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Oceangraphy
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Sediment dispersion from offshore TIN dredging along Andaman sea coast using satellite data
The Study Area
The study area is located in the Andaman sea along the coast about 35 kilmeters long from Ban Name Khem to Ban Bang Niang, Takua Padistrict, Phangnaga Province in the South of Thailand. (as shown in Figure 1)
Data used
- Satellite data : Three dates of Landsat-5, TM
digital data, path 129 row 54, were used to detect the sediment
dispersion. One which was acquired 11 days before diffuser installation
was of February 04, 1989 while the other two were after installation of
February 20, 1989 and May 11, 1989.
- Topographic maps at a scale of 1:50,000 were
used to facilitate the registration of the TM scene to the map
projection.
- Mining concession maps were used to locate the
boundaries of tin dredging sites.
- Mining concession and dredge: information such
as shown in Table 1 were also used to relate with the satellite data of
different dates in order to obtain background information for satellite
data interpretation .
Table 1 The mining concession and dredge information in the study area.
| Concession Sites |
Number of dredges |
| Feb 04, 1989 |
Feb 20, 1989 |
May 11, 1989 |
| A |
1 dredge |
10 dredges |
1 dredge |
| B |
- |
- |
Temporary close |
| C |
11 dredges |
15 dredges |
Temporary close |
| D |
Temporary close |
Temporary close |
Temporary close |
| E |
Temporary close |
Temporary close |
Temporary close |
- Tidal data.: The dredging period is in the NE
Moonsoon when the wind is quite calm during November to May, The tidal
heights used were those at Pak Nam Ranong station, Ranong province and
Khao TaphaoNoi station, Phuket province in the North and South of the
study area respectively, The two stations are located at about 100
kilometers away from Ban Nam Khem. The tidal data of both stations at
the same period as Satellite over passing between 9.00 a.m. are shown in
Tables 2 and 3.
Table 2 The tidal data at Pak Nam Ranong Station
| Date |
Water level (Decimeters) |
| 9.00 |
10.00 |
| Feb 04, 89 |
33.0 |
31.0 |
| Feb 20, 89 |
33.5 |
36.6 |
| May 11, 89 |
18.5 |
20.5 |
Table 3 The tidal data at Khao Taphao Noi station
| Date |
Water level (Decimeters) |
| 9.00 |
10.00 |
11.00 |
| Feb 04, 89 |
24.5 |
24.5 |
_ |
| Feb 20, 89 |
23.5 |
27.0 |
28.5 |
| May 11, 89 |
18.0 |
20.0 |
_ |
Image Enhancement
The Landsat digital images that were obtained from the Thai Ground Station were already rectified and geo-coded. These images were enhanced for suspended sediments pattern on the Meridian image analysis system. The contrast stretch technique was applied to the individual bands 1, 2, and 3 and combination of the three bands were used for interpretation in term of the pattern and direction of sediment dispersion with respect to mine concession boundary, number of dredges and tidal data.
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