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STUDENT CONTEST 2017

Institute for Geodesy and Geoinformation Professorship for Geodesy

An investigation into the empirical accuracy of GNSS-NHN heights using SAPOS after the introduction of the GCG2016 as a component of the integrated geodetic spatial reference 2016

The CLGE Students’ Contest 2016–2017

Bachelor’s degree programme Geodesy and Geoinformation Faculty of Agriculture University of Bonn

Paper by Vitaly Winter

Bonn 2017

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STUDENT CONTEST 2017

First Supervisor: Second Supervisor:

Prof. Dr.-Ing. H. Kuhlmann Dr.-Ing. C. Eling

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STUDENT CONTEST 2017

Abstract The consistent integrated geodetic spatial reference was introduced in 2016. This spatial reference offers the possibility to obtain normal heights above mean sea level (NHN, NormalhĂśhennull) in real-time and high quality by using global navigation satellite systems (GNSS). The network RTK (real-time kinematic) method is used by the satellite positioning service (SAPOS) for achieving precise positioning. The difficulty is to transfer the ellipsoidal 3D-coordinates from the GNSS reference system to the height and plan in the national system. In the case of the height component, a gravimetrically derived quasigeoid model represents the connection between ellipsoidal and the local vertical datum. This investigation intends to make an empirical statement about the totality of the systematic and random deviations from collected measurement data. This data is obtained in the RhineSieg county of North Rhine-Westphalia, Germany by measuring official height control points. Dependencies of variations on different factors must be considered. The first investigation is based on the evaluation of frequently repeated short measurements at a suitable reference point. This observations are used to examine the accuracy of the used GNSS method. The results of the investigation show a high degree of precision and accuracy: The mean height value from the multiple measurements corresponds to the set point height. The empirical standard deviation of the individual measurement shows a high precision of under one centimetre. Further investigations refers to control points with known height values. The documentation files of this points are given from the office for surveying. A target-actual comparison of surveyed and set point heights reveals that the empirical standard deviation of the individual measurement remains within the expected range of a few centimetres even under unfavourable measuring conditions.

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STUDENT CONTEST 2017

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STUDENT CONTEST 2017

Contents 1 Introduction 1.1 Motivation . . . . . . . . . . . . . 1.2 State of Research and Technology 1.2.1 Undulation . . . . . . . . 1.2.2 GCG2016 . . . . . . . . . R 1.2.3 SAPOS . . . . . . . . . 1.3 Concrete Problem . . . . . . . . .

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3 Analysis of Results 3.1 Results of Repeated Measurements . . . . . . . . . . . . . . 3.1.1 DOP-Values . . . . . . . . . . . . . . . . . . . . . . . 3.2 Results from HFP-Measurements . . . . . . . . . . . . . . . 3.2.1 Uncertainty of GNSS-NHN-Heights . . . . . . . . . . 3.2.2 Uncertainty and the Order of the Control Point . . . 3.2.3 Uncertainty as a Function of an own Categorisation 3.2.4 Uncertainty and Point Actuality . . . . . . . . . . . 3.3 Discussion and Conclusions . . . . . . . . . . . . . . . . . .

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2 Evaluation 2.1 Instruments . . . . . . . . . 2.2 Treatment of Outliers . . . 2.2.1 Methodology . . . . 2.3 Multiple Measurements at a

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Bibliography

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STUDENT CONTEST 2017

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STUDENT CONTEST 2017

1. Introduction 1.1

Motivation

In North Rhine-Westphalia, Germany, the new integrated geodetic spatial reference 2016 updates the previous geodetic reverence systems. The reference 2016 represents the realisations of modern, epoch-equal and uniform frames for Germany. A direct linking of geometrical and physical measured variables is provided in a high quality. For example, This linkage makes it possible to obtain normal heights above mean sea level (in the following NHN, Normalhöhennull) with RTK-GNSS measurements (real-time kinematic, global navigation satellite system) reliably and in centimetre accuracy. A network of reference stations is used to calculate and provide correction data to the user. In addition, the GNSS observations can be fitted into the land system. To determinate the NHN, undulation values are calculated with the quasigeoid model German Combined Quasigeoid (GCG) 2016. If the accuracy is sufficient for the respective task, this technology can save an enormous amount of time compared to conventional spirit levelling. With progressively improved GNSS measurement methods and a wide range of possibilities, a change in the land survey is taking place. The task of creating and preserving control point fields moves into the background. The establishment of GNSS reference stations and the provision of correction parameters are brought to the fore. The aim of this study is to elaborate the potential of the normal height determination using GNSS in the Rhine-Sieg county after the introduction of the new geospatial reference 2016.

