Barrier Landforms of Thailand - A case study in Narthiwat Province
Okkerman (1983) reported that the most recent transgressive sea level was about ±10,00 year BP. The rise of the sea level was rapid and then slow down to stand still about 3500 year BP in southwest Asia since then transgression and regressions sea level were observed as indicated by marine terraces and barriers Hastings and Liengsakul (1983) mentioned that the Pru to Daeng the peat swamp forest in the study area was dated about 3800 years BP. Pramojanee et al. (1986) reported that the regressive sea level were observed during 4800-1500 years BP. Since then about 1500 years BP the sea level becomes at the present level.
Shao Xiang Ni and Zhen Min He (1984) reported that land sat MSS data with edge enhancement and linear contrast stretching provide good mountain landform mapping but were not good for flat to gentle slope land Jones (1986) mentioned from his study of land sat TM data in arid land that unsupervised classification gives good results for geomorphologic mapping. Other computer assisted are also acceptable for landform mapping units .He recommended land sat TM data band 5 or 7 and unsupervised classification of bands 1,2,3,4,5; 4,5,7; and 1,2,3,4, for geomorphic unit mapping. Ehlers and Boker (1989) stated that barrier island and tidal landforms are. rapidly change .Therefore Land Sat TM data combination of band 1,2,3 was used to detect the change Chaimanee and Tiyapirach (1983) applied aerial photography and satellite imagery for sand bars and beach ridges in songkhla province the northern province of Narathiwat.
Aims
The aim of this study is to find a fast accurate and cheap remote sensing techniques for barriers mapping at medium scale (1:100,000- 1:50,000) in the Narathiwat province. Although aerial photographs arte available but are very restricted to many users . The authors also the disadvantage of the aerial photography and the Land sat TM data.
The Area
The study area located in southernmost province of the Kingdom is between 101o 50'-102o 05 'E longitude and 6o10'-6o 25' N latitude province .The land area is approximately 400 km2 However only barrier sand ridges along the coast are emphasized in this evaluation of barrier mapping unit .The area is in fig 1
Two selected subscences Tak sin (TK) and Saton (KO) each suitable for a computer screen are studied.
Materials and Equipment
The Materials include the following.
- Topographic map 1:50,00, 1969 by the Royal Thai
survey Department,
- Topographic maps 1:25.000 , 1982 by the Royal
Thai survey department,
- Panchromatic aerial photographs 1:40,000 1984
and 1:11,000 1988.
- Land sat TM data geometric corrected dated 7
August 1988 including CCT and hard copies.
- The DIMAPS -IBM mainframe and the ERDAS -IBM PC available in the INRDM AIT.
Procedures
This study is the by product of the previous study (H.R.H. Princess Maha Chakri Sirindhorn et.al. 1988) The aerial photographs (1:40,000) are interpreted for barrier and lagoon map units Each band 1,2,3,4,5,7 of land sat TM imaginary 1:250,00 and 1:50,000 are also delineated manually for the same units as indentifed from the aerial photographs .The computer assisted for these landform identification includes displaying of single bands more than two band combination and unsupervised and supervised classifications edge enhancement techniques are employed whenever appropriate .field work was carried out several times and soil profiles were observed on these barriers .The results of barrier and lagoon map units compared with the results from the interpreted from the aerial photograph and a relative value is given.
Results and Discussion.
- Interpretation from the aerial photography . The small scale aerial photographs provide very good information for the barrier mapping at the medium scale .The contrast of land features on barrier sand and lagoon is very distinct due to the different in vegetation types land use and soil moisture and characteristics .The barriers consist of coconut and cashew plantations and is wide .The soils are sandy low organic matter and dry .therefore the high reflectance of the electromagnetic energy is recorded on the other hand the langoons havenatural dense vegetation high organic matter and moisture content therefore low reflectance of the wave energy is recorded The smallest dimension of barrier and lagoon is about 50m in width but more than 1kms in length the reief of the barriers obtained from the topographic maps is about 2,4 m the surface slope of these landforms is very gentle to very slightly undulating.
The large scale aerial
photographs can be used for this landform mapping but it requires may
photographs for the work therefore they are used only ae reference
whenever necessary.
- Single band of the Land sat TM imagery Since it is very time consuming to work on the computer screen photographs of each display were taken directly from the computer . Photographs of each land sat Tm band were then compared with the results from the aerial photograph interpretation The land sat TM bands4,5 and 7 give good results comparable to the aerial photographs It may be noted also that 4 is probably the best.
The photographic products enlarge from each of the Landsat TM which were plotted on 22x22 cm film (1:500,000) gave similar results The Land Sat TM banda 4 and 5 are the best (table 2)
The results confirm the
appropriate wavelength and the ground resolution designed for the land
sat 4 and 5.
