L. Timmen - Academia.edu (original) (raw)

Papers by L. Timmen

Metrologia, 2020

The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organi... more The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in the spring of 2018. Here we present the list of the participants who actually performed measurements during the comparison, the data submitted by the operators as well as the results of the determination of the gravity as a function of height at the comparison sites. The measurement strategy is briefly discussed and the results of the data harmonization is documented. Finally, the results of the constrained least squares adjustment are presented including the degrees of equivalence of each gravimeter and the key comparison reference values. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer...

25th European Meeting of Environmental and Engineering Geophysics, 2019

Gravity, Geoid and Earth Observation, 2010

The second international comparison of absolute gravimeters was held in Walferdange, Grand Duchy ... more The second international comparison of absolute gravimeters was held in Walferdange, Grand Duchy of Luxembourg, in November 2007, in which twenty absolute gravimeters took part. A short description of the data processing and adjustments will be presented here and will be followed by the presentation of the results. Two different methods were applied to estimate the relative offsets between the gravimeters. We show that the results are equivalent as the uncertainties of both adjustments overlap. The absolute gravity meters agree with one another with a standard deviation of 2 μgal (1 gal = 1 cm/s 2).

Introduction ………………………………………….……………………….…….. 2 2. The absolute gravity measurements in 2005 ……………... more Introduction ………………………………………….……………………….…….. 2 2. The absolute gravity measurements in 2005 ………………..………………………. 2 2.1 The measurement conditions and the field experience in 2005 ………………… 2 2.2 Some comments concerning the definition and the use of gravity for geodetic purposes. ………………… 6 2.3 The absolute gravity measurements in Denmark in 2005. The temporary results ………………… 7 3. The relative campaigns in 2005-5D points ………………..………………………. 9 4. Results and conclusions ………………………………..……………………….…….. 12 References ………………………………..……………………….…….. 13 Appendix A. Ludger Timmen, IfE: A note on gravity measurements for sub-terrain points. …….…………………….…….. 14 Appendix B. The observation files of the two relative gravity campaigns in 2005 on 5D stations

ABSTRACT Estonia, Latvia, and Lithuania belong to the margin of the Fennoscandian postglacial reb... more ABSTRACT Estonia, Latvia, and Lithuania belong to the margin of the Fennoscandian postglacial rebound (PGR) area. Vertical rates predicted by PGR models are in the range 0 to +3 mm/yr. Our first absolute gravity campaigns in the area were performed with the JILAg-5 gravimeter in 1994-1995 when three stations were measured in each country. All three stations in Lithuania were repeated with the JILAg-5 in 2002 and one of them (Vilnius) with the FG5#221 gravimeter in 2007. In Latvia one station (Riga) was remeasured with the FG5#101 and FG5#107 (D. Stizza, NIMA) in 1986 and with the FG5#221 in 2007. In Estonia two of the stations (Suurupi and Töravere) were remeasured with the FG5#220 in 2007 and with the FG5#221 in 2008, the third (Kuressaare) was only remeasured in 2008 with the FG5#221. This amounts to seven repeated stations with time spans of 8-13 years. In interpreting gravity change, special attention must be paid to subsurface water storage, as (due to inaccessibility of crystalline bedrock) many stations are on thick sediments, the repeat measurements were partly made in different seasons, and in some cases there is evidence of strong interannual variation in hydrology. We discuss the constraints to PGR implied by the observed gravity change and compare it with PGR models and with available observations of vertical motion.

In the middle of the 1980s, the State Seismological Bureau (SSB) established a gravity network in... more In the middle of the 1980s, the State Seismological Bureau (SSB) established a gravity network in the Western Yunnan Earthquake Prediction Experiment Area (WYEPEA). The network is located in the north-western part of Yunnan province of China, and includes more than 130 gravity stations. Repeated gravity surveys have been performed 2 - 3 times a year by relative gravimetry, and continued until today. Absolute gravimetry was introduced in the 1990's in order to stabilize the network with respect to the absolute gravity level and the calibration of relative gravimeters, as well as to monitor long term gravity variations with time. The absolute gravity network was planned and surveyed within the frame of a cooperation project between the Institute of Seismology, SSB, Wuhan, China (ISSSB) and the Institut fur Erdmessung (IFE), University of Hannover, Germany. Three observation campaigns were performed in WYEPEA, in 1990, 1992 and 1995, with additional absolute measurements in Beijing (1990/1992), Wuhan (1990) and Kunming (1990, 1992 and 1995). This paper compares the results of absolute measurements in the three epochs, and evaluates their reliability by comparisons with gravity data obtained by other gravimeters. Gravity changes on the individual stations are discussed in more detail, taking gravity changes due to ground water variations and crustal deformations into account. Larger gravity changes at some stations can be mainly explained by those effects, while large-scale long term gravity variations with time could not be detected.

