and a river is crossing the north of the test field 1. So there is 
some undulation near the river but other part of area is quite flat. 
The observation was carried out in winter and hence the paddy 
field was completely dry. The test field is a square of 400m and 5 
ground control points were established in each corner of this 
square and the center of the square, and these points were 
observed by GPS (static survey: 1 hour) to compare the 
coordinate observed by laser profiling. Ground control points 
were established just before laser profiling. 
Test field 2 (long loop area) 
Long loop observations were also carried out on 10th February 
1998 to investigate the drifts of gyroscope and to compare the 
orthometric height determined by laser profiling, with the height 
determined by direct leveling. There are two benchmarks, one is 
in Geographical Survey Institute (GSI) and the other is in front of 
high-energy research center. Long loop line was started above 
GSI and then flied over test tiled through high-energy research 
center and back to GSI. First mode was selected and the flying 
height was set to 300m. Loop area was 4km East-West and 7km 
North-South. 
Two points close to first order benchmark of GSI, two points 
close to the benchmark in front of high-energy research center, 
were selected to compare orthometric height and this orthometric 
height was determined by connecting to the leveling. The results 
are next section. 
4 SURVEY RESULTS 
Test field 1 
Height: By measuring repeatability along North-South and 
East-West directions of the test area, the repeatability of five 
ground control points was estimated. Each ground control point is 
measured by flying over at least two observation lines. The 
number of lasers that were reflected by ground control point with 
the size of 60cm on one line is varied from 1 to 5. Hence, the 
repeatability of height is limited to some ten centimeters (Table 2). 
Density of the reflection is about 8 points per lm 2 (flying height is 
500m, speed is 50km/h). Since the width of the scanning is not 
regular, variations of density can be seen. Only possible way to 
increase the accuracy of repeatability is the reduction of the speed 
of aircraft or reduction of flying height. During the long loop 
observation, density was 15 points per lm 2 , which is two times 
larger than the test area. This is clear because the flying speed was 
50km/h and the flying height was 200m. The data distribution 
around ground control points is shown in Fig. 1, and heights that 
were obtained by reflections are shown in Table 2. 
Table 2 Observed orthometric height on ground control points 
Ground control point 1 
Ground control point 2 
line 
H(m) 
Ave. 
S.D. 
Line 
H(m) 
Ave. 
S.D. 
A 
11.92 
11.92 
- 
D 
11.77 
11.73 
0.07 
C 
11.88 
11.90 
0.12 
11.69 
11.79 
E 
11.90 
11.88 
0.06 
12.02 
11.84 
E 
11.95 
11.85 
0.13 
11.95 
11.95 
11.81 
11.90 
S.D. 
0.09 
11.82 
11.62 
S.D. 
0.11 
Ground control point 3 
Ground control point 4 
line 
H(m) 
Ave. 
S.D. 
Line 
H(m) 
Ave. 
S.D. 
11.77 
11.99 
11.94 
0.08 
11.93 
11.90 
0.09 
A 
11.88 
C 
11.97 
11.77 
11.92 
11.57 
11.73 
0.11 
11.91 
G 
11.81 
11.94 
11.78 
D 
11.90 
11.88 
0.05 
S.D. 
0.14 
11.84 
11.82 
S.D. 
0.11 
Ground control point 5 
line 
H(m) 
Ave. 
S.D. 
C 
10.66 
10.69 
0.04 
10.71 
B 
10.71 
10.70 
0.01 
10.69 
F 
10.69 
10.71 
0.02 
10.72 
10.71 
S.D. 
0.02 
The deviation from mean height 
Fig 3 The deviation from the mean height