Geodetic Leveling Research Articles

Comparison of ALOS PALSAR interferometry and field geodetic leveling for marshy soil thaw/freeze monitoring, case study from the Baikal lake region, Russia

Estimation of vertical ground displacements due to seasonal periods of freezing and thawing was carried out on the Selenga river mouth using differential radar interferometry. The results of seasonal radar interferometry measurements from 2008 to 2010 have been compared with the survey data for 2011, under the assumption that the seasonal deformation is comparable for different years and lies within the limits of geodetic leveling error. The difference between the interferometric and geodetic measurements is in winter months, whereas in summer, as the upper soil moisture content varies, the difference reaches 2 to 2.7 cm. It has been concluded that the moisture content and its profile should be taken into consideration in summer or when choosing the radar interferometry in winter.

A Century of Sea Level Measurements at Newlyn, Southwest England

ABSTRACTThe Newlyn Tidal Observatory is the most important sea level station in the United Kingdom. It commenced operations in 1915 as part of the Second Geodetic Levelling of England and Wales, and the mean sea level determined from the tide gauge during the first six years (May 1915–April 1921) defined Ordnance Datum Newlyn (ODN) which became the national height datum for the whole of Great Britain. The 100 years of sea level data now available have contributed significantly to many studies in oceanography, geology, and climate change. This paper marks the centenary of this important station by reviewing the sea level (and, more recently, detailed land level) measurements and Newlyn's contributions to UK cartography, geodesy and sea-level science in general. Recommendations are made on how sea and land level measurements at Newlyn might be enhanced.

Nonlinear subsidence at Fremantle, a long‐recording tide gauge in the Southern Hemisphere

AbstractA combination of independent evidence (continuous GPS, repeat geodetic leveling, groundwater abstraction, satellite altimetry, and tide gauge (TG) records) shows that the long‐recording Fremantle TG has been subsiding in a nonlinear way since the mid‐1970s due to time‐variable groundwater abstraction. The vertical land motion (VLM) rates vary from approximately −2 to −4 mm/yr (i.e., subsidence), thus producing a small apparent acceleration in mean sea level computed from the Fremantle TG records. We exemplify that GPS‐derived VLM must be geodetically connected to the TG to eliminate the commonly used assumption that there is no differential VLM when the GPS is not colocated with the TG. In the Perth Basin, we show that groundwater abstraction can be used as a diagnostic tool for identifying nonlinear VLM that is not evident in GPS time series alone.

Effect of sea level rise in the validation of geopotential/geoid models in Metro Manila, Philippines

The release of new global geopotential models (GGMs) has raised the question of whether these GGMs could now supplant the development of regional/local geoid models. For geodetic surveying purposes the importance of a geoid model fitted to the local condition will greatly help in the resolution of many vertical datum issues especially for an archipelagic country such as the Philippines. Since the geoid as a vertical reference surface is used to convert ellipsoidal heights acquired through GNSS survey to orthometric heights, it is vital that this should at least match the heights derived through geodetic levelling within the allowed accuracy. However, the issue of mean sea level (MSL) as vertical reference for geodetic levelling has introduced another issue of concern especially when it is exhibiting accelerated sea level rise (ASLR). The results of the validation and comparison of recent GGMs showed that EGM 2008 and the 2012 released EIGEN-6C2 both classified as combined type model have RMS around 14 and 13 cm respectively in the study area. These results were achieved when ASLR was considered in the validation. The local geoid model (LGM) developed using least squares modification of Stokes formula with additive corrections (LSMSA) approach has RMS around 11 cm using an integration cap of 3° from the limit of study area. The LGM validated the level of the combined type GGMs in reference to the local vertical datum in Manila Bay. Based on the result of this study, the ASLR contributed much to the departure of the latest MSL from the geoid.

Using Models of the Ocean's Mean Dynamic Topography to Identify Errors in Coastal Geodetic Levelling

Identifying errors (blunders and systematic errors) in coastal geodetic levelling networks has often been problematic, primarily for two reasons. First, mean sea level (MSL) at tide gauges cannot be directly compared to height differences from levelling because the geoid/quasigeoid and MSL are not parallel, being separated by the ocean's mean dynamic topography (MDT). Second, there is a the lack of redundancy at the edge of the levelling network. This article sets out a methodology to independently identify blunders and/or systematic errors (over long distances) in geodetic levelling using MDT models to account for the separation between the geoid/quasigeoid and MSL at tide gauges. This method is then tested in a case study using an oceanographic MDT model, MSL observations, GNSS data, and a quasigeoid model. The results are significant because the errors found could not be detected by standard levelling misclosure checks alone, with supplementary data from an MDT model, with cross-validation from GNSS-quasigeoid allowing their detection. In addition, it appears that an oceanographic-only MDT is as effective as GNSS and a quasigeoid model for detecting levelling errors, which could be particularly useful for countries with coastal levelling errors in their levelling networks that cannot be identified by conventional levelling closure checks.

