Search

The statistical relationship between supplemental adaptive intra-volume low-level scan (SAILS) usage on the Weather Surveillance Radar-1988 Doppler and National Weather Service severe storm warning performance during 2014–20 is analyzed. Results show statistically significant improvement in severe thunderstorm (SVR), flash flood (FF), and tornado (TOR) warning performance associated with SAILS-on versus SAILS-off. Within the three possible SAILS modes of one (SAILSx1), two (SAILSx2), and three (SAILSx3) additional base scans per volume, for SVR, SAILSx2 and SAILSx3 are associated with better warning performance compared to SAILSx1; for FF and TOR, SAILSx3 is associated with better warning performance relative to SAILSx1 and SAILSx2. Two severe storm cases (one that spawned a tornado, one that did not) are presented where SAILS usage helped forecasters make the correct TOR warning decision, lending real-life credence to the statistical results. Furthermore, a statistical analysis of automated volume scan evaluation and termination effects, parsed by SAILS usage and mode, yield a statistically significant association between volume scan update rate and SVR warning lead time.

This article summarizes research and risk reduction that will inform acquisition decisions regarding NOAA’s future national operational weather radar network. A key alternative being evaluated is polarimetric phased-array radar (PAR). Research indicates PAR can plausibly achieve fast, adaptive volumetric scanning, with associated benefits for severe-weather warning performance. We assess these benefits using storm observations and analyses, observing system simulation experiments, and real radar-data assimilation studies. Changes in the number and/or locations of radars in the future network could improve coverage at low altitude. Analysis of benefits that might be so realized indicates the possibility for additional improvement in severe-weather and flash-flood warning performance, with associated reduction in casualties. Simulations are used to evaluate techniques for rapid volumetric scanning and assess data quality characteristics of PAR. Finally, we describe progress in developing methods to compensate for polarimetric variable estimate biases introduced by electronic beam-steering. A research-to-operations (R2O) strategy for the PAR alternative for the WSR-88D replacement network is presented.

The National Oceanic and Atmospheric Administration (NOAA) is evaluating the feasibility of polarimetric phased array radar (PPAR) technology as a basis for its future U.S. operational meteorological radar network. A 10-cm wavelength PPAR – the Advanced Technology Demonstrator (ATD) – is a key asset for exploring associated operational benefits and evaluating solutions to key technical challenges. This paper discusses follow-on PPAR technology development to more fully meet NOAA’s next-generation operational radar requirements. A digital-at-the-element array architecture is recommended to support desired scanning capability, and to maintain data quality commensurate with the current operational weather radar. We describe our development of tile-based PPAR prototype technology that exploits novel commercial-off-the-shelf microwave processing technology to meet NOAA’s future requirements. We conclude with an outlook for integration, test, refinement and documentation of a 2-panel prototype of this digital PPAR.

After decades of research and development, the WSR-88D (NEXRAD) network in the United States was upgraded with dual-polarization capability, providing polarimetric radar data (PRD) that have the potential to improve weather observations, quantification, forecasting, and warnings. The weather radar networks in China and other countries are also being upgraded with dual-polarization capability. Now, with radar polarimetry technology having matured, and PRD available both nationally and globally, it is important to understand the current status and future challenges and opportunities. The potential impact of PRD has been limited by their oftentimes subjective and empirical use. More importantly, the community has not begun to regularly derive from PRD the state parameters, such as water mixing ratios and number concentrations, used in numerical weather prediction (NWP) models. In this review, we summarize the current status of weather radar polarimetry, discuss the issues and limitations of PRD usage, and explore potential approaches to more efficiently use PRD for quantitative precipitation estimation and forecasting based on statistical retrieval with physical constraints where prior information is used and observation error is included. This approach aligns the observation-based retrievals favored by the radar meteorology community with the model-based analysis of the NWP community. We also examine the challenges and opportunities of polarimetric phased array radar research and development for future weather observation.

