FRONT INVESTIGATING METHOD

PURPOSE:To accurately investigate an obstacle by removing receiving noise and to measure the distance up to the obstacle with high accuracy by calculating the correlation between transmitting data and receiving data to select received signals large in correlation. CONSTITUTION:The reflected wave 22 due to an obstacle 4 of the transmitting wave 21 emitted to the front earth is received by a receiver 7 and transmitting and receiving data expressed as a waveform are respectively inputted to a central monitoring control panel 10. Various noises of a receiving signal are removed by an averaging processing method to obtain only a significant receiving signal and the correlation between the signal and a transmitting signal is calculated and, further, received signals large in correlation are selected on the basis of a mutually set threshold value. The number of the obstacles 4 and the distance thereof can be judged on the basis of a plurality of groups formed of those selected signals and the output level of a remoter obstacle is small. Next, the control panel 10 calculates a receiving level to which distance correction is added on the basis of the propagation loss data corresponding to the kind of earth and sand excavated presently and calculates the distance up to the obstacle 4 on the basis of the time interval of transmitting and receiving waves and the proparation velocity of sound in the earth.