| Co-Investigator(Kenkyū-buntansha) |
SEKI Hajime Nagaoka Univ.of Tech., Dept.of Electrical Eng., Associate Porfessor, 工学部, 助教授 (00179326)
KOBAYASHI Akira Teikyou Heisei Univ., Dept.of Information Eng., Lecturer, 情報学部, 講師 (80225490)
ITO Ko-ichi Chiba Univ., Dept.Electrical and Electronic Eng., Associate Professor, 工学部, 助教授 (90108225)
KAMEI Hiroyuki Tokyo Inst.of Thch., Dept.of Computer Sci., Associate Professor, 大学院情報理工学研究科, 助教授 (60143658)
|
|---|
| Research Abstract |
A FM-CW (Frequency-Modulated Continuous Wave) ground penetrating redar acts according to a different principle a pulse radar. Compared with a pulse rader, a FM-CW radar has the following three advantages :
1. It has no ringing. A clearer image can be generated.
2. Its resolution does not depend on the frequency band of transmitted wave.
3. It has higher S/N ratio.
It is expected from these advantages that a FM-CW redar is more effective to discriminate soil layrs.
We developed a 100-500 MHz band FM-CW radar system. The antenna adopted in this system is a resistively loaded bow-tie antenna whose center frequency is 300MHz. Two antennae are used for the transmitter and the receiver. The transmitted frequency is triangularly modulated between 100 MHz and 500 MHz, and the period of the triangle waveform is selectable among 5,10,50,100 msec. If the 50-msec period is selected, the rate of frequency change becomes 16 Hz/nsec. Then, the 30-nsec delay time corresponds to 480 Hz.
A lot of experiments of field survey using this FM-CW redar were carried out at Harunotuji site (Nagasaki Pref.), Tonozuka No.1 mounded tomb (Ibaragi Pref.), tunnel tombs in Saitobaru (Miyazaki Pref.), Hirui-Otsuka mounded tomb (Gifu Pref.), Zoubisan No.1 mounded tomb (Gifu Pref.), Kaibukiyama mounded tomb (Osaka Pref.), and so on. It was proved that this FM-CW radar was superior to a pulse radar in detecting the interface between soil layrs, because the FM-CW radar could detect a moat under a wet rice field which could not be detected by a conventional pulse radar at Harunotuji site.
We also developed some methods to measure the soil permittivity in site using co-axial dipole antenna, mono-pole antenna or wire antenna.
|