1.2

State of Research and Technology

The theoretical basis for a usable height value requires a deep understanding of the physical figure of the earth and a possible approximations through geometrical shapes. The figure of the earth is irregular and thus mathematically difficult to describe. However, a strict mathematical model of the surface is required for mapping and calculations. Depending on the reference surface, a distinction is made between physical and geometrical heights.

1.2.1

Undulation

The combination of physical and geometric systems is essential for engineering and national surveying with regard to the increasing importance of satellite-based measurement technologies. A model of a geoid is required for the transition from GNSS- to NHN-heights. This transition is called the geoidal undulation N . It is the difference between the ellipsoidal height hell and an given gravimetric geoid or quasigeoid model Hphys as shown in Figure 1.1. N = hell − Hphys

(1.1)

According to Bauer [2011] the accuracy of the GNSS-NHN-height depends on two parameters: the accuracy of the reference surface and the measurement of the GNSS-height. The vertical differences between the two altitude systems vary in Germany between 34 m in the Baltic Sea and 50 m in the Alps. Address Offices in Brussels : Rue du Nord 76, BE – 1000 Bruxelles. Tel +32/2/217.39.72 Fax +32/2/219.31.47 E-mail: maurice.barbieri@clge.eu - www.clge.eu EU-Transparency Register of interest representatives - 510083513941-24

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STUDENT CONTEST 2017 1. Introduction

4

surface P

Hphys hell

quasigeoid

N ellipsoid Figure 1.1: Undulation

The reference systems described in the chapter 1.2 are realised by interconnected reference frames such as the German main height frame 2016 (DHHN, Deutsches Haupthöhennetz) and GCG2016. They and other frameworks form the pillars of the integrated spatial reference 2016. In addition to signals from GPS, the GLONASS satellites (Russian: „Global Navigation Satellite System“) were also used in the 2016 implementation. The use of American and Russian satellite systems together is called the G2 network. By highly accurate measurements on partly new reference stations the inner accuracy of the land system in the new reference 2016 was increased. It is important that this modernisation has no practical impact on the required measuring accuracy in the cadastre and engineering survey [Krickel et al., 2016].

1.2.2

GCG2016

The GCG2016 shines with a increase in accuracy to the previous model (GCG2011). For the realisation of both models extensive data were collected: gravity field disturbances from gravity measurements, quasigeoid heights from GNSS measurements and normal heights in DHHN92 and 2016, digital terrain models and bathymetry data as well as global gravity field models. However, it should be borne in mind that the actual gravity is influenced by many factors such as solid-state tides, ocean loads, nutation and even the weather. Thus, the accuracy indication varies according to the geological nature of the area [BKG, 2016]:

• flat land: 1 – 2 cm • high mountains: 3 – 4 cm • marine area: 4 – 10 cm

The Rhenish Slate Mountains and foothills of the Eifel extend in the investigation area. The topography can not be assigned to flatland but also has no high mountains. It is a mountainous landscape with maximum heights up to 460 m over NHN. Therefore, the accuracy of the GCG2016 is assumed to be 1 – 3 cm. Address Offices in Brussels : Rue du Nord 76, BE – 1000 Bruxelles. Tel +32/2/217.39.72 Fax +32/2/219.31.47 E-mail: maurice.barbieri@clge.eu - www.clge.eu EU-Transparency Register of interest representatives - 510083513941-24


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1.3. Concrete Problem

1.2.3

R SAPOS

R The satellite positioning service (SAPOS ) provides uniform services for users of satellite-based R measurement methods. A network RTK is operated by SAPOS for a nationwide supply of master or reference stations.

Depending on the case of application, the user can choose between different services. These are according to the AdV [2016]: • Echtzeit Positionierungs-Service (EPS) real-time positioning service with σlocation : 30 cm bis 80 cm and σheight : 50 cm to 100 cm • Hochpräziser Echtzeit Positionierungs-Service (HEPS) high precision real-time service with σlocation : 1 cm bis 2 cm and σheight : 2 cm to 3 cm • Geodätischer Postprocessing Positionierungs-Service (GPPS) geodetic postprocessing service with σlocation : < 1 cm and σheight : 1 cm to 2 cm At this point, it should be noted that the accuracy specification for the height component relates to an ellipsoidal height. In conjunction with the GCG2016, the HEPS offers high point accuracy in real time and is an attractive opportunity to achieve a NHN-height. It is advisable to maintain a measurement time of approximately two minutes for safety and accuracy.

