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25 pages, 6236 KiB

Open AccessArticle

Estimating Monthly River Discharges from GRACE/GRACE-FO Terrestrial Water Storage Anomalies

by Bhavya Duvvuri and Edward Beighley

Remote Sens. 2023, 15(18), 4516; https://doi.org/10.3390/rs15184516 - 14 Sep 2023

Viewed by 885

Simulating river discharge is a complex convolution depending on precipitation, runoff generation and transformation, and network attenuation. Terrestrial water storage anomalies (TWSA) from NASA’s Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission can be used to estimate monthly river [...] Read more.

Simulating river discharge is a complex convolution depending on precipitation, runoff generation and transformation, and network attenuation. Terrestrial water storage anomalies (TWSA) from NASA’s Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission can be used to estimate monthly river discharge (Q). Monthly discharges for the period April 2002–January 2022 are estimated at 2870 U.S. Geological Survey gauge locations (draining 1K to 3M km²) throughout the continental U.S. (CONUS) using two-parameter exponential relationships between TWSA and Q. Roughly 70% of the study sites have a model performance exceeding the expected performance of other satellite-derived discharge products. The results show how the two model parameters vary based on hydrologic characteristics (annual precipitation and range in TWSA) and that model performance can be affected by snow accumulation/melt, water regulation (dams/reservoirs) or GRACE signal leakage. The generally favorable model performance and our understanding of variability in model applicability and associated parameters suggest that this concept can be expanded to other regions and ungauged locations. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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23 pages, 12395 KiB

Open AccessArticle

Spatiotemporal Change in Evapotranspiration across the Indus River Basin Detected by Combining GRACE/GRACE-FO and Swarm Observations

by Lilu Cui, Maoqiao Yin, Zhengbo Zou, Chaolong Yao, Chuang Xu, Yu Li and Yiru Mao

Remote Sens. 2023, 15(18), 4469; https://doi.org/10.3390/rs15184469 - 11 Sep 2023

Viewed by 700

Abstract

Evapotranspiration (ET) is an important approach for enabling water and energy exchange between the atmosphere and the land, and it has a very close relationship with terrestrial water resources and the ecological environment. Therefore, it is of great scientific to accurately quantify the [...] Read more.

Evapotranspiration (ET) is an important approach for enabling water and energy exchange between the atmosphere and the land, and it has a very close relationship with terrestrial water resources and the ecological environment. Therefore, it is of great scientific to accurately quantify the spatiotemporal change in ET and its impact factors to understand the terrestrial water change pattern, maintaining water resource security and protecting the ecological environment. Our goal is to study the spatiotemporal characteristics of ET in the Indus River basin (IRB) and their driving factors. In our study, we first integrated the multi-source satellite gravimetry observations using the generalized three-cornered hat and least square methods to obtain the high-precision and continuous spatiotemporal evolution features of ET in the IRB from 2003 to 2021. Finally, we combined nine hydrometeorological and land cover type data to analyze the factors influencing ET. The results indicate that the algorithm used in our study can improve the ET accuracy by 40%. During the study period, ET shows a significant increasing trend (0.64 ± 0.73 mm/a), and the increasing rate presents spatial distribution characteristics of high variability in the northern areas and low variability in the southern areas of the study region. ET has a close relationship with precipitation, specific humidity, total canopy water storage, surface temperature and wind speed (with a correlation coefficients greater than 0.53 and variable importance of projection greater than 0.84). Among these factors, precipitation, specific humidity and surface temperature have significant correlations with ET (correlation coefficients greater than 0.85 and variable importance of projection greater than 1.42). And wind speed has a more significant positive effect on ET in the densely vegetated regions. The impacts of climate change on ET are significantly greater than those of land cover types, especially for similar land cover types. Ice and snow are significantly different to other land cover types. In this region, ET is only significantly correlated with precipitation, specific humidity and snow water equivalent (variable importance of projection greater than 0.81), and the impacts of precipitation and specific humidity on ET have been significantly weakened, while that of snow water equivalent is significantly enhanced. Our results contribute to furthering the understanding of the terrestrial water cycle in subtropical regions. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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24 pages, 30722 KiB

