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International cooperation and technology transfer
Fras, Mojca Kosmatin

Crocetto N. (i) - Gatti M. (ii) - Marchesini M. (iii) - Negroni F. (iv) - Russo P. (ii)
(i) Department of Civil Engineering. Second University of Naples, via Roma 29, Aversa (Italy),
(ii) Department of Engineering. University of Ferrara, via Saragat 1, Ferrara (Italy).
(iii) Guido Veronesi s.r.l., via Caselle 46, Bologna (Italy).
(iv) Studio Negroni, via Salvador Allende 32/34, Bologna (Italy).
WG VI/3 International Co-Operation and Technology Transfer and
WG IV/3 Temporal Aspects and Topographic Database Maintenance
ABSTRACT. This paper describes some experiments carried out with the RTK technique (Real Time Kinematic
Survey) to combine GPS and GLONASS measurements on carrier phases LI and L2. These experiments involved:
1) marking out transverse sections of a road embankment; 2) localising reference points in woodland for a water supply
tunnel. The measurement technique is described and compared, in terms of productivity and precision, with similar
techniques using conventional topographical instruments and satellite instruments with GPS measurements only.
RESUME. Ce document décrit quelques expériences réalisées à l’aide de la technique de cinématique temps réel
combinant les mesures GPS et GLONASS des phases de support L1 et L2. Ces expériences concernent:
1) le marquage des sections transversales d’un remblai de route ; 2) la localisation de points de référence en terrain boisé
pour la construction d’une conduite d’eau. La technique de mesure est illustrée en termes de production et de précision,
notamment dans le cadre d’expériences similaires faisant appel à des instruments topographiques traditionnels et des
instruments satellites utilisant uniquement des mesures GPS.
The GPS "Real Time Kinematic Survey" (RTK)
technique differs from the classical GPS (Continuous
Kinematic) technique in that the relative position of one
receiver (Rover receiver) with respect to another (Master
receiver) can be calculated instantaneously (Real Time).
This technique, tested in Italy since the mid-1990s (Bitelli
et al., 1994; Gatti et ah, 1995), allows us to extend the
applications of the GPS to the measurements of
traditional field surveyor. However, some factors have
inhibited its more widespread use:
1. the use of radio modem apparatuses approved for use
in Italy with maximum power in the UHF band of 1
2. the GPS satellite configuration, which is limited to
the contemporaneous presence of 7-8 satellites for
the measurements and values of PDOP greater than
3. the number of components of the signal observed and
the quality of the acquired signal.
The range of a single radio link device, at the indicated
power, is a little more than 1.5 km from the Master
receiver. This can considerably limit the operational area
of measurement '. The satellite configuration can instead
increase the times of static initialisation and dynamic re
initialisation of the Rover receiver * 2 . The components of
The range of the radio link device can obviously be increased if one
uses another radio link as a radio bridge (radio repeater).
2 For example, with at least 6 visible satellites and a PDOP less than 3,
the static initialisation with only GPS measurements is performed after
the signal and its quality can affect the instantaneous
resolution of a double difference. In unfavourable
operating conditions or in the presence of electromagnetic
fields (Gatti et al., 1998), it can be difficult to perform the
positioning in real time with GPS receivers alone. The
application of the method is thus limited to open and
sparsely inhabited zones, i.e. areas in which it is possible
to receive both the radio link signal and the GPS signal
from at least 6 satellites without interruptions of the signal
in one or more components.
The introduction on the market of receivers designed to
acquire signals on LI and L2 carrier phases from both
GPS and GLONASS satellites has greatly increased the
possibilities of employment of the RTK technique. The
acquisition of the GLONASS signal combined with the
GPS signal has led to the following advantages:
• an increased number of operational satellites, from the
usually 7-8 for the GPS system to around 10-11 for
the GPS+GLONASS system (Fig. 1)
• improved reception of the signal even in the presence
of electromagnetic disturbances poorly tolerated by
the GPS receivers alone (Misra, 1993; 1996);
• decrease of the PDOP (Fig. 2-a and 2-b) (Contreras,
at least 5 minutes of reception without interruption of the signal; the re
initialisation, which in the GPS receivers with double frequency is
performed in movement (so-called dynamic initialisation or O.T.F.),
occurs after 2 minutes of reception, i.e. after having received with
continuity at least 120 periods after the loss of the signal. If the number
of satellites decreases or the PDOP changes, the indicated times can
increase considerably.