scholarly journals Comparative Studies for the Assessment of the Quality of Near-Real-Time GPS-Derived Atmospheric Parameters

2008 ◽  
Vol 25 (5) ◽  
pp. 701-714 ◽  
Author(s):  
R. Pacione ◽  
F. Vespe

Abstract Accurate and frequent sampling of atmospheric parameters, such as water vapor, is important for enabling reliable weather forecasts and global climate studies over a wide range of spatial and temporal scales. Recent developments in global positioning system data processing have allowed the estimation of zenith total delay (ZTD), the delay of the neutral atmosphere, with a high degree of accuracy using continuously operating GPS networks. From this delay integrated water vapor can be derived by means of additional meteorological information, in particular observed pressure or numerical weather prediction model pressure. Comparisons with other independent techniques must be performed to evaluate the quality of atmospheric parameters directly estimated or retrieved from the GPS system. In this work the accuracy of GPS atmospheric parameter, namely, zenith total delay, delivered in near–real time from a European ground-based network of permanent GPS receivers has been assessed. It is compared to other GPS solutions, radiosonde profiles, and High-Resolution Limited-Area Model (HIRLAM)-derived ZTD. Intercomparisons between results from different GPS analysis centers in the framework of the Targeting Optimal Use of GPS Humidity Measurements in Meteorology (TOUGH) project show a mean ZTD station bias at the level of ±6 mm with a related standard deviation of about 7–8 mm. In the comparison with radiosondes, an overall ZTD bias of about 7 mm with a standard deviation of 9 mm is detected. Finally, the comparison of ZTD near–real time against the HIRLAM models has an average bias of about −4.8 mm and a standard deviation of 11.5 mm.

2009 ◽  
Vol 48 (7) ◽  
pp. 1302-1316 ◽  
Author(s):  
Siebren de Haan ◽  
Iwan Holleman ◽  
Albert A. M. Holtslag

Abstract In this paper the construction of real-time integrated water vapor (IWV) maps from a surface network of global positioning system (GPS) receivers is presented. The IWV maps are constructed using a two-dimensional variational technique with a persistence background that is 15 min old. The background error covariances are determined using a novel two-step method, which is based on the Hollingsworth–Lonnberg method. The quality of these maps is assessed by comparison with radiosonde observations and IWV maps from a numerical weather prediction (NWP) model. The analyzed GPS IWV maps have no bias against radiosonde observations and a small bias against NWP analysis and forecasts up to 9 h. The standard deviation with radiosonde observations is around 2 kg m−2, and the standard deviation with NWP increases with increasing forecast length (from 2 kg m−2 for the NWP analysis to 4 kg m−2 for a forecast length of 48 h). To illustrate the additional value of these real-time products for nowcasting, three thunderstorm cases are discussed. The constructed GPS IWV maps are combined with data from the weather radar, a lightning detection network, and surface wind observations. All cases show that the location of developing thunderstorms can be identified 2 h prior to initiation in the convergence of moist air.


2021 ◽  
Vol 13 (11) ◽  
pp. 2179
Author(s):  
Pedro Mateus ◽  
Virgílio B. Mendes ◽  
Sandra M. Plecha

The neutral atmospheric delay is one of the major error sources in Space Geodesy techniques such as Global Navigation Satellite Systems (GNSS), and its modeling for high accuracy applications can be challenging. Improving the modeling of the atmospheric delays (hydrostatic and non-hydrostatic) also leads to a more accurate and precise precipitable water vapor estimation (PWV), mostly in real-time applications, where models play an important role, since numerical weather prediction models cannot be used for real-time processing or forecasting. This study developed an improved version of the Hourly Global Pressure and Temperature (HGPT) model, the HGPT2. It is based on 20 years of ERA5 reanalysis data at full spatial (0.25° × 0.25°) and temporal resolution (1-h). Apart from surface air temperature, surface pressure, zenith hydrostatic delay, and weighted mean temperature, the updated model also provides information regarding the relative humidity, zenith non-hydrostatic delay, and precipitable water vapor. The HGPT2 is based on the time-segmentation concept and uses the annual, semi-annual, and quarterly periodicities to calculate the relative humidity anywhere on the Earth’s surface. Data from 282 moisture sensors located close to GNSS stations during 1 year (2020) were used to assess the model coefficients. The HGPT2 meteorological parameters were used to process 35 GNSS sites belonging to the International GNSS Service (IGS) using the GAMIT/GLOBK software package. Results show a decreased root-mean-square error (RMSE) and bias values relative to the most used zenith delay models, with a significant impact on the height component. The HGPT2 was developed to be applied in the most diverse areas that can significantly benefit from an ERA5 full-resolution model.