Open AccessArticle

A Systematic Approach for Inertial Sensor Calibration of Gravity Recovery Satellites and Its Application to Taiji-1 Mission

by Haoyue Zhang, Peng Xu, Zongqi Ye, Dong Ye, Li-E Qiang, Ziren Luo, Keqi Qi, Shaoxin Wang, Zhiming Cai, Zuolei Wang, Jungang Lei and Yueliang Wu

Remote Sens. 2023, 15(15), 3817; https://doi.org/10.3390/rs15153817 - 31 Jul 2023

Cited by 2 | Viewed by 999

Abstract

High-precision inertial sensors or accelerometers can provide references for free-falling motion in gravitational fields in space. They serve as the key payloads for gravity recovery missions such as CHAMP, the GRACE-type missions, and the planned Next-Generation Gravity Missions. In this work, a systematic [...] Read more.

High-precision inertial sensors or accelerometers can provide references for free-falling motion in gravitational fields in space. They serve as the key payloads for gravity recovery missions such as CHAMP, the GRACE-type missions, and the planned Next-Generation Gravity Missions. In this work, a systematic method for electrostatic inertial sensor calibration of gravity recovery satellites is suggested, which is applied to and verified with the Taiji-1 mission. With this method, the complete operating parameters including the scale factors, the center of mass offset vector, and the intrinsic biased acceleration can be precisely calibrated with only two sets of short-term in-orbit experiments. This could reduce the gaps in data that are caused by necessary in-orbit calibrations during the lifetime of related missions. Taiji-1 is the first technology-demonstration satellite of the “Taiji Program in Space”, which, in its final extended phase in 2022, could be viewed as operating in the mode of a high–low satellite-to-satellite tracking gravity mission. Based on the principles of calibration, swing maneuvers with time spans of approximately 200 s and rolling maneuvers for 19 days were conducted by Taiji-1 in 2022. Given the data of the actuation voltages of the inertial sensor, satellite attitude variations, precision orbit determinations, the inertial sensor’s operating parameters are precisely re-calibrated with Kalman filters and are relayed to the Taiji-1 science team. The relative errors of the calibrations are <1% for the linear scale factors, <3% for center of mass, and <0.1% for biased accelerations. Data from one of the sensitive axes are re-processed with the updated operating parameters, and the resulting performance is found to be slightly improved over the former results. This approach could be of high reference value for the accelerometer or inertial sensor calibrations of the GFO, the Chinese GRACE-type mission, and the Next-Generation Gravity Missions. This could also create some insight into the in-orbit calibrations of the ultra-precision inertial sensors for future GW space antennas because of the technological inheritance between these two generations of inertial sensors. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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17 pages, 5528 KiB

Open AccessArticle

Applying Reconstructed Daily Water Storage and Modified Wetness Index to Flood Monitoring: A Case Study in the Yangtze River Basin

by Cuiyu Xiao, Yulong Zhong, Yunlong Wu, Hongbing Bai, Wanqiu Li, Dingcheng Wu, Changqing Wang and Baoming Tian

Remote Sens. 2023, 15(12), 3192; https://doi.org/10.3390/rs15123192 - 20 Jun 2023

Cited by 2 | Viewed by 1872

Abstract

The terrestrial water storage anomaly (TWSA) observed by the Gravity Recovery and Climate Experiment (GRACE) satellite and its successor GRACE Follow-On (GRACE-FO) provides a new means for monitoring floods. However, due to the coarse temporal resolution of GRACE/GRACE-FO, the understanding of flood occurrence [...] Read more.

