| 摘要 |
<p>PURPOSE:To prevent disaster by issuing a signal indicating the occurrence of an avalanche of sand and stone when the Doppler frequency and the intensity of the reflected radio wave are changed. CONSTITUTION:The microwave having a frequency (f) is constantly generated from a transmitter 10 toward the center of a river 7 through a transmission/ reception antenna 6. Only water relatively slowly flows in the river in time of peace, and the microwave is reflected by a water current (velocity V0), and the reflected radio wave is received 11 and the Doppler frequency of the reflected microwave is calculated 12 to output a Doppler frequency DELTA0f. If the current velocity is increased from V0 to V2 because of the increase of water or an avalanche of sand and stone (current velocity V1) occurs, the Doppler frequency is changed from DELTA0f to DELTA2f or DELTA1f. A BPF 13 is so set that a frequency approximating the frequency DELTA1f passes it. Consequently, the frequency DELTA1f which passes the BPF 13 at the time of occurrence of the avalanche of sand and stone is amplified 3 and is detected 4 and amplitudes E1 and E0 of signals having frequencies DELTA1f and DELTA0f are compared 5 and an output signal (detection signal of the occurrence of avalanche of sand and stone) is outputted in case of E1>E2.</p> |
