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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
30 cm could penetrate through the plants (foliage etc.) and 
reach to the objects underneath such as ground, and etc. 
Because the soil moisture normally limits the penetration of 
waves to the depths of a few centimetres, the surface wetness 
conditions become apparent at longer wavelengths. The 
penetration of L-band radar to the several meters provides the 
observation of the moisture content under extremely dry soil 
conditions. However in many studies, the potential of SAR data 
for the retrieval of surface soil moisture was investigated not 
only with longer wave lengths but also with shorter wave 
lengths as C-band radars, and the microwave measurements 
have shown their sensitivity to surface soil moisture (Ulaby et 
al. 1978, Dobson and Ulaby, 1986, Dubois et al. 1995, Shi et al. 
1997). 
Following the evolution of SAR satellite technologies, 
researchers have been investigated the effect of dielectric 
features on backscattering. For instance, Peplinski et al. (1995) 
investigated dielectric properties of different soil types and their 
effects on backscattering. They discovered that soil texture and 
volumetric moist content had an effect on the dielectric 
coefficient. In addition, these researchers emphasized that 
dielectric coefficients of soils vary with respect to clay types, 
and as the clay specific surface area becomes wider dielectric 
conductivities increase linearly. Romshoo et al. (2002) tried to 
forecast soil moisture in Sukhothai area, using a time series of 
space-borne ERS-2 SAR satellite data for the temporal 
monitoring. In their study, it has been discovered that in the 
study area, the backscatter coefficient of SAR data was 
sensitive to volumetric soil moistures of 0-5 cm in depth. Shao 
et al. (2003) have empirically investigated the variations in 
dielectric features of moist and saline soils, the samples of 
which were taken from a salt lake, and they observed an 
increase in the backscatter as the saline content increased. Yang 
et al (2006) demonstrated a technique to estimate the retrieval 
of soil moisture change by using multi-temporal Radarsat 
ScanSAR data. Their study had two parts. First part focused on 
minimizing the effects of surface roughness by using two 
microwave radar measurements with different incidence angles. 
Second part dealt with to reduce the effects of vegetation cover 
on radar measurements by using semi-empirical vegetation 
model and measurements obtained from the sensors as Landsat 
TM and AVHRR. Throughout the surveys in more than one 
decade, it has been detected that there is a strong relation 
between the backscatter coefficient and the soil moisture. The 
researchers whether used data from only one sensor type (such 
as ERS 1/2, RADRASAT-1, ENVISAT) to analyze the 
sensitivity of SAR data to soil surface parameters at various 
polarisations or incidence angles or they used two different 
sensor data to make the comparisons (such as ERS 1/2 versus 
RADARSAT-1 or ENVISAT versus RADARSAT-1) over 
fields with different characteristics. (Baghdadi et al., 2002; 
Baghdadi et al., 2006; Boisvert et al., 1997; Beaudoin et al., 
1990; Alvarez-Mazos et al., 2005; Holah et al., 2005; Kelly et 
al., 2003; Oldak et al., 2003; Siegert and Ruecker, 2000; 
Sahebi et al., 2003; Srivastava et al., 2003; Weimann et al, 1998; 
Zribi et al., 2005a, 2005b). Researchers indicate that, the major 
difficulties in retrieving soil moisture with SAR measurements 
are due to the effects of surface roughness and vegetation cover. 
The objective of the present study is to investigate the 
behaviour of RADARSAT, ASAR and PALSAR images to 
retrieve soil moistures for bare and just seeded soil. Besides, 
tests have been carried out to obtain the cross correlation not 
only between the different bands (C/ L) but also between the 
different polarizations (VV/HH). This work will enable us to 
perceive which sensor has the best potential for extracting soil 
moisture in such an agricultural plain areas including the latest 
satellite ALOS-PALSAR data. 
2. IMPORTANCE OF SOIL CHARACTERISTICS IN 
ACTIVE AND PASSIVE REMOTE SENSING 
APPLICATIONS 
In both passive microwave and active remote sensing, it is 
important to know the soil characteristics. The soil is 
constituted from 25 % air, 25% water, 45% and 5% inorganic 
and organic substances respectively. Organic and inorganic 
substances that are the solid parts of the soil form the structure 
of the soil. Inorganic solid matter of soil is composed of various 
rock decompositions and minerals in different sizes and 
composition as well as rock pieces (Altinbas et al. 2004). The 
texture of the soil is formed from various ratios of sand, silt, 
and clay which are called inorganic substances. It is known that 
diameters of particles range between 2 and 0,02 mm, of silt 
particles between 0,02 and 0,002, and of clay particles which 
have diameters smaller than 0,002 mm. In interpreting soil 
reflection values for remote sensing applications, size of surface 
soil particles, volume of the pores, ratio of the size of a pore, 
and amount of water stored in these pores is very important. 
The pores in sandy soil texture are called macrospores and the 
pores in clay texture are called microspores. Although the size 
of pores in sandy soil is large, total volume of pores is smaller 
than that of clayey soil. In addition, reflection of 
electromagnetic radiation from the surface of soil is dependent 
on some features such as slope of the terrain, surface relief, 
structure of the soil, organic matter content, size distribution of 
the particles constituting the soil, stoniness, saltiness, iron oxide 
content, and etc. Dielectric contents of the soil play important 
role in microwave back scattering. Soil structure and moisture 
are the main characteristics that determine the dielectric 
contents of soils. For instance, while increased amount of sand 
in soil enables the soil to become less absorbent and to have 
low water holding capacity, increased amount of clay in soil 
causes the soil to become more absorbent and to have more 
water holding capacity. Increase in the amount of water causes 
the dielectric content to be increased. Spectral characteristics of 
the soil are mainly influenced by the organic matter content and 
the moisture content (Stoner et al. 1980). 
3. STUDY AREA 
The study area is in the lands of Menemen (Izmir) Plain to the 
west of Gediz Basin, and covers about 400 square km. The 
Aegean Sea lies to the west of the study area, and Manisa 
Province lies on the East. The area is also bordered by Bakircay 
Basin on the North, and Izmir Bay on the South (Figure 1).