Global Positioning System Measurements Research Articles

Precise Relative Orbit Determination for Chinese TH-2 Satellite Formation Using Onboard GPS and BDS2 Observations

TH-2 is China’s first short-range satellite formation system used to realize interferometric synthetic aperture radar (InSAR) technology. In order to achieve the mission goal of InSAR processing, the relative orbit must be determined with high accuracy. In this study, the precise relative orbit determination (PROD) for TH-2 based on global positioning system (GPS), second-generation BeiDou navagation satellite system (BDS2), and GPS + BDS2 observations was performed. First, the performance of onboard GPS and BDS2 measurements were assessed by analyzing the available data, code multipath errors and noise levels of carrier phase observations. The differences between the National University of Defense Technology (NDT) and the Xi’an Research Institute of Surveying and Mapping (CHS) baseline solutions exhibited an RMS of 1.48 mm outside maneuver periods. The GPS-based orbit was used as a reference orbit to evaluate the BDS2-based orbit and the GPS + BDS2-based orbit. It is the first time BDS2 has been applied to the PROD of low Earth orbit (LEO) satellite formation. The results showed that the root mean square (RMS) of difference between the PROD results using GPS and BDS2 measurements in 3D components was 2.89 mm in the Asia-Pacific region. We assigned different weights to geostationary Earth orbit (GEO) satellites to illustrate the impact of GEO satellites on PROD, and the accuracy of PROD was improved to 7.08 mm with the GEO weighting strategy. Finally, relative orbits were derived from the combined GPS and BDS2 data. When BDS2 was added on the basis of GPS, the average number of visible navigation satellites from TH-2A and TH-2B improved from 7.5 to 9.5. The RMS of the difference between the GPS + BDS2-based orbit and the GPS-based orbit was about 1.2 mm in 3D. The overlap comparison results showed that the combined orbit consistencies were below 1 mm in the radial (R), along-track (T), and cross-track (N) directions. Furthermore, when BDS2 co-worked with GPS, the average of the ambiguity dilution of precision (ADOP) reduced from 0.160 cycle to 0.153 cycle, which was about a 4.4% reduction. The experimental results indicate that millimeter-level PROD results for TH-2 satellite formation can be obtained by using onboard GPS and BDS2 observations, and multi-GNSS can further improve the accuracy and reliability of PROD.

A Loading Correction Model for GPS Measurements Derived from Multiple-Data Combined Monthly Gravity

Time-dependent loading deformations of the Earth’s surface, due to nontidal changes in the atmosphere, ocean, land water/ice, etc., contribute significantly to the seasonal and secular Global Positioning System (GPS) site displacements, especially for the up component. While loading deformations derived from general circulation model (GCM) outputs are usually used to correct loading signals in the GPS site displacements, this study aims to provide a loading correction model based on the multiple-data combined monthly gravity products LDCmgm90. We have adopted GPS measurements from 249 IGS reference frame stations and 3 different GCM-based loading models to test the reliability of the LDCmgm90 model. Compared to the GCM-based models, the LDCmgm90 loading correction is more effective in attenuating seasonal (especially annual) loading signals and can bring more significant improvements to most stations for both the data-trend-removed and the data-trend-retained cases. Thus, we have validated the LDCmgm90 model from the loading aspect and proved it to be a reliable loading-correction model for GPS displacements. The relatively better secular loading signals provided by the LDCmgm90 loading model may provide us a chance to study the long-term, nonloading signals in GPS data.

Rates of Natural Subsidence along the Texas Coast Derived from GPS and Tide Gauge Measurements (1904–2020)

AbstractThis study investigated the rate of natural subsidence along the Texas coast using multidecadal to century tide gauge (TG) and global positioning system (GPS) data sets. The rates of land s...

