Tobias Kersten | Leibniz Universität Hannover (original) (raw)

Paper by Tobias Kersten

Advances in Space Research, Jan 28, 2021

Multi-frequency and multi-constellation GNSS have the potential to boost the overall performance ... more Multi-frequency and multi-constellation GNSS have the potential to boost the overall performance of GNSS-based positioning, navigation and timing. This has an impact on the realisation of global reference frames, geophysical monitoring applications as well as enabling new applications. To this end, all error sources should be adequately corrected for. However, currently multi-frequency multi-GNSS receiver antenna calibration values are still missing. In this paper, the newly developed multi-frequency multi-GNSS calibration process at Institut für Erdmessung (IfE), Leibniz University Hannover, is presented. The basic concept and the assumptions for the antenna calibration are described. Resulting phase centre corrections (PCC) for GPS and Galileo for typical antennas are presented. We show that the repeatability of the estimated patterns are almost better than 2mm in terms of maximum deviation and that the used tracking strategies by the receivers have marginal impact on the patterns, at maximum 1.2mm for the studied receiver-antenna combinations. Furthermore, applying phase centre corrections for multi-frequency multi-GNSS carrier phase observations reduces significantly (up to 37%) the antenna related biases as validated on short baselines. Moreover, a validation in the coordinate domain shows that with IfE PCC a short baseline can be computed with high accuracy: the topocentric coordinate differences to the known baseline are in most cases smaller than 1mm for the horizontal components and smaller than 2.2mm in vertical.

Sensors 2020, Volume 20, Issue 9, 2463, Apr 26, 2020

Various GNSS applications require low-cost, small-scale, lightweight and power-saving GNSS device... more Various GNSS applications require low-cost, small-scale, lightweight and power-saving GNSS devices and require high precision in terms of low noise for carrier phase and code observations. Applications vary from navigation approaches to positioning in geo-monitoring units up to integration in multi-sensor-systems. For highest precision, only GNSS receivers are suitable that provide access to raw data such as carrier phase, code ranges, Doppler and signal strength. A system integration is only possible if the overall noise level is known and quantified at the level of the original observations. A benchmark analysis based on a zero baseline is proposed to quantify the stochastic properties. The performance of the consumer grade GNSS receiver is determined and evaluated against geodetic GNSS receivers to better understand the utilization of consumer grade receivers. Results indicate high similarity to the geodetic receiver, even though technical limitations are present. Various stochastic techniques report normally distributed carrier-phase noise of 2mm and code-range noise of 0.5-0.8m. This is confirmed by studying the modified Allan standard deviation and code-minus-carrier combinations. Derived parameters serve as important indicators for the integration of GNSS receivers into multi-sensor-systems.

Tagungsband Geomonitoring 2019, Mar 15, 2019

Senkungsvorgänge der Erdoberfläche stellen vor allem in urbanen Gebieten eine deutliche Gefährdun... more Senkungsvorgänge der Erdoberfläche stellen vor allem in urbanen Gebieten eine deutliche Gefährdung dar. Oftmals sind diese Senkungen durch Massenvariationen im Untergrund verursacht und führen zu langsamen, aber auch abrupten Einsenkungen der Erdoberfläche. Im Rahmen des Verbundprojektes SIMULTAN (Sinkhole Instability: MULti-scale monitoring and ANalysis) wird die Untersuchung dieser Phänomene auf Grundlage geophysikalisch-geodätischer Methoden durchgeführt, um ein tieferes Verständnis der komplexen Zusammenhänge zwischen Auslaugungsprozessen im Untergrund und den eintretenden Effekten auf der Erdoberfläche zu gewinnen. In dem hierzu angelegtem integrierten geodätisch-gravimetrischen Überwachungsnetz werden die Methoden Gravimetrie, Nivellement und GNSS zusammengeführt und die Ergebnisse der zeitlichen Variationen bzw. auftretenden Deformationen in einem urbanen Umfeld auf Signifikanz hin untersucht. Basierend auf den GNSS-Kampagnen, die in den Jahren 2015-2017 in Hamburg Groß Flottbek durchgeführt wurden, lassen sich Erkenntnisse gewinnen, auf welcher Ebene und in welchem Umfang die einzelnen Methoden und deren Kombination erfolgreich eingesetzt werden können. Es wird aufgezeigt, dass die Kombination zu sehr guten Übereinstimmungen führt und Senkungen von 1,5-2 mm durch alle Methoden nachweisbar sind, obwohl die innerstädtische Kubatur eine komplexe Vielzahl an Herausforderungen an eine präzise GNSS-Auswertung aufweist.

Proceedings of POSNAV ITS (2018), 15.-17. November 2018, Berlin, 2018

This paper describes a concept to obtain a continuous navigation and position solution of inland ... more This paper describes a concept to obtain a continuous navigation and position solution of inland vessels based on a multi-GNSS antenna system. Also known as, “Virtual Receiver” we utilize this approach as an alternative method with respect to a common dead reckoning procedure. Such an approach strengthens the geometry of visible GNSS satellites immediatelyby up to 50%. At the same time, dilution of precision values improve by up to 40%. Hence, continuous navigation solution under difficult and challenging environmental conditions improves or is even possible. Specific experiments, obtained on a trip from Hannover westward on the Mittelland Canal with the inland vessel “MS Jenny” prove that various quality measures as well as the noise of the position estimates reduce significantly by up to 0.4 m. The position availability for code based navigation reaches 94.5% w.r.t classical single point positioning with 77%.

Proceedings of Navitec (2018), 5.-7. December 2018, Noordwijk, The Netherlands, 2018

Efficient and economic guidance of inland vessels relies on a continuous, available, reliable and... more Efficient and economic guidance of inland vessels relies on a continuous, available, reliable and precise GNSS navigation solution. Hence, below other side effects, this is especially critical when passing beneath bridges or similar infrastructures that cross waterways. They have two effects: distortion (reflection, diffraction and interruption) of the incoming GNSS signal by the individual bridge structure on the one hand and along with that, the affected ambiguity resolution for carrier phase observation on the other hand. Thus, disturbances, discontinuities and jumps in the position estimates are present - an extreme critical situation especially for safety-relevant applications. A multi-antenna system for marine applications combined with the concept of a virtual receiver will be presented. This approach strengthen the overall geometry of visible GNSS satellites immediately, and provides continuous position estimates even for challenging passages. Furthermore, a bridging of observations between two or more antennas on a known rigid platform reduces signal interruptions and provides continuous navigation solution under challenging or even critical environmental conditions. Laboratory experiments, driven on a 2,5 hour turn from Hannover on the Mittelland Canal on the inland vessel MS Jenny (MS Science) prove, that various DOP values as well as noise of the position solution are reduced significantly. The observation noise is reduced by up to 0.3-0.4m whereby the position solution for a code based navigation reaches up to 94.5% w.r.t. classical single point positioning. The overall positioning performance is improved by up to 80%.