Strong in-cloud electric fields align ice particles that can be observed with polarization diversity radars. Radar data collected in the simultaneous transmission mode, wherein horizontally and vertically polarized waves are simultaneously transmitted and received (SHV), and in a mode whereby a single-polarization wave is transmitted and dual (orthogonal)-polarization waves are received simultaneously [linear depolarization (LDR) mode] are analyzed. The necessary time delay between the SHV and LDR modes for our radar was about 1–4 min. The data show that the areas of canted crystals from the LDR mode are larger than those from the SHV mode, thereby indicating that the LDR mode is more sensitive to canted ice cloud particles than the SHV mode. The data also demonstrate that the differential phase and correlation coefficient in the LDR mode are indicative of canted cloud crystals and that these variables often are more sensitive to canted crystals than the linear depolarization ratio studied earlier. Rapidly scanning radars such as those with a phased array antenna could operate sequentially in the SHV and LDR modes and thus better detect cloud volumes characterized by enhanced electric fields.

The U.S. National Oceanic and Atmospheric Administration (NOAA) has begun evaluating strategies for replacement of the current Weather Service Radar 88 Doppler (WSR-88D) by 2040, when this system is projected to reach the end of its operational lifetime. In addition to maintaining the WSR-88D’s capabilities to detect and classify meteorological scatterers with high sensitivity and spatial resolution, NOAA has articulated goals for more rapid temporal scanning and expanded low altitude coverage. Research at NOAA’s National Severe Storms Laboratory over the past 15 years has demonstrated that phased array radar (PAR) could support volume scan rates of up to once per minute, and that this would improve the ability of forecasters to warn of severe weather. The rapid scan data would also enhance the effectiveness of radar data-assimilation into “Warn on Forecast” systems. This paper discusses three key issues for meteorological PAR: (1) a plausible architecture for a phased array system meeting NOAA’s objective requirements; (2) the feasibility of calibrating co- and cross-polar radiated fields with sufficient accuracy to robustly correct polarimetric weather variable estimate biases when the beam is electronically steered off-broadside; and (3) the capability to scan significantly faster than the WSR-88D through use of multiple, simultaneously active receive beams and other adaptive techniques. Our positive outlook in each of these areas indicates that PAR’s operational benefits to NOAA should in the future be achievable.

The National Oceanic and Atmospheric Administration (NOAA) has pioneered the development and application of high-performance meteorological radar for public weather warning and forecasting services. The current operational system, the dual-polarization WSR-88D weather surveillance radar, has led to significant capability enhancements, for example, increased accuracy and lead time for severe weather and flash flood warnings. This paper summarizes research to determine whether the eventual replacement for the WSR-88D should exploit rapidly maturing phased array radar (PAR) technology. Key benefits for the rapid, adaptive scanning so enabled have been identified and work continues to mature associated data processing and numerical weather prediction (NWP) assimilation techniques. In parallel, the considerable engineering challenges associated with meteorological PAR are being addressed through modeling, hardware demonstration and data analysis. The Advanced Technology Demonstrator (ATD) - an S-band, dual polarization PAR - is described in this paper. ATD puts NOAA in a position to fully expose operational benefits and substantially advance the technical readiness level of meteorological PAR.

The deployment of small unmanned aircraft systems (UAS) to collect routine in situ vertical profiles of the thermodynamic and kinematic state of the atmosphere in conjunction with other weather observations could significantly improve weather forecasting skill and resolution. High-resolution vertical measurements of pressure, temperature, humidity, wind speed and wind direction are critical to the understanding of atmospheric boundary layer processes integral to air–surface (land, ocean and sea ice) exchanges of energy, momentum, and moisture; how these are affected by climate variability; and how they impact weather forecasts and air quality simulations. We explore the potential value of collecting coordinated atmospheric profiles at fixed surface observing sites at designated times using instrumented UAS. We refer to such a network of autonomous weather UAS designed for atmospheric profiling and capable of operating in most weather conditions as a 3D Mesonet. We outline some of the fundamental and high-impact science questions and sampling needs driving the development of the 3D Mesonet and offer an overview of the general concept of operations. Preliminary measurements from profiling UAS are presented and we discuss how measurements from an operational network could be realized to better characterize the atmospheric boundary layer, improve weather forecasts, and help to identify threats of severe weather.

