P. Häkli, Kristian Evers, L. Jivall, T. Nilsson, Sveinung Himle, K. Kollo, I. Liepiņš, E. Paršeliūnas, Olav Vestøl, M. Lidberg
Abstract Coordinates in global reference frames are becoming more and more common in positioning whereas most of the geospatial data are stored in registries in national reference frames. It is therefore essential to know the relation between global and national coordinates, i.e., the transformation, as accurately as possible. Officially provided pan-European transformations do not account for the special conditions in the Nordic and Baltic countries, namely crustal deformations caused by Glacial Isostatic Adjustment. Therefore, they do not fulfill the demands for the most accurate applications like long-term reference frame maintenance. Consequently, the Nordic Geodetic Commission (NKG) has developed customized and accurate transformations from the global ITRF to the national ETRS89 realizations for the Nordic and Baltic countries. We present the latest update, called the NKG2020 transformation, with several improvements and uncertainty estimates. We also discuss its significance and practical implementation for geodetic and geospatial communities.
{"title":"NKG2020 transformation: An updated transformation between dynamic and static reference frames in the Nordic and Baltic countries","authors":"P. Häkli, Kristian Evers, L. Jivall, T. Nilsson, Sveinung Himle, K. Kollo, I. Liepiņš, E. Paršeliūnas, Olav Vestøl, M. Lidberg","doi":"10.1515/jogs-2022-0155","DOIUrl":"https://doi.org/10.1515/jogs-2022-0155","url":null,"abstract":"Abstract Coordinates in global reference frames are becoming more and more common in positioning whereas most of the geospatial data are stored in registries in national reference frames. It is therefore essential to know the relation between global and national coordinates, i.e., the transformation, as accurately as possible. Officially provided pan-European transformations do not account for the special conditions in the Nordic and Baltic countries, namely crustal deformations caused by Glacial Isostatic Adjustment. Therefore, they do not fulfill the demands for the most accurate applications like long-term reference frame maintenance. Consequently, the Nordic Geodetic Commission (NKG) has developed customized and accurate transformations from the global ITRF to the national ETRS89 realizations for the Nordic and Baltic countries. We present the latest update, called the NKG2020 transformation, with several improvements and uncertainty estimates. We also discuss its significance and practical implementation for geodetic and geospatial communities.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"73 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89895066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The Geodetic Reference System for the Americas (Sistema de Referencia Geodésico para las Américas, SIRGAS) was initiated in 1993 for South America at an international conference organised by the International Association of Geodesy (IAG), the Pan-American Institute for Geography and History (PAIGH), the Deutsches Geodätisches Forschungsinstitut (DGFI), and the U.S. Defense Mapping Agency (DMA) in Asunción, Paraguay. The corresponding South American reference network was observed in 1995 by a ten-day GPS campaign at 58 stations. The network was extended to Central and North America in 2000 and immediately afterwards converted to a frame of continuously observing GNSS stations instead of short-term campaigns. The linear station position changes (velocities) were estimated by a multi-year least squares adjustment of weekly solutions, the first being published in 2002. The total set of station velocities served for the computation of continuous surface deformation models, the first over South America was published in 2005. Today, SIRGAS is accepted by most of the American states as the official geodetic reference frame. Besides the product generation (station positions, velocities, and surface deformation), SIRGAS is active in education and training offering schools and workshops for students, surveyors, and other stakeholders.