Data Repository Leibniz University Hannover and Leibniz University IT Service (LUIS) , 2018

This dataset contains a bundle of 5 mass market receiver (ublox Neo M8T) and three geodetic grade... more This dataset contains a bundle of 5 mass market receiver (ublox Neo M8T) and three geodetic graded receiver (Leica GNSS1200+GNSS, Septentrio PolaRx 5TR, Javad Delta TRE_G3T) combined in a zero baseline. The dataset captures 7 days of measurements with carrier phase, code phase, Doppler, carrier-to-noise ratio (C/N0) for GPS/GLONASS C/A code on frequency L1 for the mass market receiver and GPS/GLONASS/GALILEO L1/L2/L5 for geodetic receiver. All geodetic receiver were feeded by external rubidium clock (SRS FS725 Benchmark).

Data Repository Leibniz University Hannover and Leibniz University IT Service (LUIS), 2018

This dataset provides first experimental code-based GPS receiver antenna calibrations for analysi... more This dataset provides first experimental code-based GPS receiver antenna calibrations for analysis and integration in practical applications. Please note, that the data is in experimental status and no (!) official calibration product. Thus, it is free for scientific research/use only.

Several GPS receiver antennas have been calibrated and are provided in this zip-package. The author is interested on any use of the data set and any reply to improve the Code Phase Variation (CPV) estimation process.

Code Phase Variations of following GPS/GNSS receiver antennas in ATX format:
- Ublox mouse antenna with groundplane (ANN-MS_GP_CA, C/A, P-code) - Ashtec Marine 700700B (ASH700700B, C/A code)
- Ashtec Marine 700700B (ASH700700B, P1/P2 code)
- Javad RegAnt Dual coke ring (JPSRegAnt_DD_E, C/A code)
- Javad RegAnt Dual coke ring (JPSRegAnt_DD_E, P1/P2 code)
- Leica reference antenna AR25 with Radom (LEIAR25.R3_LEIT, P1/P2 code)
- Leica rover antenna AX1202GG (LEIAX1202GG, C/A code)
- Leica rover antenna AX1202GG (LEIAX1202GG,P1/P2 code)
- NavXperience rover antenna (NAX3G+C, C/A code)
- NavXperience rover antenna (NAX3G+C, P1/P2 code)
- Novatel aerial antenna (NOV512, C/A code)
- Trimble Zephyr I Geodetic (TRM41249-00, P1/P2 code)
- Trimble choke ring antenna (TRM59900-00, P1/P2 code)

Subsidence processes in dense populated urban areas are of high social relevance. As there is few... more Subsidence processes in dense populated urban areas are of high social relevance. As there is few knowledge about the evolution and the characteristic of subsidence induced land depressions or sudden sinkhole events, a detailed and interdisciplinary focus is set on this field of research especially at regions and cities with dense population. SIMULTAN (Sin-kole Instability, MULTiscale monitoring an ANalysis) aims at an interdisciplinary level to gain a deeper understanding of the complex processes, interactions and characteristics of the underground and the surface interaction in urban environments, (KERSTEN, ET AL. 2016). The aims and working packages of SIMULTAN are defined by four items:
1. Characterisation of the underground with high resolution methods (seismics, geoelectrics, downhole logging, seismology, direct push) and inverse techniques,
2. Monitoring of the surface and subsurface by combining geodetic and geological techniques (GNSS, levelling, relative and absolute gravimetry),
3. Interdisciplinary interaction and closed loop between field data and modelling of sinkhole evolutions with process simulation techniques, and finally
4. Integration of all elements into an information and hazard control platform.
This paper will focus on the second element of the SIMULTAN project and in detail on the reproducibility of derived GNSS positions and heights in inner city environments.

The research project SIMULTAN applies an advanced combination of geophysical, geodetic, and model... more The research project SIMULTAN applies an advanced combination of geophysical, geodetic, and modelling techniques to gain a better understanding of the evolution and characteristics of sinkholes. Sinkholes are inherently related to surface deformation and, thus, of increasing societal relevance, especially in dense populated urban areas. One work package of SIMULTAN investigates an integrated approach to monitor sinkhole-related mass translations and surface deformations induced by salt dissolution. Datasets from identical and adjacent points are used for a consistent combination of geodetic and geophysical techniques. Monitoring networks are established in Hamburg and Bad Frankenhausen (Thuringia). Levelling surveys indicate subsidence rates of about 4–5 mm per year in the main subsidence areas of Bad Frankenhausen with a local maximum of 10 mm per year around the leaning church tower.

Here, the concept of combining geodetic and gravimetric techniques to monitor and characterise geological processes on and below the Earth's surface is exemplary discussed for the focus area Bad Frankenhausen. For the different methods (levelling, GNSS, relative/absolute gravimetry) stable network results at identical points are obtained by the first campaigns, i.e., the results are generally in agreement.

Precise navigation and geodetic coordinate determination rely on accurate GNSS signal reception. ... more Precise navigation and geodetic coordinate determination rely on accurate GNSS signal reception. Thus, the receiver antenna properties play a crucial role in the GNSS error budget. For carrier phase observations, a spherical radiation pattern represents an ideal receiver antenna behaviour. Deviations are known as phase centre corrections. Due to synergy of carrier and code, similar effects on the code exist named code phase variations (CPV). They are mainly attributed to electromagnetic interactions of several active and passive elements of the receiver antenna. Consequently, a calibration and estimation strategy is necessary to determine the shape and magnitudes of the CPV. Such a concept was proposed, implemented and tested at the Institut für Erdmessung. The applied methodology and the obtained results are reported and discussed in this paper. We show that the azimuthal and elevation-dependent CPV can reach maximum magnitudes of 0.2-0.3m for geodetic antennas and up to maximum values of 1.8 m for small navigation antennas. The obtained values are validated by dedicated tests in the observation and coordinate domain. As a result, CPV are identified to be antenna- related properties that are independent from location and time of calibration. Even for geodetic antennas when forming linear combinations the CPV effect can be amplified to values of 0.4--0.6 m. Thus, a significant fractional of the Melbourne--Wübbena linear combination. A case study highlights that incorrect ambiguity resolution can occur due to neglecting CPV corrections. The impact on the coordinates which may reach up to the dm level is illustrated.

Evaluating the impact of receiver antenna phase centre corrections (PCCs) in geodetic positioning... more Evaluating the impact of receiver antenna phase centre corrections (PCCs) in geodetic positioning and timing applications in a general way is quite challenging, because several estimation concepts, implementation philosophies as well as different sets of PCCs exist and interact with each other and their contributions are not identifiable. In this paper, the authors present a methodology, based on investigations of Geiger (GPS-techniques applied to geodesy and surveying. Lecture notes in earth sciences, vol 19. Springer, New York, pp 210–222, 1988) and Santerre (Manuscr Geodaet 16:28–53, 1991), to classify PCCs and forecast their impact on all geodetic parameters, i.e. not only the position but also the receiver clock and troposphere parameter in a phase based precise point positioning (PPP) approach. In a first step, we introduce the mathematical model and generic PCC patterns. In the second step, simulation studies are carried out. Findings are evaluated by empirical studies using differences of PPP results to isolate the impact of different patterns. In parallel, the software impact is analysed since every software handles the observation modelling and parameter estimation differently, e.g., Kalman filter versus least squares approach. We show that all geodetic parameters are affected by PCC and that the impact on the parameters can be even amplified compared to the magnitude of the generic patterns.