Subsidence processes in dense populated urban areas are of societal relevance. SIMULTAN (Sinkhole... more Subsidence processes in dense populated urban areas are of societal relevance. SIMULTAN (Sinkhole instability: integrated multiscale monitoring and analysis) aims at a novel approach to better understand the evolution and characteristics of sinkholes, which are highly correlated with surface deformation. An integrated approach to monitor sinkhole-related mass changes and surface deformations induced by salt dissolution is set up using collocated field sites to combine geodetic and geophysical techniques. Such monitoring sites are established in Hamburg and Bad Frankenhausen (Thuringia). At the latter location, levelling surveys indicate a maximum subsidence rate of max. 4-5 mm/yr in the main subsidence areas of Bad Frankenhausen. This contribution presents a description of the geodetic and geophysical techniques applied, i.e., levelling, GNSS as well as relative/absolute gravimetry. Results from first SIMULTAN campaigns in Bad Frankenhausen are shown.

Metrologia, 2017

In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeter... more In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeters were compared in November 2015. Four gravimeters were from different NMIs and DIs, they were used to link the regional comparison to the CCM.G.K2 by means of linking converter. Combined least-squares adjustments with weighted constraint was used to determine KCRV. Several pilot solutions are presented and compared with the official solution to demonstrate influences of different approaches (e.g. definition of weights and the constraint) on results of the adjustment. In case of the official solution, all the gravimeters are in equivalence with declared uncertainties. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrang...

Journal of Applied Geodesy, 2017

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 4–5Here, the concept of combining geodetic and gravimetric techniques to monitor and characterise geological processes on and below the…

International Association of Geodesy Symposia, 1995

The Institut fur Erdmessung (IFE), University of Hannover, Germany, performed a large-scale gravi... more The Institut fur Erdmessung (IFE), University of Hannover, Germany, performed a large-scale gravity control survey between 1988 and 1991 in South America, in cooperation with university institutes and state agencies of the countries involved and supported by “Deutsche Forschungsgemeinschaft (DFG)” and “Instituto Panamericano de Geografia e Historia (IPGH)”. This control system covers a large part of South America by establishing 22 absolute gravity stations with additional local eccenters. After a first observation campaign in Venezuela in 1988 (6 stations), a project in Brazil (7 stations), Uruguay (2 stations) and Argentina (3 stations) has been performed in 1989. A final campaign in 1991 concentrated on Argentina (3 new stations) and Uruguay (1 new station, 1 reoccupied). Three gravity stations (Sta. Elena, Brasilia, Tandil) are part of the International Absolute Gravity Basestation Network (IAGBN,set A). In addition, the stations serve as absolute gravity control for geodynamic networks in the Central and Venezuelan Andes and they improve existing national gravity networks.

Bulletin Géodésique, 1993

Journal of Geodetic Science, 2015

Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observa... more Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observatory by the Institute of Geodesy of the Leibniz Universität Hannover from 2003 to 2011 and have been continued with the upgraded meter FG5X in 2014. Lantmäteriet, Gävle, with their FG5 absolute gravimeter have visited Onsala since 2007. Because small systematic errors may be inherent in each absolute gravimeter, their measuring level and a resulting bias (offset) between the instruments must be controlled over time by means of inter-comparison. From 2007 to 2014, 8 direct comparisons took place well distributed over the time span. A complete re-processing of the absolute gravity observations with the Hannover instrument has been conducted to improve the reduction of unwanted gravity effects. A new tidal model is based on continuous time series recorded with the GWR superconducting gravimeter at Onsala since 2009. The loading effect of the Kattegat is described with a varying sea bottom p...

International Association of Geodesy Symposia, 1995

Synthetic gravity tide parameters (amplitude factors and phase leads) have been computed for the ... more Synthetic gravity tide parameters (amplitude factors and phase leads) have been computed for the waves MF, Q1, O1, P1, K1, N2, M2, S2 and K2 in a worldwide 1° x 1° grid at 26995 grid points located mainly on land. The gravity tide parameters have been derived from gravity tide amplitudes of the Tamura (1987) tidal potential referring to a rigid Earth model, body tide amplitude factors using a model of an ocean-free, elastic, rotating, isotropic and ellipsoidal Earth with liquid outer core (Wahr 1981, Dehant 1987), and from ocean tide gravitation and load using a 1° x 1° ocean tide model (Schwiderski 1980). The synthetic gravity tide parameters have been compared at 31 European gravity tide stations selected from the data base DB92 of the International Center for Earth Tides (Melchior 1994) and show rms differences of 0.79% and 0.87% for the amplitude factors and 0.24° and 0.48° for the phase leads of the main waves 01 and M2 resp.

