scholarly journals GPS/BDS Medium/Long-Range RTK Constrained with Tropospheric Delay Parameters from NWP Model

2018 ◽  
Vol 10 (7) ◽  
pp. 1113 ◽  
Author(s):  
Ying Xu ◽  
Chen Wu ◽  
Lei Li ◽  
Lizi Yan ◽  
Min Liu ◽  
...  
Keyword(s):  
Long Range ◽  
Phase Measurement ◽  
Weather Prediction ◽  
Vertical Direction ◽  
Global Navigation Satellite Systems ◽  
Convergence Time ◽  
Tropospheric Delay ◽  
Gps Rtk ◽  
Nwp Model ◽  
Better Than

Tropospheric delay is a major error source that affects the performance of the Global Navigation Satellite Systems (GNSS) Real Time Kinematic (RTK) positioning especially for the medium/long-range baseline. Although high precision tropospheric delay can be estimated by GNSS carrier phase measurement, together with position and ambiguity, a relatively long period of convergence time is necessary. In this study, we develop a new GPS/BDS RTK algorithm constrained with a tropospheric delay parameters from Numerical weather prediction (NWP) model for medium/long-range baselines. The accuracy of the tropospheric delays derived from NWP is assessed through comparisons with the results of GAMIT (GNSS at MIT). The positioning performance with standard GPS RTK, standard GPS/BDS RTK, the developed NWP-constrained GPS RTK and NWP-constrained GPS/BDS RTK over medium/long-range baselines are compared in terms of the initialization time and the positioning accuracy. Experiment results show that the mean differences between the NWP and GAMIT zenith tropospheric delay (ZTD) are between −5.50 mm and 5.60 mm, and the RMS values of the NWP ZTD residuals are from 24.02 mm to 32.62 mm. A reduction in the initialization time of over 41% and 58% for medium- and long-range baselines can be achieved with the NWP-constrained RTK (both GPS alone and GPS/BDS RTK solutions) compared to the standard RTK solution, respectively. An improvement of over 30% can be found with the GPS/BDS RTK compared with that of the GPS alone RTK for both standard and the NWP-constrained modes. The positioning precision of NWP-constrained GPS/BDS RTK is better than 3 cm in the horizontal direction and better than 5 cm in the vertical direction, which satisfies the requirement of the precise positioning service.

scholarly journals Tropospheric delay parameters derived from GNSS-tracking data of a fast-moving fleet of trains

2021 ◽  
Author(s):  
Matthias Aichinger-Rosenberger ◽  
Natalia Hanna ◽  
Robert Weber
Keyword(s):  
Numerical Weather Prediction ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Tropospheric Delay ◽  
Global Networks ◽  
Numerical Weather ◽  
Station Coordinates ◽  
Nwp Model

<p>Electromagnetic signals, as broadcasted by Global Navigation Satellite Systems (GNSS), are delayed when travelling through the Earth’s atmosphere due to the presence of water vapour. Parametrisations of this delay, most prominently the Zenith Total Delay (ZTD) parameter, have been studied extensively and proven to provide substantial benefits for atmospheric research and especially the Numerical Weather Prediction (NWP) model performance. Typically, regional/global networks of static reference stations are utilized to derive ZTD along with other parameters of interest in GNSS analysis (e.g. station coordinates). Results are typically used as a contributing data source for determining the initial conditions of NWP models, a process referred to as Data Assimilation (DA).</p><p>This contribution goes beyond the approach outlined above as it shows how reasonable tropospheric parameters can be derived from highly kinematic, single-frequency (SF) GNSS data. The utilized data was gathered at trains by the Austrian Federal Railways (ÖBB) and processed using the Precise Point Positioning (PPP) technique. Although the special nature of the observations yields several challenges concerning data processing, we show that reasonable results for ZTD estimates can be obtained for all four analysed test cases by using different PPP processing strategies. Comparison with ZTD calculated from ERA5 reanalysis data yields a very high correlation and an overall agreement from the low millimetre-range up to 5 cm, depending on solution and analysed travelling track. We also present the first tests of assimilation into a numerical weather prediction (NWP) model which show the reasonable quality of the results as between 30-100 % of the observations are accepted by the model. Furthermore, we investigate means to transfer the developed ideas to an operational stage in order to exploit the huge benefits (horizontal/temporal resolution) of this special dataset for operational weather forecasting. </p>

scholarly journals A Regional NWP Tropospheric Delay Inversion Method Based on a General Regression Neural Network Model

