WET LAND AND SALT CRUST FORMATION BASED ON LANDSAT TM DATA 
Alavi Panah, S.K. * 
* Assistant Professor, Iran Desert Research Center, University of Tehran, Tehran , Iran. 
E-mail: salavipa@chamran.ut. ac.ir 
Key words: wet land, salt crust, TM data, false color composite 
Abstract 
In this study, in order to study the causes of wet land and salt crust formation in Central Iranian Deserts, different sources of data 
such as remotely sensed data, geologic geomorphologic and topographic maps were used. The result of visual interpretation and 
comparison between the false color composites in the study period led us to classify the TM images in the meaningful way. The 
visual and supervised classification revealed some changes in land cover types in the study area. Based on the obtained results we 
concluded the extension of cultivated lands which are irrigated by flood irrigation system and water erosion have the most important 
role in wet land and salt crust formation. We also concluded that remotely sensed data including TM reflective and TM thermal 
bands and geographic information system are useful tools to study the effect of microtopography and multitemporal analysis. 
1. INTRODUCTION 
Wet land is a term applied to ecosystems dominated by water in 
their formation, development and ecological functions 
(Williams, 1993). Hydrophytic vegetation, hydric soils and wet 
land hydrology are of the three basic elements for identifying 
wet lands. Precipitation, topography, soil permeability and plant 
cover may influence the wetness of an area. Causes of wet land 
formation are many and often complex. Human has accelerated 
or slowed these processes in a number of ways, sometimes 
dramatically. The places where wet land conditions occur in 
desert and where the water table lies at shallow depth, the 
capillary rise play an important role in the accumulation of salt 
on the surface. With evaporation of water from the surface, salt 
concentration increases until crystals of the halite begins to 
precipitate at its saturation point. The crust that grows from 
evaporation of saline ground water is common in the Iranian 
Desert. The change of dry land to wet land and then wet land to 
salt crust have been reported in some places in the Iranian 
deserts and playas (Alavi Panah, 1997). 
Of the many land surface parameters that can be derived from 
remotely sensed data, surface moisture is one of the least well 
characterized. Existing studies (Carlson et al, 1992) have 
produced moisture estimates from remotely sensed inputs using 
coincident field measurement of soil and foliar moisture. 
A soil line is given by the pixels that contain bare soil and dry 
vegetation (Jasinki and Eagleson, 1989). For vegetation index 
(and soil line) noise is introduced by variations in soil 
parameters (moisture content, soil color and organic matter and 
atmospheric influences). Therefore a good understanding of wet 
land and soil with different moisture condition in relation to 
other conditions of soil color and texture and structure may be 
necessary. 
There are three types spectral indices of soil moisture: those 
employing the absolute in one or more bands; those that 
examine the contrast between the visible and near infrared 
bands to the middle infrared; and those which contrast 
information at mid-infrared wavelengths only (Musick and 
Pelletier, 1988). It has long been established that reflectances at 
mid-infrared wavelengths respond primarily to water content 
(Verbyla, 1993). Verbyla (1993) contents that MIR wavelength 
are more useful under an extreme range of conditions, but fore 
less divergent situation, complication may arise as a result of 
changes in soil texture, plant canopy, and train conditions. 
2. STUDY AREAS 
2.1. Meybod depression: Our field work was carried out on 
salt crust regions in the Ardakan area. Among the places where 
salt crust has been developed, Meybod depression was 
considered for a more detailed interpretation of salt crust 
formation using standard FCC,s of MSS and TM images. Based 
on the main explanatory report of the soil survey, the main 
characteristics of soil surface horizon (layer) are: medium soil 
surface texture, which overlaid on clay loam soil. The water 
table depth is about 1.2 m and a hardpan is formed at a depth of 
about 3 m. In the lowest part of the depression, the salt crust 
with dark color was developed. The depth to moisture is 
typically only a few centimeters below the dry salt crust, due to 
recharge by acquifers. 
2.2. Lut desert: This area located between Yardang and sand 
dune regions which is characterized by an extremely arid 
climate, with excessive summer heat, winter temperature below 
freezing point. The Yardang and sand dune are rare and striking 
feature. Lut desert includes great diversity of hydroaeolian 
process with a very interesting pattern of landforms. Yardang 
which is a wind-abraded ridges of cohesive materials is one of 
the most striking geomorphologic feature in the Iranian deserts. 
Although generally, the Yardangs have been formed by wind 
erosion, an alternative explanation for aligned topography in 
Lut involves collaborative wind and stream action. Yardangs 
are parallel ridges of lacustrine sediments between wind- 
scoured furrows aligned with the dominant wind. Wind and 
water as exogenetic processes, work landscapes, such as 
tectonic and volcanic activity. Deserts have experienced great 
temporal and spatial variability of these endogenetic process in 
Iran, the Lut Desert are apparently tectonically unstable area 
(Cooke, 1993). 
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