Flying big brown bats emit a beam with two lobes in the vertical plane

The sonar beam of an echolocating bat forms a spatial window restricting the echo information returned from the environment. Investigating the shape and orientation of the sonar beam produced by a bat as it flies and performs various behavioral tasks may yield insight into the operation of its sonar system. This paper presents recordings of vertical and horizontal cross sections of the sonar beam produced by Eptesicus fuscus (big brown bats) as they fly and pursue prey in a laboratory flight room. In the horizontal plane the sonar beam consists of one large lobe and in the vertical plane the beam consists of two lobes of comparable size oriented frontally and ventrally. In level flight, the bat directs its beam such that the ventral lobe is pointed forward and down toward the ground ahead of its flight path. The bat may utilize the downward directed lobe to measure altitude without the need for vertical head movements.     

A computational sensorimotor model of bat echolocation

A computational sensorimotor model of target capture behavior by the echolocating bat, Eptesicus fuscus, was developed to understand the detection, localization, tracking, and interception of insect prey in a biological sonar system. This model incorporated acoustics, target localization processes, flight aerodynamics, and target capture planning to produce model trajectories replicating those observed in behavioral insect capture trials. Estimates of target range were based on echo delay, azimuth on the relative intensity of the echo at the two ears, and elevation on the spectral pattern of the sonar return in a match/mismatch process. Flapping flight aerodynamics was used to produce realistic model trajectories. Localization in all three spatial dimensions proved necessary to control target tracking and interception for an adequate model of insect capture behavior by echolocating bats. Target capture using maneuvering flight was generally successful when the model's path was controlled by a planning process that made use of an anticipatory internal simulation, while simple homing was successful only for targets directly ahead of the model bat.     

Spatial perception and adaptive sonar behavior

Bat echolocation is a dynamic behavior that allows for real-time adaptations in the timing and spectro-temporal design of sonar signals in response to a particular task and environment. To enable detailed, quantitative analyses of adaptive sonar behavior, echolocation call design was investigated in big brown bats, trained to rest on a stationary platform and track a tethered mealworm that approached from a starting distance of about 170 cm in the presence of a stationary sonar distracter. The distracter was presented at different angular offsets and distances from the bat. The results of this study show that the distance and the angular offset of the distracter influence sonar vocalization parameters of the big brown bat, Eptesicus fuscus. Specifically, the bat adjusted its call duration to the closer of two objects, distracter or insect target, and the magnitude of the adjustment depended on the angular offset of the distracter. In contrast, the bat consistently adjusted its call rate to the distance of the insect, even when this target was positioned behind the distracter. The results hold implications for understanding spatial information processing and perception by echolocation.     

Auditory scene analysis by echolocation in bats.

Echolocating bats transmit ultrasonic vocalizations and use information contained in the reflected sounds to analyze the auditory scene. Auditory scene analysis, a phenomenon that applies broadly to all hearing vertebrates, involves the grouping and segregation of sounds to perceptually organize information about auditory objects. The perceptual organization of sound is influenced by the spectral and temporal characteristics of acoustic signals. In the case of the echolocating bat, its active control over the timing, duration, intensity, and bandwidth of sonar transmissions directly impacts its perception of the auditory objects that comprise the scene. Here, data are presented from perceptual experiments, laboratory insect capture studies, and field recordings of sonar behavior of different bat species, to illustrate principles of importance to auditory scene analysis by echolocation in bats. In the perceptual experiments, FM bats (Eptesicus fuscus) learned to discriminate between systematic and random delay sequences in echo playback sets. The results of these experiments demonstrate that the FM bat can assemble information about echo delay changes over time, a requirement for the analysis of a dynamic auditory scene. Laboratory insect capture experiments examined the vocal production patterns of flying E. fuscus taking tethered insects in a large room. In each trial, the bats consistently produced echolocation signal groups with a relatively stable repetition rate (within 5%). Similar temporal patterning of sonar vocalizations was also observed in the field recordings from E. fuscus, thus suggesting the importance of temporal control of vocal production for perceptually guided behavior. It is hypothesized that a stable sonar signal production rate facilitates the perceptual organization of echoes arriving from objects at different directions and distances as the bat flies through a dynamic auditory scene. Field recordings of E. fuscus, Noctilio albiventris, N. leporinus, Pippistrellus pippistrellus, and Cormura brevirostris revealed that spectral adjustments in sonar signals may also be important to permit tracking of echoes in a complex auditory scene.     

