Comparison of GPS slant wet delays acquired by different techniques

This paper discusses the quality of slant wet delays (SWD) computed from GPS measurements. The SWDs are generally used as input data for GPS tomography, which allows the three-dimensional reconstruction of water vapour distribution in the atmosphere. The research presented is based on a comparison of slant wet delays acquired by different strategies based on double-differenced Global Positioning System (GPS) data. The GPS-derived SWDs were compared with those directly measured by a water vapour radiometer (WVR). The best results from the applied GPS strategies were achieved by a simple mapping of GPS-derived zenith total delays into SWD without adding horizontal gradients or post-fit residuals.Web of Science9443342

Performance Assessment of Kinematic GNSS Positioning with Smartphones Based on Post-Processing of Raw Observations

In recent years, there have been significant technological advances in the development of commonmobile devices. This broughtprogress also in the area of positioning with thesedevices. Allowingaccess to raw GNSS observationsrecorded by mobile devices opened possibilities to apply advanced positioning techniques in order toachieve higher positioning accuracy. The paper describes the results of kinematic measurements of a single-frequency Samsung Galaxy S10+smartphone and a dual-frequency Samsung Galaxy Note10+smartphone. Observations were repeatedly collected at a1.76 km long test route inan urban environment atapedestrian speed. Real-time positioning by autonomous method as well as collection of raw observations into RINEX format and their subsequent post-processing by differential techniques and Precise Point Positioning technique wererealized. The achieved results were compared against a reference linerepresenting the real trajectoryand also againstresults of ageodeticgrade GNSSreceiver.Positioning accuracy of mobile devices ranged from the first decimetres to tens of metres, depending on the environment, tested smartphone and used post-processing technique.Dual-frequency smartphone Samsung Galaxy Note 10+ provided abetter performance compared to the single-frequencydevice. Real-time positioning based on a simple autonomous technique and smoothing algorithm for route optimizationreached lower positioning errors compared to all solutions based on collecting raw observations and their consequent post-processingwith mentioned techniques

Assessment of multi-GNSS precise orbit and clock products from different analysis centers based on precise point positioning

Performance of 24h static Precise Point Positioning (PPP) solutions based on multi-GNSS precise satellite orbit and clock products from four analysis centers and seven various constellation combinations was studied to evaluate their quality and characteristics. Data from ten European and four Chinese GNSS stations and 152 days long period from year 2020 were processed. Obtained coordinates were firstly compared with those provided by IGS final weekly combined solution. In Europe, the best agreement with this reference product was reached by solutions including Galileo signals, namely by a combination of GPS+GLONASS+Galileo systems with a mean RMS of 11 mm. This situation was different in China where inclusion of Galileo always led to worse results and the best agreement was achieved by a combination of GPS+GLONASS systems. Although product provided by German Research Center for Geosciences (GFZ) could be selected as the best performing over Europe and product by Center for Orbit Determination in Europe (CODE) over China, differences between individual precise products were mostly at a minimal level. Secondly, coordinates repeatability over the processed period was computed in order to assess the positioning stability. In this regard, the lowest values in both horizontal and vertical direction were reached by GPS+GLONASS solutions. From the perspective of precise products, the repeatability results were dependent on the selected constellation where mainly a specific behavior of product from Wuhan University (WUM) for Galileo system was observed.Web of Science18339738

Multi-GNSS positioning for landslide monitoring: A case study at the Recica landslide

Global Navigation Satellite System (GNSS) positioning has characteristics of simple operation, high efficiency and high precision technique for landslide surface monitoring. In recent years, finalization of modern GNSS systems Galileo and BeiDou has brought a possibility of multi-GNSS positioning. The paper focuses on evaluation of possible benefits of multi-GNSS constellations in landslide monitoring. While simulating observational conditions of selected Recica landslide in the Czech Republic, one-month data from well-established permanent GNSS reference stations were processed. Besides various constellation combinations, differential and Precise Point Positioning techniques, observation data lengths and observation sampling intervals were evaluated. Based on the results, using a combination of GPS and GLONASS, or GPS, GLONASS and Galileo systems can be recommended, together with a static differential technique and observation periods for data collection exceeding eight hours. In the last step, data from GNSS repetitive campaigns realized at the Recica landslide during two years were processed with optimal setup and obtained displacement results were compared to standard geotechnical measurements.Web of Science19327025

Estimating the impact of Global Navigation Satellite System horizontal delay gradients in variational data assimilation