美洲大地测量参考系统(Sistema de Referencia geodsamicsico para las amsamicica, SIRGAS)是1993年由国际大地测量学会(IAG)、泛美地理和历史研究所(PAIGH)、德国Geodätisches Forschungsinstitut (DGFI)和美国国防测绘局(DMA)在巴拉圭Asunción组织的一次国际会议上为南美洲发起的。1995年在58个观测站进行了为期10天的全球定位系统运动，观测了相应的南美参考网。该网络于2000年扩展到中美洲和北美洲，随后立即转换为连续观测GNSS站的框架，而不是短期运动。线性站点位置变化(速度)是通过多年周解的最小二乘调整来估计的，第一次发表于2002年。总站速度集用于计算连续地表变形模型，第一次在南美洲发表于2005年。今天，SIRGAS被美国大多数州接受为官方大地测量参考系。除了产品生成(站点位置、速度和地表变形)，SIRGAS还积极参与教育和培训，为学生、测量员和其他利益相关者提供学校和研讨会。
{"title":"Historical development of SIRGAS","authors":"H. Drewes","doi":"10.1515/jogs-2022-0137","DOIUrl":"https://doi.org/10.1515/jogs-2022-0137","url":null,"abstract":"Abstract The Geodetic Reference System for the Americas (Sistema de Referencia Geodésico para las Américas, SIRGAS) was initiated in 1993 for South America at an international conference organised by the International Association of Geodesy (IAG), the Pan-American Institute for Geography and History (PAIGH), the Deutsches Geodätisches Forschungsinstitut (DGFI), and the U.S. Defense Mapping Agency (DMA) in Asunción, Paraguay. The corresponding South American reference network was observed in 1995 by a ten-day GPS campaign at 58 stations. The network was extended to Central and North America in 2000 and immediately afterwards converted to a frame of continuously observing GNSS stations instead of short-term campaigns. The linear station position changes (velocities) were estimated by a multi-year least squares adjustment of weekly solutions, the first being published in 2002. The total set of station velocities served for the computation of continuous surface deformation models, the first over South America was published in 2005. Today, SIRGAS is accepted by most of the American states as the official geodetic reference frame. Besides the product generation (station positions, velocities, and surface deformation), SIRGAS is active in education and training offering schools and workshops for students, surveyors, and other stakeholders.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"9 1","pages":"120 - 130"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79762711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The SIRGAS-CON network currently has more than 450 continuous GNSS stations, and it is used for geodetic purposes. In atmospheric studies, it is used for ionospheric monitoring and for the estimation of zenith tropospheric delays (ZTDs). From the Neutral Atmosphere Analysis Center of SIRGAS, Centro de Ingeniería Mendoza Argentina, the final tropospheric products of this network are generated after several stages of quality controls and filtering, in order to be published on a daily basis in the official website of SIRGAS, since 2014 (https://sirgas.ipgh.org/en/products/tropospheric-delays). These products arise from adjusting the solutions estimated by different SIRGAS analysis centers. Prior to the combination, a quality control of the individual solutions is carried out, based on the precision estimator of each parameter and an internal control of each solution with respect to the combined value. In this work, we show the quality control process of the inputs, the selected tolerance and its justification. The internal consistency analysis of tropospheric parameters for a period of 7 years was carried out. We also exposed the improvements in the estimation of tropospheric parameters implemented during 2021 and its impact in the generation of the final ZTD products (in 99% of the stations the mean standard deviation of ZTD is less than 1 mm).
{"title":"Quality control of SIRGAS ZTD products","authors":"M. Mackern, M. L. Mateo, M. F. Camisay, P. Rosell","doi":"10.1515/jogs-2022-0136","DOIUrl":"https://doi.org/10.1515/jogs-2022-0136","url":null,"abstract":"Abstract The SIRGAS-CON network currently has more than 450 continuous GNSS stations, and it is used for geodetic purposes. In atmospheric studies, it is used for ionospheric monitoring and for the estimation of zenith tropospheric delays (ZTDs). From the Neutral Atmosphere Analysis Center of SIRGAS, Centro de Ingeniería Mendoza Argentina, the final tropospheric products of this network are generated after several stages of quality controls and filtering, in order to be published on a daily basis in the official website of SIRGAS, since 2014 (https://sirgas.ipgh.org/en/products/tropospheric-delays). These products arise from adjusting the solutions estimated by different SIRGAS analysis centers. Prior to the combination, a quality control of the individual solutions is carried out, based on the precision estimator of each parameter and an internal control of each solution with respect to the combined value. In this work, we show the quality control process of the inputs, the selected tolerance and its justification. The internal consistency analysis of tropospheric parameters for a period of 7 years was carried out. We also exposed the improvements in the estimation of tropospheric parameters implemented during 2021 and its impact in the generation of the final ZTD products (in 99% of the stations the mean standard deviation of ZTD is less than 1 mm).","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"15 1","pages":"42 - 54"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81934967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Zenith Tropospheric Delays (ZTDs) are used to correct tropospheric effects that cause a delay in the signal measured by Global Navigation Satellite Systems (GNSS) receivers and obtain accurate measurements. ZTD can be estimated from GNSS processing, which means they may suffer from occasional or systematic errors. Therefore, it is necessary to assess the quality and stability of these data over time, since ZTDs are used in several applications that require centimeter precision. Within this context, this work aims to assess the available ZTD of the whole Geodetic Reference System for the Americas Continuously Operating Network (SIRGAS-CON), consisting of 467 stations, spanning the period from January 2014 to December 2020 using the most recent Numerical Weather Model ERA5 from the European Centre for Medium-Range Weather Forecasts and common stations to the International GNSS Service (IGS) for an intercomparison. Results show that 10% of the stations present some instability, such as periods of highly dispersed data or discontinuities, with more occurrence in stations located in Argentina, Uruguay and Colombia. The remaining 90% proved to have stable and reliable ZTD, both in comparison with ERA5 and IGS.
