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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