2021 ◽  
Author(s):  
Tomasz Hadas ◽  
Grzegorz Marut ◽  
Jan Kapłon ◽  
Witold Rohm

<p>The dynamics of water vapor distribution in the troposphere, measured with Global Navigation Satellite Systems (GNSS), is a subject of weather research and climate studies. With GNSS, remote sensing of the troposphere in Europe is performed continuously and operationally under the E-GVAP (http://egvap.dmi.dk/) program with more than 2000 permanent stations. These data are one of the assimilation system component of mesoscale weather prediction models (10 km scale) for many nations across Europe. However, advancing precise local forecasts for severe weather requires high resolution models and observing system.   Further densification of the tracking network, e.g. in urban or mountain areas, will be costly when considering geodetic-grade equipment. However, the rapid development of GNSS-based applications results in a dynamic release of mass-market GNSS receivers. It has been demonstrated that post-processing of GPS-data from a dual-frequency low-cost receiver allows retrieving ZTD with high accuracy. Although low-cost receivers are a promising solution to the problem of densifying GNSS networks for water vapor monitoring, there are still some technological limitations and they require further development and calibration.</p><p>We have developed a low-cost GNSS station, dedicated to real-time GNSS meteorology, which provides GPS, GLONASS and Galileo dual-frequency observations either in RINEX v3.04 format or via RTCM v3.3 stream, with either Ethernet or GSM data transmission. The first two units are deployed in a close vicinity of permanent station WROC, which belongs to the International GNSS Service (IGS) network. Therefore, we compare results from real-time and near real-time processing of GNSS observations from a low-cost unit with IGS Final products. We also investigate the impact of replacing a standard patch antenna with an inexpensive survey-grade antenna. Finally, we deploy a local network of low-cost receivers in and around the city of Wroclaw, Poland, in order to analyze the dynamics of troposphere delay at a very high spatial resolution.</p><p>As a measure of accuracy, we use the standard deviation of ZTD differences between estimated ZTD and IGS Final product. For the near real-time mode, that accuracy is 5 mm and 6 mm, for single- (L1) and dual-frequency (L1/L5,E5b) solution, respectively. Lower accuracy of the dual-frequency relative solution we justify by the missing antenna phase center correction model for L5 and E5b frequencies. With the real-time Precise Point Positioning technique, we estimate ZTD with the accuracy of 7.5 – 8.6 mm. After antenna replacement, the accuracy is improved almost by a factor of 2 (to 4.1 mm), which is close to the 3.1 mm accuracy which we obtain in real-time using data from the WROC station.</p>


Author(s):  
Mohannad Alahmadi ◽  
Peter Pocta ◽  
Hugh Melvin

Web Real-Time Communication (WebRTC) combines a set of standards and technologies to enable high-quality audio, video, and auxiliary data exchange in web browsers and mobile applications. It enables peer-to-peer multimedia sessions over IP networks without the need for additional plugins. The Opus codec, which is deployed as the default audio codec for speech and music streaming in WebRTC, supports a wide range of bitrates. This range of bitrates covers narrowband, wideband, and super-wideband up to fullband bandwidths. Users of IP-based telephony always demand high-quality audio. In addition to users’ expectation, their emotional state, content type, and many other psychological factors; network quality of service; and distortions introduced at the end terminals could determine their quality of experience. To measure the quality experienced by the end user for voice transmission service, the E-model standardized in the ITU-T Rec. G.107 (a narrowband version), ITU-T Rec. G.107.1 (a wideband version), and the most recent ITU-T Rec. G.107.2 extension for the super-wideband E-model can be used. In this work, we present a quality of experience model built on the E-model to measure the impact of coding and packet loss to assess the quality perceived by the end user in WebRTC speech applications. Based on the computed Mean Opinion Score, a real-time adaptive codec parameter switching mechanism is used to switch to the most optimum codec bitrate under the present network conditions. We present the evaluation results to show the effectiveness of the proposed approach when compared with the default codec configuration in WebRTC.


2004 ◽  
Vol 82 (1B) ◽  
pp. 361-370 ◽  
Author(s):  
Gerd GENDT ◽  
Galina DICK ◽  
Christoph REIGBER ◽  
Maria TOMASSINI ◽  
Yanxiong LIU ◽  
...  

