scholarly journals Ice flow velocities over Vostok Subglacial Lake, East Antarctica, determined by 10 years of GNSS observations

2013 ◽  
Vol 59 (214) ◽  
pp. 315-326 ◽  
Author(s):  
A. Richter ◽  
D.V. Fedorov ◽  
M. Fritsche ◽  
S.V. Popov ◽  
V.Ya. Lipenkov ◽  
...  
Keyword(s):  
Flow Velocity ◽  
East Antarctica ◽  
Global Navigation Satellite Systems ◽  
Steady Increase ◽  
Lake Area ◽  
Ice Flow ◽  
Satellite Systems ◽  
Subglacial Lake ◽  
Gnss Observations ◽  
Flow Velocities

AbstractRepeated Global Navigation Satellite Systems (GNSS) observations were carried out at 50 surface markers in the Vostok Subglacial Lake (East Antarctica) region between 2001 and 2011. The horizontal ice flow velocity vectors were derived with accuracies of 1 cm a−1 and 0.5°, representing the first reliable information on ice flow kinematics in the northern part of the lake. Within the lake area, ice flow velocities do not exceed 2 m a−1. The ice flow azimuth is southeast in the southern part of the lake and turns gradually to east-northeast in the northern part. In the northern part, as the ice flow enters the lake at the western shore, the velocity decreases towards the central lake axis, then increases slightly past the central axis. In the southern part, a continued acceleration is observed from the central lake axis across the downstream grounding line. Based on the observed flow velocity vectors and ice thickness data, mean surface accumulation rates are inferred for four surface segments between Ridge B and Vostok Subglacial Lake and show a steady increase towards the north.

scholarly journals Estimation and Analysis of GNSS Differential Code Biases (DCBs) Using a Multi-Spacing Software Receiver

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 443
Author(s):  
Ye Wang ◽  
Lin Zhao ◽  
Yang Gao
Keyword(s):  
Primary Source ◽  
Intermediate Frequency ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Software Receiver ◽  
International Gnss Service ◽  
Total Electron ◽  
Satellite Systems ◽  
Differential Code Biases ◽  
Gnss Observations

In the use of global navigation satellite systems (GNSS) to monitor ionosphere variations by estimating total electron content (TEC), differential code biases (DCBs) in GNSS measurements are a primary source of errors. Satellite DCBs are currently estimated and broadcast to users by International GNSS Service (IGS) using a network of GNSS hardware receivers which are inside structure fixed. We propose an approach for satellite DCB estimation using a multi-spacing GNSS software receiver to analyze the influence of the correlator spacing on satellite DCB estimates and estimate satellite DCBs based on different correlator spacing observations from the software receiver. This software receiver-based approach is called multi-spacing DCB (MSDCB) estimation. In the software receiver approach, GNSS observations with different correlator spacings from intermediate frequency datasets can be generated. Since each correlator spacing allows the software receiver to output observations like a local GNSS receiver station, GNSS observations from different correlator spacings constitute a network of GNSS receivers, which makes it possible to use a single software receiver to estimate satellite DCBs. By comparing the MSDCBs to the IGS DCB products, the results show that the proposed correlator spacing flexible software receiver is able to predict satellite DCBs with increased flexibility and cost-effectiveness than the current hardware receiver-based DCB estimation approach.

scholarly journals Forty-seven new subglacial lakes in the 0–110° E sector of East Antarctica

2007 ◽  
Vol 53 (181) ◽  
pp. 289-297 ◽  
Author(s):  
Sergey V. Popov ◽  
Valery N. Masolov
Keyword(s):  
Heat Flux ◽  
Scientific Work ◽  
East Antarctica ◽  
Lake Area ◽  
Geothermal Heat ◽  
Subglacial Lake ◽  
Deep Faults ◽  
Radio Echo Sounding ◽  
Subglacial Lakes ◽  
Echo Sounding

AbstractDuring the summer field seasons of 1987–91, studies of central East Antarctica by airborne radio-echo sounding commenced. This scientific work continued in the 1990s in the Vostok Subglacial Lake area and along the traverse route from Mirny, and led to the discovery of 16 new subglacial water cavities in the areas of Domes Fuji and Argus and the Prince Charles Mountains. Twenty-nine subglacial water cavities were revealed in the area near Vostok, along with a feature we believe to be a subglacial river. Two subglacial lakes were discovered along the Mirny–Vostok traverse route. These are located 50 km north of Komsomolskaya station and under Pionerskaya station. We find high geothermal heat flux in the vicinity of the largest of the subglacial lakes, and suggest this may be due to their location over deep faults where additional mantle heat is available.