European Navigation Conference, ENC2013, Jul 1, 2013

Abstract—This contribution demonstrates the analysis and application of antenna specific Group De... more Abstract—This contribution demonstrates the analysis and application of antenna specific Group Delay Variations determined by the Hannover Concept of absolute antenna calibration and the robot of the Institut für Erdmessung (IfE). Group Delay Variations (GDV) may affect the correctness of the position solution in wide area differential GPS applications.

The paper demonstrates that antenna specific GDV can occur above the code noise level and influences the correctness of the code observation by systematic effects. A detailed study provides strong evidence that code based positioning is improved by up to 0.3m (or 30%) when GDV are considered. It will be shown if also navigation applications can be improved. Furthermore, we will discuss in detail that GDV do not appear with significant magnitudes on all PS/GNSS antennas.

6th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing, (NAVITEC), 2012

The Institut für Erdmessung (IfE) is an official IGS calibration institution, calibrating phase ... more The Institut für Erdmessung (IfE) is an official IGS calibration institution, calibrating phase center variations (PCV) for receiver antennae routinely in the field, using the actual GNSS satellite signals in space. Current research activities focus on the antenna code phase calibration with the Hannover Concept of absolute antenna calibration. The receiving antenna as a part of a reception chain can introduce systematic effects, currently known as Group Delay Variations (GDV), i.e. azimuth and elevation dependent code-phase delays. This error introduces additional range variations along the line-of-sight for every satellite depending on the corresponding incident angle in the antennas body frame. Depending on the antenna design, suitable for specific applications, GDV can degrade the accuracy of code based applications, such as precise landing approaches as well as for time and frequency transfer. The paper can be subdivided into two major parts: In the first part, we focus on the current investigations on receiver antenna GDV calibration. Beside the theoretical background of a concept to determine GDV for different GPS antennae based on the Hannover Concept of absolute antenna calibration, the obtained GDV from several antennae with different characteristics will be presented and critically discussed. The second part focuses on the consequent analysis of the impact of the determined GDV on position and navigation applications. The contribution of GDV on the observation and position domain can be shown by using a special experimental set-up. In addition, GDV for a real C/A based autonomous navigation approach are investigated and critically discussed.

European Frequency and Time Forum (EFTF), 2012 , Apr 27, 2012

Group Delay Variations (GDVs) are azimuth and elevation ependent code delays that can limit the ... more Group Delay Variations (GDVs) are azimuth and elevation ependent code delays that can limit the accuracy of the GNSS code observables. This contribution focuses on the GDV etermination and discusses several solutions with respect to epeatability and separability. Onsite tests at a laboratory network as well as simulations of several time links are discussed analyzing the stochastic processes apparently introduced by GDV. The stability of the P3 links are not effected. However, offsets up to 0.6 ns can occur.

In a detailed study, GDVs are applied to an intercontinental Precise Point Positioning (PPP) time transfer link. This analysis shows that GDV are not an issue for the stability of the PPP links, since small weights reduce the impact of the P3 GDV. It can be shown that the stochastic process, induced by GDV in a PPP nalysis, is similar to a random walk noise, well below the L3 carrier phase observation noise of sigma (phi)= 6 mm. Offsets for the receiver clock estimates of up to 0.4 ns are reported for the link WTZS (Wettzell) and Boulder (NIST).

Conference Presentations by Tobias Kersten

Für hochpräzise GNSS-Anwendungen sind Trägerphasenmessungen unabdingbar. Bei solchen Messungen is... more Für hochpräzise GNSS-Anwendungen sind Trägerphasenmessungen unabdingbar. Bei solchen Messungen ist es notwendig die individuellen Antennenphasenzentrumskorrekturen (PCC) zu berücksichtigen. Ähnliche Korrekturen existieren auch für Codebeobachtungen, so genannte Codephasenvariationen (CPV). Diese sind antennenabhängige Verzögerungen der empfangenen Codephase und können bis zu mehreren Dezimetern erreichen. Solche Variationen werden bisher nicht operationell im ANTEX Format bereitgestellt. Das Institut für Erdmessung (IfE) hat ein Konzept entwickelt, mit dem neben PCC für Trägerphasenmessungen auch CPV für alle GNSS geschätzt werden können. Dafür wird ein Roboter genutzt, der es erlaubt, einen Antennenprüfling um einen Punkt zu rotieren und zu kippen. Dabei werden echte GNSS-Signale der sichtbaren Satelliten genutzt. Durch Bildung von zeitdifferenzierten Einfachdifferenzen ist es möglich, PCC und CPV zu schätzen, da diese lediglich das Pattern des Antennenprüflings beinhalten. In einem post-processing Ansatz werden mit sphärisch harmonischen Funktionen (8,8) die gewünschten Parameter geschätzt. In diesem Beitrag präsentieren wir unser Konzept zur Schätzung von CPV für GPS sowie Galileo Codephasen-Signale und die erzielten Ergebnisse. Dabei gehen wir auf die Wiederholbarkeit der Pattern unseres Verfahren ein, indem wir die Daten mehrtägige Kalibrierungen analysieren. Des Weiteren werden wir eine Validierung der geschätzten CPV auf Beobachtungs- und Koordinatenebene präsentieren.

EUREF Symposium 2019, May 22-24, Tallinn, Estonia, May 23, 2019

The Institut für Erdmessung (IfE) at the Leibniz University Hannover calibrates GNSS antennas det... more The Institut für Erdmessung (IfE) at the Leibniz University Hannover calibrates GNSS antennas determined by the well known robot based concept in the field. Our group has recently improved the calibration procedure to support absolute receiver antenna calibrations for all GNSS frequencies (GPS L1/L2/L5, GLONASS L1/L2 and Galileo E1/E5). To fully use the advantage of multi GNSS processing capabilities for absolute and relative precise positioning, accurate and consistent receiver antenna calibration patterns of ground stations are required. Currently, in IGS and EPN they are available by chamber calibration method for some antennas. However, systematic and sometimes significant differences exist between both approaches (field robot and chamber) that have to be studied in detail to identify the causes and to fix these issues. In this contribution, we present first robot based multi GNSS patterns from IfE. Furthermore, a study is performed, to show the impact from the observation domain (differences of antenna phase centre patterns) to the parameter domain (position, troposphere, ambiguities). In this study, we used reference stations from the EPN network which provide individual antenna patterns obtained from both approaches (field robot and chamber). Baselines of lengths ranging from 150-600km and one of 1670km are analysed. We found that on the one hand, differences between both pattern sets do not met the proposed "1mm-rule-of-thumb" in the most of studied cases. On the other hand, we show that in cases of consistent antenna pattern sets no significant differences in the parameter domain are obtained. However, mixing patterns from different approaches implies deviations of up to 1cm (in one case up to 2cm) mostly in the topocentric up component. These differences are directly aligned to the differences in the antenna pattern.