The terrestrial water storage anomaly (TWSA) observed by the Gravity Recovery and Climate Experiment (GRACE) satellite and its successor GRACE Follow-On (GRACE-FO) provides a new means for monitoring floods. However, due to the coarse temporal resolution of GRACE/GRACE-FO, the understanding of flood occurrence mechanisms and the monitoring of short-term floods are limited. This study utilizes a statistical model to reconstruct daily TWS by combining monthly GRACE observations with daily temperature and precipitation data. The reconstructed daily TWSA is utilized to monitor the catastrophic flood event that occurred in the middle and lower reaches of the Yangtze River basin in 2020. Furthermore, the study compares the reconstructed daily TWSA with the vertical displacements of eight Global Navigation Satellite System (GNSS) stations at grid scale. A modified wetness index (MWI) and a normalized daily flood potential index (NDFPI) are introduced and compared with in situ daily streamflow to assess their potential for flood monitoring and early warning. The results show that terrestrial water storage (TWS) in the study area increases from early June, reaching a peak on 19 July, and then receding till September. The reconstructed TWSA better captures the changes in water storage on a daily scale compared to monthly GRACE data. The MWI and NDFPI based on the reconstructed daily TWSA both exceed the 90th percentile 7 days earlier than the in situ streamflow, demonstrating their potential for daily flood monitoring. Collectively, these findings suggest that the reconstructed TWSA can serve as an effective tool for flood monitoring and early warning. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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16 pages, 27089 KiB

Open AccessFeature PaperArticle

In-Orbit Performance of the GRACE Accelerometers and Microwave Ranging Instrument

by Michael Murböck, Petro Abrykosov, Christoph Dahle, Markus Hauk, Roland Pail and Frank Flechtner

Remote Sens. 2023, 15(3), 563; https://doi.org/10.3390/rs15030563 - 17 Jan 2023

Cited by 5 | Viewed by 1657

Abstract

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided global long-term observations of mass transport in the Earth system with applications in numerous geophysical fields. In this paper, we targeted the in-orbit performance of the GRACE key instruments, the ACCelerometers (ACC) [...] Read more.

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided global long-term observations of mass transport in the Earth system with applications in numerous geophysical fields. In this paper, we targeted the in-orbit performance of the GRACE key instruments, the ACCelerometers (ACC) and the MicroWave ranging Instrument (MWI). For the ACC data, we followed a transplant approach analyzing the residual accelerations from transplanted accelerations of one of the two satellites to the other. For the MWI data, we analyzed the post-fit residuals of the monthly GFZ GRACE RL06 solutions with a focus on stationarity. Based on the analyses for the two test years 2007 and 2014, we derived stochastic models for the two instruments and a combined ACC+MWI stochastic model. While all three ACC axes showed worse performance than their preflight specifications, in 2007, a better ACC performance than in 2014 was observed by a factor of 3.6 due to switched-off satellite thermal control. The GRACE MWI noise showed white noise behavior for frequencies above 10 mHz around the level of

1.5 \times 10^{- 6} m / \sqrt{Hz}

. In the combined ACC+MWI noise model, the ACC part dominated the frequencies below 10 mHz, while the MWI part dominated above 10 mHz. We applied the combined ACC+MWI stochastic models for 2007 and 2014 to the monthly GFZ GRACE RL06 processing. This improved the formal errors and resulted in a comparable noise level of the estimated gravity field parameters. Furthermore, the need for co-estimating empirical parameters was reduced. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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19 pages, 23018 KiB

Open AccessArticle

Comparison of GRACE/GRACE-FO Spherical Harmonic and Mascon Products in Interpreting GNSS Vertical Loading Deformations over the Amazon Basin

by Pengfei Wang, Song-Yun Wang, Jin Li, Jianli Chen and Zhaoxiang Qi

Remote Sens. 2023, 15(1), 252; https://doi.org/10.3390/rs15010252 - 01 Jan 2023

Viewed by 2237

Abstract

We compute the vertical displacements in the Amazon Basin using the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) observations, including both the gravity spherical harmonic (SH) solutions from the Center for Space Research (CSR), GeoForschungsZentrum (GFZ) and Jet Propulsion Laboratory [...] Read more.

