A novel dynamical filter based on multi-epochs least-squares to integrate the carrier phase and pseudorange observation for GNSS measurement

© 2020 by the authors. The high noise of pseudorange and the ambiguity of carrier phase observation restrain the GNSS (Global Navigation Satellite System) application in military, industrial, and agricultural, to name a few. Thus, it is crucial for GNSS technology to integrate the pseudorange and carrier phase observations. However, the traditional method proposed by Hatch has obtained only a low convergence speed and precision. For higher convergence speed and precision of the smoothed pseudorange, aiming to improve positioning accuracy and expand the application of GNSS, we introduced a new method named MELS (Multi-Epochs Least-Squares) that considered the cross-correlation of the estimating parameters inspired by DELS (Double-Epochs Least-Square). In this study, the ionospheric delay was compensated, and so its impact was limited to the performance of the filters, and then exploited the various filters to integrate carrier phase observation and pseudorange. We compared the various types of Hatch's filter and LS (Least-Square) methods using simulation datasets, which confirmed that the types of LS method provided a smaller residual error and a faster convergence speed than Hatch's method under various precisions of raw pseudorange. The experimental results from the measured GNSS data showed that LS methods provided better performance than Hatch's methods at E and U directions and a lower accuracy at N direction. Nevertheless, the types of LS method and Hatch's methods improved about 12% and 9-10% at the 3D direction, respectively, which illustrated the accumulating improvement at the enhanced directions was more than the decreased direction, proving that the types of LS method resulted to better performance than the Hatch's filters. Additionally, the curve of residual and precision based on various LS methods illustrated that the MELS only provided a millimeter accuracy difference compared with DELS, which was proved by the simulated and measured GNSS datasets

A Robust Method for GPS/BDS Pseudorange Differential Positioning Based on the Helmert Variance Component Estimation

The use of global navigation satellite system (GNSS) is entering a new era of joint positioning based on the use of multifrequencies and multimodes. Ensuring the correct weighting of observations from each system and satellite has become a key problem during real-time positioning. This paper addresses the issue of weights of observations as well as the quality control of GPS/BDS pseudoranges in the context of real-time relative positioning. Thus, in the first place, the Helmert variance component estimation (VCE) is used to determine the relative weighting of observations from the two systems, and then, we introduce robustness estimation theory and construct a new method. The method is resistant to the influence of outliers in the observations by selecting weight iterations. To do this, we selected GPS/BDS observation data at baseline lengths of 40 km, 46 km, and 64 km for verification and analysis. Experimental results show that, in terms of the relative positioning of medium-to-long baseline based on GPS/BDS pseudorange observations, when observed values incorporate large gross errors, our method can reduce the weighting of suspicious or abnormal values and weaken their impact on positioning solutions, so that the positioning results will not appear to have large deviation

Analysis of one ambient seismic noise in Tianjin

During checking continuous waveform record, it was found that some stations of Tianjin such as EWZ were significantly affected by one unknown noise, and EWZ station was the most seriously affected. Long term observations had also found that this noise cannot be observed for uncertainly several days each year. This noise was all year round and did not change with day and night time, and it had been existed for many years. This noise was different from typical environmental background noise and had some fixed characteristics. This article studied the noise from several aspects such as its own characteristic, its coverage of influence, spectral characteristics, and impact on earthquake records. The research has shown that the noise was not affected by natural factors such as weather and season, and had a characteristic of amplitude decreasing as the distance increasing from EWZ station. The main frequency of this noise ranged 1～2 Hz. The impact of noise was relatively wide and it can be recorded by 12 surrounding stations, with YGZ station being the farthest and approximately 58 km away from EWZ station. Through polarization analysis, it was found that the propagation of noise had a specific directionality, so it is preliminary judged that this noise had the characteristic of fixed source noise. This noise will have an impact on seismic records, reducing the seismic phase pickup rate, and even completely submerging it in the noise. Frequency filtering can improve it