Metrologia, 2020

The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organi... more The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in the spring of 2018. Here we present the list of the participants who actually performed measurements during the comparison, the data submitted by the operators as well as the results of the determination of the gravity as a function of height at the comparison sites. The measurement strategy is briefly discussed and the results of the data harmonization is documented. Finally, the results of the constrained least squares adjustment are presented including the degrees of equivalence of each gravimeter and the key comparison reference values. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer...

25th European Meeting of Environmental and Engineering Geophysics, 2019

Gravity, Geoid and Earth Observation, 2010

The second international comparison of absolute gravimeters was held in Walferdange, Grand Duchy ... more The second international comparison of absolute gravimeters was held in Walferdange, Grand Duchy of Luxembourg, in November 2007, in which twenty absolute gravimeters took part. A short description of the data processing and adjustments will be presented here and will be followed by the presentation of the results. Two different methods were applied to estimate the relative offsets between the gravimeters. We show that the results are equivalent as the uncertainties of both adjustments overlap. The absolute gravity meters agree with one another with a standard deviation of 2 μgal (1 gal = 1 cm/s 2).

Introduction ………………………………………….……………………….…….. 2 2. The absolute gravity measurements in 2005 ……………... more Introduction ………………………………………….……………………….…….. 2 2. The absolute gravity measurements in 2005 ………………..………………………. 2 2.1 The measurement conditions and the field experience in 2005 ………………… 2 2.2 Some comments concerning the definition and the use of gravity for geodetic purposes. ………………… 6 2.3 The absolute gravity measurements in Denmark in 2005. The temporary results ………………… 7 3. The relative campaigns in 2005-5D points ………………..………………………. 9 4. Results and conclusions ………………………………..……………………….…….. 12 References ………………………………..……………………….…….. 13 Appendix A. Ludger Timmen, IfE: A note on gravity measurements for sub-terrain points. …….…………………….…….. 14 Appendix B. The observation files of the two relative gravity campaigns in 2005 on 5D stations

ABSTRACT Estonia, Latvia, and Lithuania belong to the margin of the Fennoscandian postglacial reb... more ABSTRACT Estonia, Latvia, and Lithuania belong to the margin of the Fennoscandian postglacial rebound (PGR) area. Vertical rates predicted by PGR models are in the range 0 to +3 mm/yr. Our first absolute gravity campaigns in the area were performed with the JILAg-5 gravimeter in 1994-1995 when three stations were measured in each country. All three stations in Lithuania were repeated with the JILAg-5 in 2002 and one of them (Vilnius) with the FG5#221 gravimeter in 2007. In Latvia one station (Riga) was remeasured with the FG5#101 and FG5#107 (D. Stizza, NIMA) in 1986 and with the FG5#221 in 2007. In Estonia two of the stations (Suurupi and Töravere) were remeasured with the FG5#220 in 2007 and with the FG5#221 in 2008, the third (Kuressaare) was only remeasured in 2008 with the FG5#221. This amounts to seven repeated stations with time spans of 8-13 years. In interpreting gravity change, special attention must be paid to subsurface water storage, as (due to inaccessibility of crystalline bedrock) many stations are on thick sediments, the repeat measurements were partly made in different seasons, and in some cases there is evidence of strong interannual variation in hydrology. We discuss the constraints to PGR implied by the observed gravity change and compare it with PGR models and with available observations of vertical motion.

In the middle of the 1980s, the State Seismological Bureau (SSB) established a gravity network in... more In the middle of the 1980s, the State Seismological Bureau (SSB) established a gravity network in the Western Yunnan Earthquake Prediction Experiment Area (WYEPEA). The network is located in the north-western part of Yunnan province of China, and includes more than 130 gravity stations. Repeated gravity surveys have been performed 2 - 3 times a year by relative gravimetry, and continued until today. Absolute gravimetry was introduced in the 1990's in order to stabilize the network with respect to the absolute gravity level and the calibration of relative gravimeters, as well as to monitor long term gravity variations with time. The absolute gravity network was planned and surveyed within the frame of a cooperation project between the Institute of Seismology, SSB, Wuhan, China (ISSSB) and the Institut fur Erdmessung (IFE), University of Hannover, Germany. Three observation campaigns were performed in WYEPEA, in 1990, 1992 and 1995, with additional absolute measurements in Beijing (1990/1992), Wuhan (1990) and Kunming (1990, 1992 and 1995). This paper compares the results of absolute measurements in the three epochs, and evaluates their reliability by comparisons with gravity data obtained by other gravimeters. Gravity changes on the individual stations are discussed in more detail, taking gravity changes due to ground water variations and crustal deformations into account. Larger gravity changes at some stations can be mainly explained by those effects, while large-scale long term gravity variations with time could not be detected.

