scholarly journals Thunderstorm Classification Functions Based on Instability Indices and GNSS IWV for the Sofia Plain

2019 ◽  
Vol 11 (24) ◽  
pp. 2988 ◽  
Author(s):  
Guergana Guerova ◽  
Tsvetelina Dimitrova ◽  
Stefan Georgiev
Keyword(s):  
Satellite System ◽  
Probability Of Detection ◽  
Radiosonde Data ◽  
Lightning Flash ◽  
Path Delay ◽  
Statistical Regression ◽  
Period Analysis ◽  
Supercell Thunderstorm ◽  
Global Navigation Satellite ◽  
Instability Indices

Bulgaria is a country with a high frequency of hail and thunderstorms from May to September. For the May–September 2010–2015 period, statistical regression analysis was applied to identify predictors/classification functions that contribute skills to thunderstorm forecasting in the Sofia plain. The functions are based on (1) instability indices computed from radiosonde data from Sofia station F1, and (2) combination of instability indices and Integrated Water Vapor (IWV), derived from the Global Navigation Satellite System (GNSS) station Sofia-Plana, F2. Analysis of the probability of detection and the false alarm ratio scores showed the superiority of the F2 classification function, with the best performance in May, followed by June and September. F1 and F2 scores were computed for independent data samples in the period 2017–2018 and confirmed the findings for the 2010–2015 period. Analysis of IWV and lightning flash rates for a multicell and supercell thunderstorm in June and July 2014 showed that the monthly IWV thresholds are reached 14.5 and 3.5 hours before the thunderstorm, respectively. The supercell IWV peak registered 40 min before the thunderstorm, followed by a local IWV minimum corresponding to a peak in the flash rate. In both cases, an increase of IWV during severe hail was registered, which is likely related to the hydrometeor contribution to GNSS path delay. The results of this study will be integrated into the Bulgarian Integrated NowCAsting tool for thunderstorm forecasting in the warm/convective season.

Thunderstorm Classification Functions Based on Instability Indices and GNSS IWV for the Sofia Plain

2021 ◽  
Author(s):  
Guergana Guerova ◽  
Tsvetelina Dimitrova ◽  
Stefan Georgiev
Keyword(s):  
Satellite System ◽  
Probability Of Detection ◽  
Radiosonde Data ◽  
Lightning Flash ◽  
Path Delay ◽  
Statistical Regression ◽  
Period Analysis ◽  
Supercell Thunderstorm ◽  
Global Navigation Satellite ◽  
Instability Indices

<p>Bulgaria is a country with a high frequency of hail and thunderstorms from May to September. For the May–September 2010–2015 period, statistical regression analysis was applied to identify predictors/classification functions that contribute skills to thunderstorm forecasting in the Sofia plain. The functions are based on (1) instability indices computed from radiosonde data from Sofia station F1, and (2) combination of instability indices and Integrated Water Vapor (IWV), derived from the Global Navigation Satellite System (GNSS) station Sofia-Plana, F2. Analysis of the probability of detection and the false alarm ratio scores showed the superiority of the F2 classification function, with the best performance in May, followed by June and September. F1 and F2 scores were computed for independent data samples in the period 2017–2018 and confirmed the findings for the 2010–2015 period. Analysis of IWV and lightning flash rates for a multicell and supercell thunderstorm in June and July 2014 showed that the monthly IWV thresholds are reached 14.5 and 3.5 hours before the thunderstorm, respectively. The supercell IWV peak registered 40 min before the thunderstorm, followed by a local IWV minimum corresponding to a peak in the flash rate. In both cases, an increase of IWV during severe hail was registered, which is likely related to the hydrometeor contribution to GNSS path delay. The results of this study will be integrated into the Bulgarian Integrated NowCAsting tool for thunderstorm forecasting in the warm/convective season.</p>

scholarly journals FFT Splitting for Improved FPGA-Based Acquisition of GNSS Signals

