SAPOS DGNSS Reference Station System in Germany and its ...

Abstract
UNITED NATIONS/UNITED STATES OF AMERICA
WORKSHOP ON THE USE OF GLOBAL NAVIGATION SATELLITE SYSTEMS
Vienna, Austria • 26 – 30 November, 2001
SAPOS ® DGNSS Reference Station System in Germany and its
Analogue in Bulgaria
Gerd Rosenthal, Georgi Milev,
Friedrich Rokahr Keranka Vassileva
Germany Bulgaria
Compatible geodetic reference systems and their implementation as the basis of a uniform geodetic infrastructure
are needed in connection with the increase in the economic power vested in Europe, to manage and optimise the
volume of traffic, and to meet the demands of planning, investment and the law.
It is therefore necessary to provide geodetic reference systems with high efficiency and in accordance with the
demands of a wide variety of applications. It is also necessary to reduce the costs for providing the geodetic reference
systems. Multifunctional GNSS reference station networks, providing DGNSS correction data for real-time
positioning and data for measurements for positioning with post-processing, provide a technically appropriate
way of satisfying these demands.
The German National Survey Satellite Positioning Service SAPOS ® remains a good example of high precision
GNSS reference station networks because of its technical innovations such as networked reference stations, antenna
calibration and Null antennas. SAPOS ® was established in 1994 by the German surveying authorities to
fulfil their legal responsibilities in an efficient way.
This report describes the philosophy and the current situation of SAPOS ® and discusses the importance of unified
solutions to the increasing harmonisation of Europe. It describes also the common consideration of the Bulgarian
and German partner for building up a SAPOS ® compatible reference station network in Bulgaria, too.
Introduction
In the ever increasing globalisation of economic relationships, Europe
needs an infrastructure favourable for positioning and navigation, in
order to safeguard and to strengthen the region as a whole and its economic
growth, to develop the social aspects of its cities and regions, to
manage and to optimise traffic (Beer, Rosenthal 2001) and, last but not
least, to protect its climate and environment. These constraints demand
cost-effective solutions as well as the further development of technical
capabilities and mastery of forward-looking technologies. Reliable and
up-to-date information of high quality must be always available on-line,
in a technically suitable form. Procedures and techniques must support
international standards and improve on them, as necessary, in accordance
with their respective requirements.
The technical possibilities offered by the Global Navigation Satellite
Systems (GNSS) give the state survey departments the chance to fulfil
their mission of supplying geodetic reference systems efficiently and
largely in accordance with their requirements. The availability of two
systems in parallel, NAVSTAR GPS (Navigation Satellite Timing and
Ranging – Global Positioning System) from the United States of Amer-
Map: EPN Central Bureau
Fig. 1: EUREF Permanent Network
(EPN). On test from 1995 and in regular
operation since 1997, the GPS
satellites are continuously observed at
the permanent stations of the EPN.
ica and GLONASS (Global’naya Navigatsinnaya Sputnikova Sistema) from the Russian Federation, offers the
necessary safeguards, taking into consideration the official statements relating to their continued usability and
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 1

future development. Finally, these systems will be supplemented by the European development of Galileo, the first
civilian GNSS.
With the creation in 1989 of the European Terrestrial Reference System (ETRS 89), a three-dimensional geodetic
reference system became available for the whole of Europe for the first time. Its world-wide spatial referencing
connection is maintained up-to-date, notably through the EUREF Permanent Network (EPN) which contains the
European stations of the International GPS Service (IGS) [Fig. 1] (EUREF).
For position fixing with accuracies higher than about 7 m to 20 m, which is possible with absolute GPS, DGNSS
reference station services have been set up in many European countries since the 1990s, providing differential
GNSS correction data for real-time positioning or, at least, their observation
data for DGNSS post-processing.
These conditions and developments define the basis and the direction
to enable the creation of a basic unified European geodetic infrastructure.
It is hard to judge whether this task, which is very important for
the increasing unification of Europe, can be achieved through the farreaching
standardisation of procedures and techniques. However, the
responsibilities of the state survey departments for their future business
should be evaluated and considered in accordance with the requirements
described in this paper, taking into account the significantly
increased field of application of their products.
Current requirements for the provision of a geodetic reference
system for Europe
With its products, the state survey departments provide the fundamental
infrastructure for all spatial and land-related information, thus supplying
an important basis for planning and action in the administrative,
legal, economic and scientific fields. The global influences and current
technical possibilities mentioned in the introduction have significantly
changed the profile of requirements for the provision of geodetic reference
systems:
• The need for a unified reference system for the ever more tightly
knit countries of Europe has become highly important. Especially
for navigation and positioning, but also to meet nation-wide planning
and business requirements, it is necessary in addition that in
such a unified reference system positions are described threedimensionally,
rather than separating plan position from height
data. ETRS 89 fulfils these important criteria.
