Contribution of the Vienna Center for VLBI to ITRF2020

<p>The next realization of the International Terrestrial Reference System, the ITRF2020, is planned to be released in 2021. Our joint VLBI Analysis Center VIE which runs between TU Wien and BEV is one of eleven IVS (International VLBI Service for Geodesy and Astrometry) analysis centres which provide VLBI input to the ITRF2020. The SINEX files submitted to the IVS Combination Center are produced with the Vienna VLBI and Satellite Software VieVS and contain unconstrained normal equation systems for station position, source coordinates and Earth orientation parameters. In this presentation, we document the included sessions and stations in our submission and introduce the Vienna terrestrial reference frame based on our contribution to the ITRF2020. In particular, we highlight special settings in the Vienna solution and assess the impact on the terrestrial reference frame.</p>

Control of following Force in Gimbal Suspension by Programmed Transfer of Vehicle in the Class of Spiral-Screw Trajectories

The programmed transfer of the transport vehicle in space is carried out in the class of helical trajectories, using forcing (throttling) and deviation of the following driving force in the gimbal. The paper introduces the mathematical models of the transport vehicle kinetics in space in the terrestrial reference system and in the basis of the natural trihedral of the trajectory, using the quaternion form. The kinematics of the transport vehicle in the fixed and mobile reference systems, as well as the orientation of the natural trihedral in the inertial space, are represented by the hodograph of the program helix trajectory in vector and quaternion forms. The components of the controlling driving force in the basis of the natural trihedral are determined by the kinetostatics equations of the programmed transfer of the transport vehicle along a helical trajectory in the required speed mode. The authors proposed a structural scheme of the gimbal suspension, providing the required driving force components. The authors considered two possible sequences of rotations of the moving gimbal rings and demonstrated their equivalence. Laconic formulas are established for the control angles of rotation of the moving gimbal rings.

Sistemas Geodésicos de Referência: Rumo ao GGRS/GGRF

O estabelecimento de Sistemas Geodésicos de Referência globais integrando características geométricas e físicas é um dos desafios atuais da Geodésia, principalmente devido às demandas de diversas áreas do conhecimento de que as informações relacionadas aos Sistemas de Observação da Terra (EOS – Earth Observation Systems), sejam integradas em Redes Geodésicas de Referência (RGRs) com uma acurácia de 10-9 ou melhor. O surgimento das técnicas de posicionamento espacial trouxe melhora significativa na qualidade posicional e possibilitou a substituição das RGRs clássicas por redes modernas com características globais. Hoje, a questão das coordenadas de caráter geométrico, está bem resolvida com o ITRS/ITRF (International Terrestrial Reference System/International Terrestrial Reference Frame). Todavia, aspectos associados a diversos processos físicos, tais como os reflexos das redistribuições de massa, não são atendidos por referenciais puramente geométricos. A aprovação da resolução para o GGRS/GGRF (Global Geodetic Reference System/Global Geodetic Reference Frame) surge com a visão da integração entre o referencial terrestre, o celeste, um referencial com características físicas para as altitudes e a nova rede global de gravidade absoluta. Esforços têm sido feitos para definição e realização deste referencial global para as altitudes. É uma tarefa complexa em vista das características clássicas dos referenciais verticais, heterogeneidade em termos de qualidade e distribuição espacial de dados necessários, principalmente os relacionados ao campo de gravidade da Terra. Apresentam-se como grandes desafios para o futuro a necessidade de estabelecimento de procedimentos padrão para a integração ao referencial altimétrico global e a precisão necessária para o estabelecimento dos EOS.

