Broadband Recording Research Articles

A characterization of Guyana dolphin (Sotalia guianensis) whistles from Costa Rica: The importance of broadband recording systems

Knowledge of the whistle structure in Guyana dolphins comes mostly from Brazilian populations where recordings have been made using limited bandwidth systems (18 and 24 kHz). In Brazil, Guyana dolphin whistle frequency span is 1.34-23.89 kHz, but authors have suggested that limits of their recording system may underestimate frequency span. Whistles of Guyana dolphins from Costa Rica were studied using a broadband recording system. How bandwidth limitations affect the understanding of whistle structure and species classification between sympatric dolphin species was evaluated. In addition, whistles were compared to Brazilian populations. Guyana dolphin whistle frequency span was 1.38 up to 48.40 kHz, greater than previously reported. Bandwidth limitations explained 89% of the whistle variation between studies, and increase in bandwidth improved the whistle classification of Guyana dolphins. Whistle duration and minimum frequency were the most important variables in dolphin species classification. Finally, after accounting for differences in recording systems, Costa Rican Guyana dolphins whistled with significantly higher frequency than Brazilian populations, providing evidence for a postulated increase in frequency from south to north. The study concludes that equipment with an upper frequency limit of at least 50 kHz (150 kHz for harmonics) is required to capture the entire whistle repertoire of the Guyana dolphin.

Burst pulses produced by free‐ranging bottlenose dolphins in Tampa Bay, Florida and Mississippi Sound, Mississippi

Investigations of the bottlenose dolphin's acoustic repertoire have mainly focused on whistles and echolocation clicks. However, despite their widespread occurrence, burst pulses have not received much attention. The primary function of burst pulses remains unknown and a comparative analysis can be used to advance our knowledge of the function of burst pulses. We recorded the acoustic repertoires of free‐ranging bottlenose dolphins in the Tampa Bay and Mississippi Sound areas using broadband recording equipment. The two habitats differ in their environmental features, including water temperature, ambient noise levels and water turbidity. Our preliminary data show that several acoustic parameters such as peak frequency and center frequency of burst pulses differ among habitats. We also report other acoustic parameters, such as the number of clicks, inter‐click interval, 3‐dB and rms bandwidth. In our ongoing study, we will examine relationships between environmental features of the habitats and the acoustic characteristics of burst pulses.

The freshwater dolphin Inia geoffrensis geoffrensis produces high frequency whistles

Because whistles are most commonly associated with social delphinids, they have been largely overlooked, ignored, or presumed absent, in solitary freshwater dolphin species. Whistle production in the freshwater dolphin, the boto (Inia geoffrensis geoffrensis), has been controversial. Because of its sympatry with tucuxi dolphins (Sotalia fluviatilis), a whistling species, some presume tucuxi whistles might have been erroneously assigned to the boto. Using a broadband recording system, we recorded over 100 whistles from boto dolphins in the Yasunf River, Ecuador, where the tucuxi dolphins are absent. Our results therefore provide conclusive evidence for whistle production in Inia geoffrensis geoffrensis. Furthermore, boto whistles are significantly different from tucuxi whistles recorded in nearby rivers. The Ecuadorian boto whistle has a significantly greater frequency range (5.30-48.10 kHz) than previously reported in other populations (Peru and Colombia) that were recorded with more bandwidth limited equipment. In addition, the top frequency and the range are greater than in any other toothed whale species recorded to date. Whistle production was higher during resting activities, alone or in the presence of other animals. The confirmation of whistles in the boto has important implications for the evolution of whistles in Cetacea and their association with sociality.

Thunderstorm activity dynamics during hurricanes

Results of studying the thunderstorm activity dynamics during the Pacific hurricanes in August and October 2001, using broadband recording of the time forms of atmospherics on Kamchatka, have been presented. The number of atmospherics per minute at simultaneously determined azimuths of their sources has been used as an example of thunderstorm activity. An analysis of data processing results has indicated (a) in the absence of hurricanes, the maximal atmospheric flux level (10 ± 4 pulse/min) was observed at night, and the daylight level was 3 ± 1 pulse/min; (b) thunderstorm activity increases at the stage of tropical depression regardless of depression development into hurricane; in this case the flux of atmospherics can increase to 250 pulse/min at night and can be widely variable (5–100 pulse/min) in daytime; (c) in the sate of hurricane maturity, the thunderstorm activity level is not higher than the background level. It has been indicated that IGWs in the Earth’s atmosphere and the lower ionosphere are caused by lightning strokes accompanied by shock waves during expansion of the lighning channel. The results obtained are of interest in studying anomalous effects in the natural electromagnetic field in the VLF band during increased seismic activity on Kamchatka.