We compute the vertical displacements in the Amazon Basin using the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) observations, including both the gravity spherical harmonic (SH) solutions from the Center for Space Research (CSR), GeoForschungsZentrum (GFZ) and Jet Propulsion Laboratory (JPL) and mascons from CSR, JPL and Goddard Space Flight Center (GSFC). The correlation coefficients, annual amplitude and root mean squares (RMS) reductions are calculated to assess the agreements between the GRACE/GRACE-FO and Global Navigation Satellite System (GNSS) vertical displacements at 22 selected GNSS stations. For the six GRACE/GRACE-FO products (i.e., CSR SH, GFZ SH, JPL SH, CSR mascon, GSFC mascon and JPL mascon), the mean annual amplitude reductions are 77.6%, 76.4%, 76.3%, 78.6%, 78.5% and 76.6%, respectively, the corresponding mean RMS reductions are 63.2%, 61.7%, 62.3%, 64.9%, 65.3% and 63.8%, respectively, and the mean correlation coefficients are all over 0.93. On the whole, mascon solutions agree slightly better with GNSS solutions than SH solutions do. The CSR SH and the GSFC mascon solutions show the best agreements with the GNSS solution among the 3 SH and 3 mascon products, respectively. We estimate GRACE/GRACE-FO noises using the three-cornered hat (TCH) method and find that the CSR SH and GSFC mascons also have the smallest noise variances among the SH and mascon products, respectively. By analyzing the GNSS stations from the central and southern Amazon Basin, we find that: (1) the RMS reductions when the mascon solutions are removed from GNSS height series are slightly larger than those using the SH solutions in the center, while in south all the RMS reductions are fairly close; (2) for both SH solutions and mascon solutions, the correlation coefficients in the center are slightly larger than those in the south, but conversely, the mean annual amplitude reductions in the center are much smaller than those in the south. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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15 pages, 13741 KiB

Open AccessArticle

Terrestrial Water Storage Component Changes Derived from Multisource Data and Their Responses to ENSO in Nicaragua

by Guangyu Jian, Chuang Xu, Jinbo Li, Xingfu Zhang and Li Feng

Remote Sens. 2022, 14(23), 6012; https://doi.org/10.3390/rs14236012 - 27 Nov 2022

Cited by 1 | Viewed by 5016

Abstract

Approximately 3.5 million people in Nicaragua have experienced food insecurity due to the El Niño-Southern Oscillation (ENSO)-induced drought from 2014 to 2016. It is essential to study terrestrial water storage component (TWSC) changes and their responses to ENSO to prevent the water crisis [...] Read more.

Approximately 3.5 million people in Nicaragua have experienced food insecurity due to the El Niño-Southern Oscillation (ENSO)-induced drought from 2014 to 2016. It is essential to study terrestrial water storage component (TWSC) changes and their responses to ENSO to prevent the water crisis in Nicaragua influenced by ENSO. In this paper, we investigate the TWSC changes in Nicaragua and its sub-basins derived from the Gravity Recovery and Climate Experiment (GRACE)’s temporal gravity field, hydrological model, and water level data, and then determine the connection between the TWSC and ENSO from April 2002 to April 2021 by time series analysis. The research results show that: (1) The estimated TWSC changes in Nicaragua are in good agreement with the variation of precipitation and evaporation, and precipitation is the main cause of TWSC variation. (2) According to the cross-correlation analysis, there is a significant negative peak correlation between the interannual TWSC and ENSO in western Nicaragua, especially for interannual soil moisture (−0.80). The difference in peak correlation between the western and eastern sub-basins may be due to the topographic hindrance of the ENSO-inspired precipitation process. (3) The cross-wavelet analysis indicates that the resonance periods between TWSC and ENSO are primarily 2 and 4 years. These resonance periods are related to the two ENSO modes (the central Pacific (CP) mode with a quasi-2-year period and the eastern Pacific (EP) mode with a quasi-4-year period). Furthermore, their resonance phase variation may be due to the transition to ENSO mode. This study revealed the relationship between ENSO and TWSC in Nicaragua, which can provide a certain reference for water resources regulation. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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26 pages, 33093 KiB