{"title":"Assessment of SIRGAS-CON tropospheric products using ERA5 and IGS","authors":"A. Prado, Telmo Vieira, M. Fernandes","doi":"10.1515/jogs-2022-0144","DOIUrl":"https://doi.org/10.1515/jogs-2022-0144","url":null,"abstract":"Abstract Zenith Tropospheric Delays (ZTDs) are used to correct tropospheric effects that cause a delay in the signal measured by Global Navigation Satellite Systems (GNSS) receivers and obtain accurate measurements. ZTD can be estimated from GNSS processing, which means they may suffer from occasional or systematic errors. Therefore, it is necessary to assess the quality and stability of these data over time, since ZTDs are used in several applications that require centimeter precision. Within this context, this work aims to assess the available ZTD of the whole Geodetic Reference System for the Americas Continuously Operating Network (SIRGAS-CON), consisting of 467 stations, spanning the period from January 2014 to December 2020 using the most recent Numerical Weather Model ERA5 from the European Centre for Medium-Range Weather Forecasts and common stations to the International GNSS Service (IGS) for an intercomparison. Results show that 10% of the stations present some instability, such as periods of highly dispersed data or discontinuities, with more occurrence in stations located in Argentina, Uruguay and Colombia. The remaining 90% proved to have stable and reliable ZTD, both in comparison with ERA5 and IGS.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"19 1","pages":"195 - 210"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90854850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Analysis of the gravity field, direct and inverse problems, by Fernando Sanso and Daniele Sampietro published by Birkhäuser 2022","authors":"M. Eshagh","doi":"10.1515/jogs-2022-0149","DOIUrl":"https://doi.org/10.1515/jogs-2022-0149","url":null,"abstract":"","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"43 1","pages":"244 - 245"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84135466","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The Deutsches Geodätisches Forschungsinstitut (DGFI) has been involved in the research activities of the Latin American Reference Frame SIRGAS since its establishment in 1993. DGFI coordinated the SIRGAS Global Positioning System campaigns of 1995 and 2000 and acted as an analysis centre of both campaigns contributing to the first two SIRGAS realisations known as SIRGAS95 and SIRGAS2000. In 1996, DGFI established the Regional Network Associate Analysis Centre for SIRGAS of the International GNSS (Global Navigation Satellite System) Service (IGS RNAAC SIRGAS) and took on responsibility for processing the SIRGAS continuously operating stations and generating weekly position solutions. Later followed the determination of cumulative (multi-year) solutions, consisting of station positions and constant velocities, providing accurate solutions for the SIRGAS reference frame. DGFI was integrated into the Technical University of Munich (TUM) in 2015, becoming DGFI–TUM, and based on the SIRGAS operational analyses, it continues investigating strategies to guarantee the reliability of the reference frame through time. This includes the estimation of the reference frame kinematics, evaluation, modelling, and reduction of seismic and post-seismic deformations on the reference frame, and modelling crustal kinematics in the SIRGAS region by continuous velocity models. This article summarises analysis strategies and science data products developed by DGFI–TUM as a SIRGAS analysis centre and as the IGS RNAAC SIRGAS. Special care is given to the determination of the most recent SIRGAS reference frame solution called SIRGAS2022, which is based on the second SIRGAS reprocessing campaign performed by DGFI–TUM to obtain homogeneously computed SIRGAS daily and weekly station position solutions referring to the IGS reference frame IGS14/IGb14 since January 2000.
