84
3. Observation
3.1 Observation with HFOSR
Each ORO/CRL HFOSR was set at Ohkuma and Hirono (#1 and #2, see Figure 1).
HFOSR#l at Ohkuma scanned from 90° to 172.5° and HFOSR#2 at Hirono from 7.5° to
90° clockwise to the north at an interval of 7.5°. In the observation period, there was
intermittent period of data loss of HFOSR#2 early in March because of the failure of radar
control personal computer. Finally the data from 18 March to 3 April 1993 were used for
an analysis. HFOSR data were in good condition from near the coast to 75 km off the
coast at this time.
When the current velocity changes vertically, the velocity from the surface to the depth
1/2 ;r times of the wavelength of the ocean surface current influence the phase velocity of
the ocean surface wave (Barrick et al., 1977). Therefore the ocean surface current by
HFOSR can be defined as an average from the surface to the depth of about lm.
The synthetic ocean surface velocities were calculated by two radial velocity
components measured by each HFOSR once every 2 hours without timely interpolating.
As the radial space resolving power of HFOSR was 1.5 km, the synthetic surface velocity
was spatially interpolated in 1 km X 1 km grid map.
3.2 Observation with moored current meter
The current velocities were measured by moored P-RCM4 current meters at 2 meter
depth below the surface every 15 minutes. The location of the current meters from about 1
km to 8 km off the coast as shown in Figure 1. ORO/CRL HFOSR#l could not measure
the radial current velocity around at the St.7 firmly obstructed by the land. Therefore the
current meter data except for at St. 7 were used and timely averaged in 2 hours running
mean for comparison with the synthetic current velocities by HFOSR.
4. Comparison of both data
Table 2 Results of comparison and correlation of ocean surface velocities
Station of
Current
Meter
RMS
Difference
Correlation
Coefficient
Mean
Residual
STD
of Residual
Regression Analysis
Gradient
Intercept
Speed
Dir
Speed
Dir
Speed
Dir
Speed
Dir
Speed
Dir
Speed
Dir
St.cl
7.10
37.65
0.87
0.92
5.08
21.12
6.41
33.51
0.92
0.96
4.58
15.10
St.c2
22.40
60.30
0.55
0.87
11.36
38.26
16.96
51.07
1.02
0.97
14.35
31.06
St.c3
8.44
45.70
0.94
0.90
4.39
27.87
5.64
44.24
1.12
0.98
4.07
11.00
St.c4
7.25
46.43
0.86
0.89
4.78
26.34
5.94
38.38
0.74
0.92
7.22
21.48
St.c5
42.21
85.02
0.33
0.76
21.03
45.58
28.44
60.55
1.40
0.74
27.02
44.03
St.c6
8.25
29.36
0.87
0.95
5.75
18.31
7.54
29.39
1.08
1.02
1.63
1.88
St.c8
12.96
57.11
0.71
0.82
9.30
37.23
12.10
56.98
1.08
0.93
3.30
-4.11
Mean
15.52
51.65
0.73
0.87
8.81
30.67
11.86
44.87
1.18
0.93
8.88
17.21
Mean
Except 2, 5
8.80
43.25
0.85
0.90
5.86
26.17
7.53
40.50
1.17
0.96
4.16
9.89
Table 2 shows the result of comparison of both velocities and of correlation analysis.
The number of the data was 171 respectively. The rms differences of speed at St.cl,
St.c3, St.c4, St.c6 and St.c8 are small less than 10 cm/s, indicating good agreement of