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3167
Author(s):  
Lei Li ◽  
Ying Xu ◽  
Lizi Yan ◽  
Shengli Wang ◽  
Guolin Liu ◽  
...  
Keyword(s):  
Neural Network ◽  
Long Range ◽  
Meteorological Data ◽  
Weather Prediction ◽  
New Method ◽  
General Regression Neural Network ◽  
Inversion Method ◽  
Tropospheric Delay ◽  
Nwp Model ◽  
General Regression

Tropospheric delay is a major error source that affects the initialization and re-initialization speed of the Global Navigation Satellite System’s (GNSS) medium-/long-range baseline in Network Real-Time Kinematic (NRTK) positioning. Fusing the meteorological data from the Numerical Weather Prediction (NWP) model to estimate the zenith tropospheric delay (ZTD) is one of the current research hotspots. However, research has shown that the ZTD derived from NWP models is still not accurate enough for high-precision GNSS positioning applications without the estimation of the residual tropospheric delay. To date, General Regression Neural Network (GRNN) has been applied in many fields. It has a high learning speed and simple structure, and can approximate any function with arbitrary precision. In this study, we developed a regional NWP tropospheric delay inversion method based on a GRNN model to improve the accuracy of the tropospheric delay derived from the NWP model. The accuracy of the tropospheric delays derived from reanalysis data of the European Center for Medium-Range Weather Forecasts (ECMWF) and the US National Centers for Environmental Prediction (NCEP) was assessed through comparisons with the results of the International GPS Service (IGS). The variation characteristics of the residual of the ZTD inverted by NWP data were analyzed considering the factors of temperature, humidity, latitude, and season. To evaluate the performance of this new method, the National Center Atmospheric Research (NCAR) troposphere data of 650 stations in Japan in 2005 were collected as a reference to compare the accuracy of the ZTD before and after using the new method. The experimental results showed that the GRNN model has obvious advantages in fitting the NWP ZTD residual. The mean residual and the root mean square deviation (RMSD) of the ZTD inverted using the method of this study were 9.5 mm and 12.7 mm, respectively, showing reductions of 20.8% and 19.1%, respectively, as compared to the standard NWP model. For long-range baseline (155 km and 207 km), the corrected NWP-constrained RTK showed a reduction of over 43% in the initialization time compared with the standard RTK, and showed a reduction of over 24% in the initialization time compared with the standard NWP-constrained RTK.

scholarly journals Contrail study with ground-based cameras

2013 ◽  
Vol 6 (4) ◽  
pp. 7425-7472
Author(s):  
U. Schumann ◽  
R. Hempel ◽  
H. Flentje ◽  
M. Garhammer ◽  
K. Graf ◽  
...  
Keyword(s):  
Weather Prediction ◽  
Ambient Air ◽  
Lagrangian Model ◽  
Wake Vortex ◽  
The Moon ◽  
Movement Data ◽  
Different Types ◽  
Nwp Model ◽  
Better Than

Abstract. Photogrammetric methods and analysis results for contrails observed with wide-angle cameras are described. Four cameras of two different types (view angle < 90° or whole-sky imager) at the ground at various positions are used to track contrails and to derive their altitude, width, and horizontal speed. Camera models for both types are described to derive the observation angles for given image coordinates and their inverse. The models are calibrated with sightings of the Sun, the Moon and a few bright stars. The methods are applied and tested in a case study. Four persistent contrails crossing each other together with a short-lived one are observed with the cameras. Vertical and horizontal positions of the contrails are determined from the camera images to an accuracy of better than 200 m and horizontal speed to 0.2 m s−1. With this information, the aircraft causing the contrails are identified by comparison to traffic waypoint data. The observations are compared with synthetic camera pictures of contrails simulated with the contrail prediction model CoCiP, a Lagrangian model using air traffic movement data and numerical weather prediction (NWP) data as input. The results provide tests for the NWP and contrail models. The cameras show spreading and thickening contrails suggesting ice-supersaturation in the ambient air. The ice-supersaturated layer is found thicker and more humid in this case than predicted by the NWP model used. The simulated and observed contrail positions agree up to differences caused by uncertain wind data. The contrail widths, which depend on wake vortex spreading, ambient shear and turbulence, were partly wider than simulated.