Beam pattern of sparse array for passive sonar

This work aims at sparse array without grating lobe for passive sonar, in order to increase frequency band of the passive sonar and reduce the cost. According to traditional method, the distance between two contiguous sensors in sonar array should be less than the wavelength of highest frequency of the signal; otherwise the grating lobe appears on beam pattern. The paper realizes that the conclusion of the grating lobe emergence it is not fit to the passive sonar due to the sine wave signal model in traditional method, in fact the input of passive sonar is random signal. Prom three aspect of the computer simulation, real passive sonar signal and theory analysis, it is revealed that the grating lobe does not appear on beam pattern when the distance between two contiguous sensors in passive sonar array is longer than wavelength of highest frequency. Whitening of the radiated noise can widen the frequency band, to ensure the beam pattern without the grating lobe. The conclusion of the paper is: if the band of radiated noise is wide enough (broader than 1 octave), that the wavelength of signal can be shorter than the distance between two contiguous sensors in passive sonar without grating lobe.     

Clutter interference along the target range axis in the echolocating bat, Eptesicus fuscus

The sensitivity of the echolocating bat, Eptesicus fuscus, for detection of a sonar target is impaired by the presence of additional targets located at similar distances. At a range of 54 cm, sensitivity to one target declines if the range separation to other targets is smaller than 8-9 cm. This loss of sensitivity is an example of clutter interference along the range axis, created by simultaneous masking of one set of echoes by another. Echoes that fall within an experimentally defined critical range band may sum together to contribute collectively to detection in that band. Echoes falling into separate bands may be detected independently. Acoustic glints within a band appear to be grouped together to be perceived as a single range-extended target of complex structure. Range bands may thus define what a "target" is by specifying within-target and between-target differences in range. The width of critical range bands appears to depend upon target range, with wider bands at greater ranges.     

Off-axis sonar beam pattern of free-ranging finless porpoises measured by a stereo pulse event data logger

The off-axis sonar beam patterns of eight free-ranging finless porpoises were measured using attached data logger systems. The transmitted sound pressure level at each beam angle was calculated from the animal's body angle, the water surface echo level, and the swimming depth. The beam pattern of the off-axis signals between 45 degrees and 115 degrees (where 0 degrees corresponds to the on-axis direction) was nearly constant. The sound pressure level of the off-axis signals reached 162 dB re 1 microPa peak-to-peak. The surface echo level received at the animal was over 140 dB, much higher than the auditory threshold level of small odontocetes. Finless porpoises are estimated to be able to receive the surface echoes of off-axis signals even at 50-m depth. Shallow water systems (less than 50-m depth) are the dominant habitat of both oceanic and freshwater populations of this species. Surface echoes may provide porpoises not only with diving depth information but also with information about surface direction and location of obstacles (including prey items) outside the on-axis sector of the sonar beam.     

An echolocation visualization and interface system for dolphin research

The present study describes the development and testing of a tool for dolphin research. This tool was able to visualize the dolphin echolocation signals as well as function as an acoustically operated "touch screen." The system consisted of a matrix of hydrophones attached to a semitransparent screen, which was lowered in front of an underwater acrylic panel in a dolphin pool. When a dolphin aimed its sonar beam at the screen, the hydrophones measured the received sound pressure levels. These hydrophone signals were then transferred to a computer where they were translated into a video image that corresponds to the dynamic sound pressure variations in the sonar beam and the location of the beam axis. There was a continuous projection of the image back onto the hydrophone matrix screen, giving the dolphin an immediate visual feedback to its sonar output. The system offers a whole new experimental methodology in dolphin research and since it is software-based, many different kinds of scientific questions can be addressed. The results were promising and motivate further development of the system and studies of sonar and cognitive abilities of dolphins.     

