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3.3.2 Mountains and Forests
Search and rescue mission is usually visually challenging in a forest area. Even with the aid of infrared camera, there are pos-
sibilities of failure of locating a person. The limitation of infra- red camera can be influence by many factors. Another
communication method that can be used is cell phone commu- nication. However, areas at high terrain and covered by thick
forest has less chances of having cell phone networks. Radio communication is not viable in these areas because of the eco-
nomic factors as these areas are less inhabited by people. Hence these areas have less subscribers and utilization. Typical line-of-
sight LOS link will not work due to the thick vegetation. Therefore, diffraction and reflection of a common radio signals
are the degradation factors that lead to a better communication. Radio communication must be able to transmit signal to the re-
ceiver so that meaningful data or information can be transmitted for example the location of the receiver or images of the encir-
cling areas. The clearing Fresnel Zone concept as shown in sec- tion 2.4 describes the effect of physical barrier such as trees
while the signal is being transfer. This concept relates to the space encircled by an ellipsoid of two antennas between the
ends of a radio link. Here, radio communication can always be established provided there was no disruption to the transmission
of the signals as explained in Fresnel Zone, unless there is ma- jor diffraction or other factor. However, it cannot be concluded
that failing to maintain Fresnel zone always result in communi- cation error. Sometimes, communication relies more on the sur-
rounding environment where it operates. Reflection of signal cause by objects that obstructs such trees, plants and lakes can
be the main factor for any signal loss. Even though LOS path between the transmitter and receive is less likely to exist, there
might be some gaps between the receiver and transmitter which enables one ground reflected path and one direct path through
LOS to co-exist. Therefore, the loss of signal is much dependent
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on the physical properties such as the phase connection and rel- ative amplitude between the signals transmitted through the 2
paths. The phase of reflected wave and signal amplitude de- pends on few variables namely frequency, permittivity and con-
ductivity of the reflecting surface, polarization and angle of incidence which will overlap each other and have varying ef-
fect. The ratio of LOS signal path and the ground reflected paths having Fresnel clearance determine the relative strength
of signal between those two paths. The 2 paths will have the same signal strengths if the ground reflected path lose a little
because of reflection. This will cause an increase of up to 6dB of signal across the direct path or cancellation which may cause
an extra path lost of at least 20dB which rely upon the relative phase shift of the 2 paths. A constructive interference is formed
if the 2 signals combine in a phase without a relative phrase shift. Alternately, 2 signals combining as out of phrase 180
◦ relative phase shift causes ‘destructive interference’. Tech-
niques including multiple antennas and spread spectrum are usually used to solve this matter. Moreover, transmitting from a
foggy environment can be done at a frequency of 20GHz and above. This can be used for communication system in a humid
forests condition. According to Wiki “clutter” is excessive physical disorder which refers to vegetation that affect or dis-
rupt signal transmission in wireless communication. Clutter causes deterioration and scattering of the transmission signal
that strike on an obstacles surface such as branches and leaves because of the wind, thus forming variation of signal path. The
extent of scattering depends on the characteristic and condition of obstacles such as the shape of the leaves, weight of the
leaves, water content within the leaves and many more.
3.3.3 Fire in Buildings
Among the many types of rescue missions undertaken, fire res- cue operations are the most challenging as the rescue team only
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