{"title":"SIRGAS reference frame analysis at DGFI–TUM","authors":"L. Sánchez, H. Drewes, A. Kehm, M. Seitz","doi":"10.1515/jogs-2022-0138","DOIUrl":"https://doi.org/10.1515/jogs-2022-0138","url":null,"abstract":"Abstract The Deutsches Geodätisches Forschungsinstitut (DGFI) has been involved in the research activities of the Latin American Reference Frame SIRGAS since its establishment in 1993. DGFI coordinated the SIRGAS Global Positioning System campaigns of 1995 and 2000 and acted as an analysis centre of both campaigns contributing to the first two SIRGAS realisations known as SIRGAS95 and SIRGAS2000. In 1996, DGFI established the Regional Network Associate Analysis Centre for SIRGAS of the International GNSS (Global Navigation Satellite System) Service (IGS RNAAC SIRGAS) and took on responsibility for processing the SIRGAS continuously operating stations and generating weekly position solutions. Later followed the determination of cumulative (multi-year) solutions, consisting of station positions and constant velocities, providing accurate solutions for the SIRGAS reference frame. DGFI was integrated into the Technical University of Munich (TUM) in 2015, becoming DGFI–TUM, and based on the SIRGAS operational analyses, it continues investigating strategies to guarantee the reliability of the reference frame through time. This includes the estimation of the reference frame kinematics, evaluation, modelling, and reduction of seismic and post-seismic deformations on the reference frame, and modelling crustal kinematics in the SIRGAS region by continuous velocity models. This article summarises analysis strategies and science data products developed by DGFI–TUM as a SIRGAS analysis centre and as the IGS RNAAC SIRGAS. Special care is given to the determination of the most recent SIRGAS reference frame solution called SIRGAS2022, which is based on the second SIRGAS reprocessing campaign performed by DGFI–TUM to obtain homogeneously computed SIRGAS daily and weekly station position solutions referring to the IGS reference frame IGS14/IGb14 since January 2000.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"35 1","pages":"92 - 119"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87168334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Tocho, Ezequiel D. Antokoletz, Agustín R. Gómez, H. Guagni, D. Piñón
Abstract Following the definition and realization of the International Height Reference System (IHRS), the vertical coordinate of a given point at the Earth’s surface can be obtained from the computation of the geopotential value from a harmonic expansion of a Global Gravity Model of High-Resolution (GGM-HR) or based on the computation of a local or regional pure gravimetric geoid or quasigeoid. Therefore, an evaluation of the accuracy of GGMs-HR and the geoid model available is needed in order to assess its capability to infer IHRS coordinates. In this study, different GGMs-HR are evaluated against 2287 benchmarks in Argentina. Moreover, the most recent geoid model of Argentina is also evaluated. Geoid undulations at these benchmarks are obtained based on ellipsoidal and orthometric heights in the local vertical datum. Results suggest that among the evaluated GGMs-HR, XGM2019e provides the best agreement with the observed geoid heights, but none of them is accurate enough in order to infer vertical coordinates in the IHRS. Similar conclusions are obtained for the local geoid model for Argentina demonstrating the necessity for a more precise geoid model, following the standards and recommendations given for the IHRS.
{"title":"Analysis of high-resolution global gravity field models for the estimation of International Height Reference System (IHRS) coordinates in Argentina","authors":"C. Tocho, Ezequiel D. Antokoletz, Agustín R. Gómez, H. Guagni, D. Piñón","doi":"10.1515/jogs-2022-0139","DOIUrl":"https://doi.org/10.1515/jogs-2022-0139","url":null,"abstract":"Abstract Following the definition and realization of the International Height Reference System (IHRS), the vertical coordinate of a given point at the Earth’s surface can be obtained from the computation of the geopotential value from a harmonic expansion of a Global Gravity Model of High-Resolution (GGM-HR) or based on the computation of a local or regional pure gravimetric geoid or quasigeoid. Therefore, an evaluation of the accuracy of GGMs-HR and the geoid model available is needed in order to assess its capability to infer IHRS coordinates. In this study, different GGMs-HR are evaluated against 2287 benchmarks in Argentina. Moreover, the most recent geoid model of Argentina is also evaluated. Geoid undulations at these benchmarks are obtained based on ellipsoidal and orthometric heights in the local vertical datum. Results suggest that among the evaluated GGMs-HR, XGM2019e provides the best agreement with the observed geoid heights, but none of them is accurate enough in order to infer vertical coordinates in the IHRS. Similar conclusions are obtained for the local geoid model for Argentina demonstrating the necessity for a more precise geoid model, following the standards and recommendations given for the IHRS.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"32 1","pages":"131 - 140"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84771073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Recently a number of geoid campaigns were performed to verify different types of geoid and quasigeoid modeling techniques. Typically, GNSS-leveling was employed as an independent method, but in some cases zenith camera astronomic deflection data were also used in astrogeodetic determinations of the geoid and/or quasigeoid. However, due to the uncertainty in the topographic density distribution data (and thereby in orthometric heights), we conclude that neither GNSS-leveling nor astrogeodetic techniques can reliably verify differences between gravimetric geoid models at several centimeter levels in rough mountainous regions. This is because much the same topographic data are used both in the gravimetric geoid models and in their verifications by geometric and/or astrogeodetic geoid models. On the contrary, this is not a problem in verifying gravimetric quasigeoid models, as they are independent of the topographic density distribution, and so is the related normal height used in GNSS-leveling.
