A Case Study of the 3D Water Vapor Tomography Model Based on a Fast Voxel Traversal Algorithm for Ray Tracing

A fast voxel traversal algorithm for ray tracing was applied to build a 4 × 4 × 20 tomography model using the observation data of 11 ground-based Global Navigation Satellite System (GNSS) meteorology (GNSS/MET) stations in Hebei Province, China. The precipitation water vapor (PWV) observed at 05 a.m. (Universal Time Coordinated: UTC) on 10 December 2019, was used to reconstruct three-dimensional (3D) water vapor density fields over the test area. The tomographic results (GNSS_T) show that the water vapor density above this area is mainly below 25 g/m3 and is concentrated between the first to the fourth layers. The vertical distribution conforms to the exponential characteristics, while the horizontal distribution shows a decreasing trend from southwest to northeast. In addition, the results of the 0.25° grid dataset generated by the Global Forecast System (GFS) of the National Center for Environmental Forecasting (NCEP) (GFS_L) were interpolated to the height of the tomographic grid, which is in good agreement with the tomographic results. GFS_L is larger than GNSS_T on the first floor at the surface, with an average deviation of 0.19 g/m3. In contrast, GFS_L from the second floor to the top of the model is smaller than GNSS_T, with the average deviations distributed between −0.08 and −0.15 g/m3.

Download Full-text

A Method to Improve the Distribution of Observations in GNSS Water Vapor Tomography

Sensors ◽

10.3390/s18082526 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2526 ◽

Cited By ~ 8

Author(s):

Fei Yang ◽

Jiming Guo ◽

Junbo Shi ◽

Lv Zhou ◽

Yi Xu ◽

...

Keyword(s):

Water Vapor ◽

Precipitable Water ◽

Absolute Error ◽

Satellite System ◽

Observation Data ◽

Radiosonde Station ◽

Satellite Signal ◽

Comparative Results ◽

Global Navigation Satellite ◽

Vapor Distribution

Water vapor is an important driving factor in the related weather processes in the troposphere, and its temporal-spatial distribution and change are crucial to the formation of cloud and rainfall. Global Navigation Satellite System (GNSS) water vapor tomography, which can reconstruct the water vapor distribution using GNSS observation data, plays an increasingly important role in GNSS meteorology. In this paper, a method to improve the distribution of observations in GNSS water vapor tomography is proposed to overcome the problem of the relatively concentrated distribution of observations, enable satellite signal rays to penetrate more tomographic voxels, and improve the issue of overabundance of zero elements in a tomographic matrix. Numerical results indicate that the accuracy of the water vapor tomography is improved by the proposed method when the slant water vapor calculated by GAMIT is used as a reference. Comparative results of precipitable water vapor (PWV) and water vapor density (WVD) profiles from radiosonde station data indicate that the proposed method is superior to the conventional method in terms of the mean absolute error (MAE), standard deviations (STD), and root-mean-square error (RMS). Further discussion shows that the ill-condition of tomographic equation and the richness of data in the tomographic model need to be discussed separately.

Download Full-text

An improved pixel-based water vapor tomography model

Annales Geophysicae ◽

10.5194/angeo-37-89-2019 ◽

2019 ◽

Vol 37 (1) ◽

pp. 89-100

Author(s):

Yibin Yao ◽

Linyang Xin ◽

Qingzhi Zhao

Keyword(s):

