A New Measurement System of Settlement 
At Airports Using GPS and Laser Level 
Bunji Shigematsu 
B.Shigematsu serves as Manager of PENT A OCEAN CONSTRUCTION CO.,LTD. 
ABSTRACT 
Height control measurement is an important task to determine the subsidence of ground in man-made island con 
structions and reclamation work for the construction of facilities such as airports. 
Height control of the completed airport island is also an important task to ensure safe aircraft 
operations. 
That is why the development of highly precise and efficient measuring instruments was expected. 
The new system we are reporting here was developed for the purpose of achieving high precision, energy-saving, and 
improved efficiency in height surveys, and the solution to these goals were to create a hybrid method by combining 
a laser level and computer with GPS. 
The summary of the developed system and the survey results are described in this paper. 
Key Words :RTK- GPS, Laser Level, Height measurement 
1. INTRODUCTION 
Recent airports are inevitably constructed on deep water ar 
eas or reclaimed land over very weak grounds as seen in Kansai 
International Airport and Tokyo International Airport. This 
is why countermeasures for ground subsidence has become 
an important issue. Differential settlement is expected to oc 
cur even after the airport islands are completed, addressing 
concerns for cracks in pavements and destruction of struc 
tures within the airport facility. Above all, runways, taxi- 
ways, and aprons, which are the most important basic facili 
ties of the airport, require an extremely precise flatness with a 
gradient of 1.5% or smaller. Surveys for maintenance con 
trol including subsidence control becomes an important task 
for safe airport operations. Current survey tasks are conducted 
using levels and total stations, but these methods have limita 
tions including the necessity of line-of-sight between survey 
points, limited survey ranges, and difficulties in rainy weather 
and nighttime surveys, that create difficulty in improving work 
efficiencies. Thus, a survey technology that will enable effi 
cient measurement of a large number of widely distributed 
survey points accurately and quickly was waited. In such 
situations, a positioning technology called GPS (Global Posi 
tioning System) was recently developed. GPS is a position 
ing system that uses satellites developed by the United States. 
The relative positioning method that uses a multiple number 
of GPS provides high accuracy and is used for land public 
surveys. The RTK (Real Time Kinematic) method provides 
immediate output of the survey results and is now used in a 
wide range of applications such as for maritime work ves 
sels. Based on these backgrounds, efforts to introduce GPS 
for efficient construction and maintenance control of airports 
and other facilities have begun. 
Studies showed that GPS alone could not provide the required 
accuracy in a short period of time, so the idea of combining 
supplementary optic equipment was reviewed. As a result, 
we have developed a hybrid method subsidence control sys 
tem combining the advantages of RTK-GPS and revolving 
laser level. 
This report contains the description of this subsidence control 
system. 
2. Evaluation of GPS and Conventional Survey 
Equipment 
Firstly, to determine the performance of the current survey 
system, we conducted a test to compare the performances of 
various GPS and conventional survey equipment. The re 
sults are shown in Table 1. We found out the optic equip 
ment such as the auto level provides better accuracy over short 
distances while GPS provides better accuracy over long dis- 
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