scholarly journals Improved GNSS-R bi-static altimetry and independent DEMs of Greenland and Antarctica from TechDemoSat-1

2020 ◽  
Author(s):  
Jessica Cartwright ◽  
Christopher J. Banks ◽  
Meric Srokosz
Keyword(s):  
Satellite Altimetry ◽  
Ice Sheets ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
Digital Elevation ◽  
Future Potential ◽  
The Uk ◽  
Global Navigation Satellite ◽  
The Antarctic ◽  
Rms Errors

Abstract. Improved Digital Elevation Models (DEMs) of the Antarctic and Greenland Ice Sheets are presented, derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R). This builds on a previous study (Cartwright et al., 2018) using GNSS-R to derive an Antarctic DEM but uses improved processing and an additional 13 months of measurements, totalling 46 months of data from the UK TechDemoSat-1 satellite. A median bias of under 10 m and root-mean-square (RMS) errors of under 53 m for the Antarctic and 166 m for Greenland are obtained, as compared to existing DEMs. The results represent, compared to the earlier study, a halving of the median bias to 9 m, an improvement in coverage of 18 %, and a four times higher spatial resolution (now gridded at 25 km). In addition, these are the first published satellite altimetry measurements of the region surrounding the South Pole. Comparisons south of 88° S yield RMS errors of less than 33 m when compared to NASA’s Operation IceBridge measurements. Differences between DEMs are explored and the future potential for ice sheet monitoring by this technique is noted.

scholarly journals Improved GNSS-R bi-static altimetry and independent digital elevation models of Greenland and Antarctica from TechDemoSat-1

2020 ◽  
Vol 14 (6) ◽  
pp. 1909-1917 ◽  
Author(s):  
Jessica Cartwright ◽  
Christopher J. Banks ◽  
Meric Srokosz
Keyword(s):  
Digital Elevation Models ◽  
Global Navigation Satellite Systems ◽  
Glacial Ice ◽  
Satellite Systems ◽  
Digital Elevation ◽  
Future Potential ◽  
The Uk ◽  
Global Navigation Satellite ◽  
The Antarctic ◽  
Mean Square Errors

Abstract. Improved digital elevation models (DEMs) of the Antarctic and Greenland ice sheets are presented, which have been derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R). This builds on a previous study (Cartwright et al., 2018) using GNSS-R to derive an Antarctic DEM but uses improved processing and an additional 13 months of measurements, totalling 46 months of data from the UK TechDemoSat-1 satellite. A median bias of under 10 m and root-mean-square errors (RMSEs) of under 53 m for the Antarctic and 166 m for Greenland are obtained, as compared to existing DEMs. The results represent, compared to the earlier study, a halving of the median bias to 9 m, an improvement in coverage of 18 %, and a 4 times higher spatial resolution (now gridded at 25 km). In addition, these are the first published satellite altimetry measurements of the region surrounding the South Pole. Comparisons south of 88∘ S yield RMSEs of less than 33 m when compared to NASA's Operation IceBridge measurements. Differences between DEMs are explored, the limitations of the technique are noted, and the future potential of GNSS-R for glacial ice studies is discussed.

Efficiency of Using GNSS-PPP for Digital Elevation Model (DEM) Production

2020 ◽  
Vol 55 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Ashraf Abdallah ◽  
Amgad Saifeldin ◽  
Abdelhamid Abomariam ◽  
Reda Ali
Keyword(s):  
Digital Elevation Model ◽  
Cost Effective ◽  
Volume Estimation ◽  
Global Navigation Satellite Systems ◽  
Dual Frequency ◽  
Satellite Systems ◽  
Digital Elevation ◽  
Elevation Model ◽  
Kinematic Ppp ◽  
Global Navigation Satellite

AbstractIn the developing countries, cost-effective observation techniques are very important for earthwork estimation, map production, geographic information systems, and hydrographic surveying. One of the most cost-effective techniques is Precise Point Positioning (PPP); it is a Global Navigation Satellite Systems (GNSS) positioning technique to compute precise positions using only a single GNSS receiver. This study aims to evaluate the efficiency of using Global Positioning System (GPS) and GPS/ Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) post-processed kinematic PPP solution for digital elevation model (DEM) production, which is used in earthwork estimation. For this purpose, a kinematic trajectory has been observed in New Aswan City in an open sky area using dual-frequency GNSS receivers. The results showed that, in case of using GPS/GLONASS PPP solution to estimate volumes, the error in earthwork volume estimation varies between 0.07% and 0.16% according to gridding level. On the other hand, the error in volume estimation from GPS PPP solution varies between 0.40% and 0.99%.