Many European countries have decided to introduce ETRS 89 as
an appropriate reference system. However, one can not count on
its rapid and comprehensive introduction everywhere. For Germany,
the Working Committee of the Surveying Authorities of the
States of the Federal Republic of Germany (Arbeitsgemeinschaft
der Vermessungsverwaltungen der Länder der Bundesrepublik
Deutschland, AdV) decided in 1991 on the comprehensive introduction
of ETRS 89, and reinforced this decision in 1995 by
specifying the use of plan coordinates on the Universal Transverse
Mercator Grid System (UTM) and normal heights based on the
German primary levelling network (Deutsches Haupthöhennetz
Fig. 2: GPS/GLONASS choke ring
antenna at the Berlin 1 central reference
and monitoring station of the
Berlin SAPOS ® reference station system.
Fig. 3: Berlin Alexanderplatz TV
tower, site of the SAPOS ® transmitter
for DGNSS correction data via VHF
radio and FM/RDS. The range of the
VHF radio transmitter is about 65 km.
1992, DHHN 92) for all land survey purposes. However, even in Germany the full implementation of these
decisions is running rather hesitantly, both on account of the cost and because of the need for carefully coordinated
timing.
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 2

• The traditional provision of local monumented control points and their determination in national or regional
coordinate systems no longer fulfils today’s requirements. The care and maintenance of conventional general
control networks at their former density is no longer economic.
• Many users need precise on-line and real-time positioning in order to carry out their tasks. Thus, no benefit
can be gained from conventional general control networks. Innovative solutions, with a guaranteed future and
offering a comprehensive range of products meeting accuracy, reliability and safety requirements, are necessary
to provide geodetic spatial referencing. These solutions are now represented either by GNSS or, for the
many different applications with higher requirements, by DGNSS which is based on permanent reference station
networks operating continuously.
• A technically appropriate range of media and a choice of levels of accuracy are needed, in addition to high
system availability and reliability of the results, in order to provide geodetic reference systems by means of
precise DGNSS.
• Cost-effective technical solutions for reference station operators and users can only be achieved if the industries
involved in their development and implementation are given economic incentives. In order to ensure the
safety of their investment, the use of obligatory, and preferably international, standards as well as the expectation
of high sales of relevant equipment are essential. Unfortunately, the DGNSS services currently available
in Europe vary considerably in their procedures and products, and technical conditions for their use are
often incompatible.
The SAPOS ® multi-functional satellite positioning service in Germany
The SAPOS ® DGNSS service provides an official geodetic infrastructure for all satellite-supported positioning
and navigation applications for Germany (SAPOS). By means of permanently operating, multi-functional GNSS
reference stations [Fig. 2], correction data for real-time GPS code and carrier phase measurements as well as
original observation data for GPS post-processing
are provided in internationally standardised data
formats [Fig. 3]. A multi-media multi-function system,
fulfilling requirements and going far beyond the
normal range of surveying tasks, is ensured by four
different levels of service [Table 1]:
• SAPOS ® EPS: transmission of DGNSS correction
data in co-operation with members of the
association of German public broadcasting authorities
(Arbeitsgemeinschaft der öffentlichrechtlichen
Rundfunkanstalten der Bundesrepublik
Deutschland, ARD) via FM/RDS sound
broadcasting transmitters, and in cooperation
with Deutsche Telekom AG through the
LW/RDS Mainflingen transmitter for real-time
position fixing with an accuracy of 1 m to 3 m,
as well as via the AdV’s own VHF (2 m band)
transmitters for real-time positioning enabling
an accuracy of 0.5 m to 2 m.
• SAPOS ® HEPS: transmission of DGNSS correction
data via AdV-owned VHF radio transmitters
for real-time position fixing with an accuracy
of 1cm to 5cm and, by using area correction
parameters (FKP) of networked reference
stations, an accuracy of ≤ 2 cm. In several
states, SAPOS ® HEPS is also supplied via GSM telephone.