1.3

Concrete Problem

A simplified view of the inner accuracy σp by variance propagation can be done with this: q q 2 2 σp = σGCG + σHEP S = (1 cm bis 3 cm)2 + (2 cm bis 3 cm)2 (1.2) The insertion of the values mentioned in the previous section theoretically yields an inner precision of σp = 2.2 cm - 4.2 cm. For further accuracy consideration in the evaluation, the mean value is used with σp = 3,2 cm. The aim is to validate the theoretically achievable accuracy. The results of the study depend strongly on the amount of measurements taken. Since the official height points (HFP, Höhenfestpunkte) are distributed inhomogeneous in the measurement area, the significance of the results increases with the number of recorded HFP and the coverage of the measuring area.

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STUDENT CONTEST 2017

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2. Evaluation 2.1

Instruments

In modern surveying, geodetic GNSS receivers are widely used. The following combination of control unit and receiver was used for all observations in this work: • Receiver: Leica GS16 The modern receiver is capable of using various satellite systems such as GPS, GLONASS, Galileo and Beidou. • Control unit: Leica CS20 The control unit is used to operate the GNSS receiver and to store the measured data. It saves one position per second and automatically closes the measurement after 120 positions. The elevation mask is set to 10◦ for all measurements, in order to achieve a good satellite geometry for the height determination.

Figure 2.1 Equipment

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STUDENT CONTEST 2017

2.2. Treatment of Outliers

2.2

Treatment of Outliers

Measurements near to reflective surfaces such as traffic signs are a problem. The lack of integrity of a single observation can not reveal false measurement data. Therefore, each point was monitored twice. Each observation has been individually initialised to obtain a new solution of the ambiguities. Outliers must be detected and removed before the evaluation. A measured value is considered an outlier if it deviates by the triple of the expected standard deviation of σp = 3, 2 cm from the setpoint (see table 2.1). Outliers make up about 5% of the measurements in this work. In some cases, the inconsistencies can be attributed to multipath effects and failed ambiguity solutions. This problem is a difficult one, since it can only be recognised by a comparison value. Point number 5110 5209 5307 5308 5309 5309

9 9 9 9 9 9

1. measurement [cm]

2. measurement [cm]

-594.7 -4.6 +72.5 -172.2 -458.7 -14.4

not measured +87.3 +1.5 +64.2 not measured -8.2

00006 00040 00191 00170 00193 00309

reason vegetation road sign traffic vegetation wall, vegetation road sign, building

Table 2.1: Deviations of the Detected Outliers

2.2.1

Methodology

Only the first of the two measured values per point is used for the evaluation of the measured data. Since a control measurement is available for each point, this value is subjected to a parallel control evaluation, instead of the calculation of both in one. This approach is followed to determine the actual empirical standard deviation of a single measurement sE . However, the aim is to investigate the spread of a simple measurement. To calculate the standard deviation, the assumption is made that the given control heights H given are variance-free and uncorrelated. From the difference between given and measured values, the improvements for an observation vi can be calculated to. vi = Higiven − Himeas The empirical standard deviation of the individual measurement sE is thus determined. v u n uX vi2 ...n = #observations sE = t ...f = #degrees of freedom n−f

(2.1)

(2.2)

i=1

This scattering relates to the totality of the measured values. By solving the total quantity in categories, an attempt is made to filter dependencies on certain influences as done in chapter 3.

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STUDENT CONTEST 2017 2. Evaluation

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2.3

Multiple Measurements at a Reference Point

A reference point H Ref is used to examine the inner and outer RTK-GNSS accuracy. It is intended to fulfil various conditions like the greatest possible freedom of horizon, no reflective objects or flowing traffic in a direct surrounding area. Ideal conditions are provided by a self-imposed height marker. It is connected to the DHHN2016 by levelling from an HFP of the first order, therefore the most exact available control point. The shading diagram (Figure 2.2) shows some obstacles over an elevation of 10◦ and only a few over an elevation of 20◦ . Under these conditions during measurements, 14 to 17 satellites could be used.

Figure 2.2: Shading Diagram of the Point for Repeated Measurements

Over the period of the measuring trips in the Rhine-Sieg county, measurements were repeated at the reference point. A total of seven days were measured at different times. At each epoch 25 repetition measurements are carried out with their own initialisation per measurement. The evaluation of the reference point data according to comparison and repetition conditions can be found in chapter 3.1.