European Geophysical Union (EGU) General Assembly, Apr 13, 2018

Sinkholes are slowly to suddenly developing subsidence structures at the surface, caused by solut... more Sinkholes are slowly to suddenly developing subsidence structures at the surface, caused by solution of rocks. Their hazard potential is large, especially in urban areas. In the joint research project SIMULTAN (Sinkhole Instability: integrated MULTi-scale monitoring and ANalysis) the investigation and surveillance of sinkhole areas by a combination of geophysical, petrophysical, geodetical and hydrological methods contributes to the development of an early warning system of instability, as well as, in combination with modeling, to an improved process understanding. We focus on a region in the city of Hamburg where the subsidence areas Wobbe See and Flottbek Markt are located. Subsidence rates are in the order of 1 mm/a and presumably originate from solution processes related to the Othmarschen-Langenfelde Diapir. Following an integrative geodetic-gravimetric approach, surface deformation and mass change due to subrosion are observed, likewise with the objective of surveillance of the sinkhole area. Quarterly repeated levelling and gravimetry campaigns at 8 stations (since 01/2016) provide first results. On the one hand, they indicate a trend to subsidence in the Wobbe See area, in agreement with results of GNSS measurements, and on the other hand, mainly seasonal variations of elevation differences emerge up to now around Flottbek Markt, that can be correlated with hydrology. Can we detect potential mass changes in urban areas? This is investigated by repeated high-precision gravity measurements. The results are reproducible and significant temporal variations of gravity differences of up to 12 Gal (std. dev. 1 Gal). These variations comprise hydrological induced seasonal variations as well, due to local conditions at the points, like topography and different ground sealing. By tying the local, relative measurements to a regional reference system large-scale stability control is enabled. Regional SAPOS stations are linking the local, relative GNSS network and monitor their stability. Results of ionosphere free linear combination prove the stability of the local reference. The coordinate system ETRS89 in combination with the vertical datum DHHN2016 are the common geodetic datum for all combined geophysical approaches. As local urban conditions are challenging, new approaches like adaptive, dynamic elevation masks and extended recording periods are applied. Concerning gravity, annual absolute measurements are realized at one reference station, which supports the assumption of hydrological induced effects in the observed gravity changes. The intended modelling and correction of the hydrological induced gravity effect allows to separate possibly masked small effects of mass redistribution due to solution and sinkhole development. In case of observable gravity change, e.g. the mass dependent gravity gradient dg/dh can indicate mass change

European Geophysical Union (EGU) General Assembly, Apr 9, 2019

Phase center corrections (including corrections for phase center offset and phase center variatio... more Phase center corrections (including corrections for phase center offset and phase center variations) are nowadays mandatory for high accuracy GNSS applications. Currently, only L1- and L2 frequencies for GPS and GLONASS are provided and published in the Antenna Exchange Format (ANTEX) maintained by the antenna working group of the International GNSS Service IGS. Field calibrations values for new signals like Galileo or GPS L5 are still missing. The Institut für Erdmessung (IfE) is one of the IGS accepted absolute antenna field calibration institutions and provides PCC using the so-called Hannover-Concept, i.e. using a robot to precisely rotate and tilt the antenna under test. This concept has been extended into an experimental approach where PCC of new signals are estimated in post-processing using spherical harmonics. In this contribution, we describe the extended concept and show first patterns for the GPS L5 as well as the Galileo E1 and E5 signals. After a short introduction into the method of absolute antenna field calibration, the roboter model as well as the adjustment concept will be presented.We will show that an estimation of PCC is feasible with the method developed at the IfE. The patterns will be presented and discussed for antennas typical to IGS stations.

European Geophysical Union (EGU) General Assembly, Apr 9, 2019

For high accuracy GNSS applications it is necessary to take phase center corrections (PCC) into a... more For high accuracy GNSS applications it is necessary to take phase center corrections (PCC) into account. At the moment PCC from chamber calibrations for various signals are available, however GPS L5 as well as Galileo PCC from field calibrations are still missing. The Institut für Erdmessung (IfE) provides PCC patterns in operational mode for IGS and EPN since several decades. Our group is working to develop calibrations of receiver antennas for new GNSS-signals. For the estimation of the PCC for the new signals we use a post-processing approach modelling the PCC by spherical harmonics. First results and the concept are presented by our group. The focus in this contribution is to validate and verify the resulting PCC for GPS L5 as well as Galileo. A closed loop simulation shows that the pattern can be reliably estimated by our approach. For the verification of the results with real data a short baseline common clock set up at the Physikalisch-Technische Bundesanstalt (PTB) is used, where the receivers are linked to an external ultra stable frequency input. We use various antenna combinations and calculate observed-minus-computed (OMC) values to study the impact of PCC on receiver-toreceiver- single differences.With observations from several days, the siderial repetition of GPS L5 PCC is analysed.

European Geophysical Union (EGU) General Assembly , Apr 8, 2019

Precise GNSS applications like positioning, navigation and timing (PNT) as well as troposphere st... more Precise GNSS applications like positioning, navigation and timing (PNT) as well as troposphere studies require consistent and accurate calibration values of receiver antennas. Nowadays, they are available by several calibration institutions based on robot or anechoic chamber concepts. The impact of phase centre model of receiver antennas on geodetic parameters like position, troposphere and receiver clock estimates is quite challenging as several estimation concepts, implementation philosophies and different phase centre models exist. Their interaction with the estimates is complex, their individual impact not easily identifiable and a concept to forecast the impact on associated geodetic parameters not available at present. To integrate new satellite systems in the operational service, station operators of global (IGS) regional (EPN) and national (e.g. SAPOS, Germany or similar) networks require calibration values of these new signals in space (i.e. GPS L5, Galileo, etc). They are currently provided by chamber calibrations. However, the most of operational networks are mainly equipped with robot calibrations for GPS/GLONASS L1/L2. Although deficiencies exist for individual antennas between chamber and robot, a mixture of calibration values is applied to overcome the issue of required and available phase centre corrections. Nevertheless, differences will introduce systematic discrepancies in the parameters. At present, a rule of thumb for phase centre corrections to compare chamber and robot calibrations applies, which does not directly take into account the impact on the associated geodetic parameters. In addition, discrepancies between type mean and individual calibrations of up to 6-8mm are reported in regional and global networks, which lead up to 10mm in the height and up to 4mm in the horizontal component. This contribution will present a methodology to clarify this issue and will provide a concept to verify parameters, e.g. position, receiver clock and troposphere estimates. In previous publications, the authors focus on generic patterns to determine characteristics between chamber and robot calibrations. In this contribution, we verify the impact and apply stations of the EPN network, which provide equipment with calibrations of both types. Hence, a quantification of the impact is required to answer the following question: Is the 1mm-rule of thumb is justified, or are there better thresholds available to assist station operators in the near future?