Fig. 4: Continuous measurements with SAPOS ® HEPS
and using area correction parameters (FKP), 12 January,
12.01 p.m. to 13 January 2001, 12.00 noon. Distance
between reference station and rover: 21.6 km. The site of
the rover is almost free of obstructions. More than 99.9 %
of measurements result in coordinates with an accuracy
of better than 2 cm. Three periods in the course of the 24
hours, with durations of between 20 minutes and one
hour, and affecting only a few of the solutions, indicate an
unfavourable GPS satellite configuration. These unfavourable
periods should be covered by the planned additional
use of the GLONASS satellites for SAPOS ® in
Berlin. Further measurements were able to show that
similar results can be reached with the networking solution
over significantly longer distances between reference
station and rover, and even with substantial extrapolations
outside the reference station network.
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 3

• SAPOS ® GPPS and GHPS: provision of GNSS observation data from the reference stations via the Internet
for high-precision GNSS post-processing with centimetre to sub-centimetre accuracy. Before converting data
supply completely to Internet methods in the future, observation data is currently often supplied via mailboxes
which can be interrogated by conventional or mobile phone, or using other data media.
Service level Availability Medium Accuracy Data
rate
In order to cover the whole of Germany, a network of about 250 SAPOS ® reference stations at intervals of about
40 km to 70 km is currently planned, of which more than 200 have already been set up. The hardware and software
at the reference stations comply with specific standards fixed by the AdV and updated within the framework
of SAPOS ® quality assurance measures.
Reference station sites have been chosen so as to ensure the long-term stability of the GNSS antennas. Sites and
antennas are also selected so as to provide a horizon which is as far as possible free of obstructions and so as to
avoid external radio interference and multipath effects on satellite signals. By using appropriately calibrated
choke ring antennas, possible multipath effects are further counteracted. Coordinates are determined with high
precision, both in ETRS 89/Epoch 0 and in conventional geodetic reference systems by connecting to EUREF
D/NL 93 points as well as to the denser derived networks of the German Reference Frame (DREF 91) and state
reference networks, the German primary triangulation network (Deutsches Hauptdreiecksnetz, DHDN 90) and
the German primary levelling network (Deutsches Haupthöhennetz, DHHN 92).
Only high quality geodetic GNSS dual frequency receivers are used at SAPOS ® reference stations.
User interface
SAPOS ® EPS real time FM/RDS, LW/RDS 1 to 3 m 3-5 s 7) RTCM 2.0 9)
real time VHF 1) 0,5 to 2 m 3) 1 s 7) RTCM 2.0 9)
SAPOS ® HEPS real time VHF 1) 1 to 5 cm 4)
SAPOS ® GPPS near real time postprocessing
Internet 2)
GSM/telephone,
other media
SAPOS ® GHPS post-processing Internet 2)
telephone,
other media
≤ 2 cm 5)
1 s 7) RTCM 2.1
(MSG 20, 21) 9) ,
NMEA-AdV 10)
< 1 cm 6) 1 s 8) RINEX 2.0 11)
≤ 1 cm 6) 1 s 8) RINEX 2.0 11)
(1) In some states mobile phone (GSM) also available; (2) until data supply via the Internet is fully implemented, in some cases via mailbox and/or
other data media only; (3) dependent on the mobile receiver technology installed; (4) achievable accuracy without supplementary information
from networked reference stations; (5) achievable accuracy with area correction parameters from networked reference stations; (6) dependent on
duration of observations, using precise ephemeris as necessary; (7) for transmission of DGNSS correction data for all satellites received at the
reference stations; (8) standard recording interval for observation data; by prior arrangement this can also be provided at ½ s intervals; RINEX
data can be thinned for delivery as required; (9) international standard data formats from the US Radio Technical Commission for Maritime
Services, Special Committee No. 104: RTCM SC104 versions 2.0 and 2.1, the latter using message types 20 and 21 for code and carrier phase
corrections; (10) international standard format from the National Marine Electronics Association, for data exchange between electronic devices,
enhanced in SAPOS ® for the supply of area correction parameters (FKP) from networked reference stations; (11) Receiver Independent Exchange
Format version 2.0 (Commission VIII International Coordination for Space Techniques for Geodesy and Geodynamics)
Table 1: Overview of SAPOS ® service levels and media
Positions of reference station antennas are checked regularly (four times a year) for any displacement in relation
to selected stations of the German GPS reference network (GREF), the European reference network (EUREF) and
the International GPS Service (IGS) network.
SAPOS ® is based on international standards and develops these standards, together with partners in the scientific
and business sector, in accordance with innovations in procedures and techniques. In co-operation with industry,
AdV strives for internationalisation of these standards. The SAPOS ® Technical Committee was formed in 1999,
thus enabling two-way communication between government and industry, and the discussion and coordination of
relevant activities. As a result of this co-operation, all of the well-known manufacturers of geodetic GNSS receivers
are now incorporating full SAPOS ® compatibility in their equipment, where this had not already been done.
