Estimating the Impact of Global Navigation Satellite System Horizontal Delay Gradients in Variational Data Assimilation

Zus, Florian; Douša, Jan; Kačmařík, Michal; Václavovic, Pavel; Dick, Galina; Wickert, Jens

doi:10.3390/rs11010041

Cited by 27 publications

(19 citation statements)

References 29 publications

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“…Previous studies demonstrated that the estimation of tropospheric gradients improves GNSS data processing mainly in terms of receiver position and ZTDs (Chen and Herring, 1997;Bar-Sever et al, 1998;Rothacher and Beutler, 1998;Iwabuchi et al, 2003;Meindl et al, 2004). Nowadays, tropospheric gradients are not assimilated into NWMs; however, they could be assimilated in future (see Zus et al, 2019) and they are essential for reconstructing slant total delays (STDs). The STDs represent the signal travel time delay between the satellite and the station due to neutral atmosphere and they are considered useful in Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of GNSS tropospheric gradients to processing options

et al. 2019

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Abstract. An analysis of processing settings impacts on estimated tropospheric gradients is presented. The study is based on the benchmark data set collected within the COST GNSS4SWEC action with observations from 430 Global Navigation Satellite Systems (GNSS) reference stations in central Europe for May and June 2013. Tropospheric gradients were estimated in eight different variants of GNSS data processing using precise point positioning (PPP) with the G-Nut/Tefnut software. The impacts of the gradient mapping function, elevation cut-off angle, GNSS constellation, observation elevation-dependent weighting and real-time versus post-processing mode were assessed by comparing the variants by each to other and by evaluating them with respect to tropospheric gradients derived from two numerical weather models (NWMs). Tropospheric gradients estimated in post-processing GNSS solutions using final products were in good agreement with NWM outputs. The quality of high-resolution gradients estimated in (near-)real-time PPP analysis still remains a challenging task due to the quality of the real-time orbit and clock corrections. Comparisons of GNSS and NWM gradients suggest the 3∘ elevation angle cut-off and GPS+GLONASS constellation for obtaining optimal gradient estimates provided precise models for antenna-phase centre offsets and variations, and tropospheric mapping functions are applied for low-elevation observations. Finally, systematic errors can affect the gradient components solely due to the use of different gradient mapping functions, and still depending on observation elevation-dependent weighting. A latitudinal tilting of the troposphere in a global scale causes a systematic difference of up to 0.3 mm in the north-gradient component, while large local gradients, usually pointing in a direction of increasing humidity, can cause differences of up to 1.0 mm (or even more in extreme cases) in any component depending on the actual direction of the gradient. Although the Bar-Sever gradient mapping function provided slightly better results in some aspects, it is not possible to give any strong recommendation on the gradient mapping function selection.

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Section: Introductionmentioning

confidence: 99%

Sensitivity of GNSS tropospheric gradients to processing options

et al. 2019

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“…To remove hydrostatic gradients from all slant delays, for each GNSS satellite in view, the ray‐traced hydrostatic delays were computed. For compensation of the isotropic part, the additional ray‐traced delays were determined for the same elevation angle but equidistant azimuth angles separated by 30° (Landskron & Böhm, 2018; Zus et al, 2019). The mean value of the delay was then calculated and removed.…”

Section: Gnss Tomographymentioning

confidence: 99%

TOMOREF Operator for Assimilation of GNSS Tomography Wet Refractivity Fields in WRF DA System

et al. 2020

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Global Navigation Satellite System (GNSS) tomography is a technique that aims to obtain a 3‐D field of humidity in the troposphere. It is based on observations of GNSS signal delays between satellites and ground‐based receivers. The technique has been developed in recent years, showing positive results in the monitoring of severe weather events. The previous studies on assimilation into the numerical weather prediction models are based on available observation operators which are not adjusted to the GNSS tomography data. In this study, we demonstrate an observation operator TOMOREF dedicated to the assimilation of the GNSS tomography‐derived 3‐D fields of wet refractivity in a Weather Research and Forecasting (WRF) Data Assimilation (DA) system. The new tool has been tested based on wet refractivity fields derived during a heavy precipitation event. The results were validated using radiosonde observations, synoptic data, ERA5 reanalysis, and radar data. In the presented experiment, a positive impact of the GNSS tomography data assimilation on the forecast of relative humidity (RH) has been noticed (an improvement of root‐mean‐square error up to 0.5%). Moreover, the validation of the precipitation forecasts reveals the positive impact of the GNSS data assimilation within 1 hr after assimilation (the mean bias values are reduced up to 0.1 mm). Additionally, it was observed that assimilation of GNSS tomography data has a greater influence on the WRF model than the Zenith Total Delay (ZTD) observations, which proves the potential of the GNSS tomography data for weather forecasting.

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“…GNSS tropospheric estimates are an invaluable commodity for meteorological and climate studies (e.g., Alshawaf et al, 2018;Balidakis et al, 2018) as well as operational weather forecast (Gendt et al, 2004;Guerova et al, 2016;Zus et al, 2019a;Zus et al, 2019b). The frequency of severe weather events increases, as a repercussion of global warming (e.g., Kharin et al, 2018); hence the ability of GNSS observing systems should be adapted to cope with this increased need for accuracy.…”

Section: Coherent Communicationsmentioning

confidence: 99%

Advanced technologies for satellite navigation and geodesy

Giorgi

Schmidt

Trainotti

et al. 2019

Advances in Space Research

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This manuscript reviews recent progress in optical frequency references and optical communication systems and discusses their utilizations in global satellite navigation systems and satellite geodesy. Lasers stabilized with optical cavities or spectroscopy of molecular iodine are analyzed, and a hybrid architecture is proposed to combine both forms of stabilization with the aim of achieving a target frequency stability of 10 -15 [s/s] over a wide range of sampling intervals.The synchronization between two optical frequency references in real-time is realized by means of time and frequency transfer on optical carriers. The technologies enabling coherent optical links are reviewed, and the development of an optical communication system for synchronization, ranging and data communication in space is described. An infrastructure exploiting the capabilities of both optical technologies for the realization of a modernized constellation of navigation satellites emitting highly synchronized signals is reviewed. Such infrastructure, named Kepler system, improves satellite navigation in terms intra-system synchronization, orbit determination accuracy, as well as system monitoring and integrity. The potential impact on geodetic key parameters is addressed.

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Estimating the Impact of Global Navigation Satellite System Horizontal Delay Gradients in Variational Data Assimilation

Cited by 27 publications

References 29 publications

Sensitivity of GNSS tropospheric gradients to processing options

Sensitivity of GNSS tropospheric gradients to processing options

TOMOREF Operator for Assimilation of GNSS Tomography Wet Refractivity Fields in WRF DA System

Advanced technologies for satellite navigation and geodesy

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