Inferring the Horizontal Speed of an Ionospheric Irregularity From a Single GPS Scintillation Receiver at High Latitudes

AbstractWe propose a new technique to infer the horizontal speed of ionospheric irregularity at high latitudes from the refractive components of the global positioning system (GPS) L1 (1575.42 MHz) and L2 (1227.60 MHz) carrier phases using only a single ground‐based receiver that can log measurements at 50–100 Hz. The test data at Jang Bogo Station (geographic: 74.6°S and 164.2°E; geomagnetic: 77.2°S) in Antarctica and at Sachs Harbor (geographic: 71.9°N and 234.7°E; geomagnetic: 75.6°N) in the Arctic were analyzed for a one‐year period in 2019. The results were compared with data from ground‐based radar observations, the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) in Antarctica and the Canadian Advanced Digital Ionosonde (CADI) in the Arctic, which measures the ion drift velocity at the apex. Although it is difficult to directly compare GPS and radar measurements due to the steep gradient of fast plasma motion in narrow regions at high latitudes, the probability density of the ionospheric irregularity speeds from the two different instruments were consistent with the correlation coefficients of 0.81 and 0.85 in the Southern and Northern hemispheres.

Quantifying sprint kayak training on a flowing river: Exploring the utility of novel power measures and its relationship to measures of relative boat speed

ABSTRACT Quantification of external training load for sprint kayak athletes can be challenging due to the influence of the water flow on boat velocity in a flowing river environment. Therefore, this study examined the utility of novel measures of power output (PO) and its relationship to measures of relative boat speed when training on a flowing river. Twelve (8 males, 4 female) well-trained sprint kayak athletes completed 4 separate on-water sessions comprising one time-trial session (2 × 1000-m maximal efforts) and three repeated sprint kayak training sessions (5 x split 1000-m [2 × 500-m up and down the river] submaximal efforts) in their individual (K1) kayak. For each session, a Kayak Power Meter recorded athletes’ PO, and a SpeedCoach device recorded relative land-speed via a Global Positioning System (GPS) (S GPS), and relative water-speed via an impeller mounted under the boat hull (S IMP). Non-linear least squares regression were used to evaluate the curvilinear relationship between PO and speed (S GPS and S IMP) data. The exponents of velocity in the PO-S IMP relationship (2.87 females, 2.94 males) were closer to theoretical values (3.00) and showed greater model accuracy (root mean squared error (RMSE) = 20–26 W) than the PO-S GPS relationships (speed exponents = 1.58–2.02, RMSE = 31–40 W). Overall, PO measures could better account for the influence of water flow compared to traditional S GPS measures, and therefore, may be more suitable for quantifying athletes’ external load in their training environment. Highlights Since traditional S GPS and time-to-completion measures do not adjust for the water flow, these measures appear limited for prescribing and monitoring sprint kayak training within flowing river environments. The prescription of paddling PO across a wide spectrum of relative PO values elicited similar internal and external athlete responses, regardless of the direction travelled on a flowing river (i.e. upstream or downstream). The relationship between PO and S IMP during on-water sprint kayaking appears similar to those observed in rowing, where every percent change in boat speed measured relative to water (S IMP) requires a 2.87 and 2.94-fold percent change in paddling PO in female and male sprint kayak athletes, respectively. Continued evaluation of the PO-speed relationship for individual athletes may provide further insight into modelling performance and training targets for sprint kayak athletes.

Reduced-Dynamic Precise Orbit Determination of Haiyang-2B Altimetry Satellite Using a Refined Empirical Acceleration Model

The Haiyang 2B (HY-2B) satellite requires precise orbit determination (POD) products for geodetic remote sensing techniques. An improved set of reduced-dynamic (RD) orbit solutions was generated from the onboard Global Positioning System (GPS) measurements over a 14-month period using refined strategies and processing techniques. The key POD strategies include a refined empirical acceleration model, in-flight calibration of the GPS antenna, and the resolution of single-receiver carrier-phase ambiguities. In this study, the potential periodicity of empirical acceleration in the HY-2B POD was identified by spectral analysis. In the along-track direction, a noticeable signal with four cycles per revolution (CPR) was significant. A mixed spectrum was observed for the cross-track direction. To better understand the real in-flight environment, a refined empirical acceleration model was used to cope with the time variability of empirical accelerations in HY-2B POD. Three POD strategies were used for the reprocessing for superior orbit quality. Validation using over one year of satellite laser ranging (SLR) measurements demonstrated a 5.2% improvement in the orbit solution of the refined model. Reliable correction for the GPS antenna phase center was obtained from an over-420-day dataset, and a trend in radial offset change was observed. After application of the in-flight calibration of the GPS antenna, a 26% reduction in the RMS SLR residuals was achieved for the RD orbit solution, and the carrier phase residuals were clearly reduced. The integer ambiguity resolution of HY-2B led to strong geometric constraints for the estimated parameters, and a 15% improvement in the SLR residuals could be inferred compared with the float solution.