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 4

Within the framework of SAPOS ® , technical innovations have been developed for high-precision GNSS reference
station networks, offering solutions which are of interest for other DGNSS services even at the international level,
as evidenced by the export of these solutions to other countries. The following examples give an indication of
these developments:
• The RTCM-AdV data format allowing for complete transmission of DGNSS correction data for 12 satellites
including area correction parameters (FKP) from networked reference stations with a data transmission rate
of only 2400 bits/s. The international RTCM SC 104/versions 2.0 and 2.1 and, in the future, version 2.3 data
formats can be easily generated at the user interface. Transmission of the same information using the RTCM
SC 104/version 2.1 format would require a transmission capacity of 9600 bits/s. At the same time, RTCM-
AdV provides an accounting system for prepaid service-related charges, using a Smart Card or appropriate
firmware solutions in the mobile receiver.
• Antenna calibration and the “Null antenna”, modelling the effects of antenna phase centre variations (PCV)
and of mean phase centre offsets, and so enabling GNSS antennas for reference station networks to be practically
error-free (Wübbena et al 1996b, 2001). In the RTCM SC 104 version 2.3 antenna information will be
included and the “Null antenna” is as an antenna type compatible with this data format.
• The networked reference station process, allowing the modelling of distance-dependent GNSS error components,
tropospheric, ionospheric and orbit effects (Wübbena et al 1996a). As a result, the user gains shorter
initialisation times and improved accuracy for real-time position fixing [Fig. 4].
In September, 2001 the US Radio Technical Commission for Maritime Services (RTCM) has started standardisation
discussions for the implementation of the information of networked reference station arrays as a standard of
the RTCM Sub-Committee 104 in future (Euler et al 2001).
Several state survey departments are testing procedures and solutions going beyond current standard SAPOS ®
service levels. For example, the Berlin state survey will include the Russian GLONASS in all SAPOS ® services
Fig. 5: Schematic overview of the Berlin SAPOS ® reference station system. The additional use of GLONASS, the
supply of RINEX data for the GPPS and GHPS service levels over the Internet, and the incorporation of the Potsdam
reference station in the alarm plan in regular operation are all expected in the first half of 2002.
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 5

in order to improve the availability of satellites within the conurbation. In spite of the necessary changeover of the
RTCM and RINEX data formats to their recent versions [Table 1, Fig. 5], the continued usability of today’s
technology will be ensured through full downward compatibility. GLONASS is expected to be incorporated into
regular SAPOS ® operation in Berlin in the first half of 2002.
The highly reliable service provision and system integrity of SAPOS ® are ensured by quality management measures
which are ever more widely disseminated in the state survey departments.
Taking the Berlin conurbation as a particularly prominent
example, SAPOS ® applications are used in surveying [Fig. 6], construction
logistics, public suburban transport [Fig. 7], traffic control
and police [Fig. 8] etc., and require extremely high accuracy, availability
and security of the system (Rosenthal, Rokahr 1999; Beer,
Rosenthal 2000; SenStadt 2000a; SenStadt 2000b). Three reference
stations in Berlin and another in the neighbouring state of Brandenburg
are networked and, together with the transmission equipment at the
Alexanderplatz TV tower (VHF 2m band radio) and the SFB transmit-
ter (FM/RDS), form the metropolitan SAPOS ® system [Fig. 5]. A
system availability of at least 99 % is guaranteed by the following
measures:
• All components of the Berlin 1 principal reference station, all data
links to the transmitters as well as the transmitters themselves are
duplicated. Because of networking the reference stations are in effect
quadrupled.
• The SAPOS ® reference stations and the transmitters are protected
from power fluctuations and failures by independent (uninterruptible)
power supplies (UPS) and by connection to emergency power
generators.
• EPS and HEPS DGNSS correction data broadcast on VHF and by
the SFB (Berlin City Radio) transmitter are received and checked
continuously by the reference stations Berlin 1 and Berlin 3. The
observed values for the GPPS and GHPS services are continuously
monitored. Any malfunction, disruption or loss of quality is
thus automatically recognised in real time.
• Malfunctions etc. automatically activate an alarm plan which sets
off appropriate corrective measures. Depending on the requirement,
data links, computers or transmitters are switched over and
another reference station is temporarily used as the principal station
for the supply of correction data. The system is set up so that
the technology can normally manage itself successfully and the
operation of SAPOS ® is maintained. All malfunctions etc. are
automatically logged and analysed as part of the quality management
process.