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3. Analysis of Results 3.1

Results of Repeated Measurements

The height was transferred from an HFP about 80 m away to the established point. At this new point the RTK was initialised up to twenty-five times each day/epoch. In total Seven days or R epochs have been accomplished. The internal accuracy of the SAPOS -HEPS is to be examined with this measurement data. For this purpose, the measurement data are considered in the evaluation over the total measurement period (see Fig. 3.1). Overall no outlier can be detected. In Figure 3.1 it can be seen, that a large part of the deviations are within a range of ±1 cm. On the days three, four and five, however, the deviations are conspicuously often one-sided from the set point. 62.24 62.23 62.22 62.21 62.20

Legend deviations mean target Max./Min. deviation

62.19 62.18 day 1

day 2

day 3

day 4

day 5

day 6

day 7

Figure 3.1: Scattering of Observations

On average, the GNSS height of the reference point HGN SS is the same as the set point level, which is determined by levelling Hlev . HGN SS = Hlev = 62, 211 m over NHN The uncertainty from the GNSS measurements sGN SS is considerably larger than that of the levelled height slev . sGN SS = 6, 7 mm > slev = 0, 4 mm Since the mean value corresponds to the set point, there are no systematic deviations. That the GNSS values randomly scatter around the mean value and the Figure 3.2 shows an uniform distribution of the measured values. This result highlights the enormous potential of RTK-GNSS heights. The maximum deviations lie with +1.8 cm and –2.2 cm within the expected standard deviation of σp = 3.2 cm. Address Offices in Brussels : Rue du Nord 76, BE – 1000 Bruxelles. Tel +32/2/217.39.72 Fax +32/2/219.31.47 E-mail: maurice.barbieri@clge.eu - www.clge.eu EU-Transparency Register of interest representatives - 510083513941-24

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STUDENT CONTEST 3. Analysis of2017 Results

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Figure 3.2: Histogram of Repeat Measurements

3.1.1

DOP-Values

The quality of a GNSS position depends, inter alia, from the number of satellites received and their geometry. The so-called Dilution of Precision (DOP) values are indicative of the accuracy of the GNSS measurement data. A DOP value is available for each measured value. In Figure 3.3 the amounts of the improvements are plotted against the set point value with the corresponding GDOP and PDOP values. A direct relationship between the fluctuations of the measurement and DOP values is possible in a few places, e.g. to the end of the third day. Although both DOP values continue to highly fluctuate from the fourth day onwards, the dispersion of the improvements remains constant. For this reason, the DOP values are assigned a weak power of information about the actual accuracy of the measurements. 8

2.5 Legend |v i | PDOP GDOP

6

2

1.5 4 1.0 2 0.5

0 day 1

0 day 2

day 3

day 4

day 5

day 6

day 7

Figure 3.3: DOP-Values for all 7 days

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3.2. Results from HFP-Measurements

3.2

Results from HFP-Measurements

The main part of the study, the practical measurement accuracy of GNSS-NHN heights, is based on the heights measured in the Rhine-Sieg county. Out of 254 given HFP, 232 were sought in the field. Due to various circumstances in many places no measure has been possible. Therefore, only 138 data points were collected. After deducting the seven detected outliers (see Table 2.1), 131 values are available for analysis. In Figure 3.4 the deviations of the evaluated GNSS-NHN heights are shown. The evaluation refers to the GNSS-NHN heights from the first measurement. For comparison and control, the values of the second measurement are considered and evaluated analogously to the first measurement. Both analyses yield almost identical results. Therefore, only the analysis of the first measurement is discussed below. 106

4

5.645 3

2

5.635 1

5.630 5.625

0

5.620

-1

target - actual [cm]

5.640

5.615 -2

5.610 -3

5.605 -4

3.235

3.236

3.237

3.238

3.239

3.240 107

Figure 3.4: Overview of Measuring Area

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STUDENT CONTEST 3. Analysis of2017 Results

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3.2.1

Uncertainty of GNSS-NHN-Heights

All in all the measured values differ between a maximum of +6.9 cm and a minimum of -5.2 cm from the official vertical value (see Figure 3.5). Overall, the mean of deviations is a few millimetres lower than the expected value. 8 6 4 2 0 -2 -4 deviations mean (- 4 mm) max./min. deviation

-6 -8 0

20

40

60

80

100

120

Figure 3.5: Deviations of the Measured Values

The measured values correspond to a normal distribution with parameters as in shown Figure 3.6. An empirical standard deviation of the individual measurement sE = 2.2 cm is calculated. Compared to the expected uncertainty of Ď&#x192;P from Chapter 1.3 of 3.2 cm, sE significantly exceeds this expectations. This also confirms the high accuracy of the new GCG2016.