{"title":"Geoid model validation and topographic bias","authors":"L. Sjöberg","doi":"10.1515/jogs-2022-0133","DOIUrl":"https://doi.org/10.1515/jogs-2022-0133","url":null,"abstract":"Abstract Recently a number of geoid campaigns were performed to verify different types of geoid and quasigeoid modeling techniques. Typically, GNSS-leveling was employed as an independent method, but in some cases zenith camera astronomic deflection data were also used in astrogeodetic determinations of the geoid and/or quasigeoid. However, due to the uncertainty in the topographic density distribution data (and thereby in orthometric heights), we conclude that neither GNSS-leveling nor astrogeodetic techniques can reliably verify differences between gravimetric geoid models at several centimeter levels in rough mountainous regions. This is because much the same topographic data are used both in the gravimetric geoid models and in their verifications by geometric and/or astrogeodetic geoid models. On the contrary, this is not a problem in verifying gravimetric quasigeoid models, as they are independent of the topographic density distribution, and so is the related normal height used in GNSS-leveling.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"43 1","pages":"38 - 41"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80894681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Liibusk, Sander Varbla, A. Ellmann, K. Vahter, R. Uiboupin, N. Delpeche-Ellmann
Abstract For determining precise sea surface heights, six marine GNSS (global navigation satellite system) survey campaigns were performed in the eastern Baltic Sea in 2021. Four GNSS antennas were installed on the vessel, the coordinates of which were computed relative to GNSS–CORS (continuously operating reference stations). The GNSS–CORS results are compared to the PPP (precise point positioning)-based results. Better accuracy is associated with the GNSS–CORS postprocessed points; however, the PPP approach provided more accurate results for longer than 40 km baselines. For instance, the a priori vertical accuracy of the PPP solution is, on average, 0.050 ± 0.006 m and more stable along the entire vessel’s survey route. Conversely, the accuracy of CORS-based solutions decreases significantly when the distances from the GNSS–CORS exceed 40 km, whereas the standard deviation between the CORS and PPP-based solutions is up to 0.075 m in these sections. Note that in the harbor (about 4 km from the nearest GNSS–CORS), the standard deviation of vertical differences between the two solutions remains between 0.013 and 0.024 m. In addition, the GNSS antennas situated in different positions on the vessel indicated different measurement accuracies. It is suggested for further studies that at least one GNSS antenna should be mounted above the mass center of the vessel to reduce the effects of the dominating pitch motion during the surveys.
{"title":"Shipborne GNSS acquisition of sea surface heights in the Baltic Sea","authors":"A. Liibusk, Sander Varbla, A. Ellmann, K. Vahter, R. Uiboupin, N. Delpeche-Ellmann","doi":"10.1515/jogs-2022-0131","DOIUrl":"https://doi.org/10.1515/jogs-2022-0131","url":null,"abstract":"Abstract For determining precise sea surface heights, six marine GNSS (global navigation satellite system) survey campaigns were performed in the eastern Baltic Sea in 2021. Four GNSS antennas were installed on the vessel, the coordinates of which were computed relative to GNSS–CORS (continuously operating reference stations). The GNSS–CORS results are compared to the PPP (precise point positioning)-based results. Better accuracy is associated with the GNSS–CORS postprocessed points; however, the PPP approach provided more accurate results for longer than 40 km baselines. For instance, the a priori vertical accuracy of the PPP solution is, on average, 0.050 ± 0.006 m and more stable along the entire vessel’s survey route. Conversely, the accuracy of CORS-based solutions decreases significantly when the distances from the GNSS–CORS exceed 40 km, whereas the standard deviation between the CORS and PPP-based solutions is up to 0.075 m in these sections. Note that in the harbor (about 4 km from the nearest GNSS–CORS), the standard deviation of vertical differences between the two solutions remains between 0.013 and 0.024 m. In addition, the GNSS antennas situated in different positions on the vessel indicated different measurement accuracies. It is suggested for further studies that at least one GNSS antenna should be mounted above the mass center of the vessel to reduce the effects of the dominating pitch motion during the surveys.