• Should a malfunction, a failure or a loss of quality nevertheless
demand manual intervention, two members of the SAPOS ® emergency
callout service are informed automatically by GSM telephone
by both monitoring stations. The details of any earlier
switching processes by the automated alarm plan will already have
been sent to them via GSM short messages, in parallel with the
emergency measures, so that they have access to all necessary information.
The staff of the emergency service are on call day and
night and remedy any faults without delay, either by remote repair
measures or on the spot.
Fig. 6: Satellite-supported surveying in
the centre of Berlin. With DGNSS
correction data from the SAPOS ®
HEPS (with area correction parameters)
via VHF radio, three-dimensional
position fixing can be carried out with
centimetre accuracy in real time.
Photo: BVG
Fig. 7: Berlin transport services (BVG)
bus with SAPOS ® positioning technology.
Within the framework of the computer-supported
operations management
system (Rechnergestütztes Betriebsleitsystem,
RBL) and based on
SAPOS ® EPS (VHF), the positions of
all BVG buses are continuously available
for management, control and
information processes. Thus, punctuality
and connections between services as
well as the safety of both passengers
and drivers are improved. Traffic
speeds can be increased by direct intervention
in traffic signal cycles. At
selected bus stops, and in case of disruptions
or diversions, dynamic passenger
information assists customers
on their journeys through the city.
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 6

• As already mentioned above, the positions of the reference station antennas are regularly checked for any
change four times a year, in relation to selected stations of the German GPS reference network (GREF), the
European reference network (EUREF) and the International GPS Service (IGS) network. Comprehensive absolute
calibrations are carried out individually on all reference station antennas.
Identical requirements for SAPOS ® exist not only in urban areas (Albert 1999; Peuser, Hankemeier 1999; Schulz
1999) [Fig. 9] but also far away from big cities, for positioning, navigation,
information collection and other specific applications [Figs. 10
to 12]. A particularly striking example is the movement of large vessels,
after their completion by the Meyer shipyard in Papenburg on the
Ems river, into the deep navigable water of the North Sea (Wegener
1998) [Fig. 13].
The following example illustrates the usefulness of the reliable supply
of SAPOS ® data, far beyond the normal applications of positioning
and navigation. Since March 2000 the AdV has been co-operating
with the Potsdam earth sciences research centre (Geoforschungszentrum,
GFZ) by supplying RINEX observation data from SAPOS ®
reference stations for an innovative international research project on
climate and its variability. From meteorological and GNSS observations
at reference stations and on the GPS-equipped low-orbit satellites
of the CHAMP and GRACE missions, fundamental parameters such
as pressure, temperature and water vapour content in the troposphere
and stratosphere can be determined.
Consideration and activities for a SAPOS ® compatible reference
station network in Bulgaria
The fields of application of SAPOS ® in Bulgaria are the same as
above discussed. According to the accuracy requirements the system
can be used for real-time determinations and post-processing determinations.
For example, for precise post-processing determination in
geodesy - geodetic networks, cadastre, local and regional geodynamics,
for precise real-time navigation - approach and landing of
aircraft, approach of ships in harbors etc.
In this stage of GNSS development two permanent stations exist in
Bulgaria. One of them is located near the capital of Bulgaria - Sofia
station that is also EUREF station and permanent IGS station. The
second one is located near the Black Sea - Varna station that is used
for marine navigation. Two more permanent stations are foreseen according
to the central European regional geo-dynamic project
CERGOP-2. With respect to the telecommunication, in Bulgaria it is
developed quite a good media network - VHF 2 m-Band-Radio,
UKW/Radio Data System, GSM - three operators.
Two phased concepts are proposed for establishment of a SAPOS ®
analogous reference system in Bulgaria:
Photo: Berlin Police
Fig. 8: SAPOS ® -supported operation
of the central escort and traffic commando
of the Berlin Police in action
on the occasion of a state visit. The
Central Traffic Service (ZVkD) of the
Berlin Police uses SAPOS ® -EPS
(VHF) in connection with, among
other things, escorting important state
visitors as well as while demonstrations,
parades and similar events, in
order to be able to take timely traffic
management measures as required, for
example location-dependent safety or
other precautions.
Photo: Hamburg fire brigade
Fig. 9: All fire and rescue vehicles of
the Hamburg fire brigade are equipped
with incident location and guidance
and operation control system technology,
using SAPOS ® EPS (VHF) for
precise position fixing, and offering
sufficient accuracy for the identification
of access routes into properties.