Advances in Space Research, Jan 28, 2021

Sensors 2020, Volume 20, Issue 9, 2463, Apr 26, 2020

Tagungsband Geomonitoring 2019, Mar 15, 2019

Proceedings of POSNAV ITS (2018), 15.-17. November 2018, Berlin, 2018

Proceedings of Navitec (2018), 5.-7. December 2018, Noordwijk, The Netherlands, 2018

Data Repository Leibniz University Hannover and Leibniz University IT Service (LUIS) , 2018

Data Repository Leibniz University Hannover and Leibniz University IT Service (LUIS), 2018

European Navigation Conference, ENC2013, Jul 1, 2013

6th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing, (NAVITEC), 2012

European Frequency and Time Forum (EFTF), 2012 , Apr 27, 2012

EUREF Symposium 2019, May 22-24, Tallinn, Estonia, May 23, 2019

European Geophysical Union (EGU) General Assembly, Apr 13, 2018

European Geophysical Union (EGU) General Assembly, Apr 9, 2019

European Geophysical Union (EGU) General Assembly , Apr 8, 2019

Proceeding of Positionierung und Navigation für Intelligente Verkehrssysteme: POSNAV ITS 2018, November 15.-16., 2018

Die instantan mit stationären, terrestrischen Laserscannern (TLS) aufgenommen dreidimensionalen P... more Die instantan mit stationären, terrestrischen Laserscannern (TLS) aufgenommen dreidimensionalen Punktwolken beziehen sich generell auf ein lokales Horizontsystem, dessen Lage und Orientierung gegenüber einem übergeordnetem Koordinatensystem nur durch vorausberechnete Kontrollpunkte auf das notwendige geodätische Datum überführt werden können. Um eine direkte Georeferenzierung zu ermöglichen und den Prozess zu optimieren wurde am Geodätischen Institut Hannover (GIH) ein Multi-Sensor-System (MSS) entwickelt. Die aktuelle Konfiguration setzt sich aus kosteneffizienten und gewichtsreduzierten Elementen wie z.B. zwei Ublox M8T Empfängern in Kombination mit Ashtec L1-Antennen zusammen. Diese sind mit einer Basis von ca. 1 m auf dem Laserscanner aufgebracht und derart optimiert, dass das Sichtfeld nicht beeinflusst wird. Die anschließende Prozessierung zur Bestimmung der Transformationsparameter und des lokalen Azimuts basiert auf einen rekursiven Kalman Filter innerhalb eines Extended Kalman Filter (EKF) Ansatzes. Diese Systemkonfiguration und Auswertung führt nur zu optimalen Ergebnissen, sofern das Systemrauschen auf Ebene der originären Beobachtungen quantifiziert und exakt genau bekannt ist. Die Betrachtung auf der Beobachtungsebene erlaubt den Zugang zu den Beobachtungen, die durch modifizierte funktionale und stochastische Ansätze optimal angepasst werden können und steht damit im Gegensatz zu den Genauigkeitsparametern auf der Positionsebene, die sich aufgrund der internen Verarbeitung der Beobachtungen ergeben. Im Detail sind folgende Voraussetzungen notwendig: (1) es sollte eine Normalverteilung der Beobachtungen vorliegen, (2) die Informationen zur Kovarianzmatrix sollten vorhanden sein und (3) es sollten keine Korrelationen in zeitlicher Abhängigkeit entstehen. Diese Voraussetzungen sind aufgrund vorhandener stochastischer Abhängigkeiten durch zeitliche Korrelationen im Zustandsvektor nicht vollständig erfüllt. Zudem haben vorangegangene Studien gezeigt, dass die kinematischen Zeitreihen von ca. 15 Minuten Länge im Rahmen der Untersuchung der Autokorrelation zusätzliche Abhängigkeiten aufweisen. Daraufhin wurden in Kooperation mit dem Institut für Erdmessung (IfE) langzeitstatische Messungen bezüglich einer Referenzantenne auf einer Nullbasislinie analysiert und studiert, um die Systemeigenschaften der High-Sensitivity Empfänger zu quantifizieren und nachweisbare sowie robuste Aussagen für die Parameter der EFK-Modellierung ableiten zu können. Dieser Beitrag präsentiert ein Konzept zur Evaluierung und Analyse kosteneffizienter, high Sensitivity GNSS-Ausrüstungen. Es wird gezeigt, dass die Qualität dieser Geräte für eine breite Variation von Anwendungen erheblich gute Performanz aufweist, z. B. liegt das Trägerphasenrauschen bei 2 mm im Zenitbereich und ist damit vergleichbar zu aktuellen geodätischen GNSS-Empfängern. Dennoch ergeben sich marginale Elevationsabhängigkeiten, die es zusätzlich zu berücksichtigen gilt. Die wichtigsten Testparameter für den vorgestellten Ansatz sind u.a. die Trägerphasenstabilität, das Rauschniveau sowie Inter-Frequenz Offsets. Mit Werkzeugen wie z. B. der Quantil-/Quantil-Darstellung oder der Allan-Standardabweichung lassen sich die Rauschtypen charakterisieren. Zusätzlich erlaubt eine Analyse der Allan-Standardabweichung einen Rückschluss auf die Kurz- und Langzeitstabilität aller Beobachtungstypen (Träger-, Codephase, Doppler und C/N0) solcher Geräte. Zur Kreuzvalidierung werden zusätzlich Ergebnisse kinematischer Analysen diskutiert. Eine stabile Lösung im Sinne des Ansatzes einer kinematischen Basislinie für die zwei Antennen auf dem Scanner stehen im Fokus der aktuellen Betrachtungen. Die Ergebnisse und Quantifizierungen sollen zukünftig unterstützend helfen, Systemeigenschaften von Multi-Sensor-Systemen optimal abstimmen und Anwendungsfelder von High-Sensitivity Empfängern gesichert abschätzen zu können.

Proceedings of Navitec 2018, December 5.-7., Noordwijk, The Netherlands , Dec 6, 2018

Geodetic Week 2017, September 26-28, Berlin, Germany

International Association of Geodesy (IAG) Commission 4 (Positioning and Application) Symposium, Sep 6, 2016

Stationary terrestrial laser scanning (TLS) provides a 3D point cloud in a local sensor-defined c... more Stationary terrestrial laser scanning (TLS) provides a 3D point cloud in a local sensor-defined coordinate system. The transformation parameters of such point clouds to a global coordinate system are generally obtained by pre-surveyed control points with known geodetic datum. To improve this procedure, a direct geo-referencing method of a multi-sensor system with 3D position sensors has been developed at the Geodetic Institute Hannover. The current approach uses two small scaled and light weighted, high sensitivity GNSS-receivers of type Ublox EVK-M8T and Ashtech L1 antennas as 3D position sensors. These sensor types are used to reduce weight and equipment costs. They are mounted with a mutual distance (baseline) of 1 m on top of the laser scanner that rotates about its vertical axis. The analysis of the trajectories of the 3D GNSS-points and the estimation of the transformation parameters are based on a recursive filter approach in form of an extended Kalman Filter (EKF).
With the EKF algorithm optimal results can only be provided, if the system noise is normally distributed with known variance covariance matrix and without correlations over time. That means the model requires white noise. Unfortunately, this assumption is not sufficient in our processing approach due to the stochastically time-correlated state vector. Former studies revealed that the analysis of short kinematic time series (15 minutes) yields to insufficiencies regarding, e. g. the determination of the auto-correlation. Therefore, long-term static time series (up to 7 days) of four identical high sensitivity GNSS-receivers were acquired on a zero baseline approach. The reference antenna and receiver of the Institut für Erdmessung (IfE) are used as benchmark to evaluate and study proper parameters for the EKF parameter estimation and the direct geo-referencing parameters, respectively.
This contribution presents the noise analysis of the impact and the determination of statistical quality measures for improving the EFK parameter estimation. We will critically discuss results of our benchmark test of high sensitivity GNSS-receivers of type Ublox EVK-M8T. The noise analysis is based on a zero baseline approach. Important key parameters are e.g. the carrier phase stability and the overall acceptable noise level. The Allan deviation helps to characterize the process noise for long time series with respect to short time series, as they are used in typically MSS approaches for direct geo-referencing. In addition, first results of kinematic experiments are presented and critically compared to the static derived solutions by their individual uncertainty budget.

