Recording seismic reflections using rigidly interconnected geophones

This is the publisher's version, also available electronically from "http://library.seg.org".Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys

Source-dependent frequency content of ultrashallow seismic reflection data

This is the publisher's version, also available electronically from "bssa.geoscienceworld.org".Seismic surveying within the upper few meters of the Earth's shallow subsurface requires a high-frequency source. To ascertain the important features of such sources, experiments were conducted at test sites in central and eastern Kansas using various impulsive seismic sources (4.5-kg hammer, 30.06 rifle, and .22-caliber rifle) to examine the effects of minimizing source energy on the frequency content of reflection data. Results indicate that the higher energy near-surface seismic-reflection sources (e.g., sledgehammer, large-caliber projectiles) lack some of the high-frequency energy exhibited by smaller sources, precluding the detection of reflection signal from ultrashallow depths (<3 m) at the sites tested. At the test site in eastern Kansas, the .22-caliber rifle yielded more energy above 250 Hz than either the sledgehammer or 30.06 rifle. At the test site in central Kansas, where three reflective interfaces shallower than 3 m exist, the .22-caliber rifle with subsonic ammunition yielded the largest amount of energy at frequencies above 300 Hz and produced the best data

Varying the effective mass of geophones

This is the published version. Reuse is subject to the Society of Exploration Geophysicists terms of use and conditions.Traditionally, acquiring seismic data has rested on the assumption that geophone mass should be as small as possible. When Steeples and coworkers in 1999 planted 72 geophones automatically and simultaneously with a farm tillage implement, the effective mass of each of the geophones was significantly increased. We examined how the mass of a geophone affects changes in traveltime, amplitude, frequency, and overall data quality by placing various external masses on top of 100‐Hz vertical geophones. Circular barbell weights of 1.1‐, 11.3‐, and 22.7 kg; an 8.2‐kg bag of lead shot; and a 136‐kg stack of barbell weights were placed on top of geophones during data acquisition. In addition, a very large mass in the form of a truck was parked on top of two of the geophones. Four seismic sources supplying a broad range of energies were tested: a sledgehammer, a .22‐caliber rifle, a 30.06 rifle, and an 8‐gauge Betsy Seisgun. Spectral analysis revealed that the smaller weights had the greatest effects on the capacities of the geophones to replicate the earth’s motion. Consequently, using geophones with a large effective mass as part of an automatic geophone‐planting device would not necessarily be detrimental to the collection of high‐quality near‐surface seismic data

Long-term in situ observations of biomass burning aerosol at a high altitude station in Venezuela – sources, impacts and interannual variability

First long-term observations of South American biomass burning aerosol within the tropical lower free troposphere are presented. The observations were conducted between 2007 and 2009 at a high altitude station (4765 m a.s.l.) on the Pico Espejo, Venezuela. Sub-micron aerosol volume, number concentrations of primary particles and particle absorption were observed. Orographic lifting and shallow convection leads to a distinct diurnal cycle at the station. It enables measurements within the lower free troposphere during night time and observations of boundary layer air masses during day time and at their transitional regions. The seasonal cycle is defined by a wet rainy season and a dry biomass burning season. The particle load of biomass burning aerosol is dominated by fires in the Venezuelan savannah. Increases of aerosol concentrations could not be linked to long-range transport of biomass burning plumes from the Amazon basin or Africa due to effective wet scavenging of particles. Highest particle concentrations were observed within boundary layer air masses during the dry season. Ambient sub-micron aerosol volume reached 1.4 &plusmn; 1.3 &mu;m³ cm^&minus;3, heated (300 &deg;C) particle number concentrations 510 &plusmn; 420 cm^&minus;3 and the absorption coefficient 0.91 &plusmn; 1.2 Mm^&minus;1. The respective concentrations were lowest within the lower free troposphere during the wet season and averaged at 0.19 &plusmn; 0.25 &mu;m³ cm^&minus;3, 150 &plusmn; 94 cm^&minus;3 and 0.15 &plusmn; 0.26 Mm^&minus;1. A decrease of particle concentrations during the dry seasons from 2007–2009 could be connected to a decrease in fire activity in the wider region of Venezuela using MODIS satellite observations. The variability of biomass burning is most likely linked to the El Niño-Southern Oscillation (ENSO). Low biomass burning activity in the Venezuelan savannah was observed to follow La Niña conditions, high biomass burning activity followed El Niño conditions

Near-surface common-midpoint seismic data recorded with automatically planted geophones

This is the publisher's version, also available electronically from "http://onlinelibrary.wiley.com".[1] We introduce the Autojuggie II as a device to speed the emplacement of geophones for near-surface seismic common-midpoint (CMP) surveys. Hydraulic cylinders force rigidly interconnected geophones into the ground simultaneously and automatically. We demonstrate that accurate CMP data can be recorded with geophones planted by this device, and that a CMP stacked section can be processed, from which reliable geologic information can be extracted. To make this demonstration, we compare the stacked section to a coincident and parallel section, whose data was acquired using conventionally hand-planted geophones. The two sections are very similar in amplitude, phase, and frequency. A slight difference in coherency exists in a ∼35-ms reflection; the stack corresponding to the automatically planted geophones shows better coherency relative to the comparison stack. However, the similarity of the sections indicates that accurate CMP data can be recorded using geophones planted by the Autojuggie II

The fine-scale structure of the trade wind cumuli over Barbados – An introduction to the CARRIBA project

The CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) project, focused on high resolution and collocated measurements of thermodynamic, turbulent, microphysical, and radiative properties of trade wind cumuli over Barbados, is introduced. The project is based on two one-month field campaigns in November 2010 (climatic wet season) and April 2011 (climatic dry season). Observations are based on helicopter-borne and ground-based measurements in an area of 100 km2 off the coast of Barbados. CARRIBA is accompanied by long-term observations at the Barbados Cloud Observatory located at the East coast of Barbados since early in 2010 and which provides a longer-term context for the CARRIBA measurements. The deployed instrumentation and sampling strategy are presented together with a classification of the meteorological conditions. The two campaigns were influenced by different air masses advected from the Caribbean area, the Atlantic Ocean, and the African continent which led to distinct aerosol conditions. Pristine conditions with low aerosol particle number concentrations of ∼100 cm3 were alternating with periods influenced by Saharan dust or aerosol from biomass burning resulting in comparably high number concentrations of ∼ 500 cm3. The biomass burning aerosol was originating from both the Caribbean area and Africa. The shallow cumulus clouds responded to the different aerosol conditions with a wide range of mean droplet sizes and number concentrations. Two days with different aerosol and cloud microphysical properties but almost identical meteorological conditions have been analyzed in detail. The differences in the droplet number concentration and droplet sizes appear not to show any significant change for turbulent cloud mixing, but the relative roles of droplet inertia and sedimentation in initiating coalescence, as well as the cloud reflectivity, do change substantially. © Author(s) 2013

The fine-scale structure of the trade wind cumuli over Barbados – An introduction to the CARRIBA project

The CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) project, focused on high resolution and collocated measurements of thermodynamic, turbulent, microphysical, and radiative properties of trade wind cumuli over Barbados, is introduced. The project is based on two one-month field campaigns in November 2010 (climatic wet season) and April 2011 (climatic dry season). Observations are based on helicopter-borne and ground-based measurements in an area of 100 km2 off the coast of Barbados. CARRIBA is accompanied by long-term observations at the Barbados Cloud Observatory located at the East coast of Barbados since early in 2010 and which provides a longer-term context for the CARRIBA measurements. The deployed instrumentation and sampling strategy are presented together with a classification of the meteorological conditions. The two campaigns were influenced by different air masses advected from the Caribbean area, the Atlantic Ocean, and the African continent which led to distinct aerosol conditions. Pristine conditions with low aerosol particle number concentrations of ∼100 cm3 were alternating with periods influenced by Saharan dust or aerosol from biomass burning resulting in comparably high number concentrations of ∼ 500 cm3. The biomass burning aerosol was originating from both the Caribbean area and Africa. The shallow cumulus clouds responded to the different aerosol conditions with a wide range of mean droplet sizes and number concentrations. Two days with different aerosol and cloud microphysical properties but almost identical meteorological conditions have been analyzed in detail. The differences in the droplet number concentration and droplet sizes appear not to show any significant change for turbulent cloud mixing, but the relative roles of droplet inertia and sedimentation in initiating coalescence, as well as the cloud reflectivity, do change substantially

Turbulence-induced cloud voids: observation and interpretation

The phenomenon of cloud voids, i.e., elongated volumes inside a cloud that are devoid of droplets, was observed with laser sheet photography in clouds at a mountain-top station. Two experimental cases, similar in turbulence conditions yet with diverse droplet size distributions and cloud void prevalence, are reported. A theoretical explanation is proposed based on the study of heavy inertial sedimenting particles inside a Burgers vortex. A general conclusion regarding void appearance is drawn from theoretical analysis. Numerical simulations of polydisperse droplet motion with realistic vortex parameters and Mie scattering visual effects accounted for can explain the presence of voids with sizes similar to that of the observed ones. Clustering and segregation effects in a vortex tube are discussed for reasonable cloud conditions.</p

Tight Regulation of the intS Gene of the KplE1 Prophage: A New Paradigm for Integrase Gene Regulation

Temperate phages have the ability to maintain their genome in their host, a process called lysogeny. For most, passive replication of the phage genome relies on integration into the host's chromosome and becoming a prophage. Prophages remain silent in the absence of stress and replicate passively within their host genome. However, when stressful conditions occur, a prophage excises itself and resumes the viral cycle. Integration and excision of phage genomes are mediated by regulated site-specific recombination catalyzed by tyrosine and serine recombinases. In the KplE1 prophage, site-specific recombination is mediated by the IntS integrase and the TorI recombination directionality factor (RDF). We previously described a sub-family of temperate phages that is characterized by an unusual organization of the recombination module. Consequently, the attL recombination region overlaps with the integrase promoter, and the integrase and RDF genes do not share a common activated promoter upon lytic induction as in the lambda prophage. In this study, we show that the intS gene is tightly regulated by its own product as well as by the TorI RDF protein. In silico analysis revealed that overlap of the attL region with the integrase promoter is widely encountered in prophages present in prokaryotic genomes, suggesting a general occurrence of negatively autoregulated integrase genes. The prediction that these integrase genes are negatively autoregulated was biologically assessed by studying the regulation of several integrase genes from two different Escherichia coli strains. Our results suggest that the majority of tRNA-associated integrase genes in prokaryotic genomes could be autoregulated and that this might be correlated with the recombination efficiency as in KplE1. The consequences of this unprecedented regulation for excisive recombination are discussed