Research on the ionospheric VTEC changes during period of typhoon UTOR

482-491Present article consists the GPS observation data from the IGS stations of pimo and bjfs to invert the VTEC values of the ionosphere, then use the quarterback method to analyze the ionospheric VTEC changes during the period of typhoon UTOR. The results show that: VTEC values of the pimo station increase significantly during the period of UTOR and reach the critical values of upper limit or cause disturbance. VTEC values of the bjfs station change relatively stable and occasionally reach the critical values of the upper and lower limit, but the disturbance should be independent with the typhoon UTOR

The ionospheric VTEC inversion and results analysis based on the HY-2 satellite

197-206In this paper, a new data processing method and flow is put forward to calculate the ionospheric VTEC inversely according to the features of the HY-2 satellite radar altimeter data. In order to verify the accuracy and feasibility of the data processing method and flow, the paper compares and analyzes the processed data from the aspects of time, data amount, latitude and longitude. HY-2 VTEC is also compared with the GIM VTEC which is interpolated from the GIM, and it is found that there is a good agreement between the HY-2 VTEC and the GIM VTEC. It shows that the data processing method and flow is suitable and correct. Meanwhile, the differences between HY-2 VTEC and GIM VTEC are larger in the areas where the IGS observation stations are fewer, while the agreement is good and the differences are small in the areas where the IGS observation stations are more

An Empirical Grid Model for Precipitable Water Vapor

Atmospheric precipitable water vapor (PWV) is a key variable for weather forecast and climate research. Various techniques (e.g., radiosondes, global navigation satellite system, satellite remote sensing and reanalysis products by data assimilation) can be used to measure (or retrieve) PWV. However, gathering PWV data with high spatial and temporal resolutions remains a challenge. In this study, we propose a new empirical PWV grid model (called ASV-PWV) using the zenith wet delay from the Askne model and improved by the spherical harmonic function and vertical correction. Our method is convenient and enables the user to gain PWV data with only four input parameters (e.g., the longitude and latitude, time, and atmospheric pressure of the desired position). Profiles of 20 radiosonde stations in Qinghai Tibet Plateau, China, along with the latest publicly available C-PWVC2 model are used to validate the local performance. The PWV data from ASV-PWV and C-PWVC2 is generally consistent with radiosonde (the average annual bias is −0.44 mm for ASV-PWV and −1.36 mm for C-PWVC2, the root mean square error (RMSE) is 3.44 mm for ASV-PWV and 2.51 mm for C-PWVC2, respectively). Our ASV-PWV performs better than C-PWVC2 in terms of seasonal characteristics. In general, a sound consistency exists between PWV values of ASV-PWV and the fifth generation of European Centre for Medium-Range Weather Forecasts Atmospheric Reanalysis (ERA5) (total 7381 grid points in 2020). The average annual bias and RMSE are −0.73 mm and 4.28 mm, respectively. ASV-PWV has a similar performance as ERA5 reanalysis products, indicating that ASV-PWV is a potentially alternative option for rapidly gaining PWV

Detection and Evaluation of Flood Inundation Using CYGNSS Data during Extreme Precipitation in 2022 in Guangdong Province, China

Floods are severe natural disasters that are harmful and frequently occur across the world. From May to July 2022, the strongest, broadest, and longest rainfall event in recent years occurred in Guangdong Province, China. The flooding caused by continuous precipitation and a typhoon resulted in severe losses to local people and property. During flood events, there is an urgent need for timely and detailed flood inundation mapping for areas that have been severely affected. However, current satellite missions cannot provide sufficient information at a high enough spatio-temporal resolution for flooding applications. In contrast, spaceborne Global Navigation Satellite System reflectometry technology can be used to observe the Earth’s surface at a high spatio-temporal resolution without being affected by clouds or surface vegetation, providing a feasible scheme for flood disaster research. In this study, Cyclone Global Navigation Satellite System (CYGNSS) L1 science data were processed to obtain the change in the delay-Doppler map and surface reflectivity (SR) during the flood event. Then, a flood inundation map of the extreme precipitation was drawn using the threshold method based on the CYGNSS SR. Additionally, the flooded areas that were calculated based on the soil moisture from the Soil Moisture Active Passive (SMAP) data were used as a reference. Furthermore, the daily Dry Wet Abrupt Alternation Index (DWAAI) was used to identify the occurrence of the flood events. The results showed good agreement between the flood inundation that was derived from the CYGNSS SR and SMAP soil moisture. Moreover, compared with the SMAP results, the CYGNSS SR can provide the daily flood inundation with higher accuracy due to its high spatio-temporal resolution. Furthermore, the DWAAI can identify the transformation from droughts to floods in a relatively short period. Consequently, the distributions of and variations in flood inundation under extreme weather conditions can be identified on a daily scale with good accuracy using the CYGNSS data