This abstract is for the academic institution profiles session This presentation will focus on radar research programs at the University of Oklahoma, the radar research in OU has more than 50 years history of collaboration with NOAA, and has been through tremendous growth since early 2000. Before 2010, the focus was weather radar and weather surveillance, and since the Defense, Security and Intelligence (DSI) initiative in 2011, there have many new efforts on the defense and military radar applications. This presentation will focus on the following information: (1) The history, facilities and instrumentations of Advanced Radar Research Center, (2) Focus area of polarimetric phased array systems, (3) Focus area of airborne and spaceborne radars, (4) Intelligent radar information processing, (5) Innovative antenna and components.

We discuss the challenge of managing the Multifunction Phased Array Radar (MPAR) timeline to satisfy the requirements of its multiple missions, with a particular focus on weather surveillance. This command and control (C2) function partitions the available scan time among these missions, exploits opportunities to service multiple missions simultaneously, and utilizes techniques for increasing scan rate where feasible. After reviewing the candidate MPAR architectures and relevant previous research, we describe a specific C2 framework that is consistent with a demonstrated active array architecture using overlapped subarrays to realize multiple, concurrent receive beams. Analysis of recently articulated requirements for near-airport and national-scale aircraft surveillance indicates that with this architecture, 40–60% of the MPAR scan timeline would be available for the high-fidelity weather observations currently provided by the Weather Service Radar (WSR-88D) network. We show that an appropriate use of subarray generated concurrent receive beams, in concert with previously documented, complementary techniques to increase the weather scan rate, could enable MPAR to perform full weather volume scans at a rate of 1 per minute. Published observing system simulation experiments, human-in-the-loop studies and radar-data assimilation experiments indicate that high-quality weather radar observations at this rate may significantly improve the lead time and reliability of severe weather warnings relative to current observation capabilities., United States. National Oceanic and Atmospheric Administration (Contract FA8721-05-C-0002), United States. National Oceanic and Atmospheric Administration (Contract FA8702-15-D-0001)

We demonstrate coherent beam combining of multiple Yb-doped non polarization-maintaining fiber amplifiers operating at individual power levels above 1 kW. A 2.4-kW, M2 = 1.2 output beam was generated by combining three amplifiers with a diffractive optical element (DOE). A single low-power sample of the combined output beam provided error signals for active phase and polarization locking of all three fibers. The beam combining efficiency of 80% was nearly constant with amplifier power, indicating the absence of significant thermal or nonlinear effects. Modeling anchored by precise measurements of the beam characteristics indicates potential for this architecture to scale to higher fiber counts, higher combining efficiency, and higher power.

This paper investigates the feasibility of a backend design for real-time, multiple-channel processing digital phased array system, particularly for high-performance embedded computing platforms constructed of general purpose digital signal processors. First, we obtained the lab-scale backend performance benchmark from simulating beamforming, pulse compression, and Doppler filtering based on a Micro Telecom Computing Architecture (MTCA) chassis using the Serial RapidIO protocol in backplane communication. Next, a field-scale demonstrator of a multifunctional phased array radar is emulated by using the similar configuration. Interestingly, the performance of a barebones design is compared to that of emerging tools that systematically take advantage of parallelism and multicore capabilities, including the Open Computing Language.

This paper investigates the feasibility of real-time, multiple channel processing of a digital phased array system backend design, with focus on high-performance embedded computing (HPEC) platforms constructed based on general purpose digital signal processor (DSP). Serial RapidIO (SRIO) is used as inter-chip connection backend protocol to support the inter-core communications and parallelisms. Performance benchmark was obtained based on a SRIO system chassis and emulated configuration similar to a field scale demonstrator of Multi-functional Phased Array Radar (MPAR). An interesting aspect of this work is comparison between “raw and low-level” DSP processing and emerging tools that systematically take advantages of the parallelism and multi-core capability, such as OpenCL and OpenMP. Comparisons with other backend HPEC solutions, such as FPGA and GPU, are also provided through analysis and experiments.