COORDINATES SYSTEMS HARMONIZATION IN THE FRONTIER DISTRICTS OF THE DANUBE

Геодезична мережа як віртуальна, так і реальна розглядається сьогодні як важлива інфраструктура подібна електричним мережам або транспортним. Кожна країна має свою національну мережу, яку будують так, щоб вона була якомога близько до поверхні геоїда цієї країни. Але геоїд не є правильною геометричною фігурою і саме тому при зустрічі геодезичних мереж на кордоні сусідніх країн існує так званий координатний стрибок Δx; Δy; Δz, який треба знайти та розподілити у вигляді поправок до геодезичних пунктів, розташованих близько кордону. Що стосується висотної референсної системи, то вихідні дані відлікових рівневих поверхонь також можуть відрізнятися на суттєві значення. Референсна система імплементована у вигляді закріплених на місцевості геодезичних пунктів. Так наприклад в Європі використовують такі референсні системи як ETRS (European Terrestrial Reference System) i ERTF (European Reference Terrestria Frame), а також EVRS (V- Vertical) i EVRF. В Україні використовують для планової системи координат еліпсоїд WGS 84 з визначеними параметрами та Балтійську систему висот. В роботі розглянуто можливість приведення систем координат на прикордонних ділянках на річці Дунай до загально обраної референсної системи. Метою даного дослідження є намір розробити такий алгоритм, який дозволив би привести всі системи координат, що використовують придунайські країни до гармонізованого стану, шляхом введення постійно діючих величин на кордоні цих країн. В роботі показано як можна це реалізувати на прикладі прикордонних геодезичних мереж між Україною, Румунією та Болгарією. Запропоновано використання програмного продукту DaWAT, який дозволяє автоматично трансформувати дані з вертикальної референсної системи Румунії (MN75) До Української і Болгарської (Балтійська система висот).

MARVEL mission proposal: The latest update

<p>Following the recommendations of the 2019 CNES scientific prospective seminar, a pre-Phase-A study was launched in January 2020 at CNES on the concept of the MARVEL mission. MARVEL proposed to carry out in a single mission the survey of earth mass transfers with increased precision and the determination of the terrestrial reference system, thanks to two constellations of satellites at 500 and 7000 km altitude equipped with "radial" measurement links between the constellations. The results of the first six months of this pre-Phase-A will be presented.</p> <p><br />Our work has mainly focused on two axes:<br />- a closed-loop numerical simulation to assess the scientific performance of a large number of orbital configurations, including radial links but also "Bender" and "Pendulum" configurations;<br />- a technological study to bring the precision of a laser inter-satellites chronometry link to the micrometric level.</p> <p><br />This work has, so far, highlighted:<br />1 / the poorer performance for the determination of the gravity field of the "radial" type measurements compared to a "pendular" configuration in which the satellites are at the same low altitude with the ascending nodes of their orbits slightly offset so that the measurements between the spacecraft are alternatively oriented to the right and to the left of the track, thus improving the geometric configuration compared to an in-line pair of satellites;<br />2 / the technological possibility of achieving by chronometric laser link, over a few hundred or even a few thousand km, the precision of 1 micrometer in distance and 0.1 micrometer/s in relative velocity (which is necessary for the achievement of the scientific objectives).</p> <p><br />The pre-Phase-A MARVEL, taking into account the "Mass Change" studies on the NASA side and "NGGM" on the ESA side, is therefore reoriented towards a "pendulum" type mission, abandoning the objective of determining jointly the terrestrial reference system.</p>

Comparison Between IGS and Three ITRS Realizations

Four space geodetic techniques (IGS, SLR, VLBI and DORIS) contribute to the realizations of International Terrestrial Reference System (ITRS). The GNSS-derived terrestrial reference frame generated from the second reprocessing campaign (repro2), named IG2, act as the IGS input to the most recently three realizations (ITRF2014, DTRF2014 and JTRF2014). Its origin and orientation are aligned to the IGb08, and its scale is defined by using the igs08.atx satellite antenna phase center offset (PCO) values. To study the consistencies and discrepancies between IGS solutions and the three ITRS realizations, we corrected the IG2 solutions to be uniform with the IGS14 frame and perform Helmert transformation to compare the IGS frame and the three ITRS realizations. Results indicate that IGS frame is more stable than the two secular frames especially in the periods after 2015. The similarity transformation parameters between the corrected IGS solutions and ITRF2014 show excellent agreement with a notable mean z-offset of around 1 mm. The transformation parameters between the corrected IGS solutions and DTRF2014 show linear discrepancies in the three categories parameters, where the origin offsets are around less than 5.5 mm, rotational alignment is consistent at the level of 4.5 uas/yr (about 0.15 mm/yr) and the scale exhibits a stable offset of 0.16 ppb. Unlike the two secular frames, distinct seasonal signals and interannual variations of translation time series can be observed from the comparison between JTRF2014 and the IGS solutions. The orientation of JTRF2014 is in worst agreement with the IGS solutions, which is related to biased no-net-rotation (NNR) condition due to weekly center of network (CN) variations. Moreover, the scale defined by JTRF2014 suffer from large instability variations over time.

