The unattended sensing of stationary (i.e. non-mobile) targets is important in applications ranging from counter- proliferation to law enforcement. With stationary targets, sources of seismic, acoustic, and electro-magnetic emissions can potentially be used to detect, identify, and locate the target. Stationary targets have considerably different sensing requirements than the traditional mobile-target unattended ground sensor applications. This paper presents the novel features and requirements of a system for sensing stationary targets. In particular, issues associated with long-listen time signal processing for signal detection, and array processing techniques for signal localization are presented. Example data and signal processing outputs from a stationary target will be used to illustrate these issues. The impact on sensor, electronic signal processing, battery subsystem, and communication requirements will also be discussed. The paper will conclude with a detailed comparison between mobile-target and stationary-target unattended ground sensor architectures.
A significant consideration in the design of offshore structures for seismically-active regions is their response to earthquakes. An appropriate design methodology would involve the synthesis of wave propagation/structural vibration models with in-situ soil/structural response measurements. A Seafloor Earthquake Measurement System (SEMS), designed and developed by Sandia National Laboratories, has been deployed in the Shell Oil Company Beta Field, offshore Long Beach, California. During July 1986, two significant earthquake events were simultaneously recorded by the SEMS unit and by accelerometers mounted on nearby offshore platforms. This paper describes the SEMS unit, presents SEMS data from these events, and contains a preliminary analysis of these data. The potential impact that this research will have in the design methodology of offshore structures is also indicated.
This paper will describe an algorithm for detecting and classifying seismic and acoustic signals for unattended ground sensors. The algorithm must be computationally efficient and continuously process a data stream in order to establish whether or not a desired signal has changed state (turned-on or off). The paper will focus on describing a Fourier-based technique that compares the running power spectral density estimate of the data to a predetermined signature in order to determine if the desired signal has changed state. How to establish the signature and the detection thresholds will be discussed as well as the theoretical statistics of the algorithm for the Gaussian noise case with results from simulated data. Actual seismic data results will also be discussed along with techniques used to reduce false alarms due to the inherent nonstationary noise environments found with actual data.
To apply Sandia`s expertise and technology towards the development of stimulation diagnostic technology in the areas of in situ stress, natural fracturing, stimulation processes and instrumentation systems. The approach to stimulation diagnostics is to integrate in situ stress measurements (including microfracs, anelastic strain recovery, circumferential velocity analysis, and coring-induced fractures) with natural fracture characterization, stimulation analyses (including Fracpro, other models, finite-element analyses, and various pressure analyses), and fracture diagnostics in order to validate hydraulic fracture concepts, models and diagnostic capabilities. The focus of this year`s efforts has been on the planning and development of the M-Site experiment facility for hydraulic fracture diagnostic development. A microseismic suitability test was conducted at the site with very positive results. In four small fracture treatments, over 1,000 microseismic were recorded, with most of these events having analyzable polarization and p- and s-wave arrivals. In the area of in situ stress, comparative studies are being made to evaluate stress measurement techniques, and an in situ stress topical report is being prepared. Natural fracture studies of the Frontier formation are progressing; the genesis and stratigraphic controls on two fracture sets have been hypothesized.
Abstract This paper describes a new long-life Seafloor Earthquake Measurement System (SEMS) and presents earthquake data obtained from the seafloor near an offshore oil production field. The SEMS is a battery powered (8 year life) digital data acquisition system which telemeters data via a sonar link. Seafloor earthquake data from SEMS indicate that the seafloor vertical acceleration is nearly an order of magnitude weaker than the corresponding on-shore vertical motions. The importance of the SEMS measurements in designing earthquake resistant offshore structures is also described. INTRODUCTION A significant consideration in the design of offshore structures is their response to environmental stimuli. Information regarding climatic and oceanographic environmental stimuli for most offshore areas is extensive. As such, a solid data base is available for designing offshore structures that can withstand the threats of storm winds, waves, and ice floes. In regions such as offshore southern California and offshore Alaska, an equally important environmental stimulus is the seismic vibrations induced by local earthquakes. Data on the response of seafloor sediments to earthquake-induced seism city has been scarce, thereby introducing significant uncertainty into the seismic-hazards aspect of offshore structural design. To reduce this uncertainty, a program was undertaken to develop and implement instrumentation to measure seafloor seismic motions. The result of this This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract number DE-AC04-76DP00789. program has been two-fold: the deployment of a long term, strong-motion digital seismograph offshore southern California; and the offshore recording of several significant earthquakes. Two of the earthquakes recorded by a seafloor instrument were simultaneously recorded by on-shore instruments, and by instruments located on a nearby offshore oil platform. Thus, some of the problems associated with the design of offshore earthquake resistant structures can now be addressed with supporting data. In this paper, the most recent Seafloor Earthquake Measurement System (SEMS) will be described. This system is currently operating in 210 ft of water, 10 miles offshore Long Beach, CA, in the Beta Field. Data obtained from this unit and previous prototype SEMS will be presented. The implications of this data on the design of offshore earthquake-resistant structures will also be described. INSTRUMENTATION DESCRIPTION General System Overview It has long been recognized [1] that offshore strong motion seismographs are needed to complement the onshore strong motion networks. The main difficulties associated With implementing these offshore seismographs are the remoteness of the site and the severity of the site environment. As a result, previous attempts at sea-bottom seismographs tended to be experimental in nature. Previous offshore strong-motion seismographs can be grouped into two categories: those that are tethered by a fond power and signal cable (e.g. f2]), and those that are electrically autonomous (e.g. L3). Unfortunately, the tethered-type are inappropriate for remote sites and are relatively costly to deploy and maintain. Autonomous types, while suitable for remote locations, have the added complexity of an internal power source and a data telemetry system. The use of a power source and telemetry.
In this paper, a statistical technique for multi-sensor data fusion is applied to countermine problems. The fusion method has previously been shown to be a powerful tool in SAR/ATR applications. An earlier study, using data from the separate x, y and z coils of the EM61-3D metal detector collected at the Seabee site at Ft. Carson, demonstrated that the method shows promise for countermine applications as well. This paper briefly reviews the mathematical foundation of the fusion technique and then a new application to multi-sensor data for the Mine Hunter/Killer system is discussed at length. The sensor suite includes a ground-penetrating radar, metal detectors, and an IR camera; data were collected at Fort AP Hill, VA. The results of applying the probabilistic fusion method to these multi-sensor data are present and analyzed in detail for the first time. The advantages and limitations of using this fusion approach for countermine applications are discussed.
The authors propose a robust model for characterizing the statistical nature of signals obtained from ultrasonic backscatter processes. The model can accommodate frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. On the basis of this model, statistical schemes are proposed for estimating the scatterer number density (SND) of tissues. The algorithm for estimating the scatterer number incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to waveforms obtained from ultrasonic phantoms with known number densities and in vitro mammalian tissues. There is an excellent agreement among theoretical, histological, and experimental results. The application of this technique for noninvasive clinical tissue characterization is discussed.
This paper describes a potential application of silicon surface micromachined (SMM) mirrors to a space imaging application. We have developed micromirror arrays that can be individually addressed for potential use in a spectrometer planned for NASA's Next Generation Space Telescope (NGST), which will be launched later this decade. An array of micromirrors has been designed to replace a conventional fixed slit mask that is commonly used in spectrometer instruments. The fixed slit mask is used to select the desired portions of an incoming optical signal for analysis. These mirrors are designed to operate in two states, on and off, with the on position directing the signal into the instrument. Such an array of micromirrors can then be used as a "programmable" slit mask where portions of the incoming field of view can be selected in software.