Clutter interference and the integration time of echoes in the echolocating bat, Eptesicus fuscus

The ability of the echolocating bat, Eptesicus fuscus, to detect a sonar target is affected by the presence of other targets along the same axis at slightly different ranges. If echoes from one target arrive at about the same delay as echoes from another target, clutter interference occurs and one set of echoes masks the other. Although the bat's sonar emissions and the echoes themselves are 2 to 5 ms long, echoes (of approximately equal sensation levels--around 15 dB SL) only interfere with each other if they arrive within 200 to 400 microseconds of the same arrival time. This figure is an estimate of the integration time of the bat's sonar receiver for echoes. The fine structure of the clutter-interference data reflects the reinforcement and cancellation of echoes according to their time separation. When clutter interference first occurs, the waveforms of test and cluttering echoes already overlap for much of their duration. The masking effect underlying clutter interference appears specifically due to overlap, not between raw echo waveforms, but between the patterns of mechanical excitation created when echoes pass through bandpass filters equivalent to auditory-nerve tuning curves. While the time scale of clutter interference is substantially shorter than the duration of echo waveforms, it still is much longer than the eventual width of a target's range-axis image expressed in terms of echo delay.     

Source level reduction and sonar beam aiming in landing big brown bats (Eptesicus fuscus)

Reduction of echolocation call source levels in bats has previously been studied using set-ups with one microphone. By using a 16 microphone array, sound pressure level (SPL) variations, possibly caused by the scanning movements of the bat, can be excluded and the sonar beam aiming can be studied. During the last two meters of approach flights to a landing platform in a large flight room, five big brown bats aimed sonar beams at the landing site and reduced the source level on average by 7 dB per halving of distance. Considerable variation was found among the five individuals in the amount of source level reduction ranging from 4 to 9 dB per halving of distance. These results are discussed with respect to automatic gain control and intensity compensation and the combination of the two effects. It is argued that the two effects together do not lead to a stable echo level at the cochlea. This excludes a tightly coupled closed loop feed back control system as an explanation for the observed reduction of signal SPL in landing big brown bats.     

Determination of spatial position of multiple targets by ultrasonic binaural method

The binaural technique used in ultrasonic sonars has a higher performance speed in comparison with a mechanically scanned ultrasonic beam, however, in presence of multiple targets meets a very serious ambiguity problem. In this case the number of targets detected exceeds the actual number of targets, e.g., there are additional non-existing targets found. Objective of this research was development of a simulation tool enabling to model multi-channel sonar in the environment with multiple targets of arbitrary geometry and development of robust signal processing procedures, suitable for detection of multiple targets from the data collected using the binaural method. The developed software enables to simulate operation of multi-channel sonar in an environment with multiple reflectors and predict a time history of the reflected signals. The novel algorithm for separation of real targets from the virtual ones in presence of multiple targets has been developed. Performance of the proposed algorithm was investigated both in the simulated and a real environment. The results obtained indicate a significant improvement of the sonar performance.     