An All-in-One Application for Temporal Coordinate Transformation in Geodesy and Geoinformatics

Over the years, Global Navigation Satellite Systems (GNSS) have been established in the geosciences as a tool that determines the positions of discrete points (stations) on the Earth’s surface, on global to local spatial scales in a very simple and economical manner. Coordinates obtained by space geodetic measurements ought to be processed, adjusted, and propagated in a given reference frame. As points on the Earth’s surface do not have a fixed position, but rather, are moving with associated velocities, it is inevitable to include those velocities in the coordinate transformation procedure. Station velocities can be obtained from kinematic models of tectonic plate motions. The development and realization of an all-in-one standalone desktop application is presented in this paper. The application unifies coordinate transformation between different realizations (reference frames) of the International Terrestrial Reference System (ITRS) and European Terrestrial Reference System 1989 (ETRS89) following European Reference Frame Technical Note (EUREF TN) recommendations with temporal shifts of discrete points on the Earth’s surface caused by plate tectonics by integrating no-net rotation (NNR) kinematic models of the Eurasian tectonic plate.

A Practical Procedure to Integrate the First 1:500 Urban Map of Valencia into a Tile-Based Geospatial Information System

The use of geographic data from early maps is a common approach to understanding urban geography as well as to study the evolution of cities over time. The specific goal of this paper is to provide a means for the integration of the first 1:500 urban map of the city of València (Spain) on a tile-based geospatial system. We developed a workflow consisting of three stages: the digitization of the original 421 map sheets, the transformation to the European Terrestrial Reference System of 1989 (ETRS89), and the conversion to a tile-based file format, where the second stage is clearly the most mathematically involved. The second stage actually consists of two steps, one transformation from the pixel reference system to the 1929 local reference system followed by a second transformation from the 1929 local to the ETRS89 system. The last stage comprises a map reprojection to adapt to tile-based geospatial standards. The paper describes a pilot study of one map sheet and results showed that the affine and bilinear transformations performed well in both transformations with average residuals under 6 and 3 cm respectively. The online viewer developed in this study shows that the derived tile-based map conforms to common standards and lines up well with other raster and vector datasets.

Determination of the relationship between Vietnam national coordinate reference system (VN-2000) and ITRS, WGS84 and PZ-90

In July 2000, Hanoi-72 reference system was replaced by the Vietnam reference system, namely as VN-2000 as an official geodetic background system in Vietnam. Ministry of Natural Resources and Environment of Vietnam has reported the transformation parameters between VN-2000 and WGS84. Nevertheless, there is a need to estimate a new transformation parameter set between VN-2000 and WGS84 because WGS84 has been updated. In addition, there is now a lack of an accurate published set of parameters for transformation from VN-2000 to not only the International Terrestrial Reference System ITRS but also PZ-90. In this study, coordinate transformation parameters between ITRS and VN-2000 are estimated through the use of a least square approach and the common points with known coordinates in both systems. These set of parameters was then deployed to determine the link between VN-2000 and WGS84 as well as PZ-90. The results denoted that the derived transformation parameters, on the basis of the results at the checkpoints, could generated station positions with the accuracy at several cm level for transformation from VN-2000 to the new realizations of ITRS, WGS84 and PZ90 and reversely. These achievements reveals that the set of parameters is great significance for many applications related to positioning in Vietnam.