• higher number of components of the received signal
(Codes and Phases) (Leick et ah, 1998);
• decreased times of static initialisation and dynamic re
initialisation of the Rover receiver.
Position DOP
Fig. 2-b. GPS+GLONASS PDOP (from Contreras, 1998).
1. INSTRUMENTATION
Fig. 1. GPS+GLONASS satellite constellation on Oct. 14,
1999.
Position DOP
Fig. 2-a. GPS PDOP (from Contreras, 1998).
These new possibilities have permitted the extension of
applications of satellite technology, especially to field
surveys in which reception of the signal was often
impossible with GPS receivers.
This paper describes some applications of the RTK
technique to combined GPS and GLONASS
measurements on carrier phases LI and L2.
These experiments involve:
• marking out of transverse sections of a road
embankment;
• localising reference points in woodland for a water
supply tunnel.
These experiments demonstrate the advantages of
GPS+GLONASS in terms of functionality, versatility and
ability to operate in areas subject to high levels of
disturbance.
For the experiments, we used a GPS+GLONASS RTK
surveying system composed of:
• two field surveyor receivers (Legacy, Javad
Positioning System) (Fig. 3) with 40 independent LI
channels and 20 L2 channels able to record the GPS
and GLONASS signals and to manage internally
(with the Paradigm™ chip) the functions of Real
Time calculation with firmware 2.0.
Fig. 3. The Legacy receiver.
The receivers were equipped with 16 MB of RAM
memory, which permitted the separate management of
storage of the signal (for eventual post-processing) and
the functions of RTK calculation. The receivers possessed
the JPS suppressor of the internal radio band of the CPU
and the function of active CO-OP™ Tracking. This
function allows the link of re-acquisition of the signal
from Master to Rover with a time of less than 3
milliseconds for all the satellites, temporarily blocked.
Each of the 40 main channels of the Paradigm™ chip was
also equipped with four Narrow anti-disturbance
correlators. In practice, 160 continuous search chips,
active in the phase of recording both the GPS and
GLONASS signal, provide a 13-fold reduction of the
times of static initialisation or dynamic re-initialisation
with respect to the times of conventional GPS receivers
with 12+12 independent L1+ L2 channels.