• Establishment of stations in the areas with high requirements (urban
areas, areas with hard building activity etc.) and after that accomplishing of the reference station framework
for the whole area of Bulgaria extensively,
• surface covering of the country by few stations with significantly large distances between them and a subsequent
increasing the density of the reference stations framework.
Bulgaria is situated between 22 nd and 28 th meridians and between 41 st and 44 th parallels. The surface of the country
is about 110 000 km 2 . If the distances between the reference stations will be accept to be 50-70 km then the
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 7

eference network will consist of 28 stations (Fig. 14). The achievable real-time accuracy in horizontal position
will be 1-2 cm and a little lower in the height. If the distances in a first phase will be increased to 80-100 km then
the number of reference stations will be decreased to about 10 stations. In this case, the accuracy in the horizontal
position will achieve 2-4 cm and a little lower in the height. Some stations have to be chosen as central reference
stations for the networked process. Some requirements have to be met at the establishment of the stations.
However at last there are needed about 28 reference stations for a
high quality multi-functional Bulgarian DGNSS service, which will
fulfil all discussed demands in an efficient way and in agreement
with the function.
Financing of the establishment of the system could be possible as
follows:
• entire financing by Bulgarian state institutions,
• combined financing - by state institutions and private companies,
• by project on the EC and other Programs and sources.
Conclusion
The multi-functional and multi-media services supplied by SAPOS ®
have provided a good example of the suitability of DGNSS services
as an economic and effective application of the three-dimensional
ETRS 89 reference system. The importance of a well-developed
quality management system has been discussed and illustrated by the
sample applications. Experience shows that it is beneficial for the
state survey departments to share their know-how by supporting their
customers with carefully targeted advice.
Valid, precise and reproducible connections with conventional position
and height reference systems are also possible for real-time applications
by means of official transformation parameters and height
anomaly models using appropriate software or, better by direct incorporation
into the firmware of GNSS rovers. Such solutions will
be carried out up to regional levels only, because precise positioning
over larger areas requires a multitude of suitable parameters to deal
with inhomogeneities and residual discrepancies in traditional control
point networks.
By transferring essential functions, especially those of conventional
positional control points, to the DGNSS reference stations, government
and business can achieve a satisfactory return on their investment.
Timetables should be developed and fixed for thinning out
existing general control networks, for which it is then only necessary
to neglect their maintenance. In order to guarantee the availability of
an independent geodetic spatial reference system for special survey
applications, for possible emergencies and crises as well as for national
defence purposes, a residual network of conventional control
points should still be maintained in the future in addition to the
Photo: SFB
Fig. 10: In order to ensure the supply
of broadcasting services, the ARD
broadcasting authorities must check
their transmission installations. Field
strength measurements are therefore
carried out from a helicopter, flying at
a distance of about 1 km around the
transmitter to be checked. Positioning
of the helicopter and spatial referencing
of measurements is carried out by
means of SAPOS ® EPS/FM.
Photo: Brunswick Technical University
Fig. 11: The usability of SAPOS ® VHF
for precise navigation for special aircraft
missions such as rescue operations,
security tasks or dropping relief
supplies has been successfully tested by
Brunswick University. At the ILA‘96
international aviation and space exhibition
in Berlin, the Integrated Navigation
Systems (INS) company based in
Hamburg had already demonstrated
precise landing approaches by means
of this SAPOS ® medium.
DGNSS reference station networks. It seems advisable to retain the control points of this reduced network for
technical developments and possible further requirements in the future, selecting them for their long-term suitability
for GNSS and monumenting them so as to enable their use for both position and height measurements (Rosenthal
2001b).
Reinforced co-operation between surveying institutions, aimed at creating a unified geodetic infrastructure based
on compatible DGNSS reference station networks, is important for the increasing unification of Europe. Com-
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 8

patible technology and procedures offer better opportunities to influence international standardisation and also
improve the economic prospects of investments in forward-looking and innovative solutions. As a contribution to
this process, a workshop in Berlin on “Multi-functional GNSS Reference
Station Networks as Basic Geodetic Infrastructure” is planned for
March 4-5, 2002, at which participants from about ten central and
eastern European countries are expected.
For further improvement of GNSS satellite availability under unfavourable
topographic conditions, especially in urban areas,
GLONASS should be integrated in the DGNSS reference systems in
addition to GPS, and support of European activities for the GALILEO
civilian GNSS should be continued in the future.
The need of establishment of a National Differential Global Navigation
Systems for positioning (DGNSS) in Bulgaria, based on the network
of permanent multi-functional stations, is a matter of fact.