Water Vapor ◽

Three Dimensional ◽

Satellite System ◽

Reference Station ◽

Weather Forecasts ◽

Satellite Positioning ◽

Optimal Polynomial ◽

Improved Model ◽

Global Navigation Satellite ◽

Gnss Data

Abstract. As an innovative use of Global Navigation Satellite System (GNSS), the GNSS water vapor tomography technique shows great potential in monitoring three-dimensional water vapor variation. Most of the previous studies employ the pixel-based method, i.e., dividing the troposphere space into finite voxels and considering water vapor in each voxel as constant. However, this method cannot reflect the variations in voxels and breaks the continuity of the troposphere. Moreover, in the pixel-based method, each voxel needs a parameter to represent the water vapor density, which means that huge numbers of parameters are needed to represent the water vapor field when the interested area is large and/or the expected resolution is high. In order to overcome the abovementioned problems, in this study, we propose an improved pixel-based water vapor tomography model, which uses layered optimal polynomial functions obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) by adaptive training for water vapor retrieval. Tomography experiments were carried out using the GNSS data collected from the Hong Kong Satellite Positioning Reference Station Network (SatRef) from 25 March to 25 April 2014 under different scenarios. The tomographic results are compared to the ECMWF data and validated by the radiosonde. Results show that the new model outperforms the traditional one by reducing the root-mean-square error (RMSE), and this improvement is more pronounced, at 5.88 % in voxels without the penetration of GNSS rays. The improved model also has advantages in more convenient expression.

Download Full-text

A New GNSS-Derived Water Vapor Tomography Method Based on Optimized Voxel for Large GNSS Network

Remote Sensing ◽

10.3390/rs12142306 ◽

2020 ◽

Vol 12 (14) ◽

pp. 2306 ◽

Cited By ~ 1

Author(s):

Yibin Yao ◽

Chen Liu ◽

Chaoqian Xu

Keyword(s):

Water Vapor ◽

Conventional Method ◽

Three Dimensional ◽

Absolute Error ◽

Satellite System ◽

Tomographic Method ◽

Tomography Method ◽

Gnss Network ◽

Global Navigation Satellite ◽

Gnss Networks

The Global Navigation Satellite System (GNSS) tomographic technique can be used for remote sensing of the three-dimensional water vapor (WV) distribution in the troposphere, which has attracted considerable interest. However, a significant problem in this technique is the excessive reliance on constraints (particularly in large GNSS networks). In this paper, we propose an improved tomographic method based on optimized voxel, which only considers the voxels passed by GNSS rays. The proposed method can completely prevent the tomographic algorithm interference of constraints that originated from empirical functions. Experiments in Nanjing in the periods of day-of-year (DOY) 182–184, 2019, and 244–246, 2019, show that the mean absolute error (MAE) and root mean square error (RMSE) of the WV density profile obtained using the proposed method are 0.9 and 1.3 g/m3, while those obtained using the conventional method are 1.3 and 1.8 g/m3, respectively, with respect to the radiosonde (RS) method. The numerical results show that the proposed method is reliable and has a superior accuracy to that of the conventional method.

Download Full-text

Kinematic orbit positioning applying the raw observation approach

10.5194/egusphere-egu2020-3470 ◽

2020 ◽

Author(s):

Barbara Suesser- Rechberger ◽

Torsten Mayer-Guerr ◽

Sandro Krauss

Keyword(s):

Three Dimensional ◽

Precise Orbit Determination ◽

Satellite Orbit ◽

Satellite System ◽

Low Earth Orbit ◽

Observation Data ◽

Kinematic Orbit ◽

Leo Satellites ◽

Least Squares Adjustment ◽

Global Navigation Satellite

<p>The kinematic strategy for precise orbit determination (POD) of low earth orbit (LEO) satellites uses only geometric observations to estimate the satellite orbit and does not take any forces into account. This strategy requires a large amount of observation data for one epoch to determine the three-dimensional satellite position. One possibility to get these data is the usage of the spaceborne global navigation satellite system (GNSS) technology, which provides a high number of accurate observations. Following Zehentner (2016) the kinematic orbit positioning applying the raw observation approach by using a least-squares adjustment has shown promising results with a high accuracy.</p><p>By applying this approach the kinematic orbits for several LEO satellite missions are estimated and subsequently validated by a comparison with state of the art gravity field solutions. Furthermore due to the fact that solar events causes an orbit decay, these precise determined orbit data are used to analyze solar event impacts on LEO satellites.</p>

Download Full-text

Water Vapor Retrievals from Spectral Direct Irradiance Measured with an EKO MS-711 Spectroradiometer—Intercomparison with Other Techniques

Remote Sensing ◽

10.3390/rs13030350 ◽

2021 ◽

Vol 13 (3) ◽

pp. 350

Author(s):

Rosa Delia García ◽

Emilio Cuevas ◽

Victoria Eugenia Cachorro ◽

Omaira E. García ◽

África Barreto ◽

...