Open AccessArticle

Water Storage Variation and Its Possible Causes Detected by GRACE in the Volta River Basin

by Randal D. Djessou, Xiaoyun Wan, Shuang Yi, Richard F. Annan, Xiaoli Su and Sijia Wang

Remote Sens. 2022, 14(21), 5319; https://doi.org/10.3390/rs14215319 - 24 Oct 2022

Cited by 2 | Viewed by 1693

Abstract

This study applies Gravity Recovery and Climate Experiment (GRACE) data and the WaterGAP (Water Global Analysis and Prognosis) Global Hydrology Model (WGHM) to investigate the influence of the Bui reservoir operation on water storage variation within the Volta River Basin (VRB). Variation in [...] Read more.

This study applies Gravity Recovery and Climate Experiment (GRACE) data and the WaterGAP (Water Global Analysis and Prognosis) Global Hydrology Model (WGHM) to investigate the influence of the Bui reservoir operation on water storage variation within the Volta River Basin (VRB). Variation in groundwater storage anomalies (GWSA) was estimated by combining GRACE-derived terrestrial water storage anomalies (TWSA), radar altimetry records, imagery-derived reservoir (Lake Volta and Bui) surface water storage anomalies (SWSA), and Global Land Data Assimilation System (GLDAS)-simulated soil moisture storage anomalies (SMSA) from 2002 to 2016. Results showed that TWSA increased (1.30 ± 0.23 cm/year) and decreased (−0.82 ± 0.27 cm/year) during 2002–2011 and 2011–2016, respectively, within VRB, matching previous TWSA investigations in this area. It revealed that the multi-year averages of monthly GRACE-derived TWSA changes in 2011–2016 displayed an overall increasing trend, indicating storage increase in regional hydrology; while the Lake Volta water storage changes decreased. The GRACE-minus-WGHM residuals display an increasing trend in VRB water storage during the Bui reservoir impoundment during 2011–2016. The observed trend compares well with the estimated Bui reservoir SWSA, indicating that GRACE solutions can retrieve the true amplitude of large mass changes happening in a concentrated area, though Bui reservoir is much smaller than the resolution of GRACE global solutions. It also revealed that GWSA were almost stable from 2002 to 2006, before increasing and decreasing during 2006–2011 and 2012–2016 with rates of 2.67 ± 0.34 cm/year and −1.80 ± 0.32 cm/year, respectively. The observed trends in the GRACE-derived TWSA and GWSA changes are generally attributed to the hydro-meteorological conditions. This study shows that the effects of strong El-Niño Southern Oscillation events on the GWSA interannual variability within the VRB is short-term, with a lag of 6 months. This study specifically showed that the Bui reservoir operation significantly affects the TWSA changes and provides knowledge on groundwater storage changes within the VRB. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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22 pages, 7911 KiB

Open AccessArticle

Estimation of the Center of Mass of GRACE-Type Gravity Satellites

by Zhiyong Huang, Shanshan Li, Lin Cai, Diao Fan and Lingyong Huang

Remote Sens. 2022, 14(16), 4030; https://doi.org/10.3390/rs14164030 - 18 Aug 2022

Cited by 3 | Viewed by 1699

Abstract

One of the key constraints for the accelerometer of GRACE-type gravity satellites to accurately measure the non-gravitational accelerations acting on the satellite is that the center of mass of the satellite and the proof mass of the accelerometer should maintain a coincidence. In [...] Read more.