For this purpose, the main concept, requirements and information
about the establishment of such a system are proposed. Variants for
the number of the reference stations, their equipment, possibilities for
application, financing, phased concepts for introducing have been proposed.
The successful application and use of the German SAPOS ® is a reliable
precondition for establishment of such a respective analog in Bulgaria.
Along with that the collaboration between Bulgarian and German
colleagues from the Berlin Senate during the development, establishment
and application of SAPOS ® is an important and favourable
condition for its realization. One undisputed fact is the insurance of
respective financing and there are different ways, and assistance from
state institutions as well as help from foreign countries.
References
AdV, Working Committee of the Surveying Authorities of the Länder (States) of
the Federal Republic of Germany: Online in Internet: http://www.adv-online.de
Albert, H. (1999): Der aufgeklärte Fahrgast – Dynamische Leit- und Informationssysteme
für den Hamburger ÖPNV. Telematik im Verkehr • Werkstattbericht Hamburg,
publisher: Freie und Hansestadt Hamburg, Baubehörde • Amt für Verkehr,
Hamburg, p. 25 - 46
Beer, M., Rosenthal, G. (2000): SAPOS ® im Verkehr. Vermessung und ..., publisher:
Senatsverwaltung für Stadtentwicklung Berlin, Berlin • Ministerium des
Innern des Landes Brandenburg, Potsdam, p. 28 - 30
Photo: BSH
Fig. 12: The newest survey vessel of
the Federal Administration for Marine
Navigation and Hydrography (Bundesamt
für Seeschifffahrt und Hydrographie,
BSH) including its subsidiary
boats has been equipped with SAPOS ®
VHF technology for the production of
precise hydrographic charts.
Photo: LGN
Fig. 13: SAPOS ® -navigated movement
of the Radiance of the Seas cruise ship
on the Ems river from the Meyer shipyard
in Papenburg to the North Sea on
25 and 26 January 2001. EPS corrections
supplied by VHF radion ensure
the necessary accuracy of one meter
required for this type of ship movement.
The whole on-board
SAPOS ® /DGPS technology is duplicated
in order to prevent all conceivable
failures and to avoid any damage.
Beer, M., Rosenthal, G. (2001): Verkehrstelematik – Neue Chancen im Verkehrswesen.
Nationalatlas Bundesrepublik Deutschland, Volume 9 Verkehr und Kommunikation, Spektrum Akademischer Verlag, Heidelberg
• Berlin, p. 148 - 149
Euler, H.-J., Keenan, C. R., Wübbena, G., Zebhauser, B. E. (2001): Study of a Simplified Approach in Utilizing Information from
Permanent Reference Station Arrays, Proceedings ION GPS-2001, Salt Lake City, USA
EUREF: Homepage der Sub-Commission European Reference Frame der International Association of Geodesy (IAG), online in Internet:
http://www.euref-iag.org
Milev, G., Rosenthal, G, Rokahr, F., Vassileva, K. (2001): SAPOS - System in Bulgaria. International Symposium on “Geodetic,
Photogrammetric and Satellite Technologies – Development and Integrated Application”, 08-09 November, 2001, Sofia, Bulgaria, p.
237 - 243
Peuser, M., Hankemeier, P. (1999): Individuelle Verkehrslenkung für Sicherheitsdienste und öffentlichen Nahverkehr. Telematik im
Verkehr • Werkstattbericht Hamburg, publisher: Freie und Hansestadt Hamburg, Baubehörde • Amt für Verkehr, Hamburg, p. 68 - 73
Rosenthal, G., Rokahr, F. (1999): Über die Nutzung von Geoinformationen der deutschen Landesvermessung in der Verkehrstelematik.
Zeitschrift für Vermessungswesen Volume 124, No. 4, Verlag Konrad Wittwer, Stuttgart, p. 112 - 121
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 9

Rosenthal, G. (2001a): SAPOS ® - The German
National Satellite Positioning Service. 1 st Common
Baltic Symposium on „GPS-Heightimg
based on the Concept of a Digital Height Reference
Surface (DFHRS) and Related Topics –
GPS-Heighting and National-wide Permanent
GPS Reference Systems“, June 11, 2001, Riga,
Latvia
Rosenthal, G. (2001b): SAPOS ® - Ein Netzwerk
von GNSS-Referenzstationen als Grundinfrastruktur
zur Realisierung der geodätischen Bezugssysteme.
