Field observations in a maternity colony of Myotis emarginatus (Vespertilionidae) were made during the summers of 1986 and 1987 in southern Germany. The nursery colony consisted of about 90 adult and 30 juvenile bats which roosted in a dimly lit and relatively cool church attic. Telemetry data from six adult M. emarginatus disclosed that some individuals also use secondary day roosts in trees or small buildings located close to their foraging areas. During the night, radiotagged individuals spent most of the time on the wing in forested areas (Fig. 2). Stationary bouts lasted no longer than 63 min. Individual bats returned to the same foraging areas on consecutive nights. All major foraging areas were situated in or at the fringes of forests, at distances as far as 10 km from the nursery roost. During commuting flights to the forests, M. ernarginatus avoided op.en fields and preferred flight paths which offered cover such as orchards, hedges, overhanging foliage along creeks, etc. On the way to the forests, the bats started to forage within buildings, in open spaces where aggregations of insects were present, and around or within the foliage of various types of trees at the level of tree tops or the upper third of the foliage. At these transient foraging areas close to the maternity roost, M. emarginatus displayed flexible foraging strategies: (1) They gleaned prey (mainly flies and spiders) from the substrate, (2) seized insects in aerial pursuit, and (3) occasionally hovered in front of foliage and walls.Our observations confirm the conclusion from morphometric data on the wings that M. emarginatus is a predominantly gleaning bat and contradict the suggestion that it makes only brief flights of short distances. On the contrary, our field data suggest that M. emarginatus spends most of the night on the wing and commutes over distances of at least 10 km.
In Myotis emarginatus, the patterns of echolocation sounds vary with different foraging habitats: In commuting flights the echolocation sounds are linearly frequency modulated sweeps that start at about 100 kHz, terminate at 40 kHz, and have a duration of 1-3 ms. They consist of a loud first harmonic. The second and third harmonics are at least 15 dB fainter than the first one and often undetectable. A distinctly different type of sound is emitted when the bats search for flying insects in open spaces. The sounds are reduced in bandwidth and elongated by a constant frequency component that follows the initial frequency modulated part. Typically, sounds start at about 94 kHz and terminate in a constant frequency component at about 40-45 kHz. The average duration of the constant frequency tail is 2.8 ms; this approximately doubles the length of the pulse, with the longest recorded sound lasting 7.2 ms. When bats are foraging near and within foliage, and gleaning prey from foliage, echolocation sounds are brief (average 1 ms) frequency modulated pulses with a broad bandwidth. The pulses start at about 105 kHz and sweep down to 25 kHz. During gleaning within a building, the frequency range of the sounds is shifted to higher frequencies and extends from 124 to 52 kHz. When the bats forage for aireal insects in a confined area that creates echo-clutter, they emit sounds similar to those used during gleaning within buildings except that sound durations are extended to about 1.8 ms. In each foraging area, the echolocation sounds emitted during the search for and approach to prey are similar in structure. Sound and pause durations are reduced in the approach phase. Irrespective of foraging style and habitat, immediately before capture the bat emits a rapid and stereotyped sequence of ~1 0 echolocation pulses (final buzz). These pulses are brief (0.2-0.5 ms), frequency modulated sounds with a reduced bandwidth. The sounds start at 45 kHz and sweep down to 35-20 kHz. The repetition rate is increased up to 200 pulses/s.
International audienceIn this paper, an ultrasonic technique for imaging nonlinear scatterers, such as cracks, buried in a medium is proposed. The method called amplitude modulation consists of a sequence of three acquisitions for each line of the image. The first acquisition is obtained by transmitting with all elements of the phased array. Next the second and third acquisitions are obtained by transmitting with odd elements only and even elements only, respectively. An image revealing nonlinear scattering from the medium is reconstructed line by line by subtracting the responses measured with second and third acquisitions (odd elements and even elements) from the response obtained with all elements transmitting. The method was implemented on three different conventional multi-channel electronic platforms equipped with different ultrasonic probes (center frequency 3MHz to 5MHz, 64 or 128 elements). A crack (6mm-deep x 24mm-long) in a stainless steel block was investigated. With all probes and multi-channel electronic platforms, higher detection specificity of the crack was obtained with amplitude modulation compared with conventional ultrasound imaging. Image contrast (ratio between crack response amplitude over background amplitude) was increased by 5dB with amplitude modulation compared with conventional ultrasound imaging
A B S T R A C TA new method for industrial radiography is presented to assess image quality objectively. The assessment is performed by a modelled observer developed to interpret radiographic images in order to rate the detectability of structural defects. For the purpose of qualifying radiographic NDE procedures, computational tools simulate the image, but should additionally automatically assess the associated image quality instead of relying on human interpretation. The Channelized Hotelling Model Observer (CHO) approach, originally developed for medical imaging, is here developed for industrial NDE applications to measure objectively the defect's detectability. A validation study based on a comparison of the model's efficiency of observing circular and elongated flaws shows that the CHO outperforms other detectability models used by industry. Furthermore, the model's reliability was verified by comparing it to psychophysical data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.