The U.S. Government operates seven distinct radar networks, providing weather and aircraft surveillance for public weather services, air traffic control, and homeland defense. In this paper, we describe a next-generation multimission phased-array radar (MPAR) concept that could provide enhanced weather and aircraft surveillance services with potentially lower life cycle costs than multiple single-function radar networks. We describe current U.S. national weather and aircraft surveillance radar networks and show that by reducing overlapping airspace coverage, MPAR could reduce the total number of radars required by approximately one-third. A key finding is that weather surveillance requirements dictate the core parameters of a multimission radar—airspace coverage, aperture size, radiated power, and angular resolution. Aircraft surveillance capability can be added to a phased array weather radar at low incremental cost because the agile, electronically steered beam would allow the radar to achieve the much ...

Recent progress in developing phased arrays of high-brightness solid-state lasers is summarized. We address the prospects for continued brightness-scaling via a model that extrapolates measured results to large numbers of array elements and provides a quantitative illustration of the features of coherent beam combination. This demonstrates that with present-day technology, both slab and fiber lasers have the capability to scale to unprecedented brightness levels.

Multi-sector arrays have been used for decades, including applications on ships, aircraft, vehicles, and ground-based platforms. In most of these applications, however, spatial isolation generated through the use of strategic sector placement has provided sufficient overall isolation between each sector. The United States has recently been exploring the potential for a multi-function phased array radar (MPAR) network that would provide surveillance, tracking, and detection capabilities for the nation's weather, terminal weather, and national airspace missions. Several studies have assumed a multi-sector approach on a single platform. With the goal of allowing each sector to independently operate, concerns regarding isolation between the sectors have introduced the desire to gain additional isolation through waveform design. Recent advances in frequency-modulated pulse compression techniques have afforded the ability to maximize sensitivity and sidelobe performance within a given time-bandwidth specification; however, waveform design has the potential to bring numerous other spectral efficiency advancements to the MPAR mission. A generalization of recent waveform design techniques into a multi-sector waveform group is presented. Simulations of a four-sector waveform group are carried out and optimized for minimal interference. The ability to achieve high waveform-based isolation is combined with varying spatial isolations and slight frequency offsets to drastically reduce overall spectrum usage for a multi-sector array.

Etude de l'evolution de la pensee de Wittgenstein sur le probleme de la representation par images mentales telles que les plans, les modeles et les peintures. Definissant le sujet d'une representation par la notion de cible, le moyen de sa representation en tant qu'etre par le concept de contenu et la structure complexe de la ressemblance en termes de ce qui montre, l'A. examine la question que se pose Wittgenstein dans le «Tractacus logico-philosophicaus», a savoir: qu'est-ce qui fait que cette image represente sa cible?, par analogie avec la representation propositionnelle d'un enonce par signe dans sa «Grammaire philosophique»

The effect of processing method on the microstructure and volume resistivity of polypropylene reinforced with nickel-coated graphite (NCG) fibers or stainless steel (SS) fibers is presented. Samples were produced by compression molding, extrusion, and injection molding. The volume resistivity of the composites was measured in three perpendicular test directions to determine anisotropy. The stress and thermal fields experienced during processing determine the ultimate microstructure. The measured resistivity is dependent on this processing-induced microstructure as reflected by the distribution of fiber orientation, length, and concentration. Composites in which the fiber orientation is anisotropic also exhibit anisotropic resistivity. Volume resistivity is lowest in the principal direction of fiber orientation. Samples with the greatest fiber length become conductive at the lowest fiber loadings. Resistivity decreases with an increase in fiber loading, but concentration gradients are often produced, especially in the injection molded samples. High fiber concentrations generally resulted in poor dispersion and wetting. The intertwining and bending of the SS fibers make processing difficult. A comparison between the two types of fibers reveals that, for the systems considered in this study, the SS fibers impart conductivity at lower loadings, but that the NCG fiber composites are ultimately more conductive.