Keyword(s):

Water Vapor ◽

Power Plants ◽

Precipitable Water ◽

Satellite System ◽

Infrared Spectrometry ◽

Radiative Balance ◽

Direct Normal Irradiance ◽

Routine Basis ◽

Solar Power Plants ◽

Global Navigation Satellite

Precipitable water vapor retrievals are of major importance for assessing and understanding atmospheric radiative balance and solar radiation resources. On that basis, this study presents the first PWV values measured with a novel EKO MS-711 grating spectroradiometer from direct normal irradiance in the spectral range between 930 and 960 nm at the Izaña Observatory (IZO, Spain) between April and December 2019. The expanded uncertainty of PWV (UPWV) was theoretically evaluated using the Monte-Carlo method, obtaining an averaged value of 0.37 ± 0.11 mm. The estimated uncertainty presents a clear dependence on PWV. For PWV ≤ 5 mm (62% of the data), the mean UPWV is 0.31 ± 0.07 mm, while for PWV > 5 mm (38% of the data) is 0.47 ± 0.08 mm. In addition, the EKO PWV retrievals were comprehensively compared against the PWV measurements from several reference techniques available at IZO, including meteorological radiosondes, Global Navigation Satellite System (GNSS), CIMEL-AERONET sun photometer and Fourier Transform Infrared spectrometry (FTIR). The EKO PWV values closely align with the above mentioned different techniques, providing a mean bias and standard deviation of −0.30 ± 0.89 mm, 0.02 ± 0.68 mm, −0.57 ± 0.68 mm, and 0.33 ± 0.59 mm, with respect to the RS92, GNSS, FTIR and CIMEL-AERONET, respectively. According to the theoretical analysis, MB decreases when comparing values for PWV > 5 mm, leading to a PWV MB between −0.45 mm (EKO vs. FTIR), and 0.11 mm (EKO vs. CIMEL-AERONET). These results confirm that the EKO MS-711 spectroradiometer is precise enough to provide reliable PWV data on a routine basis and, as a result, can complement existing ground-based PWV observations. The implementation of PWV measurements in a spectroradiometer increases the capabilities of these types of instruments to simultaneously obtain key parameters used in certain applications such as monitoring solar power plants performance.

Download Full-text

Modeling and Performance Evaluation of Precise Positioning and Time-Frequency Transfer with Galileo Five-Frequency Observations

Remote Sensing ◽

10.3390/rs13152972 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2972

Author(s):

Wei Xu ◽

Wen-Bin Shen ◽

Cheng-Hui Cai ◽

Li-Hong Li ◽

Lei Wang ◽

...

Keyword(s):

