| 摘要 |
PURPOSE:To detect the underwater reflected waves in front, middle and lower layers in detection of the frequencies of the underwater reflected waves for the purpose of measuring the velocity of tidal current by setting the frequency pass band width of a filter circuit in consideration for the max. Doppler shift quantity corresponding to the change in the velocity of the tidal current in the case of the waves from the front layer, and setting the frequency pass bands of the filter circuit successively from the middle to lower layers in accordance with the Doppler shift quantity from the front layer in the case of the waves from the middle and lower layers. CONSTITUTION:In accordance with the oscillation frequency signal from a variable oscillator 13 corresponding to the underwater reflection from front layer, a control voltage generating circuit 15 generates a control voltage by which the frequency pass band of a narrow band filter circuit 51 is controlled. The signal of the reflected waves from middle layer is inputted to the circuit 51. The circuit 51 has a narrow pass band width, is controlled of the pass band in accordance with the reflected waves from the front layer and allows the band passage of the signal of the reflected waves from the middle layer inputted thereto at a good S/N ratio. The reflected wave signal from the middle layer past the circuit 51 is compared with the variable frequency signal from a variable oscillator 14. An arithmetic circuit 9 operates the velocity of the tidal current in the middle layer. When the reflected waves from the lower layer is inputted to the circuit 51, the circuit 51 allows the band passage of the signals of the reflected waves from the lower layer at a gool S/N ratio and the velocity of the tidal current in the lower layer is operated as well. |