Two‐Azimuth Co‐Seismic Ionospheric Disturbances Following the 2020 Jamaica Earthquake From GPS Observations

AbstractCo‐seismic ionospheric disturbance (CID) may provide insights on understanding the coupled nature of earthquake–atmosphere geophysical processes. In this study, the CIDs following the Mw 7.7 Jamaica earthquake on January 28, 2020 are detected about 12 min after the main shock by the dual‐frequency Global Positioning System measurements. Significant CIDs at two azimuths are observed from satellite PRN03, 04 and 26 with spreading out at 3.54, 3.51 and 3.48 km/s respectively, which are close to the spreading speeds of Rayleigh waves recorded by the seismographs. The significant CID signals are found in south near‐field area and southwest far‐field area. Furthermore, CID characteristics are analyzed in terms of amplitude, elevation and azimuth angle, waveform, and frequency domain. Results show that CIDs are observed by PRN03, 04 and 26 at low elevation angles (<35°) in infrasonic wave frequency domain and the average negative amplitudes of CIDs observed by PRN26 are larger than −0.08 TECU, while the CID amplitudes observed by PRN03 and PRN04 are about −0.05 and −0.07 TECU, respectively. Moreover, the azimuthal asymmetry of CID amplitude in SW and SE azimuths and different initial polarities in disturbance signals are found and discussed from tectonic and nontectonic factors. The relations among CID, Rayleigh wave and focal mechanism are interpreted. The upward propagating secondary acoustic wave triggered by the seismic Rayleigh wave from earthquake is the main source of CIDs. These results confirm that strike‐slip earthquake can also generate pronounced co‐seismic ionospheric disturbances.

Spatial Variations of Slip and Creep Rates Along the Southern and Central Dead Sea Fault and the Carmel–Gilboa Fault System

AbstractCrustal deformation and seismic activity in the Levant is mainly related to the interplate Dead Sea Fault (DSF) and the intraplate Carmel–Gilboa Fault System (CGFS). In this study, we analyze the interseismic deformation along these fault systems using 23 years of Global Positioning System (GPS) measurements obtained from 209 campaign and 60 continuous stations. This GPS data set is the longest record and the densest data set for the DSF, the CGFS, and the Levant region. We use this data set to investigate the spatial variations of slip and creep rates along the southern and central sections of the DSF and the CGFS. Our inversion model results indicate that part of the tectonic motion is transferred from the DSF to the CGFS. We find that the left‐lateral strike‐slip motion along the DSF decreases in a rate of 0.9 ± 0.4 mm/year, from 4.8 ± 0.3 mm/year south to the intersection with the CGFS to 3.9 ± 0.4 mm/year north to this intersection. Along the CGFS, the left‐lateral strike‐slip motion ranges between ∼0.3 and 0.5 mm/year and the extension rate between ∼0.6 and 0.7 mm/year, indicating a total slip rate vector of 0.8 ± 0.4 mm/year in the DSF direction, in agreement with the reduction of slip rate along the DSF near the intersection with the CGFS. Shallow creep is found along the southern and central sections of the Dead Sea basin and the northern Jordan Valley section of the DSF, with creep rates of 3.4 ± 0.4 and 2.3 ± 0.4 mm/year, respectively. These creeping sections were identified as areas with thick Halite layers at the shallow subsurface. We suggest that shallow creep behavior along the DSF is govern by the presence and mechanical properties of the Halite, which probably allows plastic deformation and the transition to velocity strengthening at the shallow subsurface and promotes creep.