Figure 3.6: Overall Histogram

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3.2. Results from HFP-Measurements

3.2.2

Uncertainty and the Order of the Control Point

The accuracy can vary by different types of elevation determination. Now, influences on the accuracy of the GNSS-NHN heights are examined by the point order. For this purpose measured HFP are divided into groups of the first to third order. The sample size of the groups is different. Most of the measured values were measured for HFP of the second order. For comparability, the frequency of the these values is expressed as a percentage. The Figure 3.7 shows the scatter per order and its standard deviation. st

nd

rd

Figure 3.7: Deviations and the Order of the Point

Here the expectation is confirmed that the GNSS-NHN heights coincide most strongly with the first most accurate order. An explanation for this high accuracy is the actuality of the HFP values from levelling lines of the measurement campaigns for the renewal of the German main height frame. Points of the first order have additionally been determined by gravity measurements and GNSS observations. Therefore, very good fittings of the quasigeoid can be realised. The HFP of the second order were partially measured anew. In the case of third-order points, there is the expectation they are comparatively inaccurate. This assumption is made due to their high age and because they are usually not revisited in new measurement campaigns. It can not be confirmed. On the contrary, the points of the third order also show a high degree of accuracy.

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STUDENT CONTEST 3. Analysis of2017 Results

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3.2.3

Uncertainty as a Function of an own Categorisation

The extent to which environment influences the quality of the point is assessed by means of a categorisation into three groups. The classification is carried out as follows: • green or 1st category: There are ideal conditions for GNSS measurements with high horizon freedom. 44.6% of the measured values fall into this group. • yellow or 2nd category: Objects shade at least one side of the receive area so that an unfavorable satellite geometry is used. Under such moderate conditions, 36.7% of the GNSS-NHN heights have been measured. • red or 3rd category: Interfering objects are located in the direct surrounding from several sides. In spite of unfavourable conditions, a measurement is possible. Under these circumstances, 18.7% of measurements were performed. Analogous to the representation of the point orders, the corresponding classification is shown in Figure 3.8. As expected, the environmental conditions are reflected directly in uncertainty. The standard deviation of one category of the first category of s = 1.8 cm is significantly lower than that of the other categories. However, it is striking and contrary to expectation how exactly the values can be under adverse conditions. When the full number of 120 positions is recorded (two minutes measurement duration), significantly higher accuracies could be achieved than expected under difficult conditions. st

nd

rd

Figure 3.8: Deviations and Categories

There is no consistency between the three self-made categories and the official orders. This means that points of the first order can exhibit equally unfavourable conditions for GNSS observations, as those of other orders. The actual situation in situ was recorded during the measurements for all points.

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3.2. Results from HFP-Measurements

3.2.4

STUDENT CONTEST 2017

Uncertainty and Point Actuality

In a further study the effect of the point-of-date and/or the date of the last measurement is checked. Marks of heights are often unprotected on country roads and other public places. Anthropological and geological impacts can alter the position of the control points. If HFP have not been controlled for decades, significant deviations can occur. Some markers also show damage that can affect the accuracy to an unknown degree. The majority of the successfully measured GNSS-NHN heights are recorded on HFPs, which were determined in levelling fashion in 1995 or later (see Figure 3.9). Twenty values were produced at control points, which were last measured in 1988 or earlier. The empirical standard deviation sold = 2.5 cm is calculated from a targetactual comparison of this subgroup. According to this value, older HFP are just as useful as the currently measured ones. In principle, the smallest deviations have occurred in the case of actual and well maintained control points.

Figure 3.9: Deviations and Actuality

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STUDENT CONTEST 3. Analysis of2017 Results

