distribution at (x0,y0), and Sx, Sy is the
deviation to x direction and y direction
respectively. And wave direction a is yield
by using x0 and yO as Fig.4.
Secondary power spectrum at (1,j) is calculated
as follows.
power(1,j)
=, Aexp{-[(i-x0)2/sx2+(j-y0)2/sy2]/2}
eu FEAR ENR Ls ea MMC 5)
Random phase Ÿ is used to simulate the random
wave. Real part : power R and imaginary : power
I part are defined as eq.6) and 7) respectively.
powerR(ij)- power(i,j)* cos O ...............- 6)
powerlü = power(i,j)* sin 9 ........ 7)
The simulate image of marine radar is yield
through inverse FFT by using power R(i,j) and
Power I(i,j). In this case the data from marine
radar is only real part, eq.6) is used to simulate
the image of marine radar.
Fig.4 The definition sketch of the wave number
spectrum of the simulated wave
3.2 Verification of the Radar data
Analysis method
Fig.5 shows the simulated image of marine
radar. This image is simulated as the wave
direction is 45 deg. And Fig.6 shows the wave
number spectrum distribution of the wave field
defined as Fig.5. Fig.6 shows there are two
peaks in the wavenumber space, 45 deg and 225
deg. In this case sea covers O - 180 deg, the
wave direction is defined as 45 deg. This shows
that if the wave with incident angle 45 deg is
monitored by marine radar the wave direction is
estimated 45.6-49.2 deg.
When wave direction is 0, 30, 45, 60, and 90
deg and wave length is 1/8, 1/4 and 3/8 of
perimeter size of target area. It is concluded that
the accuracy of the proposed method in this
study is over 90% 4)
And Fig.7 shows the result of translating wave
direction-frequency space for coastal engineering
use through eq.4).
T Tr T
-50.0 00 500
Fig.5 The simulated image of marine radar
(wave direction: 45 deg)
| o -500
T T T T
-50.0 0.0 50.0
X
Fig.6 The wave number spectrum distribution of
the simulated wave of Fig.5 in the Kx-Ky
space.
254
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
re^
r^
——— gud ^ 5 jue — udi
