scholarly journals Rapid jamming avoidance in biosonar

2006 ◽  
Vol 274 (1610) ◽  
pp. 651-660 ◽  
Author(s):  
Erin H Gillam ◽  
Nachum Ulanovsky ◽  
Gary F McCracken
Keyword(s):  
Abrupt Change ◽  
Considerable Effort ◽  
Echolocation Call ◽  
Tadarida Brasiliensis ◽  
Radar Systems ◽  
Spectral Shifts ◽  
Processing Strategies ◽  
Jamming Avoidance ◽  
Sonar Systems ◽  
Behavioural Correlations

The sonar systems of bats and dolphins are in many ways superior to man-made sonar and radar systems, and considerable effort has been devoted to understanding the signal-processing strategies underlying these capabilities. A major feature determining the efficiency of sonar systems is the sensitivity to noise and jamming signals. Previous studies indicated that echolocating bats may adjust their signal structure to avoid jamming (‘jamming avoidance response’; JAR). However, these studies relied on behavioural correlations and not controlled experiments. Here, we provide the first experimental evidence for JAR in bats. We presented bats ( Tadarida brasiliensis ) with ‘playback stimuli’ consisting of recorded echolocation calls at one of six frequencies. The bats exhibited a JAR by shifting their call frequency away from the presented playback frequency. When the approaching bats were challenged by an abrupt change in the playback stimulus, they responded by shifting their call frequencies upwards, away from the playback. Interestingly, even bats initially calling below the playback's frequency shifted their frequencies upwards, ‘jumping’ over the playback frequency. These spectral shifts in the bats' calls occurred often within less than 200 ms, in the first echolocation call emitted after the stimulus switch—suggesting that rapid jamming avoidance is important for the bat.

scholarly journals Influence of call structure on the jamming avoidance response of echolocating bats

2015 ◽  
Vol 97 (1) ◽  
pp. 14-22 ◽  
Author(s):  
Erin H. Gillam ◽  
B. Karina Montero
Keyword(s):  
Avoidance Response ◽  
Structural Characteristics ◽  
Field Studies ◽  
Spectral Structure ◽  
Tadarida Brasiliensis ◽  
Constant Frequency ◽  
Jamming Avoidance Response ◽  
Call Structure ◽  
Dynamic Stimulus ◽  
Jamming Avoidance

Abstract Bats rely heavily on echolocation for orientation and prey detection, hence acoustic signals that interfere with echo reception are problematic. When flying in the presence of other bats, some species adjust their echolocation to avoid frequency overlap with the calls of nearby conspecifics, known as a jamming avoidance response (JAR). One aspect of JAR that has not been thoroughly examined is how the spectral structure of the jamming signal impacts the jamming response. Our objective was to examine how the structural characteristics of an echolocation broadcast impact JAR in free-flying Brazilian free-tailed bats, Tadarida brasiliensis . We created 4 echolocation playbacks that differed only in call shape and frequency modulation. We examined the response of bats when flying in the presence of an unchanging broadcast (static stimulus) and when the playback signal was abruptly switched as the bat approached the speaker (dynamic stimulus). Results revealed that the bandwidth of the interfering signal impacted the strength of the observed JAR, while the presence and/or length of a terminal quasi-constant frequency section in the interfering signal did not. Our results agree with laboratory studies documenting JAR in the presence of white noise, as well as field studies demonstrating extensive variability in the echolocation calls of Brazilian free-tailed bats. We relate these results to previous findings on JAR, including a recent study documenting no JAR in a bat species and suggest further experiments to tease apart the physiological limitations of JAR. Overall, this study provides additional insight into the signal processing capabilities of bats and improves our understanding of how bats are able to orient using sound in a noisy world.