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Jérôme Leclère ◽  
Cyril Botteron ◽  
René Jr. Landry ◽  
Pierre-André Farine
Keyword(s):  
Processing Time ◽  
Satellite System ◽  
Fpga Implementation ◽  
Probability Of Detection ◽  
Navigation Satellite ◽  
Code Search ◽  
Parallel Code ◽  
Memory Reduction ◽  
Straightforward Solution ◽  
Global Navigation Satellite

With modern global navigation satellite system (GNSS) signals, the FFT-based parallel code search acquisition must handle the frequent sign transitions due to the data or the secondary code. There is a straightforward solution to this problem, which consists in doubling the length of the FFTs, leading to a significant increase of the complexity. The authors already proposed a method to reduce the complexity without impairing the probability of detection. In particular, this led to a 50% memory reduction for an FPGA implementation. In this paper, the authors propose another approach, namely, the splitting of a large FFT into three or five smaller FFTs, providing better performances and higher flexibility. For an FPGA implementation, compared to the previously proposed approach, at the expense of a slight increase of the logic and multiplier resources, the splitting into three and five allows, respectively, a reduction of 40% and 64% of the memory, and of 25% and 37.5% of the processing time. Moreover, with the splitting into three FFTs, the algorithm is applicable for sampling frequencies up to 24.576 MHz for L5 band signals, against 21.846 MHz with the previously proposed algorithm. The algorithm is applied here to the GPS L5 and Galileo E5a, E5b, and E1 signals.

scholarly journals Comparing Winds near Tropical Oceanic Precipitation Systems with and without Lightning

2020 ◽  
Vol 12 (23) ◽  
pp. 3968
Author(s):  
Timothy J. Lang
Keyword(s):  
Satellite System ◽  
Lightning Flash ◽  
Wind Speeds ◽  
Tropical Oceans ◽  
Ocean Winds ◽  
The Difference ◽  
Microphysical Processes ◽  
Global Navigation Satellite ◽  
Matching Criteria ◽  
Rain Rates

In order to examine how robust updraft strength and ice-based microphysical processes aloft in storms may affect convective outflows near the surface, ocean winds were compared between tropical maritime precipitation systems with and without lightning. The analysis focused on Cyclone Global Navigation Satellite System (CYGNSS) specular point tracks, using straightforward spatiotemporal matching criteria to pair CYGNSS-measured wind speeds with satellite-based precipitation observations, Advanced Scatterometer (ASCAT) wind speeds, and lightning flash data from ground-based and space-based sensors. Based on the results, thunderstorms over the tropical oceans are associated with significantly heavier rain rates (~200% greater) than non-thunderstorms. However, wind speeds near either type of precipitation system do not differ much (~0.5 m s−1 or less). Moreover, the sign of the difference depends on the wind instrument used, with CYGNSS suggesting non-thunderstorm winds are slightly stronger, while ASCAT suggests the opposite. These observed wind differences are likely related to lingering uncertainties between CYGNSS and ASCAT measurements in precipitation. However, both CYGNSS and ASCAT observe winds near precipitation (whether lightning-producing or not) to be stronger than background winds by at least 1 m s−1.

scholarly journals A Tropospheric Tomography Method with a Novel Height Factor Model Including Two Parts: Isotropic and Anisotropic Height Factors

2020 ◽  
Vol 12 (11) ◽  
pp. 1848 ◽  
Author(s):  
Wenyuan Zhang ◽  
Shubi Zhang ◽  
Nan Ding ◽  
Qingzhi Zhao
Keyword(s):  
Water Vapor ◽  
Factor Model ◽  
Traditional Approach ◽  
Satellite System ◽  
Spatiotemporal Variability ◽  
Radiosonde Data ◽  
Key Factor ◽  
Improved Model ◽  
Global Navigation Satellite ◽  
Height Factor