2014 ◽  
Vol 577 ◽  
pp. 1189-1192
Author(s):  
Hai Shen Wang ◽  
Chuang Shi ◽  
Yun Chang Cao

In this article, data of stations distributed over China was used to calculate tropospheric delay. The result was compared with the tropospheric zenith delay calculated from model. The rules and Characteristic of tropospheric delay over China was analyzed from the aspect of altitude, climate, and change. The results showed that the tropospheric zenith total delay decreased from the coast to the central and western regions, the Tibetan plateau is minimum. Zenith wet delays computed from the models also show an absolute bias of over 20 mm with respect to that of sounding data. The standard deviation is more than 30 mm in the tropical monsoon zone.


2020 ◽  
Author(s):  
◽  
Juan Manuel Aragón Paz

En el presente trabajo de tesis se desarrolla el diseño e implementación de un sistema de cálculo, en tiempo casi real, de parámetros troposféricos mediante técnicas de navegación global por satélite (GNSS, del inglés Global Navigation Satellite System) para Sudamérica. El desarrollo de la llamada Meteorología GNSS se remonta a principios de la década del 90 donde se encuentran los trabajos fundacionales de esta disciplina. Con el correr de los años, nuevas contribuciones han ido definiendo los reales alcances de esta técnica, poniendo en práctica metodologías cada vez más contrastadas con los métodos de medición tradicionales. En los últimos años los esfuerzos se han enfocado en el desarrollo de procedimientos de cálculo que permitan la utilización de los datos GNSS, cada vez más numerosos, en la asimilación para modelos meteorológicos (en especial los de corto plazo), permitiendo así anticipar eventos con alto impacto a la sociedad civil (tormentas con granizo, inundaciones repentinas, eventos convectivos de mesoescala, etc). Numerosos trabajos se han centrado en la implementación de la meteorología GNSS en Europa, Estados Unidos y Japón. Para la región Sudamericana existen pocos y recientes antecedentes de la aplicación de estas metodologías. Se desarrolló un sistema de cálculo, que permite hacer uso de infraestructura existente en la región, tanto meteorológica como geodésica, enfocado en la obtención de las variables de interés meteorológico como son el retardo troposférico cenital (ZTD, del inglés Zenith Total Delay) y el vapor de agua integrado (IWV, del inglés Integrated Water Vapor). Por otra parte, se han realizado estudios en la aplicación del ZTD y el IWV a índices que permitan dar información rápida acerca de posibles eventos meteorológicos severos. En este trabajo se desarrollan las estrategias diseñadas para la adquisición de los datos, su disponibilidad y alcance. Las problemáticas en la disponibilidad de los mismos, de acuerdo a su procedencia, son descriptas y sorteadas. Seguidamente se brinda una detallada descripción de la metodología de estimación de las observaciones, haciendo especial foco en los parámetros de retardo troposférico cenital (ZTD, del ingles Zenith Tropospheric Delay) y vapor de agua integrado (IWV, del inglés Integrated Water Vapor) mediante el procesamiento de las observaciones GNSS y meteorológicas. Una vez que se tienen los resultados, la presentación de los mismos y los posibles formato de intercambio con las instituciones potenciales usuarias del dato son discutidos. Finalizando esta sección se hace un análisis de la performance del sistema de procesamiento contra las técnicas de radio sondeo (convencionales) y alguno de los modelos de reanálisis mas utilizados. En una segunda etapa se explora las distintas capacidades del IWV GNSS para representar las variaciones temporales y espaciales de la distribución del vapor de agua atmosférico frente a distintas situaciones meteorológicas. También, se describe el desarrollo de posibles índices de alerta que hagan utilización de la información disponible a partir del IWV GNSS. Basándose en bibliografía actualizada se comparan las distintas posibilidades de aplicación a la región de estudio en función de la frecuencia temporal y espacial de las observaciones. Los resultados son presentados analizando un evento de interés meteorológico para la región central de Argentina. Finalmente, los puntos mas salientes del presente trabajo son presentados en las conclusiones. Las mismas abarcan desde el sistema de descarga de datos hasta la implementación de los índices de alerta. Se formulan las posibles derivaciones del trabajo y sus implicancias en la mejora continua de este sistema, que en tiempo casi real, provee información sobre los parámetros de ZTD e IWV. Una sección final describe cuáles son las recomendaciones que permitirían mejoras en la utilización de los datos provistos para conseguir un máximo aprovechamiento de los mismos.