scholarly journals Asymmetricity of ground-based GPS slant delay data

2007 ◽  
Vol 7 (12) ◽  
pp. 3143-3151 ◽  
Author(s):  
R. Eresmaa ◽  
H. Järvinen ◽  
S. Niemelä ◽  
K. Salonen
Keyword(s):  
Standard Deviation ◽  
Global Positioning System ◽  
Weather Prediction ◽  
Small Scale ◽  
Tropospheric Delay ◽  
Observation Error ◽  
Positioning System ◽  
Global Positioning ◽  
Nwp Model ◽  
Delay Component

Abstract. The ground-based measurements of the Global Positioning System (GPS) allow estimation of the tropospheric delay along the slanted signal paths through the atmosphere. The meteorological exploitation of such slant delay (SD) observations relies on the hypothesis of azimuthal asymmetry of the information content. This article addresses the validity of the hypothesis. A new concept of asymmetricity is introduced for studying the SD observations and their model counterparts. The asymmetricity is defined as the ratio of the absolute asymmetric delay component to total SD. The model counterparts are determined from 3-h forecasts of a numerical weather prediction (NWP) model, run with four different horizontal resolutions. The SD observations are compared with their model counterparts with emphasis on cases of high asymmetricity in order to see whether the observed asymmetry is a real atmospheric signature. The asymmetricity is found to be of the order of a few parts per thousand. Thus, the asymmetric delay component barely exceeds the assumed standard deviation of the SD observation error. However, the observed asymmetric delay components show a statistically significant meteorological signal. Benefit of the asymmetric SD observations is therefore expected to be taken in future, when NWP systems will explicitly represent the small-scale atmospheric features revealed by the SD observations.

scholarly journals Azimuthal asymmetry in ground-based GPS slant delay observations and their NWP model counterparts

2007 ◽  
Vol 7 (1) ◽  
pp. 3179-3202 ◽  
Author(s):  
R. Eresmaa ◽  
H. Järvinen ◽  
S. Niemelä ◽  
K. Salonen
Keyword(s):  
Global Positioning System ◽  
Weather Prediction ◽  
Azimuthal Asymmetry ◽  
Small Scale ◽  
Tropospheric Delay ◽  
Observation Error ◽  
Global Positioning ◽  
Nwp Model ◽  
Delay Component ◽  
High Asymmetry

Abstract. The ground-based measurements of the Global Positioning System (GPS) allow estimation of the tropospheric delay along the slanted signal paths through the atmosphere. The meteorological exploitation of such slant delay (SD) observations relies on the hypothesis of azimuthal asymmetry of the information content. This article addresses the validity of the hypothesis. The asymmetric properties of the SD observations and their model counterparts are investigated. In this study, the model counterparts are based on 3-h forecasts of a numerical weather prediction (NWP) model, run with four different horizontal resolutions. The SD observations are compared with their model counterparts with emphasis on cases of high asymmetry in order to see whether the observed asymmetry is a real atmospheric signature. The asymmetric delay component is found to be of the order of a few parts per thousand of the absolute SD value, thus barely exceeding the assumed standard deviation of the SD observation error. However, the observed asymmetric delay components show a statistically significant meteorological signal. Benefit of the asymmetric SD observations is therefore expected to be taken in future, when NWP systems will explicitly represent the small-scale atmospheric features revealed by the SD observations.

scholarly journals Contrail study with ground-based cameras

2013 ◽  
Vol 6 (12) ◽  
pp. 3597-3612 ◽  
Author(s):  
U. Schumann ◽  
R. Hempel ◽  
H. Flentje ◽  
M. Garhammer ◽  
K. Graf ◽  
...  
Keyword(s):  
Weather Prediction ◽  
Ambient Air ◽  
Lagrangian Model ◽  
Wake Vortex ◽  
The Moon ◽  
Movement Data ◽  
Different Types ◽  
Nwp Model ◽  
Better Than

