakes being mapped in 1977, 1987, 1997, 2007, and 2017, respectively. Glacial lakes show heterogeneous rates of expansion in different river basins and elevation zones of Nepal, with apparent decadal emergences and disappearances. Overall, the glacial lakes exhibited ~25% expansion of surface areas from 1987 to 2017. For the period from 1987 to 2017, proglacial lakes with ice contact, among others, exhibited the highest incremental changes in terms of number (181%) and surface area (82%). The continuous amplified mass loss of glaciers, as reported in Central Himalaya, is expected to accompany glacial lake expansion in the future, increasing the risk of glacial lake outburst floods (GLOFs). We emphasize that the rapidly increasing glacial lakes in the Nepal Himalaya can pose potential GLOF threats to downstream population and infrastructure. Full article

(This article belongs to the Special Issue Environmental and Geodetic Monitoring of the Tibetan Plateau)

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