Echolocation call intensity and directionality in flying short-tailed fruit bats, Carollia perspicillata (Phyllostomidae)

The directionality of bat echolocation calls defines the width of bats' sonar "view," while call intensity directly influences detection range since adequate sound energy must impinge upon objects to return audible echoes. Both are thus crucial parameters for understanding biosonar signal design. Phyllostomid bats have been classified as low intensity or "whispering bats," but recent data indicate that this designation may be inaccurate. Echolocation beam directionality in phyllostomids has only been measured through electrode brain-stimulation of restrained bats, presumably excluding active beam control via the noseleaf. Here, a 12-microphone array was used to measure echolocation call intensity and beam directionality in the frugivorous phyllostomid, Carollia perspicillata, echolocating in flight. The results showed a considerably narrower beam shape (half-amplitude beam angles of approximately 16° horizontally and 14° vertically) and louder echolocation calls [source levels averaging 99 dB sound pressure level (SPL) root mean square] for C. perspicillata than was found for this species when stationary. This suggests that naturally behaving phyllostomids shape their sound beam to achieve a longer and narrower sonar range than previously thought. C. perspicillata orient and forage in the forest interior and the narrow beam might be adaptive in clutter, by reducing the number and intensity of off-axis echoes.     

Echolocation transmitting beam of the Atlantic bottlenose dolphin

The transmitting beam patterns of echolocation signals emitted by an Atlantic bottlenose dolphin Tursiops truncatus were measured in the vertical and horizontal planes with an array of seven hydrophones. Particular emphasis was placed on accurately verifying the animal's position on a bite-plate/tail-rest stationing device using underwater video monitoring equipment. The major axis of the vertical beam was directed at an angle of 5 degrees above the plane defined by the animal's lips. This angle was 15 degrees lower than previously measured. The vertical beam measurements indicate that the major axis of the transmitting beam is aligned with the major axis of the receiving beam. The horizontal beam was directed forward. The directivity index of 26.5 dB calculated from the beam pattern measured in both planes agreed well with previous calculation of 25.4 dB.     

微弱信号源的和波束定向方法与分裂波束定向方法的性能比较

本文讨论水下辐射噪声源的精确定向问题，给出被动声纳和波束定向与分裂波束定向方法的性能比较。指出在一定信噪比下，分裂波束精确测向技术比和波束定向技术具有较高的定向精度。但是，随着信噪比的下降，两者趋于一致。推导了估计定向精度的分析表达式，给出在直线阵和圆弧阵情况下，延时估计和声源入射角偏差之间的换算公式和数值模拟结果。同时给出数字式声纳用以计算入射信号左波束和右波束数据的互谱来实现分裂波束定向的方法。     

The role of the external ear in vertical sound localization in the free flying bat, Eptesicus fuscus

The role of the external ear in sonar target localization for prey capture was studied by deflecting the tragus of six big brown bats, Eptesicus fuscus. The prey capture performance of the bat dropped significantly in the tragus-deflection condition, compared with baseline, control, and recovery conditions. Target localization error occurred in the tragus-deflected bat, and mainly in elevation. The deflection of the tragus did not abolish the prey capture ability of the bat, which suggests that other cues are available used for prey localization. Adaptive vocal and motor behaviors were also investigated in this study. The bat did not show significant changes in vocal behaviors but modified its flight trajectories in response to the tragus manipulation. The tragus-deflected bat tended to attack the prey item from above and had lower tangential velocity and larger bearing from the side, compared with baseline and recovery conditions. These findings highlight the contribution of the tragus to vertical sound localization in the free-flying big brown bat and demonstrate flight adaptations the bat makes to compensate altered acoustic cues.     

Potential and limitations of nucleon transfer experiments with radioactive beams at REX-ISOLDE

As a tool for studying the structure of nuclei far off stability the technique of γ-ray spectroscopy after low-energy single-nucleon transfer reactions with radioactive nuclear beams in inverse kinematics was investigated. Modules of the MINIBALL germanium array and a thin position-sensitive parallel plate avalanche counter (PPAC) to be employed in future experiments at REX-ISOLDE were used in a test experiment performed with a stable ³⁶S beam on deuteron and ⁹Be targets. It is demonstrated that the Doppler broadening of γ lines detected by the MINIBALL modules is considerably reduced by exploiting their segmentation, and that for beam intensities up to 10⁶ particles/s the PPAC positioned around zero degrees with respect to the beam axis allows not only to significantly reduce the γ background by requiring coincidences with the transfer products but also to control the beam and its intensity by single particle counting. The predicted large neutron pickup cross-sections of neutron-rich light nuclei on ²H and ⁹Be targets at REX-ISOLDE energies of 2.2 MeV ^. A are confirmed. Received: 9 October 2000 / Accepted: 28 January 2001     