Evaluation of near-surface groundwater aquifers through integrated geophysical and geodetic measurements

Extensive geophysical and geodetic measurements were carried out to evaluate the groundwater aquifer, trace the basement relief, as well as detect the igneous intrusions and structural elements (mainly faults) that affect the occurrence of groundwater in the study area. The fieldwork included resistivity sounding, a geomagnetic survey, and Global Positioning System measurements. The magnetic results showed the presence of a group of main faults in East-west trend at the western part of the area and major fault at the northern part of the area of NW-SW trend. The findings also showed the presence of two igneous rock intrusions located in the middle of the eastern part of the valley. Pronounced differences in the depths of basement rocks have been identified, ranging between 0 and 900 m from the surface. Both high horizontal movements and high shear strain rates have been found to be concentrated at the southeast of the study area and it was noted that high stress was accumulated along the main observed faults and at the main groundwater aquifers. The geoelectrical results confirmed the presence of two aquifers; a shallow aquifer (Quaternary aquifer) that narrows northwards and a Nubian sandstone aquifer, which considered the main aquifer. The Nubian sandstone aquifer carries groundwater in the region, which overlies the last geoelectric unit represented by the basement complex layer and geological structures affecting the potential availability of groundwater in the study area, as proved by the geomagnetic survey and stress accumulation.

Predicting the Future of Protected Areas in the Region of the Highest Population Density in Sub-Saharan Africa

ABSTRACT The landscape surrounding protected areas (PAs) plays a big role in supporting the achievement of conservation goals. This paper examines demographic dynamics in the vicinity of Akagera National Park (ANP) both in time and space, considers its implication on land-use/land-cover (LULC) change of one of its neighboring districts, and involves the existing environmental planning policies to anticipate the fate of the ANP. Data retrieved from Rwanda Land Management and Use Authority (RLMUA) and from the National Institute of Statistics of Rwanda (NISR) were reinforced with field observation and Global Positioning System (GPS) measurements taken within Gatsibo district where the study was conducted and injected into a Geographic Information System (GIS) for mapping and analysis. Findings revealed that in the next 50 years, the increasing human settlement and associated social-economic needs will erase any remnant wildlife hotspots in the ‘Unrestricted zone’ of the district and reclaim intrusion in its ‘Restricted zone’ of which ANP is part. This raises imminent fear of growing cases of encroachment of human activities into illegal and high-risk zones and a possible second de-gazettement of the park. The reversal of this trend requires the implementation of the local LULC plan and the promotion of the ecological lifestyle.

Geodetic Observation and Modeling of the Coseismic and Postseismic Deformations Associated With the 2020 Mw 6.5 Monte Cristo Earthquake

AbstractThe 2020 Mw 6.5 Monte Cristo earthquake occurred in the northeastern Mina deflection of the central Walker Lane Belt (WLB) in Nevada, USA. The Mina deflection represents a typical stepover zone that transfers the dextral slip in the northern Eastern California Shear Zone onto the dextral faults in the central WLB. The Monte Cristo earthquake provides a rare opportunity to investigate the strain accumulation and stress transition mechanisms in the WLB. In this study, ascending and descending Sentinel‐1 images were utilized to generate coseismic and early postseismic deformations associated with this earthquake. Combined with global positioning system measurements, these images were inverted for the coseismic slip and afterslip of the Monte Cristo earthquake. The preferred coseismic slip model suggests that the causative fault is characterized by two fault segments with southward dips of 64° and 79°. The coseismic rupture was dominated by sinistral slip with obvious normal slip components in the western segment of the source fault. The coseismic slip was mainly concentrated in the 3–12 km depth range and decreased at shallower depths, suggesting a moderate amount of shallow coseismic slip deficit. Rapid afterslip was mainly confined to the 0–3 km depth range, largely compensating for the shallow slip deficit caused by the mainshock. The widely distributed normal slips in the northeastern Mina deflection revealed by the Monte Cristo earthquake suggest the transtensional model is more applicable due to its ability to account for the slip transition kinematics in the Mina deflection.