Three Dimensional ◽

Satellite Orbit ◽

Average Frequency ◽

Satellite System ◽

Observation Data ◽

Navigation Satellite ◽

Dual Frequency ◽

Time Frequency ◽

Combination Model ◽

Frequency Transfer

The present Global Navigation Satellite System (GNSS) can provide at least double-frequency observations, and especially the Galileo Navigation Satellite System (Galileo) can provide five-frequency observations for all constellation satellites. In this contribution, precision point positioning (PPP) models with Galileo E1, E5a, E5b, E5 and E6 frequency observations are established, including a dual-frequency (DF) ionospheric-free (IF) combination model, triple-frequency (TF) IF combination model, quad-frequency (QF) IF combination model, four five-frequency (FF) IF com-bination models and an FF uncombined (UC) model. The observation data of five stations for seven days are selected from the multi-GNSS experiment (MGEX) network, forming four time-frequency links ranging from 454.6 km to 5991.2 km. The positioning and time-frequency transfer performances of Galileo multi-frequency PPP are compared and evaluated using GBM (which denotes precise satellite orbit and clock bias products provided by Geo Forschung Zentrum (GFZ)), WUM (which denotes precise satellite orbit and clock bias products provided by Wuhan University (WHU)) and GRG (which denotes precise satellite orbit and clock bias products provided by the Centre National d’Etudes Spatiales (CNES)) precise products. The results show that the performances of the DF, TF, QF and FF PPP models are basically the same, the frequency stabilities of most links can reach sub10−16 level at 120,000 s, and the average three-dimensional (3D) root mean square (RMS) of position and average frequency stability (120,000 s) can reach 1.82 cm and 1.18 × 10−15, respectively. The differences of 3D RMS among all models are within 0.17 cm, and the differences in frequency stabilities (in 120,000 s) among all models are within 0.08 × 10−15. Using the GRG precise product, the solution performance is slightly better than that of the GBM or WUM precise product, the average 3D RMS values obtained using the WUM and GRG precise products are 1.85 cm and 1.77 cm, respectively, and the average frequency stabilities at 120,000 s can reach 1.13 × 10−15 and 1.06 × 10−15, respectively.

Download Full-text

Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference

Remote Sensing ◽

10.3390/rs12071170 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1170 ◽

Cited By ~ 3

Author(s):

Cintia Carbajal Henken ◽

Lisa Dirks ◽

Sandra Steinke ◽

Hannes Diedrich ◽

Thomas August ◽

...

Keyword(s):

Water Vapor ◽

Pairwise Comparison ◽

Weather Conditions ◽

Satellite System ◽

High Temporal Resolution ◽

Data Sets ◽

Frequency Distributions ◽

Temporal Sampling ◽

Global Navigation Satellite ◽

Satellite Instruments

Passive imagers on polar-orbiting satellites provide long-term, accurate integrated water vapor (IWV) data sets. However, these climatologies are affected by sampling biases. In Germany, a dense Global Navigation Satellite System network provides accurate IWV measurements not limited by weather conditions and with high temporal resolution. Therefore, they serve as a reference to assess the quality and sampling issues of IWV products from multiple satellite instruments that show different orbital and instrument characteristics. A direct pairwise comparison between one year of IWV data from GPS and satellite instruments reveals overall biases (in kg/m 2 ) of 1.77, 1.36, 1.11, and −0.31 for IASI, MIRS, MODIS, and MODIS-FUB, respectively. Computed monthly means show similar behaviors. No significant impact of averaging time and the low temporal sampling on aggregated satellite IWV data is found, mostly related to the noisy weather conditions in the German domain. In combination with SEVIRI cloud coverage, a change of shape of IWV frequency distributions towards a bi-modal distribution and loss of high IWV values are observed when limiting cases to daytime and clear sky. Overall, sampling affects mean IWV values only marginally, which are rather dominated by the overall retrieval bias, but can lead to significant changes in IWV frequency distributions.

Download Full-text

Online Near real-time Mine Disaster Monitoring System Based on Geosensor Networks

International Journal of Online Engineering (iJOE) ◽

10.3991/ijoe.v12i03.5450 ◽

2016 ◽

Vol 12 (03) ◽

pp. 64

Author(s):

Haifeng Hu

Keyword(s):

Real Time ◽

Monitoring System ◽

Satellite System ◽

Open Pit ◽

Observation Data ◽

Complex Data ◽

Disaster Monitoring ◽

Process Observation ◽

Global Navigation Satellite ◽

Safety And Stability

Abstract—An online automatic disaster monitoring system can reduce or prevent geological mine disasters to protect life and property. Global Navigation Satellite System receivers and the GeoRobot are two kinds of in-situ geosensors widely used for monitoring ground movements near mines. A combined monitoring solution is presented that integrates the advantages of both. In addition, a geosensor network system to be used for geological mine disaster monitoring is described. A complete online automatic mine disaster monitoring system including data transmission, data management, and complex data analysis is outlined. This paper proposes a novel overall architecture for mine disaster monitoring. This architecture can seamlessly integrate sensors for long-term, remote, and near real-time monitoring. In the architecture, three layers are used to collect, manage and process observation data. To demonstrate the applicability of the method, a system encompassing this architecture has been deployed to monitor the safety and stability of a slope at an open-pit mine in Inner Mongolia.