Subsidence processes in dense populated urban areas are of societal relevance. SIMULTAN (Sinkhole... more Subsidence processes in dense populated urban areas are of societal relevance. SIMULTAN (Sinkhole instability: integrated multiscale monitoring and analysis) aims at a novel approach to better understand the evolution and characteristics of sinkholes, which are highly correlated with surface deformation. An integrated approach to monitor sinkhole-related mass changes and surface deformations induced by salt dissolution is set up using collocated field sites to combine geodetic and geophysical techniques. Such monitoring sites are established in Hamburg and Bad Frankenhausen (Thuringia). At the latter location, levelling surveys indicate a maximum subsidence rate of max. 4-5 mm/yr in the main subsidence areas of Bad Frankenhausen. This contribution presents a description of the geodetic and geophysical techniques applied, i.e., levelling, GNSS as well as relative/absolute gravimetry. Results from first SIMULTAN campaigns in Bad Frankenhausen are shown.

Metrologia, 2017

In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeter... more In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeters were compared in November 2015. Four gravimeters were from different NMIs and DIs, they were used to link the regional comparison to the CCM.G.K2 by means of linking converter. Combined least-squares adjustments with weighted constraint was used to determine KCRV. Several pilot solutions are presented and compared with the official solution to demonstrate influences of different approaches (e.g. definition of weights and the constraint) on results of the adjustment. In case of the official solution, all the gravimeters are in equivalence with declared uncertainties. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrang...

Journal of Applied Geodesy, 2017

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 4–5Here, the concept of combining geodetic and gravimetric techniques to monitor and characterise geological processes on and below the…

International Association of Geodesy Symposia, 1995

The Institut fur Erdmessung (IFE), University of Hannover, Germany, performed a large-scale gravi... more The Institut fur Erdmessung (IFE), University of Hannover, Germany, performed a large-scale gravity control survey between 1988 and 1991 in South America, in cooperation with university institutes and state agencies of the countries involved and supported by “Deutsche Forschungsgemeinschaft (DFG)” and “Instituto Panamericano de Geografia e Historia (IPGH)”. This control system covers a large part of South America by establishing 22 absolute gravity stations with additional local eccenters. After a first observation campaign in Venezuela in 1988 (6 stations), a project in Brazil (7 stations), Uruguay (2 stations) and Argentina (3 stations) has been performed in 1989. A final campaign in 1991 concentrated on Argentina (3 new stations) and Uruguay (1 new station, 1 reoccupied). Three gravity stations (Sta. Elena, Brasilia, Tandil) are part of the International Absolute Gravity Basestation Network (IAGBN,set A). In addition, the stations serve as absolute gravity control for geodynamic networks in the Central and Venezuelan Andes and they improve existing national gravity networks.

Bulletin Géodésique, 1993

Journal of Geodetic Science, 2015

Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observa... more Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observatory by the Institute of Geodesy of the Leibniz Universität Hannover from 2003 to 2011 and have been continued with the upgraded meter FG5X in 2014. Lantmäteriet, Gävle, with their FG5 absolute gravimeter have visited Onsala since 2007. Because small systematic errors may be inherent in each absolute gravimeter, their measuring level and a resulting bias (offset) between the instruments must be controlled over time by means of inter-comparison. From 2007 to 2014, 8 direct comparisons took place well distributed over the time span. A complete re-processing of the absolute gravity observations with the Hannover instrument has been conducted to improve the reduction of unwanted gravity effects. A new tidal model is based on continuous time series recorded with the GWR superconducting gravimeter at Onsala since 2009. The loading effect of the Kattegat is described with a varying sea bottom p...

International Association of Geodesy Symposia, 1995

Synthetic gravity tide parameters (amplitude factors and phase leads) have been computed for the ... more Synthetic gravity tide parameters (amplitude factors and phase leads) have been computed for the waves MF, Q1, O1, P1, K1, N2, M2, S2 and K2 in a worldwide 1° x 1° grid at 26995 grid points located mainly on land. The gravity tide parameters have been derived from gravity tide amplitudes of the Tamura (1987) tidal potential referring to a rigid Earth model, body tide amplitude factors using a model of an ocean-free, elastic, rotating, isotropic and ellipsoidal Earth with liquid outer core (Wahr 1981, Dehant 1987), and from ocean tide gravitation and load using a 1° x 1° ocean tide model (Schwiderski 1980). The synthetic gravity tide parameters have been compared at 31 European gravity tide stations selected from the data base DB92 of the International Center for Earth Tides (Melchior 1994) and show rms differences of 0.79% and 0.87% for the amplitude factors and 0.24° and 0.48° for the phase leads of the main waves 01 and M2 resp.