PEMANFAATAN DIGITAL TERRAIN MODEL HASIL FOTOGRAMETRI UNMANED AERIAL VEHICLE UNTUK ESTIMASI KETINGGIAN GENANGAN AIR BANJIR HASIL DETEKSI CITRA SYNTHETIC APPERTURE RADAR

Utilization of The Unmanned Aerial Vehicle (UAV) or Drone has brought revolution in digital photogrammetry. The feature matching on surface reconstruction or Digital Surface Model (DSM) are quickly finished. However, DSM doesn’t represent itself as a part of topography, that is why DSM should be converted into Digital Terrain Model (DTM). This research is to investigate the accuracy of UAV photogrammetry’s DTM  for hydraulic modeling purpose. This study has produced 4 sets of DTMs; 2 sets of DTMs with different grid resolution which are 2 cm & 40 cm, also the 2 other sets of DTM with extra fine nature algorithm and set of filtering parameters adjustment; bulge, offset, spike and standard deviation. Every DTM are validated by Ground Control Point (GCP) from Real Time Kinematic-Different Global Positioning System (RTK-DGPS) measurement. According to the validation, the adjustment of filtering parameters is the most accurate method with Root Mean Square Error (RMSE) of 6,17 cm for 2 cm resolution; and 5,22 cm for 40 cm resolution. Next, DTM UAV is used to estimate the flood water level from Synthetic Aperture Radar (SAR) Image detection with 46 flood images on Glane and Losser area, east part of Overijssel, The Netherlands, since October 2014 to December 2017, then validated with the insitu water level measurement and resulted RMSE 6,72 cm for set of UAV DTM’s 40 cm resolution with the filtering parameters adjustment. Therefore, this DTM UAV can be used as a topography parameter in hydraulic modeling, especially at the similar flat-surface terrain where this research have been conducted.  Keywords: UAV photogrammetry, SAR detection, DTM production

Are We Ready for Unmanned Surface Vehicles in Inland Waterways? The USVInland Multisensor Dataset and Benchmark

Unmanned surface vehicles (USVs) have great value with their ability to execute hazardous and time-consuming missions over water surfaces. Recently, USVs for inland waterways have attracted increasing attention for their potential application in autonomous monitoring, transportation, and cleaning. However, unlike sailing in open water, the challenges posed by scenes of inland waterways, such as the complex distribution of obstacles, the global positioning system (GPS) signal denial environment, the reflection of bank-side structures, and the fog over the water surface, all impede USV application in inland waterways. To address these problems and stimulate relevant research, we introduce USVInland, a multisensor dataset for USVs in inland waterways. The collection of USVInland spans a trajectory of more than 26 km in diverse real-world scenes of inland waterways using various modalities, including lidar, stereo cameras, millimeter-wave radar, GPS, and inertial measurement units (IMUs). Based on the requirements and challenges in the perception and navigation of USVs for inland waterways, we build benchmarks for simultaneous localization and mapping (SLAM), stereo matching, and water segmentation. We evaluate common algorithms for the above tasks to determine the influence of unique inland waterway scenes on algorithm performance. Our dataset and the development tools are available at.1

A Vehicle-Model-Aided Navigation Reconstruction Method for a Multicopter during a GPS Outage

The integrated navigation of inertial navigation systems (INS) and the Global Positioning System (GPS) is essential for small unmanned aerial vehicles (UAVs) such as multicopters, providing steady and accurate position, velocity, and attitude information. Nevertheless, decreasing navigation accuracy is a serious threat to flight safety due to the long-term drift error of INS in the absence of GPS measurements. To bridge the GPS outage for multicopters, this paper proposes a novel navigation reconstruction method for small multicopters, which combines the vehicle dynamic model and micro-electro-mechanical system (MEMS) sensors. Firstly, an induced drag model is introduced into the dynamic model of the vehicle, and an efficient online parameter identification method is designed to estimate the model parameters quickly. Secondly, the body velocity can be calculated from the vehicle model and accelerometer measurement. In addition, the nongravitational acceleration estimated from body velocity and radar height are utilized to yield a more accurate attitude estimate. Fusing the information of the attitude, body velocity, magnetic heading, and radar height, a navigation system based on an error-state Kalman filter is reconstructed. Then, an adaptive measurement covariance algorithm based on a fuzzy logic system is designed to reduce the weight due to the disturbed acceleration. Finally, the hardware-in-loop experiment is carried out to demonstrate the effectiveness of the proposed method. Simulation results show that the proposed navigation reconstruction algorithm aided by the vehicle model can significantly improve navigation accuracy during a GPS outage.

