GPS Antenna 
Figure 6 Principle Diagram of Developed System 
day). 
5. Future Issues 
Through our experiments, we were able to confirm that our 
initial purpose is achievable. However, several issues arose 
during the tests that we must be solved before implementa 
tion, including downsizing of the system. Results of our re 
view on these issues are discussed below. 
(1) Countermeasures for GPS Becoming 
Unavailable Due to the Effects of Building structures GPS 
cannot receive waves near structures and becomes unavail 
able for positioning. 
These areas could be eliminated by using autonomous navi 
gation with the system when GPS becomes unavailable. 
In this experiment, we tentatively developed a hybrid po 
sitioning system by combining RTK- GPS and autonomous 
navigation, and were able to confirm that this was achiev 
able. 
(2) Countermeasures for Errors Caused by 
Synchronization Difference between GPS and Laser Level 
in mobile observation, we found several points where the dif 
ferences between this system and the conventional survey were 
± 15 ~ 20 mm. This may be caused by unmatching mea 
surement timings of RTK-GPS and laser level. We resolved 
this by synchronizing GPS and laser level in postprocessing 
using the synchronous pulse from GPS. 
(3) Expansion of Laser Receiver Measurement 
Range 
In the current system, the width of the measurement range 
of the laser receiver was 0.5 meters. We had to relocate the 
laser level where the height difference exceeded 0.5 meters. 
We can increase the measurement width by overlapping the 
laser level emitter. This way, for each laser transmitter added 
we gain 0.5 m of a height difference measurement width, so 
measurement of height difference of a several meters is achiev 
able. 
4) Difference between Leveling Survey and GPS Survey 
Height is based on the leveling plane in conventional sur 
veys, whereas it is based on the WGS-84 ellipsoid in GPS. In 
some places, this difference can be more than several centi 
meters for every kilometer of distance. 
We can use GPS when measuring the amount of subsid 
ence by expressing the results as difference from the previous 
measurements, but determination of absolute values would 
require measurement of a nearby leveling point and applying 
necessary corrections. 
6. CONCLUSION 
We used this system to conduct actual measurements at To 
kyo Airport, and were able to confirm that it provides higher 
accuracy compared to the conventional methods. 
We will resolve the issues that arouse through the tests, con 
tinue developments for implementation, and aim for an auto 
mated survey system in the future. 
There is a movement to unify the world wide airport coordi 
nates to WGS-84, and the possible use of GPS in surveys and 
control of airports are being discussed. 
This system may be used not only for airports, but also for a 
wide range of applications including reclamation height con 
trol and dirt quantity control in land grading projects. 
ACKNOWLEDGEMENTS 
A committee was established to discuss this development. 
This development was made possible with the technical ad 
vice, information and cooperation provided to us by our Chair 
man Shimizu, Assistant Professor of Tokyo University, and 
the people of Tokyo Aviation Bureau and Second Port and 
Harbor Construction Bureau. We wish to thank them all. 
REFERENCES 
[1] K.Soen,K.Sudo:Position Control System for Work Boat