One of the key constraints for the accelerometer of GRACE-type gravity satellites to accurately measure the non-gravitational accelerations acting on the satellite is that the center of mass of the satellite and the proof mass of the accelerometer should maintain a coincidence. In addition, the accuracy requirement is that the center of mass offset (CM-offset) in the three directions is less than 100 microns. Since the center of mass (CoM) of the satellite will change with the consumption of cold-gas fuel in the tanks, it is necessary to regularly carry out the CoM calibration maneuver. Firstly, the observation equations consisting of the accelerometer linear acceleration, angular acceleration, and the CM-offset vector are established in order to estimate the amount of CM-offset. Then, according to the estimated CM-offset, the satellite mass trim mechanisms are used to change the satellite’s CoM, so that the satellite’s CoM always approaches the proof mass of the accelerometer, with an accuracy of 100 μm per axis. The CM-offset of the satellite of GRACE-FO is estimated by using the accelerometer, star camera, magnetic torquer, magnetometer, and the precision orbit data during the GRACE-C CM-offset calibration period on 1 February 2020. Four kinds of CM-offset results are obtained by four different angular accelerations as follows: the angular acceleration based on the attitude dynamics (“MTQ angular acceleration”), the accelerometer angular acceleration calibrated by MTQ, the accelerometer angular acceleration, and the angular acceleration calculated by the star camera. By comparing the four kinds of CM-offset results that are estimated by the four different methods, all four of the results are shown to have the same level of accuracy. Based on the accelerometer (calibrated) angular acceleration, the difference with the JPL result is 0.5 μm, while the difference between the conventional method and the JPL result is 6.0 μm. All four of the methods can achieve the requirement of 50 μm accuracy and using four CM-offset estimation methods simultaneously can improve the integrity of the calibration results. Subsequently, the CM-offset results of GRACE-C since its launch are estimated here. The calibration algorithm that is proposed in this paper can be used as a reference in the calibration of gravity satellites carrying an accelerometer payload. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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20 pages, 7580 KiB

Open AccessArticle

Marine Gravimetry and Its Improvements to Seafloor Topography Estimation in the Southwestern Coastal Area of the Baltic Sea

by Biao Lu, Chuang Xu, Jinbo Li, Bo Zhong and Mark van der Meijde

Remote Sens. 2022, 14(16), 3921; https://doi.org/10.3390/rs14163921 - 12 Aug 2022

Cited by 1 | Viewed by 5419

Abstract

Marine gravimetry provides high-quality gravity measurements, particularly in coastal areas. After the update of new sensors in GFZ’s air-marine gravimeter Chekan-AM, gravimetry measurements showed a significant improvement from the first new campaign DENEB2017 with an accuracy of

0.3 / \sqrt{2} = 0.21

mGal [...] Read more.

Marine gravimetry provides high-quality gravity measurements, particularly in coastal areas. After the update of new sensors in GFZ’s air-marine gravimeter Chekan-AM, gravimetry measurements showed a significant improvement from the first new campaign DENEB2017 with an accuracy of

0.3 / \sqrt{2} = 0.21

mGal @ 1 km along the tracks, which is at the highest accuracy level of marine gravimetry. Then, these measurements were used to assess gravity data derived from satellite altimetry (about 3 mGal) and a new finding is that a bias of −1.5 mGal exists in the study area. Additionally, ship soundings were used to assess existing seafloor topography models. We found that the accuracy of SRTM model and SIO model is at a level of 2 m, while the accuracy of the regional model EMODnet reaches the lever of sub-meters. Furthermore, a bias of 0.7 m exists and jumps above 5 m in the SRTM model near the coast of Sweden. Finally, new combined gravity anomalies with sounding data are used to reveal the fine structure of ocean topography. Our estimated seafloor topography model is more accurate than existing digital elevation data sets such as EMODnet, SRTM and SIO models and, furthermore, shows some more detailed structure of seafloor topography. The marine gravimetry and sounding measurements as well as the estimated seafloor topography are crucial for future geoid determination, 3D-navigation and resource exploration in the Baltic Sea. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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22 pages, 24329 KiB

Open AccessArticle

Evaluation of the Consistency of Three GRACE Gap-Filling Data

by An Qian, Shuang Yi, Feng Li, Boli Su, Guangtong Sun and Xiaoyang Liu

Remote Sens. 2022, 14(16), 3916; https://doi.org/10.3390/rs14163916 - 12 Aug 2022

Viewed by 1660

Abstract

The Gravity Recovery and Climate Experiment (GRACE) gravity mission has become a leading platform for monitoring temporal changes in the Earth’s global gravity field. However, the usability of GRACE data is severely limited by 11 months of missing data between the GRACE and [...] Read more.