The Potential Impact of GNSS/INS Integration on Maritime Navigation

2008 ◽  
Vol 61 (2) ◽  
pp. 221-237 ◽  
Author(s):  
Terry Moore ◽  
Chris Hill ◽  
Andy Norris ◽  
Chris Hide ◽  
David Park ◽  
...  
Keyword(s):  
Field Trials ◽  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Inertial Navigation Systems ◽  
Satellite Systems ◽  
Time Period ◽  
Maritime Navigation ◽  
The Uk ◽  
Global Navigation Satellite ◽  
The Impact

A version of this paper was presented at ENC-GNSS 2007, Geneva. Its reproduction was kindly authorised by the ENC-GNSS 07 Paper Selection Committee.The General Lighthouse Authorities of the UK & Ireland commissioned an assessment of the impact that the integration of Global Navigation Satellite Systems (GNSS) with Inertial Navigation Systems (INS) would have on the aids to navigation (AtoN) services currently provided, and those to be provided in the future. There is concern about the vulnerability of GNSS, and the provision of complementary and backup systems is seen to be of great importance. The integration of INS could provide an independent and self-contained navigation system, for a limited time period, invulnerable to external intentional or unintentional interference, or the influences of changes in national policies. The study included an analysis of the potential use of GNSS-INS in three of the four phases of a vessel's voyage: coastal, port approach and docking. The project consisted of a technology assessment, looking at the different inertial technologies that might be suitable for each phase. This was followed by a technology proving stage, evaluating suitable equipment using simulation and field trials to prove that the claimed performance could be achieved in practice. The final stage of the project was to assess the effects of the availability of such systems on existing and planned aids to navigation services.

scholarly journals The Rapid and Steady Mass Loss of the Patagonian Icefields throughout the GRACE Era: 2002–2017

2019 ◽  
Vol 11 (8) ◽  
pp. 909 ◽  
Author(s):  
Andreas Richter ◽  
Andreas Groh ◽  
Martin Horwath ◽  
Erik Ivins ◽  
Eric Marderwald ◽  
...  
Keyword(s):  
Time Series ◽  
Mass Loss ◽  
A Priori ◽  
Global Navigation Satellite Systems ◽  
Mass Change ◽  
Satellite Systems ◽  
Isostatic Adjustment ◽  
Global Navigation Satellite ◽  
Gravity Recovery ◽  
The Antarctic

We use the complete gravity recovery and climate experiment (GRACE) Level-2 monthly time series to derive the ice mass changes of the Patagonian Icefields (Southern Andes). The glacial isostatic adjustment is accounted for by a regional model that is constrained by global navigation satellite systems (GNSS) uplift observations. Further corrections are applied concerning the effect of mass variations in the ocean, in the continental water storage, and of the Antarctic ice sheet. The 161 monthly GRACE gravity field solutions are inverted in the spatial domain through the adjustment of scaling factors applied to a-priori ice mass change patterns based on published remote sensing results for the Southern and Northern Patagonian Icefields, respectively. We infer an ice mass change rate of −24.4 ± 4.7 Gt/a for the Patagonian Icefields between April 2002 and June 2017, which corresponds to a contribution to the eustatic sea level rise of 0.067 ± 0.013 mm/a. Our time series of monthly ice mass changes reveals no indication for an acceleration in ice mass loss. We find indications that the Northern Patagonian Icefield contributes more to the integral ice loss than previously assumed.

e-Navigation and the Case for eLoran

2008 ◽  
Vol 61 (3) ◽  
pp. 473-484 ◽  
Author(s):  
Paul Williams ◽  
Sally Basker ◽  
Nick Ward
Keyword(s):  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Inertial Navigation Systems ◽  
Satellite Systems ◽  
Essential Components ◽  
Radio Navigation System ◽  
Regional Basis ◽  
The Uk ◽  
Global Navigation Satellite ◽  
Inertial Systems

International discussions on the concept of e-navigation have identified a robust position-fixing system as one of the essential components. Global Navigation Satellite Systems (GNSS) are known to have vulnerabilities and onboard alternatives such as inertial systems have limitations. This paper considers the case for an enhanced version of the terrestrial radio-navigation system Loran to provide an alternative with performance comparable to GNSS. The paper reviews recent studies of inertial navigation systems and concludes that they do not present a fully capable backup to GNSS at present. Trials of enhanced Loran carried out in the UK by the General Lighthouse Authorities have shown that eLoran does have the potential to provide equivalent performance to GNSS over long periods and is a fully complementary system. The steps needed to provide eLoran on at least a regional basis, covering critical waterways, are considered. The international process for the specification and standardisation of eLoran is already underway and some projections are made about the timescale for full implementation, in the context of the introduction of e-Navigation. A version of this paper was first presented at NAV 07 held in Church House, London from 30th October – 1st November 2007.