2012 ◽  
Vol 140 (8) ◽  
pp. 2706-2719 ◽  
Author(s):  
Gemma V. Bennitt ◽  
Adrian Jupp

Abstract Zenith total delay (ZTD) observations derived from ground-based GPS receivers have been assimilated operationally into the Met Office North Atlantic and European (NAE) numerical weather prediction (NWP) model since 2007. Assimilation trials were performed using the Met Office NAE NWP model at both 12- and 24-km resolution to assess the impact of ZTDs on forecasts. ZTDs were found generally to increase relative humidity in the analysis, increasing the humidity bias compared to radiosonde observations, which persisted through the forecasts at some vertical levels. Improvements to cloud forecasts were also identified. Assimilation of ZTDs using both three-dimensional and four-dimensional variational data assimilation (3D-Var/4D-Var) was investigated, and it is found that assimilation at 4D-Var does not deliver any clear benefit over 3D-Var in the periods studied with the NAE model. This paper summarizes the methods used to assimilate ZTDs at the Met Office and presents the results of impact trials performed prior to operational assimilation. Future improvements to the assimilation methods are discussed.


2016 ◽  
Vol 97 (11) ◽  
pp. 2149-2161 ◽  
Author(s):  
Bruce Ingleby ◽  
Patricia Pauley ◽  
Alexander Kats ◽  
Jeff Ator ◽  
Dennis Keyser ◽  
...  

Abstract Some real-time radiosonde reports are now available with higher vertical resolution and higher precision than the alphanumeric TEMP code. There are also extra metadata; for example, the software version may indicate whether humidity corrections have been applied at the station. Numerical weather prediction (NWP) centers and other users need to start using the new Binary Universal Form for Representation of Meteorological Data (BUFR) reports because the alphanumeric codes are being withdrawn. TEMP code has various restrictions and complexities introduced when telecommunication speed and costs were overriding concerns; one consequence is minor temperature rounding errors. In some ways BUFR reports are simpler: the whole ascent should be contained in a single report. BUFR reports can also include the time and location of each level; an ascent takes about 2 h and the balloon can drift 100 km or more laterally. This modernization is the largest and most complex change to the worldwide reporting of radiosonde observations for many years; international implementation is taking longer than planned and is very uneven. The change brings both opportunities and challenges. The biggest challenge is that the number and quality of the data from radiosonde ascents may suffer if the assessment of the BUFR reports and two-way communication between data producers and data users are not given the priority they require. It is possible that some countries will only attempt to replicate the old reports in the new format, not taking advantage of the benefits, which include easier treatment of radiosonde drift and a better understanding of instrument and processing details, as well as higher resolution.


2018 ◽  
Vol 11 (2) ◽  
pp. 819-833 ◽  
Author(s):  
Weihua Bai ◽  
Congliang Liu ◽  
Xiangguang Meng ◽  
Yueqiang Sun ◽  
Gottfried Kirchengast ◽  
...  

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new-generation payloads onboard the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. The GNOS was designed for acquiring setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou System (BDS) and the US Global Positioning System (GPS). An ultra-stable oscillator with 1 s stability (Allan deviation) at the level of 10−12 was installed on the FY-3C GNOS, and thus both zero-difference and single-difference excess phase processing methods should be feasible for FY-3C GNOS observations. In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing, in order to investigate the zero-difference feasibility for this new instrument, which after its launch in September 2013 started to use BDS signals from five geostationary orbit (GEO) satellites, five inclined geosynchronous orbit (IGSO) satellites and four medium Earth orbit (MEO) satellites. We used a 3-month set of GNOS BDS RO data (October to December 2013) for the evaluation and compared atmospheric bending angle and refractivity profiles, derived from single- and zero-difference excess phase data, against co-located profiles from European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. We also compared against co-located refractivity profiles from radiosondes. The statistical evaluation against these reference data shows that the results from single- and zero-difference processing are reasonably consistent in both bias and standard deviation, clearly demonstrating the feasibility of zero differencing for GNOS BDS RO observations. The average bias (and standard deviation) of the bending angle and refractivity profiles were found to be about 0.05 to 0.2 % (and 0.7 to 1.6 %) over the upper troposphere and lower stratosphere. Zero differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. The validation results indicate that GNOS can provide, on top of GPS RO profiles, accurate and precise BDS RO profiles both from single- and zero-difference processing. The GNOS observations by the series of FY-3 satellites are thus expected to provide important contributions to numerical weather prediction and global climate change analysis.


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