Co-location of SLR and GNSS techniques onboard Galileo and GLONASS satellites

2021 ◽  
Author(s):  
Grzegorz Bury ◽  
Krzysztof Sośnica ◽  
Radosław Zajdel ◽  
Dariusz Strugarek ◽  
Urs Hugentobler
Keyword(s):  
Orbital Plane ◽  
Terrestrial Reference Frame ◽  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Local Ties ◽  
Satellite Systems ◽  
The Impact ◽  
Space Ties ◽  
Gnss Observations

<p>All satellites of the Galileo and GLONASS navigation systems are equipped with laser retroreflector arrays for Satellite Laser Ranging (SLR). SLR observations to Global Navigation Satellite Systems (GNSS) provide the co-location of two space geodetic techniques onboard navigation satellites.</p><p>SLR observations, which are typically used for the validation of the microwave-GNSS orbits, can now contribute to the determination of the combined SLR+GNSS orbits of the navigation satellites. SLR measurements are especially helpful for periods when the elevation of the Sun above the orbital plane (β angle) is the highest. The quality of Galileo-IOV orbits calculated using combined SLR+GNSS observations improves from 36 to 30 mm for β> 60° as compared to the microwave-only solution. </p><p>Co-location of two space techniques allows for the determination of the linkage between SLR and GNSS techniques in space. Based on the so-called space ties, it is possible to determine the 3D vector between the ground-based co-located SLR and GNSS stations and compare it with the local ties which are determined using the ground measurements. The agreement between local ties derived from co-location in space and ground measurements is at the level of 1 mm in terms of the long-term median values for the co-located station in Zimmerwald, Switzerland.</p><p>We also revise the approach for handling the SLR range biases which constitute one of the main error sources for the SLR measurements. The updated SLR range biases consider now the impact of not only of SLR-to-GNSS observations but also the SLR observations to LAGEOS and the microwave GNSS measurements. The updated SLR range biases improve the agreement between space ties and local ties from 34 mm to 23 mm for the co-located station in Wettzell, Germany.</p><p>Co-location of SLR and GNSS techniques onboard navigation satellites allows for the realization of the terrestrial reference frame in space, onboard Galileo and GLONASS satellites, independently from the ground measurements. It may also deliver independent information on the local tie values with full variance-covariance data for each day with common measurements or can contribute to the control of the ground measurements as long as both GNSS and SLR-to-GNSS observations are available.</p>

scholarly journals Hybrid Wavelet and Principal Component Analyses Approach for Extracting Dynamic Motion Characteristics from Displacement Series Derived from Multipath-Affected High-Rate GNSS Observations

2019 ◽  
Vol 12 (1) ◽  
pp. 79 ◽  
Author(s):  
Mosbeh R. Kaloop ◽  
Cemal O. Yigit ◽  
Ahmed El-Mowafy ◽  
Ahmet A. Dindar ◽  
Mert Bezcioglu ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Principal Component ◽  
Dominant Frequency ◽  
Shaking Table ◽  
Global Navigation Satellite Systems ◽  
High Rate ◽  
Engineering Structures ◽  
Satellite Systems ◽  
Multipath Errors ◽  
Gnss Observations