125 Jahre Berliner Vermessungsverwaltung,
publisher: Senatsverwaltung für
Stadtentwicklung • Geoinformation, Vermessung,
Wertermittlung, Berlin, p. 31 - 38
Rosenthal, G. (2001c): Requirements for the
Implementation of Geodetic Reference Systems
and their Compliance with GNSS Reference
Station Networks. International Symposium on
“Geodetic, Photogrammetric and Satellite Technologies
– Development and Integrated Application”,
08-09 November, 2001, Sofia, Bulgaria,
p. 82 - 91
Schulz, G. (1999): Fahrzeugpositionierung bei
der Feuerwehr Hamburg. SAPOS ® 2000 - Ihr
Standpunkt • Vorträge des 2. SAPOS ® - Symposiums,
publisher: Senatsverwaltung für Bauen,
Wohnen und Verkehr • Geoinformation, Vermessung,
Wertermittlung, Berlin, p. 120 - 123
SAPOS: Homepage of the AdV online in Internet:
http://www.sapos.de
Fig. 14: Project proposal for a permanent reference station network in
Bulgaria: 28 stations with distances between 50 km and 70 km
Wegener, V. (1998): Schiffsüberführungen mit SAPOS ® Unterstützung. SAPOS ® schafft maßgeschneiderte Lösungen • Vorträge des
ersten SAPOS ® - Symposiums, publisher: Freie und Hansestadt Hamburg - Baubehörde - Amt für Geoinformation und Vermessung,
Hamburg, p. 97 - 103
Wübbena, G., Bagge, A., Seeber, G., Böder, V., Hankemeier, H. (1996a): Reducing Distance Dependent Errors for Real-Time Precise
DGPS-Applications by Establishing Reference Station Networks. Proceedings on the International Technical Meeting ION GPS-
96, Kansas City, Missouri, p. 1845 - 1852
Wübbena, G., Menge, F., Schmitz, M., Seeber, G., Völksen, C. (1996b): A New Approach for Field Calibration of Absolute Phase
Center Variations. Proceedings on the International Technical Meeting ION GPS-96, Kansas City, Missouri, p. 1205 - 1214
Wübbena, G., Schmitz, M., Boettcher, F., Menge, F., Böder, V. Seeber, G. (2001): Absolutkalibrierung: Anforderungen, aktuelle
absolute Ergebnisse, Anwendungen und Vergleiche, 3. GPS-Antennenworkshop 2001, Geodätisches Institut der Rheinischen Friedrich-
Wilhelm-Universität Bonn, 11. Mai 2001
SenStadt (2000a): SAPOS ® - Satellitenpositionierungsdienst der deutschen Landesvermessung in Berlin. publisher: Senatsverwaltung
für Stadtentwicklung III B, Berlin
SenStadt (2000b): Einsatz von satellitengestützten Vermessungsverfahren bei Katastervermessungen. Rundschreiben III Nr. 4/2000,
Senatsverwaltung für Stadtentwicklung III A, Berlin
Certified Eng. Gerd Rosenthal Prof. Dr. Eng. Georgi Milev
Senate Department for Urban Development Bulgarian Academy of Sciences
Division III - Geoinformation, Land Survey, Valuation Central Laboratory for Geodesy
III B - Geodetic Survey, Three Dimensional Geodesy Bulgaria, 1113 Sofia
Germany, 10713 Berlin, Hohenzollerndamm 177 Acad. G. Bonchev Str., Bl. 1
postal address: Senatsverwaltung Stadt, D-10702 Berlin phone: +35 92-70 04 06, 979 24 07
phone: +49 30-90 12-56 15 fax: +35 92-72 08 41
fax: +49 30-90 12-37 09 e-mail: milev@bgcict.acad.bg
e-mail: gerd.rosenthal@senstadt.verwalt-berlin.de e-mail: milev@bas.bg
Dr. Eng. Friedrich Rokahr Ass. Prof. Dr. Eng. Keranka Vassileva
Senate Department for Urban Development Bulgarian Academy of Sciences
Division III - Geoinformation, Land Survey, Valuation Central Laboratory for Geodesy
Germany, 10713 Berlin, Hohenzollerndamm 177 Bulgaria, 1113 Sofia
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 10

postal address: Senatsverwaltung Stadt, D-10702 Berlin Acad. G. Bonchev Str., Bl. 1
phone: +49 30-90 12-55 94 phone: +35 92-979 24 57
fax: +49 30-90 12-31 17 fax: +35 92-72 08 41
e-mail: friedrich.rokahr@senstadt.verwalt-berlin.de e-mail: kvassileva53@yahoo.com
SAPOS ® DGNSS Reference Station System in Germany and its Analogue in Bulgaria Page 11