JAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002 
  
  
Table 1. The proxies of the failure mechanisms which are important for monitoring 
This could be attained by digging canals in the polder parallel 
to the dike and the bottom of these canals would be allowed to 
burst open upwards due to the potential in the sand underlying 
it. At a larger distance from the dike, the depth of the canal 
would need to larger, so that seepage occurs at lower potential 
and thus reduce the potential to levels not inducing seepage 
near the dike. Obviously, this mechanism will work only if the 
canal bottom can burst. 
  
  
  
  
Figure 2. Typical cross section a dike and Seepage phenomenon 
(Barends et al., 1992) 
Figure 3. Seepage (TAW, 1994) 
  
  
3. REMOTE SENSING 
Remote sensing is the science and art of obtaining information 
about an object, area or phenomenon through the analysis of 
data acquired by a device that is not in contact with the object, 
area or phenomenon under investigation (Lillesand; Kiefer, 
2000). Electromagnetic spectrum is employed in the remote 
sensing for detection and measuring target characteristics. 
Electromagnetic spectrum is the continuum of energy that 
ranges from the very short wavelengths of the Gamma-ray 
region (measured in fractions of nanometers) to the long 
wavelengths of the radio region (measured in meters), travels at 
the speed of light and propagates through vacuum such as outer 
space. 
3.1 Thermal Infrared (TIR) 
The IR (Infrared) region is that portion of the electromagnetic 
spectrum ranging in wavelength from o.7 um to 1 mm. The IR 
portion can be classified in two methods: 
- Based on nearness to the visible Light: 
- Near Infrared 0.7 - 1.3 um 
- Middle Infrared 1.3-3 um 
- Far Infrared 3 um until 1 mm 
- According to their nature: 
- Reflected Infrared (RIR) 0.7-3 um 
- Thermal Infrared (TIR) 3-14 yum 
In this paper, the second definition is used. 
The main source of the reflected IR is sun and 40 96 of the sun's 
energy that earth has been receiving is in this portion, but the 
main source that produce the Thermal IR energy is the heat of 
earth which is due to the sun shine to the earth. All objects in 
the world that have a temperature more than 0 eK (0 °K=-273 
C) have radiant energy. For example, earth radiates energy 
both day and night, with the maximum energy radiating at 9.7 
pm wavelength. This radiant energy peak occurs in the thermal 
portion of the IR region. ; 
The reflected IR region includes the photographic IR band (0.7 
to 0.9 um), which may be detected directly by IR sensitive film. 
On IR colour photographs the red signature records IR energy 
that is strongly reflected by vegetation and is not related to 
thermal radiation. Within the IR portion of the spectrum, it 
should be noted that only Thermal IR energy is directly related 
to the sensation of heat and Reflected IR energy is not. 
Therefore photographic film does not detect TIR radiation. 
Special detectors and optical-mechanical scanners detect and 
record images in thermal IR spectral region. In the TIR images, 
the brightest tones represent the warmest radiant temperature 
and the darkest tones represent the coldest tone. 
The atmosphere does not transmit all wavelengths of thermal IR 
radiation uniformly. Carbon dioxide, ozone and water vapour 
absorb energy in certain wave length regions (call absorption 
bands). The atmosphere transmits wavelengths of 3 to 5 um 
and 8 to 14 pm (Fig. 4). The narrow absorption band of 9 to 10 
um (shown as a dashed curve in Fig. 4) is caused by the ozone 
layer at the top of the earth's atmosphere. To avoid the effects 
of this absorption band, satellite TIR systems record 
wavelengths from 10.5 to 12.5 um. Systems on aircraft, which 
fly beneath the ozone layer, are not affected and may record the 
full window from 8 to14 um. 
  
Reflected 
pon ona pecs Thermal IR 
Le iR 
  
100 O; H,0 H;O 
vtr 
   
H;O O; CO; 
   
10.5 to 12.5 um 
= band : 
0 2 4 6 8 10 12 14 
Wavelength, um 
-—— — zz — A 
3 to 5 um 8to 14 um 
band band 
   
Transmittance, 96 
    
  
  
  
Figure 4. Electromagnetic spectrum showing spectral bands 
used in the thermal IR region. Gases that cause atmospheric 
absorption are indicated (Sabins, 1997) 
380 
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