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At least 1,639 records · Page 91Linked to original sources
USGS2005

Use of decision support systems as a drought management tool

Droughts present a unique challenge to water managers throughout the world and the current drought in the western United States is taxing facilities to the limit. Coping with this severe drought requires state of the art decision support systems including efficient and accurate hydrologic process models, detailed hydrologic data bases and effective river systems management modeling frameworks. This paper will outline a system of models developed by the Bureau of Reclamation, the US Geological Survey, the University of Colorado and a number of other governmental and university partners. The application of the technology to drought management in several key western river basins will be discussed.

Conference Paper↗
USGS2005

A method for quantifying bioavailable organic carbon in aquifer sediments

The fact that naturally occurring microorganisms can biodegrade PCE and TCE allows the use of monitored natural attenuation (MNA) as a remediation strategy at chlorinated solvent-contaminated sites. Research at numerous chlorinated solvent sites indicates an active dechlorinating microbial population coupled with an ample supply of organic carbon are conditions needed to sustain reductive dechlorination. A series of extraction experiments was used to compare the ability of the different extractants to remove organic carbon from aquifer sediments. The different extractants included pyrophosphate, sodium hydroxide, and polished water. Pyrophosphate served as a mild extractant that minimally alters the organic structure of the extracted material. Three concentrations (0.1, 0.5, and 1%) of pyrophosphate extracted 18.8, 24.9, and 30.8% of sediment organic carbon, respectively. Under alkali conditions (0.5 N NaOH), which provided the harshest extractant, 30.7% of the sediment organic carbon was recovered. Amorphous organic carbon, measured by potassium persulfate oxidization, consisted of 44.6% of the sediment organic carbon and served as a baseline control for maximum carbon removal. Conversely, highly purified water provided a minimal extraction control and extracted 5.7% of the sediment organic carbon. The removal of organic carbon was quantified by aqueous TOC in the extract and residual sediment organic carbon content. Characterization of the organic carbon extracts by compositional analysis prior and after exposure to the mixed culture might indicate the type organic carbon and functional groups used and/or generated by the organisms. This is an abstract of a paper presented at the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).

Conference Paper↗
USGS2005

In situ treatability testing of reductive dechlorination in wetland sediments

In situ treatability testing was conducted in the discharge wetlands along West Branch Canal Creek at Aberdeen Proving Ground, MD. The potential for stimulating reductive dechlorination of 1,1,2,2-tetrachloroethane, tetrachloroethylene, trichloroethylene, and carbon tetrachloride in areas of preferential discharge or seeps was evaluated. Geological Survey that degrades chlorinated ethanes and ethylenes was tested using MICRO-Trac??? devices. At seep 3-4W, results of the C and BA MICRO-Trac??? treatments showed essentially no biodegradation of chlorinated solvents occurring under natural and bioaugmented conditions. Results of geochemical samples at this site indicated predominantly iron- and sulfate-reducing conditions consistent with the rapid discharge rates previously measured. The biostimulated treatment showed stimulation of methanogenic conditions and partial degradation of the parent chlorinated VOC to intermediate chlorinated compounds. The bioaugmented and bistimulated treatment showed the highest production of methane, the highest removal of parent compounds and intermediate daughter products, and the highest production of the non-chlorinated end product ethylene. This is an abstract of a paper presented at the proceedings of the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).

Conference Paper↗
USGS2005

Analysis of real-time vibration data

In recent years, a few structures have been instrumented to provide continuous vibration data in real time, recording not only large-amplitude motions generated by extreme loads, but also small-amplitude motions generated by ambient loads. The main objective in continuous recording is to track any changes in structural characteristics, and to detect damage after an extreme event, such as an earthquake or explosion. The Fourier-based spectral analysis methods have been the primary tool to analyze vibration data from structures. In general, such methods do not work well for real-time data, because real-time data are mainly composed of ambient vibrations with very low amplitudes and signal-to-noise ratios. The long duration, linearity, and the stationarity of ambient data, however, allow us to utilize statistical signal processing tools, which can compensate for the adverse effects of low amplitudes and high noise. The analysis of real-time data requires tools and techniques that can be applied in real-time; i.e., data are processed and analyzed while being acquired. This paper presents some of the basic tools and techniques for processing and analyzing real-time vibration data. The topics discussed include utilization of running time windows, tracking mean and mean-square values, filtering, system identification, and damage detection.