The modeling of the electrical conductivity of polymer composites reinforced with conductive fibers is investigated. Existing models generally can be divided into percolation theories and non-percolation theories. The basis of the percolation theory is the fact that the conductivity of the composite increases dramatically at a certain fiber concentration called the percolation threshold. This theory can be used to model the behavior of the composite or to predict the percolation threshold itself. Non-percolation theories include terms, which account for microstructural data such as fiber orientation, length, and packing arrangement. A comparison of experimental data with predictions from the various models reveals that only the percolation theory is able to accurately model the conductive behavior of an actual composite. Two alternative new models, which predict the volume resistivity of a composite using microstructural data, are evaluated. The first model relates resistivity to the concentration and orientation of the fibers, while assuming perfect fiber-fiber contact. The relationship between resistivity and fiber concentration predicted by the model is in qualitative agreement with actual data, and predictions of the anisotropy in volume resistivity compare well with experimental results. The second model accounts for the effect of fiber-fiber contact and fiber length on composite resistivity. Predictions are in excellent agreement with experimental data for polypropylene composites reinforced with nickel-coated graphite fibers.

We report on a compactly packaged Yb-doped fiber-based laser architecture featuring an actively pulse controlled, single-longitudinal-mode seeder and multistage amplifier chain terminated by a “folded” rod-type photonic crystal fiber. In this laser source, stimulated Brillouin scattering (SBS) is the power-limiting factor, but is managed by phase modulating the seeder with a pseudo-random noise signal. Pulse energy/peak power of ∼2 mJ/1.5 MW at 10 kHz repetition rate are thus obtained within ∼1.55 ns pulses of peak spectral brightness >20 kW cm−2 sr−1 Hz−1.

Two high pulse contrast (> 95 dB) polarization maintaining all-fiber amplifier chains were coherently combined to generate 0.42 mJ, 1 ns 25 kHz pulses with 79% efficiency despite 38 radians of intra-pulse phase distortion. A recursive intra-pulse phase compensation method was utilized to correct for the large nonlinear chirp providing a path for improved coherent waveform control of nanosecond pulse trains.

Two tapered fiber amplifier chains were coherently combined to generate 0.42-mJ, 1-ns pulses with 79% efficiency despite 38 radians of intra-pulse phase distortion. A recursive real-time chirp control method significantly reduced these phase errors.

We demonstrate a method for single-detector coherent sensing and co-alignment of group delays in a phased fiber array, enabling robust coherent combining of broadband sources despite initial path mismatches exceeding the laser coherence length.

Long, electrically conductive nickel-coated graphite fibers were employed to produce thermoplastic composites by compounding and processing with polypropylene resin. The fibers were blended into the resin in a Brabender mixer and the resulting composite was compression molded into square plaques. The fiber loading was varied from 2 to 20 weight percent. The effects of fiber loading on electrical and impact properties were studied and related to the composite microstructure. A device was constructed to measure the volume resistivity of the samples in two planes, longitudinal and latitudinal. A large initial decrease in resistivity occurs as fibers are added to the insulating matrix. Beyond some critical loading, the resistivity reaches a minimum and begins to level off. The resistivity is identical in the two perpendicular planes. Examination of the microstructure reveals that the fiber orientation is fairly random in the composite, which results in a uniform resistivity in the two planes. Fiber attrition is more significant at low loadings where the mixing shear is greater. Impact tests show that the addition of the fibers results in an increase in sample stiffness, thereby reducing the force and energy needed to break the samples.

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

The design of an open radar data acquisition system for the Terminal Doppler Weather Radar is presented. Adaptive signal transmission and processing techniques that take advantage of the enhanced capabilities of this new system are also discussed. Results displaying data quality improvements with respect to problems such as range-velocity ambiguity and moving clutter are shown.