The millimeter wave spectrum of cis-HCOOH in the ground state and in the v9=1 and v7=1 excited vibrational states, and cis-H 13COOH in the ground state

A broadband recording of the millimeter/submillimeter wave spectrum of formic acid heated to 170 °C with the FASSST spectrometer has yielded a multitude of rotational transitions of HCOOH in excited vibrational states. These include transitions of the cis-rotamer, the analysis of which is reported here. The data for the ground state could be significantly extended (546 lines), and the first information on rotational structure in vibrationally excited cis-HCOOH in the v 9=1 and v 7=1 states was obtained. Finally, transitions of cis-H 13COOH in the ground state were also observed. The rotational parameters resulting from the analysis of each of these spectra are reported, together with an initial determination of the Coriolis coupling parameters for the 7 1/9 1resonance interaction, an experimental force field calculation and a new structure determination.

Azimuthal anisotropy in the D″ layer beneath the Caribbean

The lowermost mantle beneath Central America has anisotropic seismic velocity structure manifested in shear wave splitting of signals from South American earthquakes recorded at North American broadband recording stations. Prior studies of deep mantle anisotropy in this region have characterized the structure as having vertical transverse isotropy (VTI), which is sufficient to explain a general trend of early tangential (SH) component arrivals. However, VTI models cannot quantitatively match systematic waveform complexities in the onset of many of the shear waves that graze this region. After accounting for splitting effects of upper mantle anisotropy beneath the recording stations, we model the corrected waveform data using full wave theory for mantle velocity models with an anisotropic D″ layer. This is the first attempt to quantitatively model a large data set including azimuthal anisotropy in D″. The models include transverse isotropy with either a vertical or tilted symmetry axis, the latter resulting in azimuthal anisotropy. For some initial shear wave polarizations, tilted transverse isotropy (TTI) produces small, reversed polarity arrivals on the SV components at the arrival time of SH, consistent with the data. Geographical variations in the azimuth of the TTI symmetry axis are indicated by the data. The lack of azimuthal coverage prevents unique resolution of the TTI orientation and also precludes distinguishing between TTI and other azimuthal anisotropy structures such as that predicted for lattice preferred orientation of minerals. Nonetheless, our modeling demonstrates the need for laterally varying anisotropic structure of more complex form than VTI for this region.

Broad-band transient recording and characterization of acoustic emission events in composite laminates

Acoustic emission (AE) transients due to different kinds of microdamage, such as matrix cracking, fiber breakage and local delaminations, have been recorded in glass/epoxy composite laminates. Different stacking sequences, [0°, 90° 2] S , [90° 2, 0°] S , [+45°, −45°] S and [0° 4], were used in order to trigger different crack mechanisms during tensile testing. The AE transients were recorded as functions of time by the use of broad-band AE transducers. In the experiments, it was observed that different types of cracks generated acoustic emission signals varying in amplitude, duration time and frequency content. It was also seen that the same type of crack produced signals with different characteristics depending on the layer in which the crack appeared and its orientation compared to the location of the transducer. The majority of signals from the tests could be divided into a few main groups. Typical signals and characteristics representing these groups are presented in the paper. The observations show that there is a potential in future development of quantitative methods for identification of damage development in composite laminates.

Higher degree moment tensor inversion of Mani earthquake using far-field broadband recording

Breakthrough point source model, extended earthquake source model is used to calculate more seismic source parameters in this paper. We express seismic source using higher degree moment tensors, to reduce a large number terms originally presenting in high degree moment tensor representation, Haskell rupture model is used. We inverted the source parameters of Mani earthquake in Tibet using broad-band body wave of 32 stations of Global Seismograph Network (GSN), the results show that it is a strike-slip fault, rupture direction is 75°, rupture duration is 19 s, the fault plan is φ=77°, δ=88°, λ=0°, the auxiliary plane is φ=347°, δ=90°, λ=178°, and the fault dimension is 47 km×28 km. These results will give new quantitative data for earth dynamics and have practical meaning for seismic source tomography research.