Analysis of ionospheric VTEC disturbances before and after the Yutian Ms7.3 earthquake in the Xinjiang Uygur Autonomous Region

An earthquake with a magnitude of Ms7.3 hit Yutian in the Xinjiang Uygur Autonomous Region on February 14, 2014. This research investigates the interference phenomena in solar activities and geomagnetics, and adopts the quartile method to analyze the Global Ionosphere Map (GIM) Vertical Total Electron Content (VTEC) data provided by the Center for Orbit Determination in Europe (CODE), as well as the difference between GIM VTEC and International Reference Ionosphere (IRI) VTEC data. The ionospheric VTEC disturbances at the earthquake epicenter are examined before and after the event. At UTC 8 :00 on February 2, a strong VTEC disturbance emerged in the sky near the epicenter. A strong VTEC disturbance also emerged in the sky of the southern Hemisphere area, which is symmetric with the areas north of the equator. The methods used in analysis of the difference between GIM VTEC and IRI VTEC information can effectively fill the gaps in analysis that uses only the GIM VTEC data

Combination of GPS, HY-2A and COSMIC observations to establish global ionospheric map

1000-1010The systematic biases of the HY-2A altimetry satellite observations and COSMIC observations between ground-based GNSS observations are taken into account, and they were estimated together with the unknown coefficients of SH expansion by least squares. Meanwhile, Helmert variance component estimation method was used to determine the precise weights of each observations taking into account of the different accuracy of each observations. As an example, three types of observations in DOY 101, 2015 were used to establish a combined GIM in two-hourly snapshots. The differences of the combined GIM and GIM published by IGS were also analyzed. Compared with the RMS map of GIM published by IGS, it found that the accuracy of the combined GIM improved about 0.3TECU after adding HY-2A altimetry satellite and COSMIC observations. The accuracy improved more obvious in the ocean areas where HY-2A altimetry satellite observed

Extra-Wide Lane Ambiguity Resolution and Validation for a Single Epoch Based on the Triple-Frequency BeiDou Navigation Satellite System

The ambiguity resolution (AR) and validation of the global navigation satellite system (GNSS) have been challenging tasks for some decades. Considering the reliability problem of extra-wide-lane (EWL) ambiguity in the triple-carrier ambiguity resolution (TCAR), a method for validating the reliability of the EWL ambiguity using a single epoch was proposed for the BeiDou Navigation Satellite System (BDS). For the initial EWL ambiguity, obtained using a rounding estimator with a geometry-free (GF) model, the double-difference ionospheric delay was first estimated to construct a relative positioning model with an initial fixed ambiguity. Second, based on the theory of gross error detection and the AR characteristics of EWL, the second-best ambiguity candidate was constructed. Finally, among the two sets of ambiguities, the one with the smaller posterior variance was taken as the reliable ambiguity. The study showed that, for a single epoch, when only one or two satellites had incorrect ambiguities, the AR success rate after ambiguity validation and correction could reach 100% for medium baselines. For long baselines, due to the increase of atmospheric error, the validation was affected to some extent. However, the AR success rates for two long baselines increased from 96.82% and 98.44% to 98.80% and 99.67%, respectively