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Tham khảo tài liệu 'robotic subsurface mapping using gpr part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | There also have been some work in automatic pipe excavation by Whittaker et al. Whit-taker Swetz 86 . In this case no subsurface sensor is employed the retrieval is done by carefully removing thin layers of soil until the pipe is detected by sonars. This is not suited for sensitive and explosive objects since the objects might be struck before they are detected by the sonars. 27 28 Chapter 3. Ground Penetrating Radar 3.1. Selection of Subsurface Sensors There are many sensors that can be used to sense different types of buried objects. These sensors range from a simple device such as a metal detector to a very complicated chemical detection device such as a Thermal Neutron Activation TNA sensor. These sensors use different sensing modalities which are suitable for different tasks. A list of subsurface sensors along with their sensing modalities advantages and disadvantages is listed in Table 9. From these various sensors we pick GPR because it can sense metallic and nonmetallic buried objects. It can also obtain geometric information about the buried objects as well as its depth and horizontal location. GPR is also operable in propagation medium other than soil such as fresh water Mellet 93 which enables us to find buried objects at the bottom of lakes or rivers. All of these capabilities make GPR a much more versatile sensor compared to other subsurface sensors. 3.1.1. Method of Operation Ground Penetrating Radar GPR is a special radar unit that is designed to transmit electromagnetic pulses down to the ground instead to the air. Therefore the main difference with a conventional radar is the medium of propagation. In the case of a conventional radar the .