Global Navigation Satellite System (GNSS) tomography has developed into an efficient tool for sensing the high spatiotemporal variability of atmospheric water vapor. The integration of GNSS top signals and side rays for tropospheric tomography systems using a novel height factor model (HFM) is proposed and discussed in this paper. Within the HFM, the sectional slant wet delay (SWD) of inside signals (the part of the side signal inside the tomography area), which is considered a key factor for modeling side rays, is separated into isotropic and anisotropic components. Correspondingly, two height factors are defined to calculate the isotropic and anisotropic part of tropospheric delays in the HFM. In addition, the dynamic tomography top boundary is first analyzed and determined based on 30-year radiosonde data to reasonably divide signals into top and side rays. Four special experimental schemes based on different tomography regions of Hong Kong are performed to assess the proposed HFM method, the results of which show increases of 33.42% in the mean utilization of rays, as well as decreases of 0.46 g/m3 in the average root mean square error (RMSE), compared to the traditional approach, revealing the improvement of tomography solutions when the side signals are included in the modeling. Furthermore, compared with the existing correction model for modeling side rays, the water vapor profiles retrieved from the proposed improved model are closer to the radiosonde data, which highlights the advantages of the proposed HFM for optimizing the GNSS tomography model.

scholarly journals A New Approach of the Global Navigation Satellite System Tomography for Any Size of GNSS Network

2020 ◽  
Vol 12 (4) ◽  
pp. 617
Author(s):  
Yuchen Wang ◽  
Nan Ding ◽  
Yu Zhang ◽  
Long Li ◽  
Xiaoyan Yang ◽  
...  
Keyword(s):  
Global Navigation Satellite System ◽  
Satellite System ◽  
Radiosonde Data ◽  
Navigation Satellite ◽  
New Approach ◽  
Novel Approach ◽  
Global Navigation ◽  
Gnss Network ◽  
High Flexibility ◽  
Global Navigation Satellite

Global Navigation Satellite System (GNSS) tomography is a popular method for measuring and modelling water vapor in the troposphere. Presently, most studies use a cuboid-shaped tomographic region in their modelling, which represents the modelling region for all measurement epochs. This region is defined by the distribution of the GNSS signals skywards from a network of ground based GNSS stations for all epochs of measurements. However, in reality at each epoch the shape of the GNSS tomographic region is more likely to be an inverted cone. Unfortunately, this fixed conic tomographic region does not properly reflect the fact that the GNSS signal changes quickly over time. Therefore a dynamic or adaptive tomographic region is better suited. In this study, a new approach that adjusts the GNSS tomographic model to adapt the size of the GNSS network is proposed, which referred to as The High Flexibility GNSS Tomography (HFGT). Test data from different numbers of the GNSS stations are used and the results from HFGT are compared against that of radiosonde data (RS) to assess the accuracy of the HFGT approach. The results showed that the new approach is feasible for different numbers of the GNSS stations when a sufficient and uniformed distribution of GNSS signals is used. This is a novel approach for GNSS tomography.

scholarly journals Establishment and Evaluation of a New Meteorological Observation-Based Grid Model for Estimating Zenith Wet Delay in Ground-Based Global Navigation Satellite System (GNSS)

2018 ◽  
Vol 10 (11) ◽  
pp. 1718 ◽  
Author(s):  
Yibin Yao ◽  
Zhangyu Sun ◽  
Chaoqian Xu
Keyword(s):  
Global Navigation Satellite System ◽  
State Of The Art ◽  
Satellite System ◽  
The State ◽  
Radiosonde Data ◽  
Navigation Satellite ◽  
Meteorological Observation ◽  
Grid Model ◽  
Zenith Wet Delay ◽  
Global Navigation Satellite

With the availability to high-accuracy a priori zenith wet delay (ZWD) data, the positioning efficiency of the precise point positioning (PPP) processing can be effectively improved, including accelerating the convergence time and improving the positioning precision, in ground-based Global Navigation Satellite System (GNSS) technology. Considering the limitations existing in the state-of-the-art ZWD models, this paper established and evaluated a new in-situ meteorological observation-based grid model for estimating ZWD named GridZWD using the radiosonde data and the European Centre for Medium-Range Weather Forecasts (ECWMF) data. The results show that ZWD has a strong correlation with the meteorological parameter water vapor pressure in continental and high-latitude regions. The root of mean square error (RMS) of 24.6 mm and 36.0 mm are achievable by the GridZWD model when evaluated with the ECWMF data and the radiosonde data, respectively. An accuracy improvement of approximately 10%~30% compared with the state-of-the-art models (e.g., the Saastamoinen, Hopfield and GPT2w models) can be found for the new built model.