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3.3

Discussion and Conclusions

The results of the empirical investigations relate only to the Rhein-Sieg county. In this area, a high quality of the used service and a precise modeling of the quasigeoid by GCG2016 can be inferred. The point quality depends primarily on a free horizon at the measuring site. In direct comparison to the gravity-related point heights, the most recent points of the first order are the most accurate in precision. With regard to the connection of the ellipsoidal heights with level heights, an accurate GCG2016 is to be expected and thus a precise undulation. In fact, no significant influence of the terrain level in the study area can be observed. With the empirically determined standard deviation of the individual measurement sE = 2.2 cm, the GNSS usage heights are suitable for various tasks in cadastral and engineering surveys. The availability of the system plays a decisive role in surveying. During the investigation, a connection to the HEPS was always available with sufficient free horizon. Problems occur in very heavily forested areas. Tall trees cause too much shading for an ambiguity solution even in forest aisles along country roads. The destruction of survey markers is also a problem as seen in the Figure 3.10. According to the evaluation, a height of approximately 1 cm to 3 cm can be measured within approximately R two minutes using HEPS from SAPOS . In this uncerFigure 3.10: Skew HFP tainty, the deviations from RTK-GNSS observations, the quasigeoid model GCG2016 and the DHHN2016 are included. The GCG2016 can be considered as very well adapted and precise. A systematic offset of - 4 mm was determined in the entire measuring area. On the one hand, the cause of the deviation may lie in the sample itself. This is due to the exposition of markers to environmental influences whose effects are unknown. On the other hand, it reflects the tendency of the earthâ&#x20AC;&#x2122;s crust to rise in the Rhine-Sieg county, which has been found in previous levelling campaigns [Klein, 2016]. The HFPs are therefore also used as geosensors. Despite the the current levelling lines from the renewal campaign, the last measurement of the HFPs used here is in average 15 years ago. The shading problem is more serious. To counter this, a combination of GNSS-NHN height as a point of support for spirit levelling seems to be a viable solution. In the future there is the prospect of using the European navigation satellite system Galileo. The addition of another system for position determination promises a better availability of many satellites and an increase in accuracy. Nevertheless, multiple measurements are essential to control a GNSS-NHN height. Since the quality of the quasigeoid undulation is based on gravity measurements, the main levelling lines remain essential in the future.

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Bibliography AdV (2016): SAPOS-Dienste. 16.01.2016].

http://www.sapos.de/dienste-im-ueberblick.html [Zugriff:

Bauer, M. (2011): Vermessung und Ortung mit Satelliten: Globales Navigationssatellitensystem (GNSS) und andere satellitengestützte Navigationssysteme. Wichmann, Berlin. BKG (2016): Quasigeoid der Bundesrepublik Deutschland. www.bkg.bund.de/DE/Produkteund-Services/Shop-und-Downloads/Digitale-Geodaten/Quasigeoid/quasigeoid.html [Zugriff: 29.12.2016]. Feldmann-Westendorff, U., G. Liebsch, M. Sacher, J. Müller, C.-H. Jahn, W. Klein, A. Liebig und K. Westphal (2015): Das Projekt zur Erneuerung des DHHN: Ein Meilenstein zur Realisierung des integrierten Raumbezugs in Deutschland. zfv – Zeitschrift für Geodäsie, Geoinformation und Landmanagement 140(3), S. 180–184. Heckmann, B., G. Berg, S. Heitman, C.-H. Jahn, B. Klauser, G. Libsch und R. Liebscher (2016): Der bundeseinheitliche geodätische Raumbezug – integriert und qualitätsgesichert. zfv – Zeitschrift für Geodäsie, Geoinformation und Landmanagement 141(5), S. 354–367. Hofmann-Wellenhof, B., H. Lichtenegger und J. Collins (2001): Global Positioning System. Springer-Verlag, Wien. Klein, W. (2016): Eine interdisziplinäre Betrachtung der vertikalen Bodenbewegungen in der Eifel. zfv – Zeitschrift für Geodäsie, Geoinformation und Landmanagement (1/2016), S. 27– 34. Krickel, B., E. Kurtenbach und J. Riecken (2016): Neuer Raumbezug 2016 für NRW. In: NÖV Nachrichten aus dem öffentlichen Vermessungswesen Nordrhein-Westfalen. NÖV 2, S. 19–27. Leica Geosystems AG (2016): Leica LS Digitalnivelliere Datenblatt. http://www.leicageosystems.de/de/Leica-LS10-LS15_107401.html [Zugriff: 29.12.2016]. R NRW: Aktuelle Information - Neuer Raumbezug 2016 im SAPOS NRW (2016): SAPOS R NRW zum 01.12.2016. http://www.sapos.de/dienste-im-ueberblick.html [ZuSAPOS griff: 09.02.2016].

Sparla, B. W. P. (2010): Vermessungskunde und Grundlagen der Statistik für das Bauwesen. Wichmann, Berlin. Torge, W. (2003): Geodäsie. de Gruyter, Berlin.

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AN INVESTIGATION INTO THE EMPIRICAL ACCURACY OF GNSS-NHN HEIGHTS USING SAPOS AFTER THE INTRODUCTION  

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