Several contributions and papers in geodesy intensively discuss the impact of the variability of ... more Several contributions and papers in geodesy intensively discuss the impact of the variability of GPS/GNSS
absolute phase centre corrections (PCCs) directly on the positioning domain, neglecting any studies on the
observation domain. Furthermore, it is very complex to evaluate in a general way the impact of several PCCs
in geodetic positioning due to the different positioning concepts (e.g. PPP, relative positioning in networks) as
well as implementation philosophy. Up to know, it is not clear how accurate different PCCs have to be for an
individual geodetic grade antenna, in order to assume no significant and negative impact on the geodetic parameter
estimation. Currently, individual calibrations have to be comparable of at least below 1mm.
The poster will cover this topic by studying the observation domain as well as the geodetic position domain.
The used approach based on a pragmatic method, investigated by Geiger (1988), using generic PCC pattern.
The contribution is divided into an analytical approach and an empirical approach. The analytical step discusses
in detail the mathematical model and the propagation of error functions, classified by several antenna models.
The empirical step evaluates these findings by practical experiments carried out with pre-defined errors on PCCs
within a geodetic positioning estimation (PPP) using different software packages.
We will show on the one side that some symmetrical error contributions of typical geodetic antenna designs
can be described very well by this simple and pragmatic approach. The theoretical findings are compared
to PPP solutions, revealing differences between the used software packages. On the other side, we show that
asymmetrical error contributions are highly correlated with the satellite constellation and the geographical location.

References:
Geiger A. (1988): Modeling of Phase Centre Variation and its Influence on GPS-Positioning, In GPS-Techniques
Applied to Geodesy and Surveying, Lecture Notes in Earth Sciences, Springer, Volume 19, pages 210-222

Precise Point Positioning (PPP) is used in a broad variety of applications to determine very econ... more Precise Point Positioning (PPP) is used in a broad variety of applications to determine very economically high
precision parameters for positioning, navigation and timing. In comparison to traditional differential approaches,
PPP with undifferenced phase measurements is highly attractive, since the effort on the user side can be reduced to
minimum, e.g. due to an unnecessary reference station. The quality of obtained position solutions is comparable
to those obtained from a differential approach.
One of the most important limiting factor is the long integration time to determine (float) ambiguities. Furthermore,
it is critical to consider adequately all occurring error sources. In this context, receiver phase biases are
one of the limiting factors and very complex to model. At least they are highly correlated with the ambiguities
during the estimation process, (Laurichesse et al. 2009).
This contribution presents an alternative method to estimate carrier phase biases of different GPS/GNSS
receivers and signals w.r.t. a reference receiver. Receiver phase biases are estimated on a zero baseline and in
combination with a very stable and precise clock (H-Maser) using single differences. The presented method
will be discussed in detail. This includes a critical look to the estimability of bias values for several GPS/GNSS
receivers as well as a discussion on the stability and universality of these bias values. Finally relative phase biases
are quantified and it will be discussed how GPS/GNSS observation equations have to be extended, to take these
bias values correctly into account.
References:
Laurichesse D., Mercier F., Berthias J.P., Broca P., Cerri L. (2009): Integer ambiguity resolution on undifferenced
GPS phase measurements and its application to PPP and satellite precise orbit determination, In: NAVIGATION,
Journal of the Institute of Navigation, Volume 56, Number 2, pages: 135 - 149

Für die GNSS-Antennenkalibrierung nach dem Hannoverschen Verfahren ist eine geometrisch präzise V... more Für die GNSS-Antennenkalibrierung nach dem Hannoverschen Verfahren ist eine geometrisch präzise Verdrehung und Verkippung des GNSS-Antennenprüflings in einem fixen Punkt erforderlich. Abweichungen der Anfahrtspositionen des PowerCube-Roboters, wie er am Institut für Erdmessung (IfE) verwendet wird, sind durch ein ausführliches geometrisch-mechanisches Robotermodell parametrisiert. Die notwendigen Modellparameter werden präzise durch Kalibriermessungen mit dem Lasertracker LTD640 bestimmt, wodurch eine wiederholbare Anfahrtsgenauigkeit von 0.25 mm gewährleistet wird.

In diesem Beitrag wird die mathematische Erweiterung und Verbesserung des geometrischen Robotermodells in den Vordergrund der Diskussion gestellt. Durch die Erweiterung des geometrischen Parametermodells konnte sowohl die Reduktion korrelierter Modellparameter erreicht sowie zusätzlich der Kalibrieraufwand um bis zu 70% reduziert werden. Eine Revision der Kalibriereinrichtung und der Austausch eines Robotermoduls im Frühjahr 2014 machten die Neukalibrierung des Roboters mittels Lasertracker notwendig. Anhand dieses Datensatzes wird zum einen die hohe zeitliche Stabilität der Kalibrierparameter analysiert und zum anderen die Auswirkungen dieser Parameter auf die Korrekturen des GNSS-Trägerphasenzentrums (PCC) sowie der Codephasen Variationen (GDV) diskutiert.

The International GNSS Service's (IGS) provides receiver and satellite antenna phase center corre... more The International GNSS Service's (IGS) provides receiver and satellite antenna phase center corrections (PCC) with its ANTEX file. Currently, five calibration institutions including the Institut für Erdmessung (IfE) are contributing to the IGS PCC file. Different approaches, like e.g., field calibrations and anechoic chamber measurements are in use. Additionally, the computation and parameterization of the PCC are different within the methods and only few information about the procedures applied are available. As a consequence, the consistency of antenna calibrations is based on PCC comparisons. The advent of extensive use of multi-frequency, multi-GNSS analysis software and products (e.g. MGEX) also affect the PCC data provided in the ANTEX file. In this poster, we will highlight the challenges in comparing antenna phase center corrections. From a mathematical point of view, the degrees of freedom in the computation of PCC will be explained resulting in a proposition for sound comparisons and interpretations of PCC on the observation level. Furthermore, based on generic PCC patterns, rules of thumbs will be proposed that allow the easy assessment of differences in PCC on the estimated parameters, like e.g., the coordinates, tropospheric delays and receiver clock parameters.

The Institut für Erdmessung (IfE) is an official IGS calibration institution, calibrating carrier... more The Institut für Erdmessung (IfE) is an official IGS calibration institution, calibrating carrier-phase center variations (PCV) for receiver antennas rountinely in the field, using the actual GNSS satellite signals in space. Current research activities are focussed on the antenna codephase calibration with the Hannover Concept of absolute antenna calibration. Besides PCV,
the receiving antenna introduces systematic effects, currently known as Group Delay Variations (GDV), i.e. azimuth and elevation dependent code-phase delays.

These delays can be determined by precisely rotating and tilting the antenna under test. Forming time-differenced single differences with respect to a near (ca. 8m) fixed reference station, the GDV can be seperated from further systematic effects like tropospheric delays, which are reduced far below the code observation noise level. Depending on the antenna design, suitable for specific applications, different magnitudes and features of GDV has been determined at IfE.