scholarly journals Evaluation of the ZWD/ZTD Values Derived from MERRA-2 Global Reanalysis Products Using GNSS Observations and Radiosonde Data

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6440
Author(s):  
Liangke Huang ◽  
Lijie Guo ◽  
Lilong Liu ◽  
Hua Chen ◽  
Jun Chen ◽  
...  
Keyword(s):  
Satellite System ◽  
Reanalysis Data ◽  
Radiosonde Data ◽  
Tropospheric Delay ◽  
International Gnss Service ◽  
Vapor Detection ◽  
Lower Accuracy ◽  
Temporal And Spatial Characteristics ◽  
Global Navigation Satellite ◽  
Better Than

Tropospheric delay is one of the main errors affecting high-precision positioning and navigation and is a key parameter of water vapor detection in the Global Navigation Satellite System (GNSS). The second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) is the latest generation of reanalysis data collected by the National Aeronautics and Space Administration (NASA), which can be used to calculate tropospheric delay products with high spatial and temporal resolution. However, there is no report analyzing the accuracy of the zenith tropospheric delay (ZTD) and zenith wet delay (ZWD) calculated from MERRA-2 data. This paper evaluates the performance of the ZTD and ZWD values derived from global MERRA-2 data using global radiosonde data and International GNSS Service (IGS) precise ZTD products. The results are as follows: (1) Taking the precision ZTD products of 316 IGS stations from around the world from 2015 to 2017 as the reference, the average root mean square (RMS) of the ZTD values calculated from the MERRA-2 data is better than 1.35 cm, and the accuracy difference between different years is small. The bias and RMS of the ZTD values show certain seasonal variations, with a higher accuracy in winter and a lower accuracy in summer, and the RMS decreases from the equator to the poles. However, those of the ZTD values do not show obvious variations according to elevation. (2) Relative to the radiosonde data, the RMS of the ZWD and ZTD values calculated from the MERRA-2 data are better than 1.37 cm and 1.45 cm, respectively. Furthermore, the bias and RMS of the ZWD and ZTD values also show some temporal and spatial characteristics, which are similar to the test results of the IGS stations. It is suggested that MERRA-2 data can be used for global tropospheric vertical profile model construction because of their high accuracy and good stability in the global calculation of the ZWD and ZTD.

scholarly journals A method to improve the utilization of GNSS observation for water vapor tomography

2016 ◽  
Vol 34 (1) ◽  
pp. 143-152 ◽  
Author(s):  
Y. B. Yao ◽  
Q. Z. Zhao ◽  
B. Zhang
Keyword(s):  
Water Vapor ◽  
Absolute Error ◽  
Satellite System ◽  
Research Area ◽  
Radiosonde Data ◽  
Gps Data ◽  
Full Potential ◽  
Research Areas ◽  
Global Navigation Satellite ◽  
Areas Of Interest

Abstract. Existing water vapor tomographic methods use Global Navigation Satellite System (GNSS) signals penetrating the entire research area while they do not consider signals passing through its sides. This leads to the decreasing use of observed satellite signals and allows for no signals crossing from the bottom or edge areas especially for those voxels in research areas of interest. Consequently, the accuracy of the tomographic results for the bottom of a research area, and the overall reconstructed accuracy do not reach their full potential. To solve this issue, an approach which uses GPS data with both signals that pass the side and top of a research area is proposed. The advantages of proposed approach include improving the utilization of existing GNSS observations and increasing the number of voxels crossed by satellite signals. One point should be noted that the proposed approach needs the support of radiosonde data inside the tomographic region. A tomographic experiment was implemented using observed GPS data from the Continuously Operating Reference System (CORS) Network of Zhejiang Province, China. The comparison of tomographic results with data from a radiosonde shows that the root mean square error (RMS), bias, mean absolute error (MAE), and standard deviation (SD) of the proposed approach are superior to those of the traditional method.

scholarly journals Analysis and Mitigation of Crosstalk Effect on Coastal GNSS-R Code-Level Altimetry Using L5 Signals from QZSS GEO