Download Full-text

A Joint Dual-Frequency GNSS/SINS Deep-Coupled Navigation System for Polar Navigation

Applied Sciences ◽

10.3390/app8112322 ◽

2018 ◽

Vol 8 (11) ◽

pp. 2322 ◽

Cited By ~ 2

Author(s):

Lin Zhao ◽

Mouyan Wu ◽

Jicheng Ding ◽

Yingyao Kang

Keyword(s):

Navigation System ◽

Density Ratio ◽

Satellite System ◽

The Arctic ◽

Observation Data ◽

Dual Frequency ◽

Vector Tracking ◽

Time Observation ◽

Global Navigation Satellite ◽

Navigation Accuracy

The strategic position of the polar area and its rich natural resources are becoming increasingly important, while the northeast and northwest passages through the Arctic are receiving much attention as glaciers continue to melt. The global navigation satellite system (GNSS) can provide real-time observation data for the polar areas, but may suffer low elevation problems of satellites, signals with poor carrier-power-to-noise-density ratio (C/N0), ionospheric scintillations, and dynamic requirements. In order to improve the navigation performance in polar areas, a deep-coupled navigation system with dual-frequency GNSS and a grid strapdown inertial navigation system (SINS) is proposed in the paper. The coverage and visibility of the GNSS constellation in polar areas are briefly reviewed firstly. Then, the joint dual-frequency vector tracking architecture of GNSS is designed with the aid of grid SINS information, which can optimize the tracking band, sharing tracking information to aid weak signal channels with strong signal channels and meet the dynamic requirement to improve the accuracy and robustness of the system. Besides this, the ionosphere-free combination of global positioning system (GPS) L1 C/A and L2 signals is used in the proposed system to further reduce ionospheric influence. Finally, the performance of the system is tested using a hardware simulator and semiphysical experiments. Experimental results indicate that the proposed system can obtain a better navigation accuracy and robust performance in polar areas.

Download Full-text

EGNOS Based APV Procedures Development Possibilities In The South-Eastern Part Of Poland

Annual of Navigation ◽

10.1515/aon-2015-0007 ◽

2014 ◽

Vol 21 (1) ◽

pp. 85-94 ◽

Cited By ~ 3

Author(s):

Wojciech Z. Kaleta

Keyword(s):

Three Dimensional ◽

Dimensional Accuracy ◽

Satellite System ◽

Civil Aviation ◽

The South ◽

South Eastern ◽

System Integrity ◽

New Instrument ◽

Global Navigation Satellite ◽

First Time

AbstractOn 14th and 15th March 2011 for the first time approach with vertical guidance (APV-I) was conducted on Polish territory in Katowice, Kraków and Mielec. This was the milestone for GNSS (Global Navigation Satellite System) and Area Navigation (RNAV) use as a new instrument approach chance for NPA (Non-Precision Approach) and PA (Precision Approach) in Poland. The paper presents the experiment study of EGNOS SIS (Signal in Space) due to APV (Approach with Vertical Guidance) procedures development possibilities in the south-eastern part of Poland. Researches were conducted from January 2014 till June 2014 in three Polish cities: Warszawa, Kraków and Rzeszów. EGNOS as SBAS (Satellite Based Augmentation System) in according with ICAO's Annex 10 has to meet restrictive requirements for three dimensional accuracy, system integrity, availability and continuity of SIS. Because of ECAC (European Civil Aviation Conference) states to EGNOS coverage in the eastern part of Europe, location of mention above stations, shows real usefulness for SIS tests and evaluation of the results [EUROCONTROL, 2008].

Download Full-text