Conference Paper↗
USGS2005

Recent advances to obtain real - Time displacements for engineering applications

This paper presents recent developments and approaches (using GPS technology and real-time double-integration) to obtain displacements and, in turn, drift ratios, in real-time or near real-time to meet the needs of the engineering and user community in seismic monitoring and assessing the functionality and damage condition of structures. Drift ratios computed in near real-time allow technical assessment of the damage condition of a building. Relevant parameters, such as the type of connections and story structural characteristics (including geometry) are used in computing drifts corresponding to several pre-selected threshold stages of damage. Thus, drift ratios determined from real-time monitoring can be compared to pre-computed threshold drift ratios. The approaches described herein can be used for performance evaluation of structures and can be considered as building health-monitoring applications.

Conference Paper↗
USGS2005

Natural attenuation software (NAS): Assessing remedial strategies and estimating timeframes

Natural Attenuation Software (NAS) is a screening tool to estimate remediation timeframes for monitored natural attenuation (MNA) and to assist in decision-making on the level of source zone treatment in conjunction with MNA using site-specific remediation objectives. Natural attenuation processes that NAS models include are advection, dispersion, sorption, non-aqueous phase liquid (NAPL) dissolution, and biodegradation of either petroleum hydrocarbons or chlorinated ethylenes. Newly-implemented enhancements to NAS designed to maximize the utility of NAS for site managers were observed. NAS has expanded source contaminant specification options to include chlorinated ethanes and chlorinated methanes, and to allow for the analysis of any other user-defined contaminants that may be subject to microbially-mediated transformations (heavy metals, radioisotopes, etc.). Included is the capability to model co-mingled plumes, with constituents from multiple contaminant categories. To enable comparison of remediation timeframe estimates between MNA and specific engineered remedial actions , NAS was modified to incorporate an estimation technique for timeframes associated with pump-and-treat remediation technology for comparison to MNA. This is an abstract of a paper presented at the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).

Conference Paper↗
USGS2006

Small satellite multi mission C2 for maximum effect

This paper discusses US Air Force, US Army, US Navy, and NASA demonstrations based around the Virtual Mission Operations Center (VMOC) and its application in fielding a Multi Mission Satellite Operations Center (MMSOC) designed to integrate small satellites into the inherently tiered system environment of operations. The intent is to begin standardizing the spacecraft to ground interfaces needed to reduce costs, maximize space effects to the user, and allow the generation of Tactics, Techniques and Procedures (TTPs) that lead to Responsive Space employment. Combining the US Air Force/Army focus of theater command and control of payloads with the US Navy's user collaboration and FORCEnet consistent approach lays the groundwork for the fundamental change needed to maximize responsive space effects.

