Mapping of Salt-Affected Soils using Remote Sensing and Geograp
Information Systems: A Case Study of Nakhon Ratchaslma, Thailandl
Awadh k. sah, Apisit Eiumnoh, Shunji Murai and Preeda Parkpian
Space Technology Applications and Research Program,
Asian Institute of Technology
GPO Box 2754, Bangkok 10501, Thailand
Abstract
This paper is based on a research carried out to develop a methodology to classify the salt-affected soils using remote sensing and GIS. Taking salt crust as a criterion, Landsat TM with bands other than two and six was found effective, to a greater extent, in classifying the extremely and moderately saline area. Integration of GIS was found effective in classifying low and potential saline area as well as in correcting some of such area misclassified as extremely or moderately. The confirmation of resulted six salinity classes with field check, existing map and soil analysis proved it as reliable one. However, similar pattern of soil salinity was obtained from the study compared to the existing map of 1989 prepared from Landsat MSS at scale 1: 250, 000, the classification result was found to show more details. The study concluded that integration of GIS with digital image processing of TM was very effective for classifying and monitoring of saline soils.
1.0 Introduction
Salt-affected soils have been identified as one of the three main hurdles against crop production in northeast region of Thailand (Mitsuchi et al., 1986) where out of3.61 million hectare of such soils in whole territory, as high as 2.58 million hectare, i.e. 17% of total regional area, is prevailing (Arunin, 1992). The widespread deforestation of past is considered as the main cause in bringing the salts from lower strata up to soil surface which despite of various control measures, has resulted in rapid expansion of salt-affected areas. Such the dynamic condition calls for up-to-date information regarding its extent and nature as pre-requisite for the sound management. Unfortunately, until present, this usually remains inadequate mainly due to lacking of efficient assessment method. However, Satellite Remote Sensing (SRS) with higher spatial resolution is now available for this purpose (Singh and Dwivedi, 1989) which in combination with Geographic information Systems (GIS) may yield more reliable result (Battle-Sales and Abad-Franch, 1992). Under this context, the present study was carried out with the objectives (i) to develop a methodology for mapping the salt-affected soils using SRS and GIS , (ii) to assess the capability of GIS for comprehensive classification when interfaced with SRS data, and (iii) to interpret the salinity classes with respect to crop production.
2. 0 The Study Area
The study area, encompassing 469 square kilometers, lies between 14° 56' and 15° 12' North latitude and 101° 53' and 102° 08' East longitude in Nakhon Ratchasima province of northeast region of Thailand. Mean annual rainfall of the locality, as revealed from meteorological data for 34 years (1961-94), is 1060 mm out of which nearly 85% occurs within six months (May to October) while along with mean monthly maximum temperature between 29.8° to 37.0°, the mean annual evaporation is as high as 1873 mm. Lam Takong irrigation project covers 20.4% of the whole study area extending mainly in flood plain and basin. The altitude ranges from 170 to 210 m above mean sea level. 85.7% of whole study area is under cultivation while forest is covering only in 1% area. Paddy and cassava are the two major crops occupying the low and up land, respectively.
3.0 Methodology
An integrated approach of digital image processing of satellite data combined with GIS was carried out in this study.
3.1 Collection of Ancillary Data
Besides the above facts, two field surveys were conducted, the fIrst mainly to observe the dominance and spatial
relationship of salt crusts and the second to verify field and to collect soil samples. Following satellite data and source maps, were used: Thailand.
-
Landsat-5 TM data of path/row 128-050, acquired on 10 January 1994.
- Existing Maps:
-
Topographic map (scale 1:50,000) of year 1969.
- Geology map (scale 1:250,000) of year 1976.
- Soil map (scale 1:100,000) of year 1978.
- Land use map (scale 1:250,000) of year 1987.
- Ground Water Quality and Well Yield map (1:100,000) of year 1988.
- Salinity map (scale 1:250,000) of year 1989.