A Model of Recent Vertical Movements of Earth's Surface of the Territory of Lithuania

The precise geodetic levelling reveals the recent activity of the vertical movements of the earths crust. However, the main shortcoming of the levelling networks is a scarceness of the measurement tracks that can not be compensated by high density of the levelling sites within the tracks. The pattern and trends of vertical movements between the measured lines remains unknown. A special approach has been developed in order to allow the prediction of the vertical movements within the polygons. It is based on the multicomponent statistical correlation of the levelling data with the significant geological parameters. The correlations between different parameters were derived separately for each particular polygon and than combined in one common model. It allowed compilation of a rather detailed map of the recent vertical movements of Lithuania during the past 30-40 years. The rate of the vertical movements of the earths surface obtained from the geodetic levelling varies from-2.7 mm to 3.5 mm/y. A close correlation suggests that the heterogeneity of the crust is important for the distribution of the vertical movements. The application of the close correlation with geoparameters allowed considerable improvement of the map of the vertical movements of Lithuania.

The Stability of Tide Gauges in the South Pacific Determined from Multiepoch Geodetic Levelling, 1992 to 2010

Tide gauge data is important for determining global or local sea level rise with respect to a global geocentric reference frame. Data from repeated precise levelling connections between the tide gauges and a series of coastal and inland benchmarks, including Continuous GPS (CGPS) benchmarks, are used to determine the stability of tide gauges at 12 locations in the South Pacific. The method for determining this stability is based on a constant velocity model which minimises the net movement amongst a set of datum benchmarks surveyed since the installation of the tide gauges. When assessed at a 95% confidence interval, and with the exception of the Solomon Islands, none of the tide gauges were found to be in motion relative to their CGPS benchmarks. The Solomon Islands estimate is considered to be unreliable since the CGPS benchmark was recently established and has been surveyed fewer than three times. In Tonga and Cook Islands, the tide gauges were found to be disturbed or affected by survey errors whereas the Vanuatu results were affected by earthquakes.

DEM and GIS analysis of geomorphic indices for evaluating recent uplift of the northeastern margin of the Tibetan Plateau, China

The northeastern margin of the Tibetan Plateau is a tectonically active region consisting of a series of faults with bounded intermountain basins and is located in the transition zone between the Tibetan Plateau and the Loess Plateau. Active deformation that may affect the topography in this region can be quantified using geomorphic indices. Therefore, we applied geomorphic indices such as the hypsometric integral and the stream length gradient index to infer neo-tectonics in the northeastern margin of the Tibetan Plateau. Different time-scaled geodetic leveling data and river incision rates were also integrated into the investigation. The results show that the hypsometric integrals are not significantly affected by lithology but spatially correspond to the hanging walls of thrust faults. The hypsometric integrals are also positively correlated with the leveling data. Although the stream length gradient index is influenced by lithology, its most pronounced anomalies of the stream length gradient are associated with the thrust faults. Consequently, the uplift in the northeast margin of the Tibetan Plateau appeared to be concentrated along the hanging walls of the thrust faults.

Influence of vertical crust movements on accuracy of reference geodetic levelling network

Influence of vertical crust movements on accuracy of reference geodetic levelling network

Analysis of vertical movements in eastern Sicily and southern Calabria (Italy) through geodetic leveling data

The analysis of repeated high precision leveling observations during the last 40 years along lines of the Italian fundamental network allowed us to estimate very recent vertical movements in eastern Sicily and southern Calabria (Italy). The network is measured by the Italian Istituto Geografico Militare (IGM) and we have analyzed three leveling lines. Because of the lack of an absolute reference datum, we have conducted the analyses in terms of relative elevation changes compared to reference benchmarks. Although the processing of the different time series obtained from the high precision leveling has allowed us to estimate only relative rates, their extreme accuracy, together with the large extension of networks, makes this type of measurement fundamental for the estimate of recent vertical deformation. In addition, correlating instrumental and geological data makes it possible to identify active tectonic structures whose elastic strain accumulation could be responsible for vertical deformation. In particular, vertical motion can be related to the activity of a W-E trending fault separating the Catania Plain from the Hyblean Plateau in southeastern Sicily, a N-S trending normal fault occurring north of the Messina town and the NE-SW trending Scilla normal fault in south-western Calabria. The last two are located on the sides of the Messina Straits, an area of broad interest for the planning of the single-span bridge between Sicily and mainland Italy.