Nowadays, the high rate GNSS (Global Navigation Satellite Systems) positioning methods are widely used as a complementary tool to other geotechnical sensors, such as accelerometers, seismometers, and inertial measurement units (IMU), to evaluate dynamic displacement responses of engineering structures. However, the most common problem in structural health monitoring (SHM) using GNSS is the presence of surrounding structures that cause multipath errors in GNSS observations. Skyscrapers and high-rise buildings in metropolitan cities are generally close to each other, and long-span bridges have towers, main cable, and suspender cables. Therefore, multipath error in GNSS observations, which is typically added to the measurement noise, is inevitable while monitoring such flexible engineering structures. Unlike other errors like atmospheric errors, which are mostly reduced or modeled out, multipath errors are the largest remaining unmanaged error sources. The high noise levels of high-rate GNSS solutions limit their structural monitoring application for detecting load-induced semi-static and dynamic displacements. This study investigates the estimation of accurate dynamic characteristics (frequency and amplitude) of structural or seismic motions derived from multipath-affected high-rate GNSS observations. To this end, a novel hybrid model using both wavelet-based multiscale principal component analysis (MSPCA) and wavelet transform (MSPCAW) is designed to extract the amplitude and frequency of both GNSS relative- and PPP- (Precise Point Positioning) derived displacement motions. To evaluate the method, a shaking table with a GNSS receiver attached to it, collecting 10 Hz data, was set up close to a building. The table was used to generate various amplitudes and frequencies of harmonic motions. In addition, 50-Hz linear variable differential transformer (LVDT) observations were collected to verify the MSMPCAW model by comparing their results. The results showed that the MSPCAW could be efficiently used to extract the dynamic characteristics of noisy dynamic movements under seismic loads. Furthermore, the dynamic behavior of seismic motions can be extracted accurately using GNSS-PPP, and its dominant frequency equals that extracted by LVDT and relative GNSS positioning method. Its accuracy in determining the amplitude approaches 91.5% relative to the LVDT observations.

scholarly journals Validating HY-2A CMR Precipitable Water Vapor Using Ground-based and Shipborne GNSS Observations

2020 ◽  
Author(s):  
Zhilu Wu ◽  
Yanxiong Liu ◽  
Yang Liu ◽  
Jungang Wang ◽  
Xiufeng He ◽  
...  
Keyword(s):  
Water Vapor ◽  
Microwave Radiometer ◽  
Precipitable Water ◽  
Global Navigation Satellite Systems ◽  
High Temporal Resolution ◽  
Satellite Systems ◽  
The Indian Ocean ◽  
Global Navigation Satellite ◽  
Gnss Data ◽  
Gnss Observations

Abstract. The calibration microwave radiometer (CMR) onboard Haiyang-2A satellite provides wet tropospheric delays correction for altimetry data, which can also contribute to the understanding of climate system and weather processes. Ground-based Global Navigation Satellite Systems (GNSS) provide precise PWV with high temporal resolution and could be used for calibration and monitoring of the CMR data, and shipborne GNSS provides accurate PWV over open oceans, which can be directly compared with uncontaminated CMR data. In this study, the HY-2A CMR water vapor product is validated using ground-based GNSS observations of 100 IGS stations along the coastline and 56-day shipborne GNSS observations over the Indian Ocean. The processing strategy for GNSS data and CMR data is discussed in detail. Special efforts were made to the quality control and reconstruction of contaminated CMR data. The validation result shows that HY-2A CMR PWV agrees well with ground-based GNSS PWV with 2.67 mm in RMS within 100 km. Geographically, the RMS is 1.12 mm in the polar region and 2.78 mm elsewhere. The PWV agreement between HY-2A and shipborne GNSS shows a significant correlation with the distance between the ship and the satellite footprint, with an RMS of 1.57 mm for the distance threshold of 100 km. Ground-based GNSS and shipborne GNSS agree with HY-2A CMR well with no obvious system error.

scholarly journals GNSS-based Orbital Filter for Earth Moon Transfer Orbits

2015 ◽  
Vol 69 (4) ◽  
pp. 745-764 ◽  
Author(s):  
Vincenzo Capuano ◽  
Francesco Basile ◽  
Cyril Botteron ◽  
Pierre- André Farine
Keyword(s):  
Model Simulation ◽  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Satellite Systems ◽  
Transfer Orbits ◽  
Low Earth Orbits ◽  
Global Navigation Satellite ◽  
Navigation Accuracy ◽  
Earth Orbits ◽  
Gnss Observations

Numerous applications, not only Earth-based, but also space-based, have strengthened the interest of the international scientific community in using Global Navigation Satellite Systems (GNSSs) as navigation systems for space missions that require good accuracy and low operating costs. Indeed, already successfully used in Low Earth Orbits (LEOs), GNSS-based navigation systems can maximise the autonomy of a spacecraft while reducing the burden and the costs of ground operations. That is why GNSS is also attractive for applications in higher Earth orbits up to the Moon, such as in Moon Transfer Orbits (MTOs). However, the higher the altitude the receiver is above the GNSS constellations, the poorer and the weaker are the relative geometry and the received signal powers, respectively, leading to a significant navigation accuracy reduction. In order to improve the achievable GNSS performance in MTOs, we consider in this paper an adaptive orbital filter that fuses the GNSS observations with an orbital forces model. Simulation results show a navigation accuracy significantly higher than that attainable individually by a standalone GNSS receiver or by means of a pure orbital propagation.

