Doppler-shift compensation in the Taiwanese leaf-nosed bat (Hipposideros terasensis) recorded with a telemetry microphone system during flight

Biosonar behavior was examined in Taiwanese leaf-nosed bats (Hipposideros terasensis; CF-FM bats) during flight. Echolocation sounds were recorded using a telemetry microphone mounted on the bat's head. Flight speed and three-dimensional trajectory of the bat were reconstructed from images taken with a dual high-speed video camera system. Bats were observed to change the intensity and emission rate of pulses depending on the distance from the landing site. Frequencies of the dominant second harmonic constant frequency component (CF2) of calls estimated from the bats' flight speed agreed strongly with observed values. Taiwanese leaf-nosed bats changed CF2 frequencies depending on flight speed, which caused the CF2 frequencies of the Doppler-shifted echoes to remain constant. Pulse frequencies were also estimated using echoes returning directly ahead of the bat and from its sides for two different flight conditions: landing and U-turn. Bats in flight may periodically alter their attended angles from the front to the side when emitting echolocation pulses.     

Echolocation and flight strategy of Japanese house bats during natural foraging, revealed by a microphone array system

Using only a microphone array system, echolocation pulses and three-dimensional flight paths in the frequency-modulated bat, Pipistrellus abramus, during natural foraging, were simultaneously examined. During the search phase, the inter-pulse interval, pulse duration, and moving distance of the bat between successive emissions were relatively constant at around 89.5 ± 18.7 ms, 6.90 ± 1.31 ms, and 0.50 ± 0.20 m, respectively. The bats started to decrease these acoustical parameters within 2-3 m of the prey capture point. For every emission along a flight path, the distance between a bat and its prey capture point was calculated as both direct distance to capture (DDC), which corresponded to the target distance, and flight distance to capture (FDC) along the flight path. The DDC matched the FDC after the start of the approach phase, indicating that foraging bats followed a straight-ahead path to the target. In addition, the duration of the quasi-constant frequency component of emitted pulses was slightly extended just before the convergence of the DDC with the FDC. These findings suggest that the bats confirm the presence of target prey by extending the duration of the pulse and then select a straight-ahead approach by forecasting the movement of the prey.     

Accuracy of distance measurement in the bat Eptesicus fuscus: theoretical aspects and computer simulations

Behavioral experiments of Simmons [J. Acoust. Soc. Am. 54, 157-173 (1973) and Science 204, 1336-1338 (1979)] on the ranging accuracy in the bat Eptesicus fuscus have led to far-reaching postulates on the existence of optimal and phase-conserving processing mechanisms in the bat. In this paper, the results of computer simulations of these experiments are presented. Two receiver types are investigated: the fully coherent cross-correlation receiver and the cross-correlation receiver with envelope processing (semicoherent). It is shown that Simmons' experiments cannot be treated as a simple estimation of distance, but require at least two (range difference experiment; see Simmons, 1973) or four (range jitter experiment; see Simmons, 1979) echolocation sounds for one decision. The performance of the bat in both experiments is much worse than predicted for a coherent and a semicoherent receiver type. The bat's accuracy in Simmons' range difference experiment is at least 18 dB worse than predicted for an optimal receiver. The results of the jitter experiment cannot be interpreted in a simple way as proof that bats are able to evaluate phase information as in a fully coherent cross-correlation receiver.     

Range discrimination by big brown bats (Eptesicus fuscus) using altered model echoes: implications for signal processing

The sonar emissions of two big brown bats (Eptesicus fuscus) were modeled to create a "normal" echolocation signal for each bat which was then used as an artificial echo to synthesize a phantom target. The bat's task was to indicate which of two phantom targets (presented singly) was the "near" target and which the "far" target. Threshold range discrimination at a nominal target distance of 80 cm was about 0.6 cm for both bats. The normal signal was then modified to change the relative energy in each harmonic, the signal duration, the curvature of the frequency sweep, the absolute frequency, the phase of the second and third harmonics relative to the first, or the Doppler shift of the signal. To determine which modifications affected ranging performance, the altered models were used in tests of range discrimination that were interleaved on a day-to-day basis with tests using the normal model. Of the 12 modifications tested, only those changing the curvature of the frequency sweep affected performance. This result appears not to be predicted by current models of echo processing in FM bats. Eptesicus may be able to compensate for certain types of distortions of a returning echo, an ability possibly related to Doppler tolerance or to the characteristics of the natural variation in a bat's emissions.     

无人机GPS接收机超宽谱电磁脉冲效应与试验分析

基于无人机GPS接收机干扰容限,分析了GPS超宽谱强电磁脉冲效应机理,开展了高重复频率超宽谱电磁脉冲干扰机对典型微型无人机的效应试验,测试分析了在不同位置、不同高度、不同状态、不同飞行模式下无人机GPS接收机的高重复频率超宽谱电磁脉冲干扰效应。试验结果表明,高重复频率超宽谱电磁脉冲对无人机GPS、图传系统、下视传感器均有不同程度的干扰作用,导致无人机无法正常起飞、失控等异常现象,验证了高重复频率超宽谱电磁脉冲干扰GPS接收机的可行性。     

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.     

