| 摘要 |
PROBLEM TO BE SOLVED: To enable high speed processing by shortening the operation time without using the difference in frequency characteristic in suppressing reverberation. SOLUTION: The level of the signal received by a receiving beam is detected for each range, and the average value B of the signal level is calculated in a range except the level projecting by a certain distance from a detected signal level. The conversion maximum level L2 as the upper limit value of the signal level to be level-converted is determined based on the average value B, and the signal level not higher than the conversion maximum level L2, of the detected signal level 1, is converted into a signal level lower than this. COPYRIGHT: (C)2009,JPO&INPIT
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