Unification of European height system realizations

AbstractA suitable representation of the regional gravity field is used to estimate relative offsets between national height system realizations in Europe. The method used is based on a gravimetric approach and benefits from the significant improvements in the determination of the global gravity field by the recent satellite gravity missions the Gravity Recovery and Climate Experiment (GRACE) and the Gravity field and steady-state Ocean Circulation Explorerr (GOCE). The potential of these missions for the unification of height reference frames is analyzed in terms of accuracy and spatial resolution. The results of the gravimetric approach are compared to the independent results of the geodetic leveling approach. Advantages and drawbacks of both methods are discussed.

Determining the Subsidence of Oil Storage Tank Walls from Geodetic Leveling

In this paper the monitoring for subsidence in crude oil storage tanks by the method of Geodetic leveling is discussed. The monitoring network consisted of three control points established about 100m from the tank and 16 studs established at the base of the tank. From the control points, the stud locations were leveled using a geodetic level with parallel plate micrometer and telescopic staves. All levels were run in forward and reverse directions and the measurements were carried out in 2003, 2004 and 2008. Adjustment of observation was carried out using the least squares estimation model to determine the elevation of each stud position in the three measurement epochs together with their accuracy standards. Comparisons were made of the calculated movements from the three measurement epochs and the associated accuracies calculated from the least squares model. Analysis of the results indicated that with the exception of one stud ( stud 8), all other studs emplaced had moved and the movements ranged from 0.91mm to 13.06mm

Vertical Displacement Rate Field of Taiwan From Geodetic Levelling Data 2000-2008

We have developed the most precise vertical displacement rate field of Taiwan Island to date from four sets of precise geodetic levelling data between 2000 and 2008. More than 4000 km of levelling lines between solidly constructed benchmarks were repeatedly surveyed by 1st-order levelling. Strict specifications for field work procedures and comprehensive corrections for systemic errors were applied to the levelling data. Furthermore, in order to account for the vertical deformations caused by four major earthquakes during the data span, coseismic offset corrections were computed and applied. The adjusted orthometric heights and vertical displacement rates of the benchmarks were obtained by least-squares estimation (LSE). The estimated standard deviations of the vertical rates are in the range of ± 0.41 mm/yr and ± 2.47 mm/yr, with a mean value of ± 1.64 mm/yr. These highly accurate results reveal that the most significant subsidence rate is observed in SW Taiwan at -109.4 mm/yr. Land uplift is widely observed in the Central Range and the Coastal Range, with the largest uplift rate of +29.4 mm/yr in SE Taiwan, at the convergence boundary of the Philippine Sea and the Eurasian plates.

The role of deep processes in late 20th century subsidence of New Orleans and coastal areas of southern Louisiana and Mississippi

[1] Geodetic leveling observations from Biloxi, MS, to New Orleans, LA, and water level gauge measurements in the New Orleans–Lake Pontchartrain area were analyzed to infer late 20th century vertical motions. These data were used to test the validity of previous subsidence rate measurements and the models that predict the location and causes of subsidence. Water gauges attached to bridge foundations and benchmarks affixed to deep rods that penetrate Holocene strata subsided as much as 0.8 m locally between 1955 and 1995. The observed deep-seated subsidence far exceeds model predictions and demonstrates that shallow processes such as compaction and consolidation of Holocene sediments are inadequate by themselves to explain late 20th century subsidence. Deep-seated subsidence occurring east and north of the normal faults marking the Gulf of Mexico basin margin can be explained by local groundwater withdrawal, and regional tectonic loading of the lithosphere by the modern Mississippi River delta (MRD). Sharp changes in subsidence coincide with strands of the basin margin normal faults. Displacements are consistent with activity and show motions consonant with fault creep. Deep subsidence of the region to the south, including New Orleans, can be explained by a combination of groundwater withdrawal from shallow upper Pleistocene aquifers, the aforementioned lithospheric loading, and perhaps, nongroundwater-related faulting. Subsidence due to groundwater extraction from aquifers ∼160 to 200 m deep dominated urbanized areas and is likely responsible for helping to lower local flood protection structures and bridges by as much as ∼0.8 m.

