It is usually expressed by the decibels which is the straight beam probe tested the second time subtracting from the first bottom surfaceecho amplitude.
通常用纵波直探头测试的第几次与第一次底面回波幅度所差的分贝数表示。
2
Such surfaces reflect most of the bats' echolocation energy away from it, but some energy hits the surface perpendicularly, sending an echo back directly beneath the bat.
这样的平面反射了大部分蝙蝠的声波，但是有一部分能量垂直撞击到表面上，声波回传至蝙蝠。
3
Hotel lobby entrance even corridor area top surface is a circular arc shape, and the lobby reception desk top arc surface of the hand in photograph echo, gourd shape, take money.