Abstract. Photogrammetric methods and analysis results for contrails observed with wide-angle cameras are described. Four cameras of two different types (view angle < 90° or whole-sky imager) at the ground at various positions are used to track contrails and to derive their altitude, width, and horizontal speed. Camera models for both types are described to derive the observation angles for given image coordinates and their inverse. The models are calibrated with sightings of the Sun, the Moon and a few bright stars. The methods are applied and tested in a case study. Four persistent contrails crossing each other, together with a short-lived one, are observed with the cameras. Vertical and horizontal positions of the contrails are determined from the camera images to an accuracy of better than 230 m and horizontal speed to 0.2 m s−1. With this information, the aircraft causing the contrails are identified by comparison to traffic waypoint data. The observations are compared with synthetic camera pictures of contrails simulated with the contrail prediction model CoCiP, a Lagrangian model using air traffic movement data and numerical weather prediction (NWP) data as input. The results provide tests for the NWP and contrail models. The cameras show spreading and thickening contrails, suggesting ice-supersaturation in the ambient air. The ice-supersaturated layer is found thicker and more humid in this case than predicted by the NWP model used. The simulated and observed contrail positions agree up to differences caused by uncertain wind data. The contrail widths, which depend on wake vortex spreading, ambient shear and turbulence, were partly wider than simulated.

From InSAR derived relative tropospheric Slant Total Delay maps to absolute Zenith Total Delay maps: comparisons between tropospheric delay products to define a strategy for meteorological applications.

2020 ◽  
Author(s):  
Stefano Barindelli ◽  
Andrea Gatti ◽  
Martina Lagasio ◽  
Marco Manzoni ◽  
Alessandra Mascitelli ◽  
...  
Keyword(s):  
Positive Impact ◽  
Weather Prediction ◽  
Circulation Model ◽  
Tropospheric Delay ◽  
Total Delay ◽  
Zenith Total Delay ◽  
Iterative Interpolation ◽  
Physically Based ◽  
The Difference ◽  
Nwp Model

&lt;p&gt;InSAR derived Atmospheric Phase Screens (APSs) contain the difference between the atmospheric delay along the SAR sensor line-of-sight of two acquisition epochs: the slave and the master epochs. Using estimates of the atmospheric state at the master epoch, coming from independent sources, the APSs can be transformed into maps of tropospheric Zenith Total Delay (ZTD), that is related to the columnar atmospheric water vapor content. Assimilation experiments of such products into numerical weather prediction (NWP) models have shown a positive impact in the prediction of convective storms.&lt;/p&gt;&lt;p&gt;In this work, a systematical comparison between various APS and ZTD products aims at determining the optimal procedure to go from APSs to InSAR-derived absolute ZTD maps, i.e. to estimate the master delay map. Two different approaches are compared.&lt;/p&gt;&lt;p&gt;The first is based on a stack of ZTD maps produced with the assimilation of GNSS ZTD observations into an NWP model. This acts as a physically based interpolator of the GNSS values, which have a spatial resolution much coarser than the InSAR APS one.&lt;/p&gt;&lt;p&gt;The second is based on a stack of ZTD maps derived by an Iterative Tropospheric Decomposition (ITD) model, as implemented in the GACOS service. In this case, the high-resolution ZTD maps are obtained by an iterative interpolation of a global atmospheric circulation model values and GNSS values where available.&lt;/p&gt;&lt;p&gt;The results of the comparisons and sensitivity tests on the number of ZTD maps needed to derive the unknown master delay map are shown.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;

Quality Control and Verification of Weather Radar Wind Profiles

2005 ◽  
Vol 22 (10) ◽  
pp. 1541-1550 ◽  
Author(s):  
Iwan Holleman
Keyword(s):  
Quality Control ◽  
Weather Prediction ◽  
Weather Radar ◽  
Ground Level ◽  
Limited Area ◽  
Wind Profiles ◽  
Nwp Model ◽  
Radial Velocity Data ◽  
Better Than

Abstract Weather radar wind profiles (WRWPs) have been retrieved from Doppler volume scans using different implementations of the velocity–azimuth display (VAD) and volume velocity processing (VVP) methods. An extensive quality control of the radial velocity data and the retrieved wind vectors has been applied. The quality and availability of the obtained wind profiles have been assessed by comparisons with collocated radiosonde observations and numerical weather prediction (NWP) data over a 9-month period. The comparisons reveal that the VVP methods perform better than the VAD methods, and that the simplest implementation of the VVP (VVP1) method performs the best of all. The availability fraction of VVP1 wind vectors is about 0.39 at ground level and drops below 0.16 at a 6-km altitude. The observation minus background statistics of the VVP1 wind profiles against the High Resolution Limited Area Model (HIRLAM) NWP model are at least as good as those of the radiosonde profiles. This result clearly demonstrates the high quality of (quality controlled) weather radar wind profiles.

scholarly journals Global Assessment of the GNSS Single Point Positioning Biases Produced by the Residual Tropospheric Delay

