International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
  
radiance or reflectance (Ritchie et al. 1976, 
1990; Curran and Novo 1988) because the 
amount of reflected radiance tends to saturate as 
suspended sediment concentrations increase. 
The point of saturation is wavelength 
dependent, with the shorter wavelength 
saturating at lower concentrations. 
If the range of suspended sediments is 
between 0 and 50 mg/l, reflectance from almost 
any wavelength will be significantly related to 
suspended sediment concentrations (Ritchie and 
Schiebe 2000). As the range of suspended 
sediments increases to 200 mg/l or higher, 
curvilinear relationships have to be developed 
with reflectance in the longer wavelength. 
Significant relationships have been shown 
between suspended sediments and radiance or 
reflectance from spectral wave bands or 
combinations of wave bands on satellite 
sensors. Ritchie et al. (1976) using in situ 
studies concluded that wavelengths between 
700 and 800 nm were most useful for 
determining suspended sediments in surface 
waters. Many studies have developed 
algorithms for the relationship between the 
concentration of suspended sediments and 
radiance or reflectance (Mobasheri, 2003). A 
few studies have taken the next step and used 
these algorithms to estimate suspended 
sediments for another time or place (Ritchie and 
Cooper 1988). 
Variations of sediment type (grain size and 
refractive index) and changing illumination 
conditions affect the reflectance signal of 
coastal waters and limit the accuracy of 
sediment-concentration estimations from 
remote-sensing measurements (Doxaran et al., 
2003). 
: The six MODIS channels centered at 
0.55, 0.66, 0.86, 1.24, 1.64, and 2.1 m are being 
used for aerosol retrieving algorithm and 
deriving aerosol models and aerosol optical 
depths. Water leaving reflectance is assumed to. 
be zero in the 0.86-, 1.24-, 1.64-, and 2.13- m 
channels (Rong-Rong et al, 2003). The 
reflectance at channel 1 and 4 was assumed to 
be the typical clear water reflectance. Any 
unaccounted elevated values of the water 
leaving reflectance were interpreted as an 
increase in the optical thickness of the fine 
aerosol particles. Sediments and shallow waters 
provided such unaccounted high reflectance and 
resulted in systematic overestimate of the 
aerosol optical thickness. It is believed that the 
main differences between the two types of 
waters are located in the 0.4-0.7 m spectral 
range (Rong-Rong et al., 2003) where the turbid 
water has significantly larger reflectance than 
the clear water. This formed the basis for the 
detection of turbid water and SSC estimation 
Algorithms. The penetration depths at the level 
of 90% light attenuation is as high as 40meters 
for channel 3 and as low as less than a 
millimeter for channel 7 (Mobasheri, 1995). 
Thus, the turbidity in water can affect reflect- 
ance in visible channels and even at 0.86 u. 
However, for the longer wavelengths 
(1.2, 1.6, and 2.1 p) the penetration depths of 
sunlight into the water are very small, 
eliminating the possibility of the reflection by 
sediments. On the other hand, the blue channel 
(0.47 p) is very sensitive to atmospheric 
molecular scattering, but less sensitive to the 
additional reflection by sediments. For coastal 
waters, this channel is not nearly as sensitive as 
the 0.551 channel to sediment reflection 
because of strong absorption by dissolved 
organic matters (yellow substances) at 0.471. In 
summary, the MODIS measurements over the 
ocean at 0.47, 1.2, 1.6, and 2.1 p are influenced 
mainly by aerosol scattering and absorption and 
can be used to derive the atmospheric spectral 
power law (Rong-Rong, et al; ‘ 2003). 
Measurements at 0.55-0.86 p are influenced 
both by the aerosol and the sediments. The 
excess reflectance at 0.55-0.86 p beyond the 
power law values can be associated to the 
presence of sediments and consequently is used 
for their detection in this work. 
2- Methodology and Data Collection 
Bahmansheer River is situated at the 
southwest of Iran and is 80 km long parallel to 
Arvand River, which is the border of Iran and 
Iraq (fig 1). This river carries large amount of 
sediments to the Persian Gulf (varies with tide). | 
The tidal current influences the water level even 
at the junction of this river with the Arvand 
River some 80 km far from its estuary. 
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