Range estimation by echolocation in the bat Eptesicus fuscus: trading of phase versus time cues

Bats of the species Eptesicus fuscus have been trained to discriminate a stationary simulated target from a target with a virtual distance that jitters from sound to sound. Similar to Simmons [Science 207, 1336-1338 (1979)], a jitter-detection threshold below 1 microsecond was found. However, Simmons' decreased performance at a time delay jitter of 30 microseconds could not be replicated, a critical feature used to postulate the idea that bats employ a coherent cross-correlation receiver for ranging. Such a receiver uses all phase information in the signal for delay estimation and therefore will be biased by phase manipulations. To test for such a bias, a phase jitter of +/- 45 degrees and a time jitter in the echo were overlaid. It was not found that there was a combination of both where their effects canceled. Full phase information is thus not used in delay estimation. However, bats were able to detect a pure phase jitter, e.g., polarity inversion of the signal. Bats could also detect phase jitter in the presence of randomized time jitter and vice versa. Phase jitter and time jitter, therefore, are separable features for a bat. The underlying physiological mechanism is not clear.     

Wind turbines and bat mortality: Doppler shift profiles and ultrasonic bat-like pulse reflection from moving turbine blades

Bat mortality resulting from actual or near-collision with operational wind turbine rotors is a phenomenon that is widespread but not well understood. Because bats rely on information contained in high-frequency echoes to determine the nature and movement of a target, it is important to consider how ultrasonic pulses similar to those used by bats for echolocation may be interacting with operational turbine rotor blades. By assessing the characteristics of reflected ultrasonic echoes, moving turbine blades operating under low wind speed conditions (<6 m s(-1)) were found to produce distinct Doppler shift profiles at different angles to the rotor. Frequency shifts of up to ±700-800 Hz were produced, which may not be perceptible by some bat species. Monte Carlo simulation of bat-like sampling by echolocation revealed that over 50 rotor echoes could be required by species such as Pipistrellus pipistrellus for accurate interpretation of blade movement, which may not be achieved in the bat's approach time-window. In summary, it was found that echoes returned from moving blades had features which could render them attractive to bats or which might make it difficult for the bat to accurately detect and locate blades in sufficient time to avoid a collision.     

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.     

转动圆柱和圆锥的激光距离多普勒像分析模型

提出了一个新的转动圆柱和圆锥的激光距离多普勒像分析模型.该模型能分析圆柱和圆锥的几何参量、表面材料、姿态和脉冲宽度对这两种目标的距离多普勒像的影响,并能退化到平面波下的圆柱和圆锥的多普勒谱分析模型.数值分析了几何参量、表面材料、姿态和脉冲宽度对距离多普勒像的影响.理论和测量相结合,这个分析模型能用来进行圆柱和圆锥参量的识别.这个分析模型的解析表达式对于多普勒速度计和激光雷达应用有着重要的意义. 关键词： 光散射 双向反射分布函数 距离多普勒 目标识别     

Humidity and aggregate content correction factors for air-coupled ultrasonic evaluation of concrete

This paper describes the use of non-contact ultrasound for the evaluation of concrete. Micromachined capacitance transducers are used to transmit ultrasonic longitudinal chirp signals through concrete samples using air as the coupling medium, and a pulse compression technique is then employed for measurement of time of flight through the sample. The effect on the ultrasonic wave speed of storing concrete samples, made with the same water/cement ratio, at different humidity levels is investigated. It is shown that there is a correlation between humidity and speed of sound, allowing a correction factor for humidity to be derived. A strong positive linear correlation between aggregate content and speed of sound was then observed; there was no obvious correlation between compressive strength and speed of sound. The results from the non-contact system are compared with that from a contact system, and conclusions drawn concerning coupling of energy into the samples.     

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.     

High-frequency pulsed laser diode application in multi-component laser Doppler anemometry

High-frequency pulsed AlGaAs semiconductor lasers with pulse durations in the nanosecond range show a distinctive enhancement of the time-averaged optical output power compared with continuous-wave mode operation. Hence, the signal-to-noise ratio is drastically increased in connection with fast Si-Avalanche photodetectors that show a maximum spectral sensitivity in the emission range of AlGaAs lasers. The emission behaviour and the application of sequential and phase- synchronized pulsed laser diodes in a multi-component laser Doppler anemometer with only one receiver, one signal processing chain and identical wavelength for all components, are outlined.     

Stabilization of perceived echo amplitudes in echolocating bats. II. The acoustic behavior of the big brown bat, Eptesicus fuscus, when tracking moving prey.