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"41 1","pages":"1 - 21"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87493483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The most common approaches for assigning weights to observations in minimum L1-norm (ML1) is to introduce weights of p or p sqrt{p} , p being the weights vector of observations given by the inverse of variances. Hence, they do not take covariances into consideration, being appropriated only to independent observations. To work around this limitation, methods for decorrelation/unit-weight reduction of observations originally developed in the context of least squares (LS) have been applied for ML1, although this adaptation still requires further investigations. In this article, we presented a deeper investigation into the mentioned adaptation and proposed the new ML1 expressions that introduce weights for both independent and correlated observations; and compared their results with the usual approaches that ignore covariances. Experiments were performed in a leveling network geometry by means of Monte Carlo simulations considering three different scenarios: independent observations, observations with “weak” correlations, and observations with “strong” correlations. The main conclusions are: (1) in ML1 adjustment of independent observations, adaptation of LS techniques introduces weights proportional to p sqrt{p} (but not p); (2) proposed formulations allowed covariances to influence parameters estimation, which is unfeasible with usual ML1 formulations; (3) introducing weighs of p provided the closest ML1 parameters estimation compared to that of LS in networks free of outliers; (4) weighs of p sqrt{p} provided the highest successful rate in outlier identification with ML1. Conclusions (3) and (4) imply that introducing covariances in ML1 may adversely affect its performance in these two practical applications.
在最小l1范数(ML1)中，最常用的方法是引入p或p sqrt{p}的权值，p是由方差的倒数给出的观测值的权值向量。因此，它们不考虑协方差，只适用于独立的观测。为了解决这一限制，最初在最小二乘(LS)背景下开发的观测值的去相关/单位权重减少方法已应用于ML1，尽管这种适应仍需要进一步研究。在本文中，我们对上述自适应进行了更深入的研究，并提出了新的ML1表达式，该表达式为独立和相关观测引入了权重;并将他们的结果与通常忽略协方差的方法进行比较。通过蒙特卡罗模拟，在一个水准网几何中进行了实验，考虑了三种不同的场景:独立观测、“弱”相关性观测和“强”相关性观测。主要结论是:(1)在独立观测值的ML1平差中，LS技术的自适应引入了与p sqrt{p}成比例的权重(而不是p);(2)提出的公式允许协方差影响参数估计，这在通常的ML1公式中是不可行的;(3)在不存在异常值的网络中，引入p的权重提供了比LS更接近的ML1参数估计;(4) p sqrt{p}的权重对ML1的离群值识别成功率最高。结论(3)和(4)表明，在ML1中引入协方差可能会对其在这两个实际应用中的性能产生不利影响。
{"title":"Introducing covariances of observations in the minimum L1-norm, is it needed?","authors":"S. Suraci, L. Oliveira, I. Klein, R. Goldschmidt","doi":"10.1515/jogs-2022-0135","DOIUrl":"https://doi.org/10.1515/jogs-2022-0135","url":null,"abstract":"Abstract The most common approaches for assigning weights to observations in minimum L1-norm (ML1) is to introduce weights of p or p sqrt{p} , p being the weights vector of observations given by the inverse of variances. Hence, they do not take covariances into consideration, being appropriated only to independent observations. To work around this limitation, methods for decorrelation/unit-weight reduction of observations originally developed in the context of least squares (LS) have been applied for ML1, although this adaptation still requires further investigations. In this article, we presented a deeper investigation into the mentioned adaptation and proposed the new ML1 expressions that introduce weights for both independent and correlated observations; and compared their results with the usual approaches that ignore covariances. Experiments were performed in a leveling network geometry by means of Monte Carlo simulations considering three different scenarios: independent observations, observations with “weak” correlations, and observations with “strong” correlations. The main conclusions are: (1) in ML1 adjustment of independent observations, adaptation of LS techniques introduces weights proportional to p sqrt{p} (but not p); (2) proposed formulations allowed covariances to influence parameters estimation, which is unfeasible with usual ML1 formulations; (3) introducing weighs of p provided the closest ML1 parameters estimation compared to that of LS in networks free of outliers; (4) weighs of p sqrt{p} provided the highest successful rate in outlier identification with ML1. Conclusions (3) and (4) imply that introducing covariances in ML1 may adversely affect its performance in these two practical applications.","PeriodicalId":44569,"journal":{"name":"Journal of Geodetic Science","volume":"131 1","pages":"65 - 74"},"PeriodicalIF":1.3,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86352708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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