The Gravity Recovery and Climate Experiment (GRACE) gravity mission has become a leading platform for monitoring temporal changes in the Earth’s global gravity field. However, the usability of GRACE data is severely limited by 11 months of missing data between the GRACE and GRACE Follow-on (GRACE-FO) missions. To date, several approaches have been proposed to fill this data gap in the form of spherical harmonic coefficients (an expression of the Earth’s gravity field, SHCs). However, systematic analysis to reveal the characteristics and consistency of the datasets produced by these latest gap-filling techniques is yet to be carried out. Here, three SHC gap-filling products are systematically analyzed and compared: (1) Combining high–low satellite-to-satellite tracking with satellite laser ranging (SLR) observations (QuantumFrontiers, QF), (2) SLR-based recovery incorporating the GRACE empirical orthogonal function decomposition model proposed by the Institute of Geodesy and Geoinformation at the University of Bonn (hereafter, denoted as IGG), and (3) applying the singular spectrum analysis approach (SSA). The results show that (1) the SHCs of the QF, IGG, and SSA data are consistent up to degree 12; (2) the IGG and SSA data give similar results over the 11 gap months, but the IGG shows a faster increase in the mean ocean water mass and the SSA appears to better capture the interannual variation in the terrestrial water storage; and (3) the noise level increases significantly in the high-degree terms (l > 16) of the QF data, so these data are only applicable for large-scale mass migration research. These results provide a reference for users to select a gap-filling product. Finally, we propose a new scheme based on the triple collocation method to derive a weight matrix to fuse these three datasets into a more robust solution. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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12 pages, 2114 KiB

Open AccessTechnical Note

Basin-Scale Sea Level Budget from Satellite Altimetry, Satellite Gravimetry, and Argo Data over 2005 to 2019

by Yuanyuan Yang, Wei Feng, Min Zhong, Dapeng Mu and Yanli Yao

Remote Sens. 2022, 14(18), 4637; https://doi.org/10.3390/rs14184637 - 16 Sep 2022

Cited by 3 | Viewed by 1621

Abstract

Monitoring sea level changes and exploring their causes are of great significance for future climate change predictions and the sustainable development of mankind. This study uses multiple sets of satellite altimetry, satellite gravity, and ocean temperature and salinity data to study the basin-scale [...] Read more.

Monitoring sea level changes and exploring their causes are of great significance for future climate change predictions and the sustainable development of mankind. This study uses multiple sets of satellite altimetry, satellite gravity, and ocean temperature and salinity data to study the basin-scale sea level budget (SLB) from 2005 to 2019. The basin-scale sea level rises significantly at a rate of 2.48–4.31 mm/yr, for which the ocean mass component is a main and stable contributing factor, with a rate of 1.77–2.39 mm/yr, while the steric component explains a ~1 mm/yr sea level rise in most ocean basins, except for the Southern Ocean. Due to the drift in Argo salinity since 2016, the residuals of basin-scale SLB are significant from 2016 to 2019. The worst-affected ocean is the Atlantic Ocean, where the SLB is no longer closed from 2005 to 2019. If halosteric sea level change trends from 2005 to 2015 are used to revise salinity data after 2016, the SLB on the ocean basin scale can be kept closed. However, the SLB on the global scale is still not closed and requires further study. Therefore, we recommend that Argo salinity products after 2016 should be used with caution. Full article

(This article belongs to the Special Issue GRACE for Earth System Mass Change: Monitoring and Measurement)

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