Conference Paper↗
USGS2006

The ionospheric impact on GPS performance in southern polar region

The primary objective of this paper is to present the results of the study of the effects of varying ionospheric conditions on the GPS signal tracking in the southern polar region. In the first stage of this study, the data collected by the OSU/USGS team in October-November 2003 within the TAMDEF (Transantarctic Mountains Deformation) network were used together with some IGS Antarctic stations to study the effect of severe ionospheric storms on GPS hardware. Note that TAMDEF is a joint USGS/OSU project with the primary objective of measuring crustal motion in the Transantarctic Mountains of Southern Victoria Land using GPS techniques. This study included ten Antarctic stations equipped with different dual-frequency GPS hardware, and the data were evaluated for two 24-hour periods of severe ionospheric storm (2003/10/29) and moderate ionospheric conditions (minor storm of 2003/11/11). The results of this study were presented at the LAG Assembly in Cairns, Australia (Grejner-Brzezinska et al., 2005). Additional tests, in a more controlled environment, were carried out at the US Antarctic station, McMurdo, between January 10 and February 6, 2006, under varying ionospheric conditions, where several different types of receivers were connected to the same antenna located on the rooftop of the Crary Laboratory (the primary test site). In this scenario, each antenna was subject to identical ionospheric effects during each day of the test, and no spatial decorrelation effects were present, as seen in the previous study, due to the spatial separation of the receivers tested. It should be noted, however, that no moderate or severe ionospheric storms occurred during the experiment, so, unfortunately, this type of conditions was not tested here. The test was repeated with different receivers connected to different antenna types; a total of four 5-day sessions were carried out. The following receiver types were used at the primary site: Trimble 5700, Ashtech Z-Surveyor, JNS Euro-80 and Novatel DL-4, with the following antennas: Trimble Zephyr Geodetic, Ashtech D/M and Ashtech E/M chokering. In addition, data collected by the MCM4 IGS station, MCMD UNAVCO station, and CRAR USGS station, all located within 300 m from the primary test site, were used in the analyses. These stations were equipped with the following receiver/antenna combinations: ADA SNR-12/AOAD/MJT chokering (MCM4), Trimble NETRS/AOAD/MJT chokering (MCMD), and TPS ODYSEY_E/JPSREGANT_DD_E (CRAR). The UNAVCO TEQC software was used to carry out the analyses. Depending on the data sampling rate and the mask angle, the expected numbers of observations per receiver/satellite were compared to the actual number of measurements collected during the ionospheric events, with a special emphasis on L2 data. A total number of cycle slips and losses of lock were computed and compared among the hardware types. The results presented here indicate that there is no significant effects on the GPS receivers during minor ionospheric storms (Kp<5). However, the results reported in ibid, indicate significant differences in the hardware performance under severe ionospheric storms. Thus, careful hardware selection is needed to assure data quality/continuity when observations may be affected by severe ionospheric disturbances, while under calm to minor ionospheric activity level there is no significant difference in performance among the hardware tested here.

Conference Paper↗
USGS2006

Research approach to teaching groundwater biodegradation in karst aquifers

TSU in partnership with the USGS has conducted extensive research regarding biode??gradation of contaminants in karst aquifers. This research resulted in the development of a numerical approach to modeling biodegradation of contaminants in karst aquifers that is taught to environmental engineering students in several steps. First, environmental engineering students are taught chemical-reaction engineering principles relating to a wide variety of environmental fate and transport issues. Second, as part of TSU's engineering course curriculum, students use a non-ideal flow laboratory reactor system and run a tracer study to establish residence time distribution (RTD). Next, the students couple that formula to a first-order biodegradation rate and predict the removal of a biodegradable contaminant as a function of residence time. Following this, students are shown data collected from karst bedrock wells that suggest that karst aquifers are analogous to non-ideal flow reactors. The students are challenged to develop rates of biodegradation through lab studies and use their results to predict biodegradaton at an actual contaminated karst site. Field studies are also conducted to determine the accuracy of the students' predictions. This academic approach teaches biodegradation processes, rate-kinetic processes, hydraulic processes and numerical principles. The students are able to experience how chemical engineering principles can be applied to other situations, such as, modeling biodegradation of contaminants in karst aquifers. This paper provides background on the chemical engineering principles and karst issues used in the research-enhanced curriculum. ?? American Society for Engineering Education, 2006.

Conference Paper↗
USGS2006

Description of the L1C signal

Detailed design of the modernized LI civil signal (L1C) signal has been completed, and the resulting draft Interface Specification IS-GPS-800 was released in Spring 2006. The novel characteristics of the optimized L1C signal design provide advanced capabilities while offering to receiver designers considerable flexibility in how to use these capabilities. L1C provides a number of advanced features, including: 75% of power in a pilot component for enhanced signal tracking, advanced Weilbased spreading codes, an overlay code on the pilot that provides data message synchronization, support for improved reading of clock and ephemeris by combining message symbols across messages, advanced forward error control coding, and data symbol interleaving to combat fading. The resulting design offers receiver designers the opportunity to obtain unmatched performance in many ways. This paper describes the design of L1C. A summary of LIC's background and history is provided. The signal description then proceeds with the overall signal structure consisting of a pilot component and a carrier component. The new L1C spreading code family is described, along with the logic used for generating these spreading codes. Overlay codes on the pilot channel are also described, as is the logic used for generating the overlay codes. Spreading modulation characteristics are summarized. The data message structure is also presented, showing the format for providing time, ephemeris, and system data to users, along with features that enable receivers to perform code combining. Encoding of rapidly changing time bits is described, as are the Low Density Parity Check codes used for forward error control of slowly changing time bits, clock, ephemeris, and system data. The structure of the interleaver is also presented. A summary of L 1C's unique features and their benefits is provided, along with a discussion of the plan for L1C implementation.