Sea Ice Classification and Altimetry using Grazing Angle Reflected GNSS Signals Measured by Spire’s Nanosatellite Constellation

2021 ◽  
Author(s):  
Jessica Cartwright ◽  
Vu Nguyen ◽  
Philip Jales ◽  
Oleguer Nogues-Correig ◽  
Takayuki Yuasa ◽  
...  
Keyword(s):  
Sea Ice ◽  
Weather Prediction ◽  
Grazing Angle ◽  
Surface Characteristics ◽  
Global Navigation Satellite Systems ◽  
Ice Age ◽  
The Arctic ◽  
Satellite Systems ◽  
Global Navigation Satellite ◽  
The Antarctic

<p>Global Navigation Satellite Systems-Reflectometry (GNSS-R) offers novel observations over the cryosphere with the use of reflected navigation signals (eg. GPS or Galileo) as signals of opportunity. This technique has the potential for higher resolution measurements over sea ice than routinely acquired by passive microwave systems with a footprint of around 5 km2 and is much lower in power consumption, mass and therefore cost. Here we present sea ice classification and altimetry as observed at grazing angles by Spire’s Radio Occultation (RO) Satellite constellation, repurposed for GNSS-R.</p><p>The Spire RO constellation of 37 operational satellites (and growing) is relied upon to support critical numerical weather prediction and has been collecting GNSS signals as they refract through the atmosphere. The reprogramming of these satellites to receive signals reflected at grazing angle allows these signals to instead inform on Earth surface characteristics. From smooth surfaces, these signals are phase coherent at L-Band frequencies (~19 - 24 cm wavelength) and allow the detection of the roughness of the sea ice in addition to the height of the surface to several centimetres of precision. Three months of these operational sea ice detection and classification products are presented from Spring of 2020; with ice extent in agreement with external passive and active sources to around 98% in the Antarctic and 94% in the Arctic, and ice age classification (First Year/Multi-Year) agreeing in the Arctic to around 70%. First results are shown for the potential to detect other ice characteristics such as the Antarctic Marginal Ice Zone extent and floe size / type.</p>

scholarly journals Optimum Combinations of GGM and GDEM Models for Precise National Geoid Modelling

2021 ◽  
Author(s):  
Essam Mohamed Al-Karargy ◽  
Gomaa Mohamed Dawod
Keyword(s):  
Least Square ◽  
Global Navigation Satellite Systems ◽  
Geoid Model ◽  
Satellite Systems ◽  
Long Wavelength ◽  
Geopotential Models ◽  
Digital Elevation ◽  
Least Square Collocation ◽  
Global Navigation Satellite ◽  
Local Geoid

This study aims to develop a Local Geoid Model (LGM) for Egypt to determine the optimal combinations of global models with Global Navigation Satellite Systems (GNSS/Levelling) data. A precise national geodetic dataset, four Global Geopotential Models (GGMs), and three global Digital Elevation Models (DEMs) have been utilized. Hence, twelve gravimetric LGMs have been developed using the Least-Square Collocation (LSC) method fitted to GNSS/Levelling data and judged over 100 checkpoints. Results revealed that improvements in local geoid accuracy are attributed mainly to GGMs models representing the long wavelength of the Earth's gravitational field. Regarding DEMs, the accuracy of LGMs does not significantly depend on the utilized DEM. Based on the available data, the attained optimum geoid of Egypt has been developed with a standard deviation, equals 0.129 m.

scholarly journals Sensitivity of TDS-1 GNSS-R Reflectivity to Soil Moisture: Global and Regional Differences and Impact of Different Spatial Scales

2018 ◽  
Vol 10 (11) ◽  
pp. 1856 ◽  
Author(s):  
Adriano Camps ◽  
Mercedes Vall·llossera ◽  
Hyuk Park ◽  
Gerard Portal ◽  
Luciana Rossato
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Incidence Angle ◽  
Spatial Scales ◽  
Ground Truth ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
Left Hand ◽  
The Uk ◽  
Global Navigation Satellite

The potential of Global Navigation Satellite Systems-Reflectometry (GNSS-R) techniques to estimate land surface parameters such as soil moisture (SM) is experimentally studied using 2014–2017 global data from the UK TechDemoSat-1 (TDS-1) mission. The approach is based on the analysis of the sensitivity to SM of different observables extracted from the Delay Doppler Maps (DDM) computed by the Space GNSS Receiver–Remote Sensing Instrument (SGR-ReSI) instrument using the L1 (1575.42 MHz) left-hand circularly-polarized (LHCP) reflected signals emitted by the Global Positioning System (GPS) navigation satellites. The sensitivity of different GNSS-R observables to SM and its dependence on the incidence angle is analyzed. It is found that the sensitivity of the calibrated GNSS-R reflectivity to surface soil moisture is ~0.09 dB/% up to 30° incidence angle, and it decreases with increasing incidence angles, although differences are found depending on the spatial scale used for the ground-truth, and the region. The sensitivity to subsurface soil moisture has been also analyzed using a network of subsurface probes and hydrological models, apparently showing some dependence, but so far results are not conclusive.

Sign in / Sign up

Export Citation Format

Share Document