Abstract
Landsat TM CCT data on 29th July 1988, 4 December 1988 and 30 June 1989, which were before, during and after the catastrophic flood of November 1988. Were analyzed. Enhancement techniques by false colours composite and band ratio ere employed. Classification with principal component analysis was done to investigate the extent of the flood, the environmental change at Songkhla coast of Thailand, which were sediment pattern and accumulation, estuarine circulation, drainage pattern and coastal morphology. This paper is only the preliminary study of the research project on "Environmental Change After the Severe Flood in November 1988 on the Coastal zone of Southern Thailand" which is sponsored by the National Research Council of Thailand, by using remote sensing.

Introduction
The heaviest rainfall ever occurred in the meteorological record of Thailand on 22 November 1988 caused catastrophic flood in the 14 provinces of Southern Thailand. On the upland mountainous area, the flood lasted only 1 week, but on the coastal area, the high river runoff with high mean sea level caused the flood to extend about a month. In Singkhla Province, the major damage was at Amphoe Haadyai, the main business city of the South, because the topography of the area is as the joining place of a number of streams. However, our main interest is on the coastal zone. This paper is only a preliminary study of the effect of this flood on the Sonkhla coast by utilizing remote sensing.

Objectives
The application of remote sensing to detect the environmental changes at Songkhla coast of Thailand from the catastrophic flood of November 1988.

Material and method
Landsat -5 TM CCT Data on 29 July 1988 (before), 4 December 1988 (during) and 30 June 1989 (after) the catastrophic flood were processed at University of Tokyo Murai Laboratory. Enhancement techniques of band ratio and false colour composite were employed. The classification by principal component analysis was also done to investigate the effect of the flood on environmental change at the Songkhla coast. Ground truth data with base maps were also compiled for interpretation.

Results
Songkhla coast is a typical of barrier beach and lagoon system. On the barrier coast, there are a number of beach ridges, which is evident of old, shoreline, parallel to the coastline. The lagoon system is composed of 3 lakes: Thale Noi, the northernmost and the smallest; Thale Luang, the middle and the largest; an Thalesap Songkhla, the southernmost, see Fig 1. The water depth is very shallow approximate 1 meter deep with extensive mudflat and mangrove swamps. The salinity of Thale Noi is nearly as fresh water especially in the rainy season. Thale Luang is brackish water and Thalesap songkhla is more salty owing to its opening inlet to the sea, the Gulf of Thailand. The biota in the 3 lakes also an indicator of the salinity of water in the lakes as well. This lagoon is an productive reservoir and fishermen have cached abundant of fishes for their living. It is also a biggest bird sanctuary in the country. On the barrier cost, there are paddy field and palm tress with Sandy beach on the outermost to the sea.

The accumulation of sediment is rather high especially in Thale Luang owing to the numerous streams of sediment into an extensive shallow basin. The inlet to Thalesap Songkhla is restricted, thus, most of the sediment deposit in the inner 2 lakes. Thale Noi is nearly an enclosed lake. The barrier coast also progrades seaward every year. The area of the mudflats and islets in Thale Luang enlarge as the time goes on. These features are well seen from the TM images, see Figs 2.