ESTIMATION OF ACCURACY OF AIRBORNE LASER PROFILING
Koukichi Kimura. Teruvoshi Fujiwara. Yukihide Akiyama
Aero Asahi Corporation
Masaki Murakami
Geographical Survey Institute
JAPAN
Teruyosh i. Fuj i wara@aeroasah i-tc. co .j p
KEY WORDS: Airborne Laser Profiling, Repeatability
ABSTRACT
A helicopter was used as the mobile body and experiments were carried out to investigate the repeatability of points and to check the
agreement of the existing survey results (horizontal position and height) with the results of airborne laser profiling. Five square ground
control point with the size of 60cm were established in each corner and as well as in the center of square test field whose size is 300m.
Static GPS observations were carried out for over one hour at each of five ground control point and the coordinates were calculated. In
addition to the GPS observations, laser profiling was carried put within the test field and the 3D data were acquired along four North-
South observation lines and three East-West observation lines. The observations were designed so as to each ground control point lies
between at least two observation lines. Comparison with the GPS horizontal positioning showed that the mean difference of distances
was 40cm.
According to the above results it is concluded that the positioning accuracy of laser profiling is around 50cm and it is largely depend on
the accuracy of the GPS data. However, if there are no discontinuities, accuracy of the relative position tend to be good and hence, it is
possible to correct by using an adjustment procedure with known points such as ground control points.
1 INTRODUCTION
In recent years, navigation of mobile body using GPS has been
developed and it was successfully utilized for shipping, aviation
and automobiles. Among the recent application of kinematics
GPS, airborne laser profiling technology is tremendously being
popular. In this application, a laser beam is transmitted from
helicopter of which gyroscope is connected and 3D positions of
the points of reflection are determined by means of the position of
GPS receiver which is connected to the same aircraft.
The laser profiling tend to be one of survey system of public
survey in Japan, however it hasn't yet been implemented. How is
accuracy of position? Are there any possibilities to replace
photogrammetry by laser profiling or to combine the merit of laser
profiling and photogrammetry?
In the following section we present an overview of System of
Airborne Laser Profiling. The purpose is to clarify accuracy,
especially repeatability. We present the comparison between the
result of airborne laser profiling and GPS results, leveling.
2 SYSTEM OF AIRBORNE LASER PROFILING
Outline of System
As for airborne laser profiling. Saab Top Eye (Saab Survey
System, Sweden) and FLI-MAP (JECA, USA) etc. have been
developed. In the present study. ALTM1025. developed by
Optech inc.. was used.
3D position of ground control points is determined by 3 basic
elements, that is, position of helicopter determined by GPS-IMU,
distance from helicopter to ground control point measured by
laser range finder and scanning angle with respect to vertical line
using IMU from helicopter to ground control point
Setting and calibration of IMU
IMU is an apparatus for measuring inertia. By measuring the three
accelerations of three Gyroscopes along three straight axes, it can
be compensated the defects by combining the data of inertia and
GPS positioning data alternatively. In the case of GPS
observations, some irregularities might be generated due to
multipath etc. However, continuos and smooth observations can
be done by IMU. Conversely, some drifts might be occurred for
long time observations by IMU. No drifts may occur in GPS
observations.
3 SURVEY DESCRIPTION
Z-12 of ASTECH GPS receivers were used in the aircraft and also
on the earth. Since GPS and IMU are combined, observations
were done by the instruments, which are designed for aerial
surveying based on Kalman filter, on 10th February 1998.
Test field 1
Test field 1, that is 4km north to geographical survey institute,
was selected as the test field. Almost of all the area is paddy field