2021 ◽  
Vol 13 (6) ◽  
pp. 1202
Author(s):  
Ling Yang ◽  
Jinfang Wang ◽  
Haojun Li ◽  
Timo Balz
Keyword(s):  
Single Point ◽  
Vertical Direction ◽  
Global Scale ◽  
Global Navigation Satellite Systems ◽  
Tropospheric Delay ◽  
Distributed Monitoring ◽  
International Gnss Service ◽  
Satellite Systems ◽  
Single Point Positioning ◽  
Point Positioning

The tropospheric delay is one of the main error sources that degrades the accuracy of Global Navigation Satellite Systems (GNSS) Single Point Positioning (SPP). Although an empirical model is usually applied for correction and thereby to improve the positioning accuracy, the residual tropospheric delay is still drowned in measurement noise, and cannot be further compensated by parameter estimation. How much this type of residual error would sway the SPP positioning solutions on a global scale are still unclear. In this paper, the biases on SPP solutions introduced by the residual tropospheric delay when using nine conventionally Zenith Tropospheric Delay (ZTD) models are analyzed and discussed, including Saastamoinen+norm/Global Pressure and Temperature (GPT)/GPT2/GPT2w/GPT3, University of New Brunswick (UNB)3/UNB3m, European Geostationary Navigation Overlay System (EGNOS) and Vienna Mapping Functions (VMF)3 models. The accuracies of the nine ZTD models, as well as the SPP biases caused by the residual ZTD (dZTD) after model correction are evaluated using International GNSS Service (IGS)-ZTD products from around 400 globally distributed monitoring stations. The seasonal, latitudinal, and altitudinal discrepancies are analyzed respectively. The results show that the SPP solution biases caused by the dZTD mainly occur on the vertical direction, nearly to decimeter level, and significant discrepancies are observed among different models at different geographical locations. This study provides references for the refinement and applications of the nine ZTD models for SPP users.

scholarly journals Initial Assessment of BDS PPP-B2b Service: Precision of Orbit and Clock Corrections, and PPP Performance

2021 ◽  
Vol 13 (11) ◽  
pp. 2050
Author(s):  
Zhixi Nie ◽  
Xiaofei Xu ◽  
Zhenjie Wang ◽  
Jun Du
Keyword(s):  
Global Navigation Satellite Systems ◽  
Convergence Time ◽  
Initial Assessment ◽  
Satellite Orbits ◽  
Navigation Satellite ◽  
Positioning Accuracy ◽  
Global Navigation ◽  
Kinematic Ppp ◽  
Global Navigation Satellite ◽  
Better Than

On 31 July 2020, the Beidou global navigation satellite system (BDS-3) was officially announced as being commissioned. In addition to offering global positioning, navigation, and timing (PNT) services, BDS-3 also provides precise point positioning (PPP) augmentation services. The satellite orbit correction, clock correction and code bias correction of BDS-3 and other global navigation satellite systems (GNSS) are broadcast by the BDS-3 geostationary earth orbit (GEO) satellites through the PPP-B2b signal. The PPP-B2b service is available for users in China and the surrounding area. In this study, an initial assessment of the PPP-B2b service is presented, with collected 3-day PPP-B2b messages. Based on broadcast ephemeris and PPP-B2b messages, the precise satellite orbits and clock offsets can be recovered. This precision is evaluated with the precise ephemeris from the GeoForschungsZentrum Potsdam (GFZ) analysis center as references. The results indicate that the accuracy of BDS-3 satellite orbits in the direction of radial, along-track, and cross-track is 0.138, 0.131, and 0.145 m, respectively, and for GPS a corresponding accuracy of 0.104, 0.160, and 0.134 m, respectively, could be obtained. The precision of clock offsets can reach a level of several centimeters for both GPS and BDS-3. Both the performance of static PPP and kinematic PPP are evaluated using the observations from four international GNSS monitoring assessment service (iGMAS) stations. Regarding static PPP, the average convergence time is 17.7 minutes to achieve a horizontal positioning accuracy of better than 0.3 m, and a vertical positioning accuracy of better than 0.6 m. The average positioning accuracy in the direction of east, north, and up-directions are 2.4, 1.6, and 2.3 cm. As to kinematic PPP, the average RMS values of positioning errors in the direction of east, north, and up are 8.1 cm, 3.6 cm, and 8.0 cm after full convergence.

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