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HIGH PRECISION KINEMATIC DGPS : 
A POWERFUL TOOL FOR SENSOR POSITIONING AND PLATFORM NAVIGATION 
Marc Cocard 
Institute of Geodesy and Photogrammetry 
Swiss Federal Institute of Technology (ETH-Zurich) 
CH-8093 Zurich 
  
KEYWORDS : DGPS, Navigation, high precision trajectory, sensor orientation, ambiguity resolution *on the fly’ 
ABSTRACT: 
In many remote sensing applications there is a need for high quality orientation information of different kind of sensors. 
For example in the photogrammetric aerotriangulation a very precise positioning of a few centimeter is required. GPS is 
a powerful tool to fulfill this task. In this paper the different operation modes and their accuracy are discussed. The 
highest level of accuracy can only be reached by integrating phase measurements in the differential mode. The best 
result in this case is obtained when all initial phase ambiguities are solved. Therefore special emphasis is put on the 
problem of the ambiguity resolution in the kinematic mode for an on-line differential phase solution. Its stringent re- 
quirements and limitations are discussed and compared to the broader possibilities of an off-line solution. 
1. INTRODUCTION 
At the end of the seventies the Department of Defense (DoD) of the United States started installing the Global Position- 
ing System (GPS) conceived for navigational purposes. The first test constellation on orbit became available in the 
early eighties. From then on the number of satellites increased from year to year. Today in mid-latitudes an average 
constellation of 6 simultaneous satellites can be observed over the day. Simultaneously the number of users increased 
from day to day. A better constellation and improvements in the receiver technology allows new applications to be 
considered. 
2. THE DIFFERENT OBSERVATION TYPES 
Code : The basic navigation concept of the GPS is based on pseudo range measurements and requires a minimum of 4 
satellites in order to derive the three dimensional position and the synchronization error of the receiver. The pseudo 
range measurement corresponds to the traveling time of the signal corrupted by an unknown synchronization error of 
the receiver clock. The quality of the code measurements depends on the code used (C/A- or P-code) and the perform- 
ance of the receivers. Its resolution typically ranges between 20 cm and 3 meter. Under 'Anti-spoofing' (an artificial 
degradation introduced by the DoD for military reasons), the precise P-code is no longer available to the civilian user. 
However improvement in receiver technology often allows a measurement of the C/A code at the submeter level. 
  
Phase rate : The phase rate measurement corresponds to the Doppler shift of the carrier phase. Its resolution is in the 
order of some millimeters/sec. The phase rate is not often used for geodetic applications in the static mode, as phase 
measurements are prevailing. For kinematic applications, however, they may be of interest. 
Integrated Carrier Phase: The carrier phase measurement is the main observable for geodetic applications. Its advan- 
tage is the high resolution of a few millimeters compared to the code measurements. However, the phase measurements 
are ambiguous. Two different carrier phases are available at a frequency of 1.57542 MHz (L1-band) and 1.22760 MHz 
(L2-band). 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995