scholarly journals Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications

2006 ◽  
Vol 166 (3) ◽  
pp. 991-998 ◽  
Author(s):  
Jens Wendt ◽  
Reinhard Dietrich ◽  
Mathias Fritsche ◽  
Anja Wendt ◽  
Alexander Yuskevich ◽  
...  
Keyword(s):  
Ice Flow ◽  
Lake Vostok ◽  
Subglacial Lake ◽  
Flow Velocities

scholarly journals The control of an uncharted pinning point on the flow of an Antarctic ice shelf

2016 ◽  
Vol 62 (231) ◽  
pp. 37-45 ◽  
Author(s):  
SOPHIE BERGER ◽  
LIONEL FAVIER ◽  
REINHARD DREWS ◽  
JEAN-JACQUES DERWAEL ◽  
FRANK PATTYN
Keyword(s):  
Global Navigation Satellite Systems ◽  
Ice Shelf ◽  
Alos Palsar ◽  
Secondary Importance ◽  
Ice Flow ◽  
Ice Shelves ◽  
Satellite Systems ◽  
Flow Models ◽  
Ice Velocity ◽  
Global Navigation Satellite

ABSTRACTAntarctic ice shelves are buttressed by numerous pinning points attaching to the otherwise freely-floating ice from below. Some of these kilometric-scale grounded features are unresolved in Antarctic-wide datasets of ice thickness and bathymetry, hampering ice flow models to fully capture dynamics at the grounding line and upstream. We investigate the role of an 8.7 km2 pinning point at the front of the Roi Baudouin Ice Shelf, East Antarctica. Using ERS interferometry and ALOS-PALSAR speckle tracking, we derive, on a 125 m grid spacing, surface velocities deviating by −5.2 ± 4.5 m a−1 from 37 on-site global navigation satellite systems-derived velocities. We find no evidence for ice flow changes on decadal time scales and we show that ice on the pinning point virtually stagnates, deviating the ice stream and causing enhanced horizontal shearing upstream. Using the BISICLES ice-flow model, we invert for basal friction and ice rigidity with three input scenarios of ice velocity and geometry. We show that inversion results are the most sensitive to the presence/absence of the pinning point in the bathymetry; surface velocities at the pinning point are of secondary importance. Undersampling of pinning points results in erroneous ice-shelf properties in models initialised by control methods. This may impact prognostic modelling for ice-sheet evolution in the case of unpinning.

scholarly journals The use of products from ground-based GNSS observations in meteorological nowcasting

2010 ◽  
Vol 26 ◽  
pp. 77-82 ◽  
Author(s):  
E. Terradellas ◽  
B. Téllez
Keyword(s):  
Water Vapour ◽  
Horizontal Distribution ◽  
Global Navigation Satellite Systems ◽  
Full Potential ◽  
Atmospheric Humidity ◽  
Satellite Systems ◽  
Close Relationship ◽  
Integrated Water Vapour ◽  
Global Navigation Satellite ◽  
Gnss Observations

Abstract. Convective rainfall is often focalized in areas of moisture convergence. A close relationship between precipitation and fast variations of vertically-integrated water vapour (IWV) has been found in numerous cases. Therefore, continuous monitoring of atmospheric humidity and its spatial distribution is crucial to the operational forecaster for a proper nowcasting of heavy rainfall events. The microwave signals continuously broadcasted by the Global Navigation Satellite Systems (GNSS) satellites are influenced by the water vapour as they travel through the atmosphere. Estimates of IWV retrieved from ground-based GNSS observations may, then, constitute a source of information on the horizontal distribution and the time evolution of atmospheric humidity. At the Spanish Meteorological Agency (AEMET), a near-real-time map of IWV estimates retrieved from ground GNSS measurements in the Iberian Peninsula and West Mediterranean region is operationally built and presented to the forecaster. The maps are generated every 15 minutes following a one-dimensional variational assimilation scheme with the previous map as the background state. A case study is presented in order to illustrate some strengths and weaknesses of the product, to assess the potential benefit of using GNSS products in nowcasting and to define the steps to be done in order to make use of the full potential of the method.

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