Conference Paper↗
USGS2006

Striping artifact reduction in lunar orbiter mosaic images

Photographic images of the moon from the 1960s Lunar Orbiter missions are being processed into maps for visual use. The analog nature of the images has produced numerous artifacts, the chief of which causes a vertical striping pattern in mosaic images formed from a series of filmstrips. Previous methods of stripe removal tended to introduce ringing and aliasing problems in the image data. This paper describes a recently developed alternative approach that succeeds at greatly reducing the striping artifacts while avoiding the creation of ringing and aliasing artifacts. The algorithm uses a one dimensional frequency domain step to deal with the periodic component of the striping artifact and a spatial domain step to handle the aperiodic residue. Several variations of the algorithm have been explored. Results, strengths, and remaining challenges are presented. ?? 2006 IEEE.

Conference Paper↗
USGS2006

Gaussian-based filters for detecting Martian dust devils

The ability to automatically detect dust devils in the Martian atmosphere from orbital imagery is becoming important both for scientific studies of the planet and for the planning of future robotic and manned missions. This paper describes our approach for the unsupervised detection of dust devils and the preliminary results achieved to date. The algorithm centers upon the use of a filter constructed from Gaussian profiles to match dust devil characteristics over a range of scale and orientation. The classification step is designed to reduce false positive errors caused by static surface features such as craters. A brief discussion of planned future work is included. ?? 2006 IEEE.

Conference Paper↗
USGS2005

Probabilistic liquefaction triggering based on the cone penetration test

Performance-based earthquake engineering requires a probabilistic treatment of potential failure modes in order to accurately quantify the overall stability of the system. This paper is a summary of the application portions of the probabilistic liquefaction triggering correlations proposed recently proposed by Moss and co-workers. To enable probabilistic treatment of liquefaction triggering, the variables comprising the seismic load and the liquefaction resistance were treated as inherently uncertain. Supporting data from an extensive Cone Penetration Test (CPT)-based liquefaction case history database were used to develop a probabilistic correlation. The methods used to measure the uncertainty of the load and resistance variables, how the interactions of these variables were treated using Bayesian updating, and how reliability analysis was applied to produce curves of equal probability of liquefaction are presented. The normalization for effective overburden stress, the magnitude correlated duration weighting factor, and the non-linear shear mass participation factor used are also discussed.

Conference Paper↗
USGS2005

Cambro-ordovician sea-level fluctuations and sequence boundaries: The missing record and the evolution of new taxa

The evolution of early Palaeozoic conodont faunas shows a clear connection to sea-level changes. One way that this connection manifests itself is that thick successions of carbonates are missing beneath major sequence boundaries due to karstification and erosion. From this observation arises the question of how many taxa have been lost from different conodont lineages in these incomplete successions. Although many taxa suffered extinction due to the environmental stresses associated with falling sea-levels, some must have survived in these extreme conditions. The number of taxa missing in the early Palaeozoic tropics always will be unclear, but it will be even more difficult to evaluate the missing record in detrital successions of higher latitudes. A common pattern in the evolution of Cambrian-Ordovician conodont lineages is appearances of new species at sea-level rises and disappearances at sea-level drops. This simple picture can be complicated by intervals that consistently have no representatives of a particular lineage, even after extensive sampling of the most complete sections. Presumably the lineages survived in undocumented refugia. In this paper, we give examples of evolution in Cambrian-Ordovician shallowmarine conodont faunas and highlight problems of undiscovered or truly missing segments of lineages. ?? The Palaeontological Association.