Eavesdropping by bats on the feeding buzzes of conspecifics

2007 ◽  
Vol 85 (7) ◽  
pp. 795-801 ◽  
Author(s):  
E.H. Gillam
Keyword(s):  
Echolocation Call ◽  
Tadarida Brasiliensis ◽  
Echolocation Calls ◽  
Insect Prey ◽  
Bat Activity

Echolocation calls of most bats are emitted at high intensities and subject to eavesdropping by nearby conspecifics. Bats may be especially attentive to “feeding buzz” calls, which are emitted immediately before attack on airborne insects and indicate the potential presence of prey in the nearby area. Although previous work has shown that some species are attracted to feeding buzzes, these studies did not provide a well-controlled test of eavesdropping, as comparisons were made between responses to natural and altered signals (e.g., forward versus backward broadcasts of calls). In this study, I assessed the importance of feeding buzzes by conducting playbacks of controlled echolocation stimuli. I presented free-flying Brazilian free-tailed bats, Tadarida brasiliensis (I. Geoffroy, 1824), with echolocation call sequences in which feeding buzz calls were either present or absent, as well as a silence control. I determined levels of bat activity by counting the number of echolocation calls and bat passes recorded in the presence of each stimulus, and found significantly greater bat activity in response to broadcasts that contained feeding buzzes than to broadcasts without feeding buzzes or to the silence control. These results indicate that bats are especially attentive to conspecific feeding buzz calls and that eavesdropping may allow a bat to more readily locate rich patches of insect prey.

Conspecifics influence call design in the Brazilian free-tailed bat, Tadarida brasiliensis

2004 ◽  
Vol 82 (6) ◽  
pp. 966-971 ◽  
Author(s):  
John M Ratcliffe ◽  
Hannah M. ter Hofstede ◽  
Rafa Avila-Flores ◽  
M Brock Fenton ◽  
Gary F McCracken ◽  
...  
Keyword(s):  
Traffic Control ◽  
Air Traffic Control ◽  
Peak Frequency ◽  
Air Traffic ◽  
Tadarida Brasiliensis ◽  
Jamming Avoidance ◽  
Design Variation ◽  
Virtual Pairs ◽  
Broad Continuum

The Brazilian free-tailed bat, Tadarida brasiliensis (Saint-Hilaire, 1824), uses calls that represent a broad continuum of design variation which is dependent upon habitat and situation, and exhibits characteristic changes in call design as bats close in on airborne targets. Here we demonstrate the influence of conspecifics on call design. We found that the peak frequency used in calls varies more as the number of bats flying in the same space increases (measured from single bats and pairs of bats). We investigated this phenomenon through comparing call-parameter differences found between two bats recorded flying together (actual pairs) with call-parameter differences between two bats each recorded flying alone at different locations that were randomly assigned to one another (virtual pairs). We found that actual pairs of bats used calls which differed in peak frequency more so than did virtual pairs. This result is particularly striking given that these frequency differences were greater between bats in the same space than between bats in two different habitats. We argue that these differences indicate that this species is practicing jamming avoidance, air traffic control, or both.

scholarly journals Editorial for Special Issue “Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms”

2020 ◽  
Vol 12 (8) ◽  
pp. 1272 ◽  
Author(s):  
Stefano Perna ◽  
Francesco Soldovieri ◽  
Moeness Amin
Keyword(s):  
Radar Imaging ◽  
Electromagnetic Modeling ◽  
Ground Vehicles ◽  
Area Of Interest ◽  
Microwave Radar ◽  
Radar Systems ◽  
Processing Strategies ◽  
Effective Signal ◽  
Security Surveillance ◽  
Remotely Sense

Microwave radar imaging plays a key role in several civilian and defense applications, such as security, surveillance, diagnostics and monitoring in civil engineering and cultural heritage, environment observation, with particular emphasis on disasters and crisis management, where it is required to remotely sense the area of interest in a timely, safe and effective way. To address these constraints, a technological opportunity is offered by radar systems mounted onboard smart and flexible platforms, such as ground-based ones, airplanes, helicopters, drones, unmanned aerial and ground vehicles (UAV and UGV). For this reason, radar imaging based on data collected by such platforms is gaining interest in the remote sensing community. However, a full exploitation of smart and flexible radar systems requires the development and use of image formation techniques and reconstruction approaches able to exploit and properly deal with non-conventional data acquisition configurations. The other main issue is related to the need to operate in challenging environments, and still deliver high target detection, localization and tracking. These environments include through the wall imaging, rugged terrain and rough surface/subsurface. In these cases, one seeks mitigation of the adverse effects of clutter and multipath via the implementation of effective signal processing strategies and electromagnetic modeling.

scholarly journals Brazilian free-tailed bats (Tadarida brasiliensis) adjust foraging behaviour in response to migratory moths