In previous papers the authors could elaborate that GDV are an antenna specific property which affects the code observations (with up to 1.8m) and their derived coordinates systematically. The significane of the impact belongs to the corresponding magnitudes of the GDV pattern. Althought the GDV are not a limiting factor for the GNSS code based time and frequency comparison, improvements of up to 2 m could be obtained by static code based single point positioning (SPP) as well as for code based differential SPP during several studies.

This contribution discusses the current investigations of GDV within combined code and carrier phase processing strategies. This is of special interest for the combined calculation of code and carrier phase observations in Wide- and Narrowlane Linear Combinations, since effects on both frequencies are amplified. The impact on the wide lane is analysed with respect to a possible impovement of the ambiguity solution or an improved cycle slip detection, since the GDV have magnitudes of much more than one complete carrier phase cycle.

References
Kersten, T.; Schön, S. (2013): Analysis of IfE-Robot based Group Delay Variations for the Positioning and Navigation of Mobile Platforms. Proceedings of the European Navigation Conference 2013, 22-25. April, 10p., Vienna, Austria

Urban environments still form a challenge for Global Navigation Satellite System (GNSS) positioni... more Urban environments still form a challenge for Global Navigation Satellite System (GNSS) positioning due to its diffcult conditions for signal propagation. Many obstruction sources disturb the GNSS signal, signal loss or multipath are examples for effects occurring in these cases. This work focuses on an approach which distinguishes visible line-of-sight (LOS) satellite signals from obstructed non-line-of-sight (NLOS) signals. These are determined in a self-developed algorithm with the help of a 3D CityModel that is provided by the city of Hanover. For the evaluation, a kinematic experiment is conducted with geodetic and high-sensitivity receivers in a repeated trajectory. Further sensors were used to generate a reference trajectory. Open questions not only concern the signal characterization with respect to LOS/NLOS properties but also to what extent NLOS observations can be used in a constructive sense. Therefore, reflection points of NLOS signals are calculated, examined and intro...

$Research paper thumbnail of Urban GNSS campaigns from 2015-2017 in Hamburg Gro\xdf-Flottbek from SIMULTAN project$

This data set contains the raw data bundle of all gnss campaigns carried out in the years between... more This data set contains the raw data bundle of all gnss campaigns carried out in the years between autumn 2015 unti autumn 2017. Campaigns were measured semi annual and summarized in technical reports, which are elements of this data set.\r\nThe campaings are captured under urban conditions and contain a lot of cycle slips and multipath. \r\nThe aim of these gnss campaings have been the monitoring of surface displacements caused by subsidence processes.

The file "IfE20_2132.atx" contains Phase Centre Corrections (PCC) for receiver\r\nanten... more The file "IfE20_2132.atx" contains Phase Centre Corrections (PCC) for receiver\r\nantennas in the ATX format for following frequencies:\r\n* GPS: GL1C (G01), GL2W (G02) and GL5X (G05)\r\n* Galileo: EL1X (E01) and EL5X (E05)\r\n\r\nFollowing antennas are included in the file:\r\n* NOV703GGG.R2 NONE12420040\r\n* LEIAR25.R3 LEIT08360013\r\n\r\nThe PCC are estimated using spherical harmonics up to degree and \r\norder eight, whereby during the least square adjustment the odd parameters \r\n(e.g. a21, b21, a30, ...) are restricted to zero.\r\n\r\nPlease note, that the data is in experimental status and no (!) official \r\ncalibration product. Thus, it is free for scientific research/use only.

on the Ambiguity Resolution Tobias Kersten and Steffen Schön (AGU2013, #G53B-0920) Institut für E... more on the Ambiguity Resolution Tobias Kersten and Steffen Schön (AGU2013, #G53B-0920) Institut für Erdmessung | Leibniz Universität Hannover Introduction This contribution discusses the current investigations at the Institut für Erdmessung (IfE) on Code Phase Variations (GDV) within a combined code and carrier phase processing strategy. An analysis of the GDV impact on the important Melbourne-Wübbena linear combination (MW-LC) which is widely used for cycle slip detection and ambiguity resolution is of special interest since effects which origin from GDV are amplified on both code phases (P1 and P2). GNSS Receiver Antenna Code Phase Variations (GDV) Variations of the Code Phase Observation at GNSS Antennas?

Stationary terrestrial laser scanning (TLS) provides a 3D point cloud in a local sensor-defined c... more Stationary terrestrial laser scanning (TLS) provides a 3D point cloud in a local sensor-defined coordinate system. The transformation parameters of such point clouds to a global coordinate system are generally obtained by pre-surveyed control points with known geodetic datum. To improve this procedure, a direct geo-referencing method of a multi-sensor system with 3D position sensors has been developed at the Geodetic Institute Hannover. The current approach uses two small scaled and light weighted, high sensitivity GNSS-receivers of type Ublox EVK-M8T and Ashtech L1 antennas as 3D position sensors. These sensor types are used to reduce weight and equipment costs. They are mounted with a mutual distance (baseline) of 1 m on top of the laser scanner that rotates about its vertical axis. The analysis of the trajectories of the 3D GNSS-points and the estimation of the transformation parameters are based on a recursive filter approach in form of an extended Kalman Filter (EKF). With the EKF algorithm optimal results can only be provided, if the system noise is normally distributed with known variance covariance matrix and without correlations over time. That means the model requires white noise. Unfortunately, this assumption is not sufficient in our processing approach due to the stochastically time-correlated state vector. Former studies revealed that the analysis of short kinematic time series (15 minutes) yields to insufficiencies regarding, e. g. the determination of the auto-correlation. Therefore, long-term static time series (up to 7 days) of four identical high sensitivity GNSS-receivers were acquired on a zero baseline approach. The reference antenna and receiver of the Institut für Erdmessung (IfE) are used as benchmark to evaluate and study proper parameters for the EKF parameter estimation and the direct geo-referencing parameters, respectively. This contribution presents the noise analysis of the impact and the determination of statistical quality measures for improving the EFK parameter estimation. We will critically discuss results of our benchmark test of high sensitivity GNSS-receivers of type Ublox EVK-M8T. The noise analysis is based on a zero baseline approach. Important key parameters are e.g. the carrier phase stability and the overall acceptable noise level. The Allan deviation helps to characterize the process noise for long time series with respect to short time series, as they are used in typically MSS approaches for direct geo-referencing. In addition, first results of kinematic experiments are presented and critically compared to the static derived solutions by their individual uncertainty budget.