A 1.26-kW, multi-stage Yb fiber MOPA was coherently combined using active polarization and phase control with 94% visibility to a second fiber amplifier, consistent with estimated decoherence effects from fiber nonlinearity, linewidth, and phasing accuracy.

Franklin Fiber whisker-reinforced silicone rubber composites were molded using both transfer and compression molding. Processing parameters, such as sprue design, milling procedure, and mold temperature were varied. The fiber orientation in the composites is anisotropic and independent of sprue design and mold temperature, but dependent on milling procedure. Fiber attrition is significant for all samples. The Young's modulus is affected by fiber orientation. The experimental modulus values are higher than those predicted by the Halpin-Tsai equations for short fibers.

A diffractive optical element (DOE) is used as a beam combiner for an actively phase-locked array of fiber lasers. Use of a DOE eliminates the far-field sidelobes and the accompanying loss of beam quality typically observed in tiled coherent laser arrays. Using this technique, we demonstrated coherent combination of five fiber lasers with 91% efficiency and M2=1.04. Combination efficiency and phase locking is robust even with large amplitude and phase fluctuations on the input laser array elements. Calculations and power handling measurements suggest that this approach can scale to both high channel counts and high powers.

A four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light. The results of this experiment as well as comparisons to other fiber array approaches will be presented.

This paper discusses inter-related studies and development activities that address the significant challenges of implementing air traffic management initiatives in airspace impacted by thunderstorms. We briefly describe current thrusts that will improve the quality and precision of thunderstorm forecasts, work in progress to convert these forecasts into estimates of future airspace capacity, and an initiative to develop a robust ATM optimization model based on future capacity estimates with associated uncertainty bounds. We conclude with a discussion of the thunderstorm ATM problem in the context of future advanced airspace management concepts.

We have developed and demonstrated a fiber amplifier based architecture capable of high peak power pulsed operation that is scalable to high average powers g10 kW. Our approach uses a mode-locked master oscillator to provide the short pulse waveform and an array of fiber amplifiers to provide high efficiency power amplification using a coherently phased, wavelength multiplexed approach. The mode-locked oscillator input is decomposed into its individual modes using a grating, the individual wavelengths are then amplified in a CW format in the fiber amplifier array, recombined with a second grating, and phased to reproduce a high peak power, short pulsewidth, mode-locked output train. We report the initial demonstration of this architecture with an array of 4 fiber amplifiers. 4 modes of the master oscillator output were selected and amplified from 1 mW to 1 Watt each, followed by recombination and phasing. The phased output pulse train effectively reproduced the master oscillator pulse shape, providing a mode-locked output train of 50 psec pulses. The phase control is performed in parallel for each element of the amplifier array and is directly scalable to high average powers by increasing the power of the individual amplifiers and increasing the size of the amplifier array.

A four-element fiber array has been constructed to yield 8 watts of coherently phased, linearly polarized light energy in a single far field spot. Each element consists of a 2-W single-mode fiber-amplifier chain. Phase control of each element is achieved with a lithium-niobate phase modulator. A master laser provides a linearly polarized, narrow linewidth signal that is split into five channels. Four channels are individually amplified using polarization maintaining fiber power amplifiers. Frequency broadening of the signal is necessary to avoid stimulated Brillouin scattering. The fifth channel is used as a reference arm. It is frequency shifted and then combined interferometrically with a portion of each channel's signal. Detectors sense the heterodyne modulation signal, and an electronics circuit measures the relative phase for each channel. Compensating adjustments are then made to each channel's phase modulator. The stability of the optical train is an essential contributor to its success. A state-of-the-art interferometer was built with mountless optics. A lens array was constructed using nano-positioning tolerances, where each lens was individually aligned to its respective fiber to collimate its output and point it at a common far field spot. This system proved to be highly robust and handled any acoustic perturbations.