附加球面相位引致Airy光束在单轴晶体传输时的两次镜像演化

利用单轴晶体光束传输理论,求得了具有附加球面相位Airy光束在单轴晶体中的传输公式.数值模拟计算结果表明,线偏振附加球面相位Airy光束在晶体中传输时仍为线偏振,但不是传输不变的.粗略地讲,具有附加球面相位的Airy光束在晶体中传输时,近场是传输不变的;而在由晶体寻常与非寻常折射率和球面半径共同确定的两个特定传输距离处,传输光束转换成了取向不同的Gaussian-Airy光束,且高斯依赖的束宽度敏感地与截断因子相关;而当光束依次穿过此两位置时光斑花样先后相对于两横向轴平面做镜像演化,且镜像演化顺序也与晶体寻常和非寻常折射率相对大小密切相关,其总的效果是远场强度花样能恢复原样但花样取向产生了关于对过横平面二、四象限平分平面的镜像演化.这些结果表明,通过恰当选择晶体材料(即折射率)和附加球面相位的半径R,可以调控光束花样的形状、取向及表征各向异性材料的相关性质.     

Dolphin (Tursiops truncatus) echoic angular discrimination: effects of object separation and complexity

A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between arrays of vertically oriented air-filled PVC rods. The blindfolded dolphin was required to station in a submerged hoop 2 radial m from the stimuli and indicate if an array with two rods (S+) was to the right or the left of a single rod (S-). The angular separation between the two rods (thetaw) was held constant within each experiment while the angle between the S+ and the S-stimuli (thetab) varied to produce angular differences (deltatheta= thetab-thetaw) ranging from 0.25 to 4 degrees. In experiment I, thetaw was maintained at 2 degrees and in experiment II, thetaw was maintained at 4 degrees. Resulting 75% correct thresholds (method of constant stimuli) were 1.5 and 0.7 degrees, respectively. The two main findings of this study are: (1) decreasing the number of targets does not aid in localization, and (2) increasing the space between the rods enhances localization. Taken as a whole, the experiments suggest dolphins have a well-developed ability to resolve spatial information through sonar.     

Morphology-induced information transfer in bat sonar

It has been argued that an important part of understanding bat echolocation comes down to understanding the morphology of the bat sound processing apparatus. In this Letter we present a method based on information theory that allows us to assess target localization performance of bat sonar, without a?priori knowledge on the position, size, or shape of the reflecting target. We demonstrate this method using simulated directivity patterns of the frequency-modulated bat Micronycteris microtis. The results of this analysis indicate that the morphology of this bat's sound processing apparatus has evolved to be a compromise between sensitivity and accuracy with the pinnae and the noseleaf playing different roles.     

第五讲新型光纤水听器和矢量水听器

光纤水听器和矢量水听器作为当前水声研究领域最具有代表性的两大技术倍受业界关注。光纤水听器的重要贡献在于，从一个全新的角度出发，试图解决传统的水声传感和声纳数据传输一体化设计和实现的一系列问题，这有助于改善声纳系统的可靠性，并且有可能降低其制造、使用和维护的总成本。矢量水听器则由于其特有的指向性和矢量一相位处理方法，在低频和甚低频水声微弱目标探测方面具有潜在的优势．经过不懈的努力，光纤水听器和矢量水听器系统已经从实验室逐渐进入到工程应用阶段．这些对未来声纳系统的发展会产生相当重要的影响．文章尝试从声纳设计的角度对这两者的技术现状进行简要综述，包括它们各自的物理基础、工作原理、关键技术和应用领域．