Big brown bats, Eptesicus fuscus, can be trained to use echolocation to track a small microphone with a food reward attached when it is moved rapidly toward them. This situation mimics prey interception in the wild while allowing very precise recording of the sonar pulses emitted during tracking behavior. The results show that E. fuscus intensity compensates, reducing emitted intensity by 6 dB per halving of target range so that the intensity incident upon the target is constant and echo intensity increases by 6 dB per halving of range. This increase in echo intensity is effectively canceled by the reduction in auditory sensitivity due to automatic gain control (AGC) of 6 to 7 dB per halving of range. Intensity compensation behavior and AGC therefore form a dual-component, symmetrical system that stabilizes perceived echo amplitudes during target approach. The same system is present in the fishing bat, Noctilio leporinus, suggesting that it may be widespread in echolocating bats. Correlation analysis shows that, despite large changes in the duration of the pulses emitted by E. fuscus during an approach, the pulse frequency structure is such that the spatial image of the target perceived along the range axis is highly stable. Pulse duration is not reduced in the manner theoretically necessary to eliminate potential echo distortion effects due to AGC, but is reduced in such a way that this distortion is insignificant. During the terminal buzz, a high degree of temporal overlap (relative to pulse duration) occurs between emitted pulse and returning echo.     

Echo-intensity compensation in echolocating bats (Pipistrellus abramus) during flight measured by a telemetry microphone

An onboard microphone (Telemike) was developed to examine changes in the basic characteristics of echolocation sounds of small frequency-modulated echolocating bats, Pipistrellus abramus. Using a dual high-speed video camera system, spatiotemporal observations of echolocation characteristics were conducted on bats during a landing flight task in the laboratory. The Telemike allowed us to observe emitted pulses and returning echoes to which the flying bats listened during flight, and the acoustic parameters could be precisely measured without traditional problems such as the directional properties of the recording microphone and the emitted pulse, or traveling loss of the sound in the air. Pulse intensity in bats intending to land exhibited a marked decrease by 30 dB within 2 m of the target wall, and the reduction rate was approximately 6.5 dB per halving of distance. The intensity of echoes returning from the target wall indicated a nearly constant intensity (-42.6 +/- 5.5 dB weaker than the pulse emitted in search phase) within a target distance of 2 m. These findings provide direct evidence that bats adjust pulse intensity to compensate for changes in echo intensity to maintain a constant intensity of the echo returned from the approaching target at an optimal range.     

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.     

An overview of the laser ranging method of space laser altimeter

Space laser altimeter is an active remote sensing instrument to measure topographic map of Earth, Moon and planetary. The space laser altimeter determines the range between the instrument and laser footprint by measuring round trip time of laser pulse. The return pulse reflected from ground surface is gathered by the receiver of space laser altimeter, the pulsewidth and amplitude of which are changeable with the variability of the ground relief. Meantime, several kinds of noise overlapped on the return pulse signal affect its signal-to-noise ratio. To eliminate the influence of these factors that cause range walk and range uncertainty, the reliable laser ranging methods need to be implemented to obtain high-precision range results. Based on typical space laser altimeters in the past few decades, various ranging methods are expounded in detail according to the operational principle of instruments and timing method. By illustrating the concrete procedure of determining time of flight of laser pulse, this overview provides the comparison of the employed technologies in previous and undergoing research programs and prospect innovative technology for space laser altimeters in future.     

The sonar beam pattern of a flying bat as it tracks tethered insects

This paper describes measurements of the sonar beam pattern of flying echolocating bats, Eptesicus fuscus, performing various insect capture tasks in a large laboratory flight room. The beam pattern is deduced using the signal intensity across a linear array of microphones. The positions of the bat and insect prey are obtained by stereoscopic reconstruction from two camera views. Results are reported in the form of beam-pattern plots and estimated direction of the beam axis. The bat centers its beam axis on the selected target with a standard deviation (sigma) of 3 degrees. The experimental error is +/- 1.4 degrees. Trials conducted with two targets show that the bat consistently tracks one of the targets with its beam. These findings suggest that the axis of the bat sonar beam is a good index of selective tracking of targets, and in this respect is analogous to gaze in predominantly visual animals.     

LOW COHERENCE PULSED DOPPLER LIDAR WITH AMPLIFIED REFERENCE BEAM STORAGE

In this paper, we have successfully developed a new low coherence pulsed Doppler lidar concept for wind speed measurements, in which a pulsed laser is used as the source for measurement and reference beam. A fraction of the transmitted pulse is stored in a fiber optic ring resonator with a path length longer than the pulse. The output of the resonator is a pulse train that is used as the reference beam and can be mixed with the Doppler shifted measurement signal. Because this reference has traveled a distance equivalent to the measurement beam’s path length, low coherence sources can be used. Inserting an erbium-doped fiber amplifier into the resonator ensures that the stored pulses do not decay in amplitude. Careful control of gain and amplified spontaneous emission is required to prevent laser oscillation while maintaining sufficient gain for the signal. Experiments prove that 16 reference pulses of sufficient amplitude and stability can be generated. Computer simulations suggest that 70 pulses should be achievable, which would be equivalent to a Doppler lidar measurement range of 2,550 m.     

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.