In this communication we described how, with nonuniform sampling, the concept of bandlimited extrapolation can be used to obtain unambiguous Doppler velocity estimates in the supra-Nyquist region. The proposed method coherently processes a multi-PRI sample using a generalized form of periodogram analysis. The work is described in the context of meteorologic Doppler processing and includes a discussion of effective suppression for stationary ground clutter when multi-PRI schemes are used. >

The UNISYS Corporation has developed a microburst prediction radar (MBPR) to provide detection and short-term predictions of the most hazardous form of low altitude wind shear in the vicinity of an airport. The MBPR is intended for deployment on- or near-airport so as to minimize range coverage (and associated radar power-aperture) requirements. Like the airport surveillance radar wind shear processor (ASR-WSP), the cost of the MBPR is significantly less than that of the terminal Doppler weather radar (TDWR) so that its deployment at smaller airports might be economically justified if the performance is operationally acceptable. Field tests of engineering prototypes of the MBPR have been conducted in conjunction with FAA-sponsored TDWR and WSP demonstration programs. We assess the capabilities and limitations of each of these systems using a consistent methodology that emphasizes the comparative analysis of the significant parameters of each radar in relation to wind shear phenomenology. An extensive database on wind shear event radar cross section, spatial structure and intensity distribution-derived through our FAA-sponsored testing of TDWR and ASR-WSP prototypes is an important asset in developing this comparison.

Discusses data processing techniques that can provide high quality, automated weather information using the FAA's existing Airport Surveillance Radars (ASR-9). The cost of modifying the ASR-9 is significantly less than that for deployment of the dedicated terminal Doppler weather radar. These techniques have been implemented on a prototype ASR-9 weather surveillance processor (WSP) and have been tested operationally at the Orlando, FL and Albuquerque, NM air traffic control towers. The key to the success of this system has been the development of innovative data processing techniques that accommodate the non-optimum parameters of the ASR as a weather sensor. The authors motivate the development of the ASR-9 WSP system and describe in detail the data processing techniques that have been employed to achieve an operationally useful capability. They provide an overview of the WSP and the ongoing system development and test program. They provide specifics on the data processing algorithms that have been key to successful implementation of this capability.

Seismic depth migration continues to be an important, but expensive, tool for reducing exploration risks. Newly acquired high-resolution gravity data provide a low-cost method to enhance the seismic depth migration process by providing an independently measured constraint to the seismic velocity model. State-of-the-art commercial software tools enable rapid integration of the gravity and seismic data. In many geologic settings, integrated density/velocity modeling yields a more accurate velocity model than can be derived from the seismic data alone. A case study is presented to illustrate both steps employed in the data integration process and the resulting improvement in depth-migrated seismic data. End_of_Record - Last_Page 241

The Diode Array Pumped Kilowatt Laser (DAPKL) has demonstrated more than an order of magnitude increase in brightness and average power for short pulse diode-pumped solid-state lasers since its inception in 1991. Significant advances in component technology has been demonstrated, including development of a diffusion bonding process for producing large slabs of Nd:YAG laser material. Phase conjugation by stimulated Brillouin scattering has been demonstrated with high reflectivity and fidelity in a simple focused geometry with input powers of 100 W. Pulse energies at 1.06 μm of up to 10 J per pulse have been demonstrated with a beam quality of 1.25 times diffraction limited at 33 Hz. An average power of 940 Watts at 100 Hz has been obtained with two times diffraction limited beam quality. Efficient frequency doubling with an average power of 165 W has been demonstrated with 5 J per pulse at 0.53 μm. The system has been packaged in a compact brassboard for long term stability and reliability of operation.