Performance of water vapour retrieval from MODIS and ECMWF and their validation with ground based GPS measurements over Varanasi

Water vapour is highly variable over tropical region and sensitive to weather condition, monsoon onset, green house effect, and pollution level in Ganga River. In the present study, variability in water vapour derived from Global Positioning System (GPS) over Varanasi (25°20′N, 82°59′E) during the period 2007–2010 has been studied. The GPS-derived water vapour (WV) has been compared with those retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) and ECMWF. The GPS-WV data concurrent to MODIS and ECMWF timing has been correlated to perform further analysis. To study the accuracy of water vapour retrieved from the MODIS and ECMWF, root mean square error (RMSE), absolute error (AE), correlation and standard deviation in it are computed with respect to GPS-derived water vapour. Analysis shows an annual correlation R2 = 86%, RMSE = 9.5 mm and AE (MODIS–GPS) = 7.0 mm in MODIS retrieval and annual correlation R2 = 86%, RMSE = 6.1 mm and AE (ECMWF–GPS) = 2.4 mm in ECMWF reanalysis retrieval. Correlation of ECMWF and MODIS datasets with the GPS datasets are found to vary significantly with seasons. The correlation is high during monsoon season and low during spring season. Water vapour is found to be an indicator for the onset of monsoon.

New Constraints on Slip Deficit on the Aleutian Megathrust and Inflation at Mt. Veniaminof, Alaska From Repeat GPS Measurements

AbstractWe employ an enhanced data set of Global Positioning System (GPS) velocities to reassess the slip deficit along the plate interface of the Alaska‐Aleutian subduction zone. An examination of velocities of sites near Mt Veniaminof, located in the southwest Alaska Peninsula, shows that existing models for tectonic deformation do not accurately predict the local velocity field along this section of the peninsula. In a combined model, we solve for the volcanic inflation signal on the edifice of Mt. Veniaminof and reassess the variations in trench coupling outboard of the volcano. The interseismic deformation near Veniaminof and the eastern Shumagin islands requires an additional model segment with higher slip deficit than the western Shumagin islands. This segment appears to have been the main rupture patch of the 2020 M 7.9 Simeonof earthquake. The volcano inflated over the time period of 2005–2017, although at a lower rate than in 2002–2005.

Implementation of Non-Linear Non-Parametric Persistent Scatterer Interferometry and Its Robustness for Displacement Monitoring.

To derive surface displacement, interferometric stacking with synthetic aperture radar (SAR) data is commonly used, and this technique is now in the implementation phase in the real world. Persistent scatterer interferometry (PSI) is one of the most universal approaches among in- terferometric stacking techniques, and non-linear non-parametric PSI (NN-PSI) was proposed to overcome the drawbacks of PSI approaches. The estimation of the non-linear displacements was successfully conducted using NN-PSI. However, the estimation of NN-PSI is not always stable with certain displacements because wider range of the velocity spectrum is used in NN-PSI than the conventional approaches; therefore, a calculation procedure and parameter optimization are needed to consider. In this paper, optimized parameters and procedures of NN-PSI are proposed, and real data processing with Sentinel-1 in the Kanto region in Japan was conducted. We confirmed that the displacement estimation was comparable to the measurement of the permanent global positioning system (GPS) stations, and the root mean square error between the GPS measurement and NN-PSI estimation was less than 3 mm in two years. The displacement over 2 ambiguity, which the conventional PSI approach wrongly reconstructed, was also quantitatively validated and successfully estimated by NN-PSI. As a result of the real data processing, periodical displacements were also reconstructed through NN-PSI. We concluded that the NN-PSI approach with the proposed parameters and method enabled the estimation of several types of surface displacements that conventional PSI approaches could not reconstruct.