Special Papers in Palaeontology↗
USGS2005

Seismic hazard in the South Carolina coastal plain: 2002 update of the USGS national seismic hazard maps

The damaging 1886 moment magnitude ???7 Charleston, South Carolina earthquake is indicative of the moderately likely earthquake activity along this portion of the Atlantic Coast. A recurrence of such an earthquake today would have serious consequences for the nation. The national seismic hazard maps produced by the U.S. Geological Survey (USGS) provide a picture of the levels of seismic hazard across the nation based on the best and most current scientific information. The USGS national maps were updated in 2002 and will become part of the International Codes in 2006. In the past decade, improvements have occurred in the scientific understanding of the nature and character of earthquake activity and expected ground motions in the central and eastern U.S. The paper summarizes the new knowledge of expected earthquake locations, magnitudes, recurrence, and ground-motion decay with distance. New estimates of peak ground acceleration and 0.2 s and 1.0 s spectral acceleration are compared with those displayed in the 1996 national maps. The 2002 maps show increased seismic hazard in much of the coastal plain of South Carolina, but a decrease in long period (1 s and greater) hazard by up to 20% at distances of over 50 km from the Charleston earthquake zone. Although the national maps do not account for the effects of local or regional sediments, deep coastal-plain sediments can significally alter expected ground shaking, particularly at long period motions where it can be 100% higher than the national maps.

Conference Paper↗
USGS2006

L1C signal design options

Design activities for a new civil signal centered at 1575.42 MHz, called L1C, began in 2003, and the Phase 1 effort was completed in 2004. The L1C signal design has evolved and matured during a Phase 2 design activity that began in 2005. Phase 2 has built on the initial design activity, guided by responses to international user surveys conducted during Phase 1. A common core of signal characteristics has been developed to provide advances in robustness and performance. The Phase 2 activity produced five design options, all drawing upon the core signal characteristics, while representing different blends of characteristics and capabilities. A second round of international user surveys was completed to solicit advice concerning these design options. This paper provides an update of the L1C design process, and describes the current L1C design options. Initial performance estimates are presented for each design option, displaying trades between signal tracking robustness, the speed and robustness of clock and ephemeris data, and the rate and robustness of other data message contents. Planned remaining activities are summarized, leading to optimization of the L1C design.

Conference Paper↗
USGS2007

The case for infrasound as the long-range map cue in avian navigation

Of the various 'map' and 'compass' components of Kramer's avian navigational model, the long-range map component is the least well understood. In this paper atmospheric infrasounds are proposed as the elusive longrange cues constituting the avian navigational map. Although infrasounds were considered a viable candidate for the avian map in the 1970s, and pigeons in the laboratory were found to detect sounds at surprisingly low frequencies (0.05 Hz), other tests appeared to support either of the currently favored olfactory or magnetic maps. Neither of these hypotheses, however, is able to explain the full set of observations, and the field has been at an impasse for several decades. To begin, brief descriptions of infrasonic waves and their passage through the atmosphere are given, followed by accounts of previously unexplained release results. These examples include 'release-site biases' which are deviations of departing pigeons from the homeward bearing, an annual variation in homing performance observed only in Europe, difficulties orienting over lakes and above temperature inversions, and the mysterious disruption of several pigeon races. All of these irregularities can be consistently explained by the deflection or masking of infrasonic cues by atmospheric conditions or by other infrasonic sources (microbaroms, sonic booms), respectively. A source of continuous geographic infrasound generated by atmosphere-coupled microseisms is also proposed. In conclusion, several suggestions are made toward resolving some of the conflicting experimental data with the pigeons' possible use of infrasonic cues.

Conference Paper↗
USGS2005

Rainfall-induced landslides in Puerto Rico: An overview

Rainfall-induced landslides are common in Puerto Rico (PR). The presence of steep slopes in mountainous terrain, coupled with weathered soils and intense rainfall, leads to severe slope-stability problems throughout the island. Episodic triggering events such as hurricanes and earthquakes further exacerbate these problems. All physiographic provinces of the island have experienced landslides. The stability of natural and man-made slopes is a serious concern for government authorities and the civil engineering community in Puerto Rico. This paper presents an overview of the rainfall induced landslide problem in PR, a summary of literature published on this subject, and proposes a rainfall intensity landslide threshold based on landslide events data from 1959 to 2003. This threshold can be used as part of a potential landslide warning system.

Conference Paper↗