Abstract There is an increasing number of marine 3D seismic surveys being acquired with concurrently recorded high resolution gravity and magnetics data. Instrumentation, navigation, and processing advances have led to significantly increased gravity and magnetics data resolution. State of the art workstation software tools provide a means for the integration of seismic, gravity, and magnetic data. Interpretations have aided in the delineation of complex imaging problems including the verification and enhancement of seismic velocity models. A review is given of technical developments, economic considerations, and case studies in support of integrated 3D marine surveys utilizing gravity, magnetics, and seismic data. Introduction Using new interpretation case studies from the Gulf of Mexico and offshore Europe, it is possible to gain insights into enhancing and constraining the interpretation of 3D seismic data using gravity and magnetics methods. Using digital horizons interpreted from a 3D seismic volume and high resolution gravity and magnetics data, an integrated and constrained 3D geologic model can be quickly built and tested. The acquisition of high resolution gravity and magnetic data in conjunction with 3D seismic surveys is now an accepted normal in Europe, and is quickly gaining acceptance in the Gulf of Mexico. Over 300 OCS blocks of 3D-acquired gravity and major areas of high resolution aeromagnetic data have been and are now being recorded in the Gulf of Mexico. The use of high resolution gravity in seismic velocity analysis and the use of velocity grids for localized, focused density input to gravity models is now possible. A detailed example of a localized conversion of a velocity cube to a density volume is provided from the Southern Additions, offshore Louisiana. A brief review of instrumentation, processing techniques, costs, and integrated software applications is provided to set the framework for the interpretation case studies. Gravity and magnetic instrumentation has decreased in size and increasedin sampling and resolution power. Processing of the data using high quality DGPS positioning data has resulted in a dramatic increase in the resolution of shipbome gravity. Workstation applications are now in use which facilitate the direct transfer of data and models between seismic and gravity/ magnetic modeling software systems. Data Acqulsltlon and Processing: The State of the Art With the development of digitally controlled marine gravity systems as described by LaFehret the restrictions of hardware-defined filtering have been removed. This is a major factor in recovering maximum signal in final processed results, by allowing the data processor to quantitatively determine optimum filter parameters for specific sea conditions and induced noise levels. Marine surveys are now routinely producing results of 0.1-0,5 regal resolution over 500 to 1000 meter minimum wavelengths. This change reflects a) the new digital gravity meter technologies, b) benefits of DGPS positioning for the removal of vehicular motion effects on the gravity meter, and c) the benefit of huger, more stable multi-streamer seismic vessels.

We demonstrate a simplified approach toward active polarization control in coherently combined laser architectures. By leveraging optical phase dithers applied by a phase controller, polarization error signals are generated for an entire laser array from a single beam sample of the combined output, enabling closed-loop polarization locking of non-polarization-maintaining fibers. The concept is shown to be compatible with both hill-climbing and synchronous multidither phase control methods. Simultaneous phase locking and polarization locking was demonstrated for a five-fiber array with >99% phasing efficiency and >20 dB polarization extinction ratio.

We demonstrate a method for single-detector coherent sensing and automated coalignment of group delays in a coherently combined laser array, enabling robust coherent combining of broadband sources despite initial path mismatches exceeding the laser coherence length. The method is based on Fourier-domain filtering of the coherently combined laser beam to extract error signals, and it is equally applicable to controlling both spatial and temporal misalignments.

Thulium-doped fiber lasers (TFLs) emitting retina-safe 2-μm wavelengths offer substantial power-scaling advantages over ytterbium-doped fiber lasers for narrow linewidth, single-mode operation. This article reviews the design and performance of a pump-limited, 600 W, single-mode, single-frequency TFL amplifier chain that balances thermal limitations against those arising from stimulated Brillouin scattering (SBS). A simple analysis of thermal and SBS limits is anchored with measurements on kilowatt class Tm and Yb fiber lasers to highlight the scaling advantage of Tm for narrow linewidth operation. We also report recent results on active phase-locking of a TFL amplifier to an optical reference as a precursor to further parallel scaling via coherent beam combining.

A three-stage Yb-fiber amplifier emitted 1.43 kW of single-mode power when seeded with a 25 GHz linewidth master oscillator (MO). The amplified output was polarization stabilized and phase locked using active heterodyne phase control. A low-power sample of the output beam was coherently combined to a second fiber amplifier with 90% visibility. The measured combining efficiency agreed with estimated decoherence effects from fiber nonlinearity, linewidth, and phase-locking accuracy. This is the highest-power fiber laser that has been coherently locked using any method that allows brightness scaling.