10.3.3 Coastal Dynamics Index (CDI)
To investigate the coastline change, JERS-1/SAR data were used. JERS-1 is the
satellite which was launched by NASDA (National Space Development Agency of
Japan) in 1992 and discontinued in 1998. JERS-1 loaded the SAR (Synthetic
Aperture Radar). The SAR sensor is an active microwave sensor. SAR emits
microwaves and receives the reflected waves from the earth. Therefore, SAR can
acquire images even at night or on rainy, cloudy, and smoky days. JERS-1/SAR
used the L-band which was long wave. L-band can observe the ground regardless of
forest cover because the wave passes through the trees and reflects from the land
surface. The digital value of the data is called the backscattering coefficient. When
the soil water is high, the pixel shows blackish and the water surface shows black.
Conversely, artificial things show whitish because the radio wave reflection is high;
and the backscattering coefficient is high.
The 1990s in the Red River Delta is an important era. Construction of Hoa Binh
Dam began, and the areas of the paddy fields rapidly expanded (GSO 2014) and
coastal erosion accelerated remarkably. In this study, eight sheets of satellite
images, which were taken from 1994 to 1998 were collected: September
30, 1994; February 9, 1995; September 17, 1995; January 27, 1996; January
13, 1997; October 4, 1997; February 13, 1998; September 21, 1998. JERS-1/SAR
provided by NASDA had been running from 1992 to 1998. However, the satellite
images in the first two years could not be used because of strong noise. So data after
1994 was used to calculate CDI in this analysis.
A total of 149 measuring points were tracked across the coastline with an
interval of 500 m. The measurement lines, which were perpendicular to the
coastline, were laid down on the each measuring point. The coastline change was
recorded based on the coastline on September 30, 1994. Next, the CDIs of seasonal
change were calculated by subtracting a CDI from the CDI of the next season.
PCI Geomatica Ver. 7 software in a PC was used to conduct the image analysis.
The nearest neighbor interpolation was used in all of the JERS-1/SAR Images, and
15 GCP points were secured in each satellite image based on the topographic map
with a 1:50,000 scale.
The RMS error between the topographic map and the satellite image was 1.2,
and the RMS error between each satellite image was under 0.5. Frost Filtering was
used to diminish the speckle noise in each satellite image (Frost et al. 1982).
10.3.4 Production of the Coastal Erosion Risk Map
10.3.4.1 Parameters for Assessing Coastal Erosion
CDIs are closely related to coastal erosion in the southern Red River Delta.
Therefore, a risk map of the coastal erosion based on CDIs was prepared.
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To investigate the coastline change, JERS-1/SAR data were used. JERS-1 is the
satellite which was launched by NASDA (National Space Development Agency of
Japan) in 1992 and discontinued in 1998. JERS-1 loaded the SAR (Synthetic
Aperture Radar). The SAR sensor is an active microwave sensor. SAR emits
microwaves and receives the reflected waves from the earth. Therefore, SAR can
acquire images even at night or on rainy, cloudy, and smoky days. JERS-1/SAR
used the L-band which was long wave. L-band can observe the ground regardless of
forest cover because the wave passes through the trees and reflects from the land
surface. The digital value of the data is called the backscattering coefficient. When
the soil water is high, the pixel shows blackish and the water surface shows black.
Conversely, artificial things show whitish because the radio wave reflection is high;
and the backscattering coefficient is high.
The 1990s in the Red River Delta is an important era. Construction of Hoa Binh
Dam began, and the areas of the paddy fields rapidly expanded (GSO 2014) and
coastal erosion accelerated remarkably. In this study, eight sheets of satellite
images, which were taken from 1994 to 1998 were collected: September
30, 1994; February 9, 1995; September 17, 1995; January 27, 1996; January
13, 1997; October 4, 1997; February 13, 1998; September 21, 1998. JERS-1/SAR
provided by NASDA had been running from 1992 to 1998. However, the satellite
images in the first two years could not be used because of strong noise. So data after
1994 was used to calculate CDI in this analysis.
A total of 149 measuring points were tracked across the coastline with an
interval of 500 m. The measurement lines, which were perpendicular to the
coastline, were laid down on the each measuring point. The coastline change was
recorded based on the coastline on September 30, 1994. Next, the CDIs of seasonal
change were calculated by subtracting a CDI from the CDI of the next season.
PCI Geomatica Ver. 7 software in a PC was used to conduct the image analysis.
The nearest neighbor interpolation was used in all of the JERS-1/SAR Images, and
15 GCP points were secured in each satellite image based on the topographic map
with a 1:50,000 scale.
The RMS error between the topographic map and the satellite image was 1.2,
and the RMS error between each satellite image was under 0.5. Frost Filtering was
used to diminish the speckle noise in each satellite image (Frost et al. 1982).
10.3.4 Production of the Coastal Erosion Risk Map
10.3.4.1 Parameters for Assessing Coastal Erosion
CDIs are closely related to coastal erosion in the southern Red River Delta.
Therefore, a risk map of the coastal erosion based on CDIs was prepared.
204
M. Murooka et al.