4 . The satellite communication is most cost effective in remote and hilly areas , such as Ladakh , Himachal Pradesh etc .
5 . The satellite communication permits transmission of data at rate .
6 . The satellite communication is very accurate and economical search . rescue and navigation purposes .
Demerits of Satellite Communication
1 . If a system on the satellite goes out of order due to environmental stresses , it is almost impossible to repair it .
2 . In satellite communication , there is a time delay between transmission and reception , due to extremely large communication path length ( greater than 2 x 36000 km ). This delay causes a time gap during talking , which proves quite annoying .
Remote Sensing
It is a technique of observing or measuring the characteristics of the object at a distance . A polar satellite is utilized for this purpose .
Distance upto which a signal can be obtained from an antenna is given by
d = √2hR where , h is height of antenna and R is radius of earth .
LED and Diode Laser in Communication
Light Emitting . Diode ( LED ) and diode laser are preferred sources for optical communication links to the following features .
1 . Each produces light of suitable power required in optical communication . Diode laser provides light which is monochromatic and coherent . This light is obtained as a parallel beam . It is used in very long distance transmission .