2021 ◽  
Vol 13 (22) ◽  
pp. 4553
Author(s):  
Yunqiao He ◽  
Tianhe Xu ◽  
Fan Gao ◽  
Nazi Wang ◽  
Xinyue Meng ◽  
...  
Keyword(s):  
Satellite System ◽  
Path Delay ◽  
Direct Signal ◽  
Geo Satellite ◽  
Reflected Signal ◽  
L5 Signal ◽  
Global Navigation Satellite ◽  
Marine Environment Monitoring ◽  
Signal Crosstalk

Coastal Global Navigation Satellite System Reflectometry (GNSS-R) can be used as a valuable supplement for conventional tide gauges, which can be applied for marine environment monitoring and disaster warning. Incidentally, an important problem in dual-antenna GNSS-R altimetry is the crosstalk effect, which means that the direct signal leaks into the down-looking antenna dedicated to the reflected signals. When the path delay between the direct and reflected signals is less than one chip length, the delay waveform of the reflected signal is distorted, and the code-level altimetry precision decreases consequently. To solve this problem, the author deduced the influence of signal crosstalk on the reflected signal structure as the same as the multipath effect. Then, a simulation and a coastal experiment are performed to analyze the crosstalk effect on code delay measurements. The L5 signal transmitted by the Quasi-Zenith Satellite System (QZSS) from a geosynchronous equatorial orbit (GEO) satellite is used to avoid the signal power variations with the elevation, so that high-precision GNSS-R code altimetry measurements are achieved in the experiment. Theoretically and experimentally, we found there exists a bias in proportion to the power of the crosstalk signals and a high-frequency term related to the phase delay between the direct and reflected signals. After weakening the crosstalk by correcting the delay waveform, the results show that the RMSE between 23-h sea level height (SSH) measurements and the in-situ observations is about 9.5 cm.

scholarly journals Assessments of the Retrieval of Atmospheric Profiles from GNSS Radio Occultation Data in Moist Tropospheric Conditions Using Radiosonde Data

2020 ◽  
Vol 12 (17) ◽  
pp. 2717
Author(s):  
Ying Li ◽  
Yunbin Yuan ◽  
Xiaoming Wang
Keyword(s):  
Radio Occultation ◽  
Satellite System ◽  
Specific Humidity ◽  
Radiosonde Data ◽  
Temperature Profiles ◽  
Standard Deviations ◽  
Mean Differences ◽  
June July ◽  
Global Navigation Satellite ◽  
Humidity Profiles

The Global Navigation Satellite System (GNSS) Radio Occultation (RO) retrieved temperature and specific humidity profiles can be widely used for weather and climate studies in troposphere. However, some aspects, such as the influences of background data on these retrieved moist profiles have not been discussed yet. This research evaluates RO retrieved temperature and specific humidity profiles from Wegener Center for Climate and Global Change (WEGC), Radio Occultation Meteorology Satellite Application Facility (ROM SAF) and University Corporation for Atmospheric Research (UCAR) Boulder RO processing centers by comparing with measurements from 10 selected Integrated Global Radiosonde Archive (IGRA) radiosonde stations in different latitudinal bands over 2007 to 2010. The background profiles used for producing their moist profiles are also compared with radiosonde. We found that RO retrieved temperature profiles from all centers agree well with radiosonde. Mean differences at polar, mid-latitudinal and tropical stations are varying within ±0.2 K, ±0.5 K and from −1 to 0.2 K, respectively, with standard deviations varying from 1 to 2 K for most pressure levels. The differences between RO retrieved and their background temperature profiles for WEGC are varying within ±0.5 K at altitudes above 300 hPa, and the differences for ROM SAF are within ±0.2 K, and that for UCAR are within 0.5 K at altitudes below 300 hPa. Both RO retrieved and background specific humidity above 600 hPa are found to have large positive differences (up to 40%) against most radiosonde measurements. Discrepancies of moist profiles among the three centers are overall minor at altitudes above 300 hPa for temperature and at altitudes above 700 hPa for specific humidity. Specific humidity standard deviations are largest at tropical stations in June July August months. It is expected that the outcome of this research can help readers to understand the characteristics of moist products among centers.

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