2018 ◽  
Vol 96 (6) ◽  
pp. 513-520 ◽  
Author(s):  
J.J. Krauel ◽  
J.M. Ratcliffe ◽  
J.K. Westbrook ◽  
G.F. McCracken
Keyword(s):  
Foraging Behaviour ◽  
Ground Level ◽  
Prey Detection ◽  
Echolocation Call ◽  
Tadarida Brasiliensis ◽  
Call Duration ◽  
Above Ground Level ◽  
Bat Activity ◽  
Moth Migration

Insect migrations represent large movements of resources across a landscape, which are attractive to predators capable of detecting and catching them. Brazilian free-tailed bats (Tadarida brasiliensis (I. Geoffroy, 1824)) consume migratory noctuid moths, which concentrate in favourable winds resulting in aggregations of prey that attract bats hundreds of metres above ground. Although T. brasiliensis are known to feed on these aggregations of migratory moths, changes in their foraging behaviours have not been linked to moth migration events. We investigated possible shifts in the bats’ foraging behaviours when moths are migrating with respect to altitude and moth abundance. We recorded 1104 echolocation call passes of T. brasiliensis at ground level and at altitudes of ∼100 and ∼200 m above ground level. We found proportionally more bat activity at higher altitudes when migratory moth abundance was high. We also found that bats decreased call frequency and bandwidth and increased call duration at higher altitudes and behaved similarly with increasing moth abundance even at ground level. Our results support predictions that bats change foraging behaviour in response to seasonal availability of migratory moths and document alterations in echolocation call parameters that are consistent with optimizing prey detection.

The Nature of Oxide Surfaces: Topographic and Electronic Structure

1993 ◽  
Vol 51 ◽  
pp. 966-967
Author(s):  
Dawn A. Bonnell ◽  
Yong Liang
Keyword(s):  
Transition Metal Oxides ◽  
Electronic Structures ◽  
Recent Progress ◽  
Spatial Localization ◽  
Level Of Detail ◽  
Scanning Tunneling ◽  
Oxide Surfaces ◽  
Tunneling Microscopy ◽  
Considerable Effort ◽  
Complete Understanding

Recent progress in the application of scanning tunneling microscopy (STM) and tunneling spectroscopy (STS) to oxide surfaces has allowed issues of image formation mechanism and spatial resolution limitations to be addressed. As the STM analyses of oxide surfaces continues, it is becoming clear that the geometric and electronic structures of these surfaces are intrinsically complex. Since STM requires conductivity, the oxides in question are transition metal oxides that accommodate aliovalent dopants or nonstoichiometry to produce mobile carriers. To date, considerable effort has been directed toward probing the structures and reactivities of ZnO polar and nonpolar surfaces, TiO2 (110) and (001) surfaces and the SrTiO3 (001) surface, with a view towards integrating these results with the vast amount of previous surface analysis (LEED and photoemission) to build a more complete understanding of these surfaces. However, the spatial localization of the STM/STS provides a level of detail that leads to conclusions somewhat different from those made earlier.

The Mere Exposure Effect and Recognition Depend on the Way You Look! *S. W. and J. D. contributed equally to this study.

2010 ◽  
Vol 57 (3) ◽  
pp. 185-192 ◽  
Author(s):  
Sylvie Willems ◽  
Jonathan Dedonder ◽  
Martial Van der Linden
Keyword(s):  
Differential Effect ◽  
Recognition Task ◽  
Mere Exposure ◽  
Perceptual Processing ◽  
Processing Strategy ◽  
Mere Exposure Effect ◽  
Exposure Effect ◽  
Processing Strategies ◽  
Explicit Recognition ◽  
Analytic Strategy

In line with Whittlesea and Price (2001) , we investigated whether the memory effect measured with an implicit memory paradigm (mere exposure effect) and an explicit recognition task depended on perceptual processing strategies, regardless of whether the task required intentional retrieval. We found that manipulation intended to prompt functional implicit-explicit dissociation no longer had a differential effect when we induced similar perceptual strategies in both tasks. Indeed, the results showed that prompting a nonanalytic strategy ensured performance above chance on both tasks. Conversely, inducing an analytic strategy drastically decreased both explicit and implicit performance. Furthermore, we noted that the nonanalytic strategy involved less extensive gaze scanning than the analytic strategy and that memory effects under this processing strategy were largely independent of gaze movement.

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