FM echolocating bats shift frequencies to avoid broadcast-echo ambiguity in clutter
FM echolocating bats shift frequencies to avoid broadcast-echo ambiguity in clutter
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DOI：
10.1073/pnas.1000429107
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发表时间：
2010-04-13
影响因子：
11.1
通讯作者：
Riquimaroux, Hiroshi
中科院分区：
文献类型：
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作者：
Hiryu, Shizuko;Bates, Mary E.;Riquimaroux, Hiroshi
声纳广播之后是来自不同距离物体的不同延迟的回声。当广播在杂乱的环境中快速发射时，来自连续广播的回声流重叠，并导致将回声与相应广播匹配的歧义。为了识别在杂乱中对模糊的反应，会发出多种调频声音的回声定位蝙蝠被训练飞向密集的、延伸的障碍物阵列(多排垂直悬挂的链条)，而蝙蝠发出的声纳声音是用蝙蝠携带的微型无线电麦克风记录的。飞行路线是根据热红外视频记录重建的。连续的一排排链条深度超过6米，因此每次广播后都会有一系列来自多排链条的回声，持续时间长达40ms。蝙蝠以较短(20-40毫秒)的脉冲间隔(IPI)和较长的IPI(>；50毫秒)交替发出声音。对于许多短IPI，第一个广播的回声流在第二个广播发出时仍在到达。这种重叠导致了将回声与广播匹配的模棱两可。蝙蝠将每个频闪组中第一个声音的频率向上移动，第二个声音的频率向下移动3-6 khz。当重叠和歧义停止时，频移也停止了。与75-80 kHz宽的总广播频段相比，频差较小，但回声的谐波结构增强了频谱的差异。蝙蝠可以使用回声与广播的时频比较，将回声分配给相应的广播，从而避免模棱两可。
Sonar broadcasts are followed by echoes at different delays from objects at different distances. When broadcasts are emitted rapidly in cluttered surroundings, echo streams from successive broadcasts overlap and cause ambiguity in matching echoes to corresponding broadcasts. To identify reactions to ambiguity in clutter, echolocating bats that emit multiple-harmonic FM sounds were trained to fly into a dense, extended array of obstacles (multiple rows of vertically hanging chains) while the sonar sounds the bat emitted were recorded with a miniature radio microphone carried by the bat. Flight paths were reconstructed from thermal-infrared video recordings. Successive rows of chains extended more than 6 m in depth, so each broadcast was followed by a series of echoes from multiple rows of chains that lasted up to 40 ms. Bats emitted sounds in pairs ("strobe groups") at short (20-40 ms) interpulse intervals (IPIs) alternating with longer IPIs (>50 ms). For many short IPIs, the stream of echoes from the first broadcast was still arriving when the second broadcast was emitted. This overlap caused ambiguity about matching echoes with broadcasts. Bats shifted frequencies of the first sound in each strobe group upward and the second sound downward by 3-6 kHz. When overlap and ambiguity ceased, frequency shifts ceased also. Frequency differences were small compared with the total broadcast band, which was 75-80 kHz wide, but the harmonic structure of echoes enhances the differences in spectrograms. Bats could use time-frequency comparisons of echoes with broadcasts to assign echoes to the corresponding broadcasts and thus avoid ambiguity.