Research on coding and decoding method for digital levels

A new coding and decoding method for digital levels is proposed. It is based on an area-array CCD sensor and adopts mixed coding technology. By taking advantage of redundant information in a digital image signal, the contradiction that the field of view and image resolution restrict each other in a digital level measurement is overcome, and the geodetic leveling becomes easier. The experimental results demonstrate that the uncertainty of measurement is 1 mm when the measuring range is between 2 m and 100 m, which can meet practical needs.

Recent and active tectonics of the external zone of the Northern Apennines (Italy)

We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy) by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region. This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure.

Reliability Analysis for a Robust M-Estimator

The least-squares estimation exhibits a poor performance in the presence of gross errors. One of the typical approaches to control the influence of outliers is to use robust estimation techniques. The well-established geodetic reliability theory is comprised of two main components: internal and external reliability. Both reliability measures are important diagnostic tools for inferring the strength of the model validation. To gain further insight into robust M-estimation performance, the variation characteristics of internal and external reliability measures are addressed for a particular robust estimator. Theoretical analyses show that, during the iterative reweighting procedure for uncorrelated observations, the internal reliability measures as represented by minimal detectable bias become larger and larger. For purpose of illustration, a numerical example associated with a simulated geodetic leveling network is provided. As expected, for the outlying observations, their corresponding external reliability measures get smaller and smaller when the iteratively reweighted least-squares method is implemented.

Erosion-driven uplift of the modern Central Alps

We present a compilation of data of modern tectono-geomorphic processes in the Central European Alps which suggest that observed rock uplift is a response to climate-driven denudation. This interpretation is predominantly based on the recent quantification of basin-averaged Late Holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling. Furthermore, a GPS data-based synthesis of Adriatic microplate kinematics suggests that the Central Alps are currently not in a state of active convergence. Finally, we illustrate that the Central Alps have acted as a closed system for Holocene redistribution of sediment in which the peri-Alpine lakes have operated as a sink for the erosional products of the inner Central Alps. While various hypotheses have been put forward to explain Central Alpine rock uplift ( e.g. lithospheric forcing by convergence, mantle processes, or ice melting) we show with an elastic model of lithospheric deformation, that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading. Thus, erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens. Rather, we suggest that the geomorphic response of the Alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift. Therefore, in a non-convergent orogen such as the Central European Alps, the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion.

Use of the particle swarm optimization algorithm for second order design of levelling networks

The weight problem in geodetic networks can be dealt with as an optimization procedure. This classic problem of geodetic network optimization is also known as second-order design. The basic principles of geodetic network optimization are reviewed. Then the particle swarm optimization (PSO) algorithm is applied to a geodetic levelling network in order to solve the second-order design problem. PSO, which is an iterative-stochastic search algorithm in swarm intelligence, emulates the collective behaviour of bird flocking, fish schooling or bee swarming, to converge probabilistically to the global optimum. Furthermore, it is a powerful method because it is easy to implement and computationally efficient. Second-order design of a geodetic levelling network using PSO yields a practically realizable solution. It is also suitable for non-linear matrix functions that are very often encountered in geodetic network optimization. The fundamentals of the method and a numeric example are given.

The Use of Geodetic Leveling For Crustal Motion and Deformation Studies: A 30-Year Case Study in Ahmadu Bello University, Zaria

This paper examines the stability of some benchmarks on the main campus of Ahmadu Bello University, Zaria, and reports the deformation studies of the area around the University dam. This dam serves as the main storage reservoir for the water supply to the University and surrounding communities. In order to study the deformation around the University dam and the stability of benchmarks, several surveys were carried out between 1976 and 2006. Within the period under review, it was revealed that the maximum downward displacement (settlement) of 96.44mm was recorded between 1976 and 2006 for a monitoring station (CP4) situated centrally along the embankment of the dam. The maximum upward displacement (uplift) of 8.03mm was recorded between 1976 and 2002 at a ground point (CP12) located in a roundabout in front of Faculty of Medicine of the University. The monitoring Station CP4 had the greatest average absolute displacement of 3.22mm per annum over the period of thirty years. Detailed results and analysis will be discussed in this paper.. The Information Manager Vol. 7 (2) 2007: pp. 28-39