Broadband recording of Strombolian explosions and associated very‐long‐period seismic signals on Mount Erebus Volcano, Ross Island, Antarctica

In December 1996 and January 1997, broadband seismometers were deployed on the summit plateau of Mount Erebus at radial distances of 0.7, 1.4 and 1.9 km from the central crater and lava lake. Strombolian explosions at Erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 Hz. New observations document significant energy with spectral peaks as grave as 20 s. Nearly identical very‐long‐period (VLP) signals begin ∼1.5 s prior to explosions, have dilatational onsets and persist for up to 150 s. Similar VLP waveforms were recorded at all three stations, indicating that the seismograms are essentially source‐dominated. Particle motions suggest an initial depth for the VLP source of up to several hundred meters, migrating deeper in the course of ∼15 s. Such explosion‐associated VLP signals may indicate a nondestructive lossy resonance or nonlinear fluid‐flow excitation within the shallow magmatic system.

An implosive seismoacoustic source for seismic experiments on the ocean floor

Bottom shots have been used for a number of years in seismic studies on the ocean floor. Most experiments utilized explosives as the energy source, though researchers have recognized the usefulness of collapsing water voids to produce seismoacoustic signals. Implosive sources, however, suffered generally from a lack of control of source depth. We present a new experimental tool, called SEEBOSEIS, to carry out seismic experiments on the seafloor utilizing hollow glass spheres as controlled implosive sources. The source is a 10-inch BENTHOS float with penetrator. Inside the sphere we place a small explosive charge (two detonators) to destabilize the glass wall. The time of detonation is controlled by an external shooting device. Test measurements on the Ninetyeast Ridge, Indian Ocean, show that the implosive sources can be used in seismic refraction experiments to image the subbottom P-wave velocity structure in detail beyond that possible with traditional marine seismic techniques. Additionally, the implosions permit the efficient generation of dispersed Scholte waves, revealing upper crustal S-wave velocities. The frequency band of seismic energy ranges from less than 1 Hz for Scholte modes up to 1000 Hz for diving P-waves. Therefore, broadband recording units with sampling rates >2000 Hz are recommended to sample the entire wave field radiated by implosive sources.

Broadband characteristics of spinner dolphin (Stenella longirostris) social acoustic signals

A predisposition generally exists among delphinids for hearing high-frequency signals, raising the question: How much do dolphins actually use the ultrasonic range for social signaling? To answer this question, a low-budget, portable broadband recording system was developed to collect whistles and burst pulses from a population of Hawaiian spinner dolphins resident off the leeward coast of Oahu, Hawaii. This system employs a PCMCIA A/D converter to digitize signals directly into a laptop computer and has a maximum upper frequency limit of 140 kHz. Signals collected using this system reveal that spinner dolphins use the ultrasonic range extensively. Although the fundamental frequencies of whistles tend to be restricted below approximately 23 kHz, strong harmonics are often clearly visible up to 70 kHz. Even more high frequency in nature are the burst pulses. These signals often have little or no energy below 20 kHz and can extend beyond the recording limits of the system. Furthermore, high-frequency burst pulses are pervasive in the acoustic output of spinner dolphins, making it reasonable to assume that the ultrasonic range may, in fact, be important not only for echolocation, but also social signaling purposes.

Broadband recording of social acoustic signals of the Hawaiian spinner and spotted dolphins

The social and communication signals of several species of free-ranging delphinids have been analyzed and characterized by a number of workers over the past 3 decades. Most of the past works have used bandlimited recording equipment and have focused on the sonic components of the signals. Therefore, most discussions of delphinid whistles and nonecholocation pulsed signals have been limited almost exclusively to below approximately 20 kHz. A technique has been developed that allows one to collect high-fidelity recordings of signals up to 55 kHz in frequency. By digitizing signals directly into a laptop computer through a PCMCIA A/D converter, the sonic and ultrasonic components of the whistles and burst pulses of two populations of Hawaiian spinner and spotted dolphins (Stenella longirostris and S. attenuata) resident along the leeward coast of Oahu, Hawaii are being studied. Preliminary results show that the ultrasonic range above 20 kHz is rich with whistle harmonics and components of pulsed signals.

Towards the identification of later seismic phases

SUMMARY The location of seismic events can be improved if accurate picks can be assigned for later seismic phases, which requires both the detection of an arrival and the recognition of its character. Such phase identifications are particularly valuable if they can be provided in real-time as the seismic disturbance passes across a broad-band seismic recording station. A simple but promising scheme for characterizing arrivals can be constructed by analysing the energy content of the seismic trace as a function of time. Such an approach can be used to detect arrivals by using a method comparing the short-term average energy to a long-term average, with averaging windows that are adaptive to the local frequency of the seismic disturbance. The phase detector can be tuned to different classes of arrivals by utilizing three-component records. By comparing the energy on the vertical component of motion to that in the horizontal plane, it is possible to start to separate P and S arrivals. Phase assignments can be refined by the use of adaptive filtering and by including polarization information. With an estimate of the azimuth of propagation it is possible to use approximate projection methods which attempt to compensate for the influence of the free surface, since the surface corrections are not a strong function of slowness for teleseismic arrivals. By this means, an instantaneous estimate can be made of the relative contributions of P, SVand SH arrivals which can be very helpful in determining the phase assignment for a particular arrival.

