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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
The third one is to rectify the image to get quantitative spatial
information. Figure 1 shows the flow chart of the procedure to
get intertidal topography information.
Digital Image Observation of Intertidal
Bottom Topography(Flood)
Survey for
the height of
Boundary
Survey for
the Image
Rectification
a te ian.
TU of Boundary Lines between Flood
and Field from the Observation Images.
dui
Image Rectification
Estimation of Spatial Coordinates(x,y,z)
for the Flood Boundary Lines
Observation of 3-D Intertidal Bottom
topography via Integration of Data
Figure 1 Flow chart to extract 3-D intertidal bottom topography
from the time series images during the flood
Gathering images for the depth contours is done during a flood
because dried portion of the land makes it easier to extract the
water lines compared to the period of an ebb tide. The time
interval of images depends on the slope. For example, in case
of intertidal region with 1.2 km width and 6 hour flooding, the
water line migrates 33 m for 10 minutes. Figure 2 is the
example of time series images taken during a flood.
Figure 2. An example of time series image data showing the
change of boundary between water and field in the intertidal
zone during a flood.
The principle to get depth contours from time series images is
shown in Figure. 3. The Top figure shows the migration of
water level line from the low water line to the high water line
during a flood. The bottom figure illustrates depth
contours extracted from each water lines in the top figure.
Figure 3 explains the simplest case for the plane beach with
constant slope, but the advantage of this technique is that it can
even present irregular and various features of bottom with
details. In order to label each water lines with depth value,
field survey is executed to get a depth profile during an ebb
tide along a line seen clearly on the image. This survey can be
substituted by measuring the change of water level outside the
1175
low water’ line. One of the most important procedure for this
technique is a rectification of image.
Om
m "14m
r2 m
~~ 3m
pete 8)
—_ 5m
T
Intertidal Zone
The Change of Flood Line
High Water Level Depth Contout ; Low Water Level
pee me
do
| |
|: - Um ^ -
LE LLL T
Figure 3. Schematic map to show the relationship between
water level and depth contours.
The rectified image from the oblique image provides
quantitative value on the distance between two points shown in
the image such as a scaled map. For the rectification, field
survey is needed to measure the distances between the
GCPs(Ground Control Points). In order to extract the boundary
lines between water and land automatically, edge detection
image process is applied using RGB or HSV characteristics of
water and land.
Through the processes explained above, spatial coordinates(x,
y, Z) for each water lines extracted from images are achieved.
Three dimensional bottom topography is constructed
integrating all the water lines into one data set and resampling
the depth data at the new regular grids. This process is shown
in Figure 4.
(x, Y, 20
Integration of Time
Series Image Data Construction of
Depth Contour
7 f
|
|
Intertidal Zone Depth Contour
Figure 4. Construction of depth contours by integrating image
data