&amp;lt;p&amp;gt;In order to obtain highly precise positions with Global Navigati... more &amp;lt;p&amp;gt;In order to obtain highly precise positions with Global Navigation Satellite Systems (GNSS), it is mandatory to take all error sources adequately into account. This includes phase center corrections (PCC), composed of a phase center offset (PCO) and corresponding azimuthal and elevation-dependent phase center variations (PCV). These corrections have to be applied to the observations since the pattern of the GNSS receiver antennas deviate from an ideal omnidirectional radiation pattern.&amp;lt;br&amp;gt;The Institut f&amp;amp;#252;r Erdmessung (IfE) is one of the IGS accepted institutions for absolute antenna calibration. Recently, the operationally calibration procedure has been further developed to a post processing approach. Thus, PCC can also be estimated for all frequencies (including e.g. GPS L2C, L5) and systems like Galileo and Beidou. Additionally, the newly developed approach allows to assess the impact of using different receivers with different settings on an individual calibration.&amp;amp;#160;&amp;lt;br&amp;gt;Previous studies already have shown, that the geodetic receivers used during the absolute calibration of antennas have an impact on the estimated PCC. However, currently this impact is only analysed at the level of the respective patterns and not in the coordinate domain. Moreover, the results are always only valid for the respective antenna-receiver combination. Therefore, more samples of different combinations are required.&amp;lt;br&amp;gt;In this contribution, we study calibration results of several antenna-receiver combinations using a zero baseline configuration during the calibration process in order to assess the receiver&amp;amp;#8217;s impact due to different signal tracking modes. The resulting PCC are analysed on the pattern level regarding (i) the repeatability of individual calibrations and (ii) differences between different antenna-receiver combinations. Finally, the impact of the different PCC are validated in the coordinate domain by a well controlled short baseline and common clock set-up. Here, again a zero baseline configuration with the identical receivers used during the calibration process is performed. Consequently, the impact of the respective antenna-receiver combination with individually estimated PCC on the positioning is analysed.&amp;lt;/p&amp;gt;

Eine genaue Positionsbestimmung mittels GNSS basiert auf einem prazisen Signalempfang. Im Falle v... more Eine genaue Positionsbestimmung mittels GNSS basiert auf einem prazisen Signalempfang. Im Falle von Tragerphasenmessung stellt ein gleichformiger Kugelstrahler eine ideale Empfangerantenne dar. Abweichungen von dieser idealen Phasenfront werden als Phasenzentrumskorrektionen (PCC) bezeichnet. In dem vom IGS bereitgestellten Antennenkorrekturen sind zurzeit nur PCC fur GPS und GLONASS L1 und L2 vorhanden. Kalibrierwerte fur GPS L5 und Galileo-Signale werden bislang nicht vom IGS bereitgestellt. Lediglich im EPN stehen teilweise Kammerkalibrierwerte fur diese Signale zur Verfugung. Allerdings haben Untersuchungen unserer Arbeitsgruppe gezeigt, dass bei einer Mischung von Kammer- sowie Roboterkalibrierwerten in grosraumigen Netzen signifikante Abweichungen in der Positionsebene auftreten. Daher ist der Bedarf an absoluten Feldkalibrierwerten gegeben. Das Institut fur Erdmessung (IfE) ist eine vom IGS anerkannte Kalibrierinstitution und kalibriert operationell nach dem absoluten Verfahr...

For time and frequency transfer as well as navigation applications, like, e.g., precise guided la... more For time and frequency transfer as well as navigation applications, like, e.g., precise guided landing approaches, GNSS code observables are widely used. In addition to the well known error budget, code observables seem to be affected by Group Delay Variations (GDV), induced by the radiation pattern of the receiving antenna. The performance of the acquisition depends on the antenna and receiver ensemble. GDV degrade the precision of code observables and induce errors in timing and frequency applications. In this contribution we analyzed the GDV for different antennas and receivers to quantify the net effect on the code observables and time and frequency transfer applications. The paper is divided into two parts: GDV were estimated using the Hannover Concept of absolute antenna calibration with the current GNSS satellite signals in space. The GDV are parameterized using orthogonal base functions for L1(P) and L2(P) to describe variations in elevation and azimuth. Variations in elevat...

Schlussbericht zum BMBF-Verbundvorhaben - Förderkennzeichen FKZ 03G0843 (A bis J). Hannover : Technische Informationsbibliothek Hannover, 2019

Das Verbundprojekt SIMULTAN erforscht die Früherkennung für Instabilität, Unruhe und Kollaps von ... more Das Verbundprojekt SIMULTAN erforscht die Früherkennung für Instabilität, Unruhe und Kollaps von Erdfällen. Der neuartige Forschungsansatz kombiniert strukturelle, geophysikalische, petrophysikalische und hydrologische Kartierungsmethoden, die von Sensorentwicklung und mulit-skaliger Überwachung flankiert werden, und umfasst eine Informationsplattform. Kollapsprozesse an Erdfällen finden generell in den obersten wenigen 100 Metern der Erdkruste statt. Individuelle Prozesskomponenten können einfach sein und verstanden werden. Aber es wechselwirken auch Prä-Kollapsprozesse und Vorläufer auf unterschiedlichen raum-zeitlichen Skalen und mit kleinen Variationen miteinander. Dies erfordert innovative, multi-skalige Beobachtungen, Analysen und integrierte Früherkennungskonzepte, besonders für urbane Bereiche, die bisher noch nicht vollständig entwickelt verfügbar sind und auch noch nicht als automatische operationelle Systeme arbeiten. Zur Identifizierung und Quantifizierung von Subrosionsbereichen zeigten sich bohrlochseismische Verfahren mit kombinierten P- und S-Wellen als zielführend. Als besonderer Indikator, der sich auch für Langzeitmonitoring eignet, hat sich dabei das ungewöhnliche Konversionsverhalten der Wellen in Subrosionszonen gezeigt. Neue Prozessingverfahren zur Detektion kleiner seismischer Ereignisse und für emergente Einsätze unterstützen den Ansatz von angepassten Arraymessungen. Geodätisch-gravimetrische Überwachungsnetze sind auch unter urbanen Bedingungen geeignet, durch Subrosion verursachte Oberflächendeformationen und Massenverlagerungen räumlich-zeitlich zu erfassen und zu überwachen. Nivellements liefern bezüglich der Oberflächendeformation höchste Genauigkeiten; zugleich sind sie vergleichsweise kostengünstig zu realisieren. Die Integration von GNSS hat in Verbindung mit dem Nivellement die räumliche Auflösung im Untersuchungsgebiet zusätzlich gestützt und hat das Potenzial, diese großräumig zu kontrollieren. Gravimetrische Messungen sind mit einem sehr hohen Aufwand verbunden. Die Kombination oberflächengeophysikalischer Verfahren mit einer vertikal hochaufgelösten direct push-basierten Erkundung im Raum mit einem maßgeschneiderten hydrogeologischen Monitoring bietet eine zuverlässige Grundlage für numerische Prozessmodellierungen und ermöglichen es, erdfallrelevante Prozesse abzubilden und zu erfassen. Karstaquifer- und geomechanische Modellierungen konnten die Prozesse in den Fokusgebieten erfolgreich abbilden, sobald diese mit realistischen Werten unterlegt wurden. Es zeigt sich somit insgesamt, dass sowohl flächenhafte Messungen und zeitlich wiederholte Kampagnen sehr vorteilhaft sind, da sie es erlauben, Fehler zu verringern und beanspruchte Bereiche einzugrenzen. Erst dieses integrierte Vorgehen ermöglicht es, potenzielle Wegsamkeiten im Untergrund hochauflösender als bisher abzubilden und zu bewerten. Als solches stellt es ein Instrumentarium zur Charakterisierung und angepassten Überwachung von Untergrundbereichen im Allgemeinen zur Verfügung. Diese Ergebnisse und Szenarien stehen der Öffentlichkeit auf einer Informationsplattform zur Verfügung (http://simultan.gfz-potsdam.de).