Permeability measurement on ferromagnetic thin films from 50 MHz up to 18 GHz

The needs for permeability measurements on ferromagnetic materials at high frequencies are driven by the development of broad-band recording systems. However, measurements above 500 MHz on ferromagnetic films are difficult. Wide band permeability measurements are reported only up to a few GHz. Measurements at higher frequencies can be performed using resonant cavities, as it is done in ferromagnetic resonance, but only at discrete frequencies. In contrast, we present a technique for measuring high frequency permeability of ferromagnetic films over a wide band. It works in a frequency range (50 MHz to 18 GHz or higher) that allows direct observation of the gyromagnetic resonance even on non-saturated samples, and can yield permeability in different directions for anisotropic films. In our technique a surface of about 0.5 dm 2 of the ferromagnetic material has to be wound to obtain proper sample geometry. As a consequence, our technique is restricted to coatings deposited on thin flexible substrates and to thin self supported ribbons produced by rapid solidification. Comparison with another measurement technique working up to 3 GHz, and with calculated gyromagnetic response, yield a satisfactory agreement. The limitations of our method are discussed. Spectroscopic permeability measurements are reported for several alloys.

Shear wave splitting in refracted waves returned from the upper mantle transition zone beneath northern Australia

The broadband recording site at Warramunga (WRA) in the Northern Territory of Australia provides good coverage of seismic wave propagation through the upper mantle for sources in the earthquake belt through Indonesia and New Guinea. S waves recorded on the radial (SV) and tangential (SH) components are of comparable quality because the hard‐rock recording site minimizes the influence of coupling to P on the radial component. Refracted S waves from the uppermantle transition zone show a clear advance of SH wave arrivals compared with SV. Eleven polarization analyses of waves returned from the transition zone yield an average time shift of 2.3 s with the fast direction scattered about the transverse direction. Nine polarization measurements of waves returned from the top of the lower mantle yield an average time shift of 1.7 s, again with the fast direction near the transverse. No appreciable time differences are observed between the radial and transverse polarizations for paths refracted within the lithospheric lid. Because the observations of shear wave splitting in waves passing through the low‐velocity zone, the transition zone, and the top of the lower mantle are not coherent in their absolute polarization, the cause cannot lie in azimuthal anisotropy at shallow depths under the WRA station. The most plausible explanation is transverse isotropy in shear within the low‐velocity zone under the unusually thick mantle “lid” under Australia. A possible contribution may come from anisotropy in β—olivine at the top of the upper mantle transition zone. Transverse isotropy in the 200‐km‐thick layer below the lithosphere down to the transition zone with a 1% faster shear wave speeds for horizontal polarization compared with vertical polarization will explain the splitting data. For this asthenospheric region the level of anisotropy is quite reasonable and the polarization is consistent with lateral flow. The geometry of the available paths for waves propagating within the mantle lid is not sufficient to place constraints on the anisotropic properties of this heterogeneous and low‐loss region.

Highlights from a seismic broadband array on Stromboli Volcano

An array of nine three‐component broadband seismometers was deployed in two different configurations on Stromboli volcano. The analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano. These new observations are restricted to the low‐frequency range below 1 Hz and underline, therefore, the superiority of broadband recordings over conventional short‐period observations. Surprisingly simple wavelets indicate an initially contracting source mechanism. Gas‐jets, that could not be seen in a short‐period seismic record at all, generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism. The analysis of particle motion and seismic array techniques permits a location of the seismic source. We find low‐frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption‐related events. A video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals.