We developed operators to assimilate Global Navigation Satellite System (GNSS) Zenith Total Delays (ZTDs) and horizontal delay gradients into a numerical weather model. In this study we experiment with refractivity fields derived from the Global Forecast System (GFS) available with a horizontal resolution of 0.5 degrees. We begin our investigations with simulated observations. In essence, we extract the tropospheric parameters from the GFS analysis, add noise to mimic observation errors and assimilate the simulated observations into the GFS 24h forecast valid at the same time. We consider three scenarios: (1) the assimilation of ZTDs (2) the assimilation of horizontal delay gradients and (3) the assimilation of both ZTDs and horizontal delay gradients. The impact is measured by utilizing the refractivity fields. We find that the assimilation of the horizontal delay gradients in addition to the ZTDs improves the refractivity field around 800 hPa. When we consider a single station there is a clear improvement when horizontal delay gradients are assimilated in addition to the ZTDs because the horizontal delay gradients contain information that is not contained in the ZTDs. On the other hand, when we consider a dense station network there is not a significant improvement when horizontal delay gradients are assimilated in addition to the ZTDs because the horizontal delay gradients do not contain information that is not already contained in the ZTDs. Finally, we replace simulated by real observations, that is, tropospheric parameters from a Precise Point Positioning solution provided with the G-Nut/Tefnut software, in order to show that the GFS 24h forecast is indeed improved when GNSS horizontal delay gradients are assimilated in addition to GNSS ZTDs; for the considered station (Potsdam, Germany) and period (June and July, 2017) we find an improvement in the retrieved refractivity of up to 4%.Web of Science111art. no. 4

Monitoring non-linear ground motion above underground gas storage using GNSS and PSInSAR based on Sentinel-1 data

Several methods allow accurate measurement of terrain surface motions. Global navigation satellite systems (GNSSes) and interferometry with synthetic aperture radar (InSAR) stand out in terms of measurement accuracy among them. In principle, both methods make it possible to evaluate a three-dimensional vector of the motion of points on the terrain surface. In this work, we dealt with the evaluation of motions in the up-down (U-D) and east-west direction (E-W) over underground gas storage (UGS) from InSAR. One crucial step in breaking down PSInSAR line of sight (LOS) measurements to U-D and E-W components is getting time series derived from individual tracks to the same time frame. This is usually performed by interpolation, but we used an innovative approach: we analyzed individual time series using the Lomb-Scargle periodogram (LSP), which is suitable for periodic noisy and irregularly sampled data; we selected the most significant period, created LSP models, and used them instead of the original time series. Then, it was possible to derive time series values for any arbitrary time step. To validate the results, we installed one GNSS receiver in the Tvrdonice UGS test area to perform independent measurements. The results show a good agreement in the evaluation of motions by both methods. The correlation coefficient between horizontal components from both PSInSAR and GNSS was 0.95 in the case of the E-W component, with an RMSE of 1.75 mm; for U-D they were 0.78 and 2.35 mm, respectively. In addition to comparing the motions in the U-D and E-W directions, we also created a comparison by converting GNSS measurements to a line of sight of the Sentinel-1 satellite to evaluate the conformity of InSAR and GNSS measurements. Based on descending track, the correlation coefficient between LOS from both methods is, on average, 0.97, with an RMSE of 2.70 mm.Web of Science1419art. no. 489

Control Methods of Invasive Plant Species and the Influence of Cultural Vegetation on the Microclimate within the Central Wastewater Treatment Plant in Ostrava – Pilot Results

This study is a pilot document focusing on two subjects. The first one concernscontrol methods of invasive plant species in the floodplain of the river Odra, specifically on wooded wetlands with pools. The second presents the influence of cultural vegetation on the microclimate within the Central Wastewater Treatment Plant in Ostrava (CWWTP).The problem is the spread of invasive plant species, especially the Canadian goldenrod (Solidago canadensis) and the Himalayan balsam (Impatiens glandulifera), which are expanding in the area to such an extent that they create monodominant invasive vegetation. Variousmethods of controllinginvasive species were gradually tested indefined areas in the forested wetland. Both mechanical and chemical methods were used, as well as their combinations,to find outthe most effective one. The processincludes partial works,such as the selection of areas, the determination of diversity by using phytosociology, the subsequent application of selected interventions,andthe monitoring of given invasive plants with growing accompanying species. This research is time-consuming; therefore,longer application,in termsof years,is assumed, which should lead to much more relevantresults.The CWWTP area acts as a heated island, where surfaces are regularly overheated, negatively affecting the biota and the working environment. One of the working results will be the design of suitable vegetation composition,effectively reducingextreme surface temperatures, especially insummer. The determination of diversity is linked to this sinceany vegetation of different diversity can contribute to a favourablemicroclimate. An area inventory of tree and shrub vegetation and a phytosociological analysis of selected areas are used to evaluate diversity.These surveys were carried out in the wetland ecosystem and the CWWTP area.Another important step is the measurement of surface temperatures of cultural vegetation and built-up areas in the area of the CWWTP, which was carried out by remote sensing. Later, it will be possible to assesswhich of the existing biotopes contributesmore and which less to the cooling function of the urban heat islandand,at the same time,how tocare forthis vegetation so that it fulfillsits role.In the article, we present the results of the pilot survey. For the control oftheinvasive species Impatiens glanduliferaand Solidago canadensis, three control methods were chosen: mechanical (mowing), chemical (herbicide with the active ingredients of triclopyr and fluroxypyr (A.),and herbicide with pelargonic acid (B.)),and combined (A. + mowing, mowing + B.). The initial reactions of these plants to the interventions were visible after about 20–30 days. It was most pronounced in the area withthe dead-end river branch with the combination of A. + mowing, where Impatiens glanduliferaoccurred, and then in the forest area with the occurrence of Solidago canadensiswith the application of herbicide A. When measuring the surface temperatures of the cultural vegetation and built-up areas in the CWWTP area as a heat island, approximate temperatures were recorded: on average, the cultural vegetation ranged from 26.43 to 34.45 °C, the average temperature of the built-up areas was from 47.26to 58.32 °C,and the water surfaces (CWWTP reservoirs) then around 20.65 °C. As part of the tree and shrub layer inventory, we recorded 17 tree species and 5 shrub species in the wetland ecosystem. The phytosociological analysis showed that due to the massive occurrence of invasive plants, theareas in the wetland ecosystem are poorer in species than theareas of the CWWTP with cultural vegetation