TEC derived from local GPS network in Pakistan and comparison with IRI-2016 and IRI-PLAS 2017

The existing global network of continuously operating stand-alone GNSS reference stations provides an opportunity to estimate total electron content (TEC) from raw Global Positioning System (GPS) measurements. The TEC driven from a local GPS network in Pakistan was compared to two international models: IRI-2016 and IRI-PLAS 2017. The performance was analyzed statistically based on residual analysis, RMSE and correlation. It is observed that the TEC estimated by all three methods follows the same diurnal trend where it maximizes around noon ( $$12:00 {-} 14:00 LT$$ ) and reduces in the afternoon ( $$15:00 {-} 17:00 LT$$ ). Both empirical models provide a better estimation of nighttime TEC as compared to daytime TEC and exhibit maximum deviation in the month of April with the lowest deviation in December. The IRI-2016 underestimates TEC by $$5 - 10 TECU,$$ whereas the IRI-PLAS 2017 overestimates TEC by $$10 - 22 TECU$$ . However, the IRI-2016 conforms better to GPS-TEC ( $$\overline{\gamma } = 0.9710$$ ) as compared to IRI-PLAS 2017 ( $$\overline{\gamma } = 0.8337$$ ). The study shows that local GNSS stations in collaboration with TEC estimated from global models may be used in development of an efficient local TEC model over Pakistan which will not only assist in local ionosphere studies but also aid in improving the positioning accuracy.

Monitoring In-Situ Seismic Response on Rock Slopes Using Ambient Noise Interferometry: Application to the 2019 Changning (Mw 5.7) Earthquake, China

Study of the mechanical response of rock slopes to moderate earthquakes is important for understanding the local rheology of landslide and earthquake interactions and for mitigating the risks associated with subsurface geological processes in tectonically active mountainous belts. To complement existing point measurements from surface observations (e.g., global positioning system and interferometric synthetic-aperture radar measurements), measuring the ambient noise-based velocity change (δv/v) allows for remote observations of mechanical state changes of the slope, at depth and continuously in time. We herein investigate the seismic responses of the Pubugou rock slope, a typical steep rock slope in south-west China, to the 2019 Mw 5.7 Changning earthquake. We apply ambient noise interferometry to the slope and measure the coda wave velocity changes at frequencies from 2 to 20 Hz with a 1-h temporal resolution, 2 days before and 14 days after the earthquake. We observe a significant co-seismic wave velocity decrease caused by the Changning earthquake of up to 0.9% followed by a gradual logarithmic recovery process over 2 weeks. The earthquake-induced stress sensitivity of δv/v on the slope is estimated as ∼3.2×10−8 Pa−1. Through the analysis of the co-seismic and post-seismic δv/v with different time lapses of the coda, we characterize the healing process on the slope and also constrain such changes to 75 m in depth. This study highlights the possibility of quantitatively characterizing the slope weakness using moderate earthquakes in mountainous areas in the future.

The Assessment of Hydrologic- and Flood-Induced Land Deformation in Data-Sparse Regions Using GRACE/GRACE-FO Data Assimilation

The vertical motion of the Earth’s surface is dominated by the hydrologic cycle on a seasonal scale. Accurate land deformation measurements can provide constructive insight into the regional geophysical process. Although the Global Positioning System (GPS) delivers relatively accurate measurements, GPS networks are not uniformly distributed across the globe, posing a challenge to obtaining accurate deformation information in data-sparse regions, e.g., Central South-East Asia (CSEA). Model simulations and gravity data (from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO)) have been successfully used to improve the spatial coverage. While combining model estimates and GRACE/GRACE-FO data via the GRACE/GRACE-FO data assimilation (DA) framework can potentially improve the accuracy and resolution of deformation estimates, the approach has rarely been considered or investigated thus far. This study assesses the performance of vertical displacement estimates from GRACE/GRACE-FO, the PCRaster Global Water Balance (PCR-GLOBWB) hydrology model, and the GRACE/GRACE-FO DA approach (assimilating GRACE/GRACE-FO into PCR-GLOBWB) in CSEA, where measurements from six GPS sites are available for validation. The results show that GRACE/GRACE-FO, PCR-GLOBWB, and GRACE/GRACE-FO DA accurately capture regional-scale hydrologic- and flood-induced vertical displacements, with the correlation value and RMS reduction relative to GPS measurements up to 0.89 and 53%, respectively. The analyses also confirm the GRACE/GRACE-FO DA’s effectiveness in providing vertical displacement estimates consistent with GRACE/GRACE-FO data while maintaining high-spatial details of the PCR-GLOBWB model, highlighting the benefits of GRACE/GRACE-FO DA in data-sparse regions.