The digital array at Anza, California: Processing and initial interpretation of source parameters

Seismicity along the San Jacinto fault suggests that a 40‐km‐long section near the town of Anza may constitute a gap in the occurrence of ML = 6–7 earthquakes. The potential for a gap‐filling shock and the high rate of seismicity at the southern end of the gap (five events of 4.0 ≤ ML ≤ 5.5 since 1970) provided the impetus for deploying a digital seismic array to collect high‐quality ground motion recordings of all events 2 ≤ ML ≤ 4.5 (on‐scale recording for shocks with magnitudes above ML = 4 can be obtained from an existing array of eight strong motion accelerographs). The Anza site also had the advantage of being in the southern California batholith, which appears to be relatively homogeneous compared to the Franciscan/Gablian contrast of the central San Andreas; we expected that the granitic rocks of the batholith would yield relatively accurate earthquake locations and efficiently propagate high frequencies. The field instrumentation is specifically designed for broadband recording (up to 70 Hz) and high dynamic range (96 dB in the on‐site digitizer alone), since both are necessary for determining the rupture history of earthquakes. Both local VHF and microwave digital telemetry transmit the data from the Anza region to San Diego for computer data logging. In the first 30 months of the array's operation, approximately 292 events have been recorded, located, and processed for source parameters. Most events occur in one of five clusters or in a diffuse zone near the Buck Ridge fault. Two of these clusters are located at right‐stepping en echelon offsets (Coyote Creek‐San Jacinto and San Jacinto‐Hot Springs); two others are directly below and about 8 km west of Anza, respectively. The fifth cluster is just to the northeast of the Hot Springs fault. Although event depths are generally between 11 and 14 km, at the southern end of the Hot Springs fault, depths extend to 18 km; these are some of the deepest strike‐slip earthquakes on the San Andreas system. We calculate source parameters such as the scalar moment and stress drop for the analysis of high‐frequency waves, scaling relations, and earthquake interaction. The largest event recorded thus far had a moment of 4.4 × 1021 dyn cm (M = 3.8) and a stress drop of 55 bars. Both arms and Brune stress drops increase with moment; source radius increases only slowly with moment. The maximum values of both the Brune and arms stress drops increase with depth down to 10 km, remain approximately constant to 14 km, and may decrease below 14 km. The data suggest that stress drops of a group of earthquakes can be related to the strength of the upper crust calculated from frictional and quasi‐plastic flow laws, although individual events may not be related. Stress drops on the San Jacinto fault are high compared to those on the central creeping section of the San Andreas, where stress drops are about 10 bars or less. This observation is consistent with the relative rupture area of events of equal ML (5.5) and may be related to the lithologie differences between the two fault segments and the amount of normal stress compared to shear stress.

Multifunctional broad-band recording system of an independent-reception radiointerferometer

Multifunctional broad-band recording system of an independent-reception radiointerferometer

How and Why to Record Broad Band Seismic Signals

MOST seismological observatories operate narrow band recording systems that record only that part of the seismic spectrum in which the signal/noise ratio is usually a maximum. These systems are ideal for detecting small seismic signals (say body wave magnitude mb 4.0 to 5.0) such as those generated by underground explosions of a few kton but have the disadvantage that the recorded signals are distorted versions of the true ground motion. To study seismic source functions particularly from body waves requires a broad band (BB) system such as the Kirnos system operated in the USSR1 which has a constant magnification over the range 0.1 Hz to 10 Hz. The drawback of such systems is that the recording band includes the strong microseismic peak at around 0.17 Hz and thus only relatively large signals, above ∼mb = 5.5, are recorded. Here we describe how both broad band and narrow band recordings can be obtained from a single conventional long period (LP) seismometer. The chief cost of adding a broad band system to an established observatory is then the provision of a suitable recorder. We also try to demonstrate the advantages of BB recording.

The Microbarographic Detection of Nuclear Explosions

In order to study the atmospheric pressure perturbations produced by the passages of gravity and acoustic-gravity waves through the atmosphere, a sensitive rate of change instrument (microbarovariograph) has been developed at Lamont. Similar instruments of different design have also been in successful opertion at several other institutions here and abroad. In general, this instrumentation has also proven capable of recording the pressure variations from nuclear explosions in the megaton range for distances which depend on the magnitude and elevation of the initial explosion. The Lamont pressure transducer is a U-tube manometer using a stable liquid plasticizer, dioctyl sebacate, of very low thermal expansion, vapor pressure and creep. One side of the system is connected to a fixed insulated air reservoir or compliant volume. An adjustable leak in parallel controls the long period time constants. Fluctuations of the liquid level in the open end are sensed by a moving coil in a differential transformer whose 60-cycle output is directly proportional in magnitude to the level changes, provided such changes are small. The signal, amplified and demodulated, gives a sensitivity of about 0.030 millibars (30 dynes per cm2) per cm of scale deflection for a stop displacement. A DC post amplifier can give a sensitivity of about 0.001 millibars (1 dyne per cm2) per cm of scale deflection. At the higher sensitivity, special hydraulic filtering procedures must be employed on the transducer in order to reduce atmospheric noise. Broad band recording is best accomplished at the lower sensitivity.