Benchmark campaign and case study episode in central Europe for development and assessment of advanced GNSS tropospheric models and products

Initial objectives and design of the Benchmark campaign organized within the European COST Action ES1206 (2013–2017) are described in the paper. This campaign has aimed to support the development and validation of advanced Global Navigation Satellite System (GNSS) tropospheric products, in particular high-resolution and ultra-fast zenith total delays (ZTDs) and tropospheric gradients derived from a dense permanent network. A complex data set was collected for the 8-week period when several extreme heavy precipitation episodes occurred in central Europe which caused severe river floods in this area. An initial processing of data sets from GNSS products and numerical weather models (NWMs) provided independently estimated reference parameters – zenith tropospheric delays and tropospheric horizontal gradients. Their provision gave an overview about the product similarities and complementarities, and thus a potential for improvements of a synergy in their optimal exploitations in future. Reference GNSS and NWM results were intercompared and visually analysed using animated maps. ZTDs from two reference GNSS solutions compared to global ERA-Interim reanalysis resulted in accuracy at the 10 mm level in terms of the root mean square (rms) with a negligible overall bias, comparisons to Global Forecast System (GFS) forecasts showed accuracy at the 12 mm level with the overall bias of −5 mm and, finally, comparisons to mesoscale ALADIN-CZ forecast resulted in accuracy at the 8 mm level with a negligible total bias. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and an accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications, such as severe weather event monitoring and weather nowcasting. The GNSS products revealed a capability of providing more detailed structures in atmosphere than the state-of-the-art numerical weather models are able to capture. In an initial study on the contribution of hydrometeors (e.g. cloud water, ice or snow) to GNSS signal delays during severe weather, the effect reached up to 17 mm, and it was suggested that hydrometeors should be carefully accounted for within the functional model. The reference products will be further exploited in various specific studies using the Benchmark data set. It is thus going to play a key role in these highly interdisciplinary developments towards better mutual benefits from advanced GNSS and meteorological products.Web of Science973008298

Sensitivity of GNSS tropospheric gradients to processing options

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 degrees 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.Web of Science37344642

Inter-technique validation of tropospheric slant total delays

An extensive validation of line-of-sight tropospheric slant total delays (STD) from Global Navigation Satellite Systems (GNSS), ray tracing in numerical weather prediction model (NWM) fields and microwave water vapour radiometer (WVR) is presented. Ten GNSS reference stations, including collocated sites, and almost 2 months of data from 2013, including severe weather events were used for comparison. Seven institutions delivered their STDs based on GNSS observations processed using 5 software programs and 11 strategies enabling to compare rather different solutions and to assess the impact of several aspects of the processing strategy. STDs from NWM ray tracing came from three institutions using three different NWMs and ray-tracing software. Inter-techniques evaluations demonstrated a good mutual agreement of various GNSS STD solutions compared to NWM and WVR STDs. The mean bias among GNSS solutions not considering post-fit residuals in STDs was -0.6 mm for STDs scaled in the zenith direction and the mean standard deviation was 3.7 mm. Standard deviations of comparisons between GNSS and NWM ray-tracing solutions were typically 10 mm +/- 2 mm (scaled in the zenith direction), depending on the NWM model and the GNSS station. Comparing GNSS versus WVR STDs reached standard deviations of 12 mm +/- 2 mm also scaled in the zenith direction. Impacts of raw GNSS post-fit residuals and cleaned residuals on optimal reconstructing of GNSS STDs were evaluated at intertechnique comparison and for GNSS at collocated sites. The use of raw post-fit residuals is not generally recommended as they might contain strong systematic effects, as demonstrated in the case of station LDB0. Simplified STDs reconstructed only from estimated GNSS tropospheric parameters, i.e. without applying post-fit residuals, performed the best in all the comparisons; however, it obviously missed part of tropospheric signals due to non-linear temporal and spatial variations in the troposphere. Although the post-fit residuals cleaned of visible systematic errors generally showed a slightly worse performance, they contained significant tropospheric signal on top of the simplified model. They are thus recommended for the reconstruction of STDs, particularly during high variability in the troposphere. Cleaned residuals also showed a stable performance during ordinary days while containing promising information about the troposphere at low-elevation angles.Web of Science1062208218