Motion Planning for Optimal Information Gathering in Opportunistic Navigation Systems

Motion planning for optimal information gathering in an opportunistic navigation (OpNav) environment is considered. An OpNav environment can be thought of as a radio frequency signal landscape within which a receiver locates itself in space and time by extracting information from ambient signals of opportunity (SOPs). The receiver is assumed to draw only pseudorange-type observations from the SOPs, and such observations are fused through an estimator to produce an estimate of the receiver’s own states. Since not all SOP states in the OpNav environment may be known a priori, the receiver must estimate the unknown SOP states of interest simultaneously with its own states. In this work, the following problem is studied. A receiver with no a priori knowledge about its own states is dropped in an unknown, yet observable, OpNav environment. Assuming that the receiver can prescribe its own trajectory, what motion planning strategy should the receiver adopt in order to build a high-fidelity map of the OpNav signal landscape, while simultaneously localizing itself within this map in space and time? To answer this question, first, the minimum conditions under which the OpNav environment is fully observable are established, and the need for receiver maneuvering to achieve full observability is highlighted. Then, motivated by the fact that not all trajectories a receiver may take in the environment are equally beneficial from an information gathering point of view, a strategy for planning the motion of the receiver is proposed. The strategy is formulated in a coupled estimation and optimal control framework of a gradually identified system, where optimality is defined through various information-theoretic measures. Simulation results are presented to illustrate the improvements gained from adopting the proposed strategy over random and pre-defined receiver trajectories.Aerospace Engineering and Engineering Mechanic

The Price of Anarchy in Active Signal Landscape Map Building

Multiple receivers with a priori knowledge about their own initial states are assumed to be dropped in an unknown environment comprising multiple signals of opportunity (SOPs) transmitters. The receivers draw pseudorange observations from the SOPs. The receivers’ objective is to build a high-fidelity signal landscape map of the environment, which would enable the receivers to navigate accurately with the aid of the SOPs. The receivers could command their own maneuvers and such commands are computed so to maximize the information gathered about the SOPs in a greedy fashion. Several information fusion and decision making architectures are possible. This paper studies the price of anarchy in building signal landscape maps to assess the degradation in the map quality should the receivers produce their own maps and make their own maneuver decisions versus a completely centralized approach. In addition, a hierarchical architecture is proposed in which the receivers build their own maps and make their own decisions, but share relevant information. Such architecture is shown to produce maps of comparable quality to the completely centralized approach.Aerospace Engineering and Engineering Mechanic

Intracavity Dye-Laser Absorption Spectroscopy (IDLAS) for application to planetary molecules

Time-resolved, quasi-continuous wave, intracavity dye-laser absorption spectroscopy is applied to the investigation of absolute absorption coefficients for vibrational-rotational overtone bands of water at visible wavelengths. Emphasis is placed on critical factors affecting detection sensitivity and data analysis. Typical generation-time dependent absorption spectra are given

Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System

Background theory, a reference design, and demonstration results are given for a Global Navigation Satellite System (GNSS) interference localization system comprising a distributed radio-frequency sensor network that simultaneously locates multiple interference sources by measuring their signals’ time difference of arrival (TDOA) between pairs of nodes in the network. The end-to-end solution offered here draws from previous work in single-emitter group delay estimation, very long baseline interferometry, subspace-based estimation, radar, and passive geolocation. Synchronization and automatic localization of sensor nodes is achieved through a tightly-coupled receiver architecture that enables phase-coherent and synchronous sampling of the interference signals and so-called reference signals which carry timing and positioning information. Signal and crosscorrelation models are developed and implemented in a simulator. Multiple-emitter subspace-based TDOA estimation techniques are developed as well as emitter identification and localization algorithms. Simulator performance is compared to the CramérRao lower bound for single-emitter TDOA precision. Results are given for a test exercise in which the system accurately locates emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic

A Graphical Approach to GPS Software-Defined Receiver Implementation

Global positioning system (GPS) software-defined receivers (SDRs) offer many advantages over their hardwarebased counterparts, such as flexibility, modularity, and upgradability. A typical GPS receiver is readily expressible as a block diagram, making a graphical approach a natural choice for implementing GPS SDRs. This paper presents a real-time, graphical implementation of a GPS SDR, consisting of two modes: acquisition and tracking. The acquisition mode performs a twodimensional fast Fourier transform (FFT)-based search over code offsets and Doppler frequencies. The carrier-aided code tracking mode consists of the following main building blocks: correlators, code and carrier phase detectors, code and carrier phase filters, a code generator, and a numerically-controlled oscillator. The presented GPS SDR provides an abstraction level that enables future research endeavors.Aerospace Engineering and Engineering Mechanic

GPS Carrier Tracking Loop Performance in the presence of Ionospheric Scintillations

The performance of several GPS carrier tracking loops is evaluated using wideband GPS data recorded during strong ionospheric scintillations. The aim of this study is to determine the loop structures and parameters that enable good phase tracking during the power fades and phase dynamics induced by scintillations. Constant-bandwidth and variable-bandwidth loops are studied using theoretical models, simulation, and tests with actual GPS signals. Constant-bandwidth loops with loop bandwidths near 15 Hz are shown to lose phase lock during scintillations. Use of the decision-directed discriminator reduces the carrier lock threshold by ∼1 dB relative to the arctangent and conventional Costas discriminators. A proposed variablebandwidth loop based on a Kalman filter reduces the carrier lock threshold by more than 7 dB compared to a 15-Hz constant-bandwidth loop. The Kalman filter-based strategy employs a soft-decision discriminator, explicitly models the effects of receiver clock noise, and optimally adapts the loop bandwidth to the carrier-to-noise ratio. In extensive simulation and in tests using actual wideband GPS data, the Kalman filter PLL demonstrates improved cycle slip immunity relative to constant bandwidth PLLs.Aerospace Engineering and Engineering Mechanic

Effects of Dredge Material Placement on Macroinvertebrate Communities: Phase 1

ID: 8809; issued October 1, 1998INHS Technical Report prepared for Rock Island District, US Army Corps of Engineer

Collaborative Opportunistic Navigation

Aerospace Engineering and Engineering Mechanic

Into the Light: Diurnality has Evolved Multiple Times in Geckos

Geckos are the only major lizard group consisting mostly of nocturnal species. Nocturnality is presumed to have evolved early in gecko evolution and geckos possess numerous adaptations to functioning in low light and at low temperatures. However, not all gecko species are nocturnal and most diurnal geckos have their own distinct adaptations to living in warmer, sunlit environments. We reconstructed the evolution of gecko activity patterns using a newly generated time-calibrated phylogeny. Our results provide the first phylogenetic analysis of temporal activity patterns in geckos and confirm an ancient origin of nocturnality at the root of the gecko tree. We identify multiple transitions to diurnality at a variety of evolutionary time scales and transitions back to nocturnality occur in several predominantly diurnal clades. The scenario presented here will be useful in reinterpreting existing hypotheses of how geckos have adapted to varying thermal and light environments. These results can also inform future research of gecko ecology, physiology, morphology and vision as it relates to changes in temporal activity patterns

Analysis of Ionospheric Scintillations using Wideband GPS L1 C/A Signal Data

A non-real-time GPS receiver has been developed and tested for use in scintillation analysis. The receiver consists of a digital storage receiver and non-real-time software acquisition and tracking algorithms. The goal of this work is to shed light on the behavior of strongly scintillating signals: signals which cause conventional GPS receivers to lose carrier lock. The receiver collects wideband GPS L1 digital data sampled at 5.7 MHz using an RF front-end and stores it on disk for post-processing. It processes the data off-line to determine carrier signal amplitude and phase variations during scintillations. The main processing algorithms are traditional code delay and carrier frequency acquisition algorithms and special signal processing algorithms that effectively function as a delay-locked loop and phase-locked loop. The tracking algorithms use non-causal smoothing techniques in order to optimally reconstruct the phase and amplitude variations of a scintillating signal. These techniques are robust against the deep power fades and strong phase fluctuations characteristic of scintillating signals. To test the receiver, scintillation data were collected in Cauchoeira Paulista, Brazil, from December 4 to 6, 2003. The data set spans several hours and includes times when one or more satellite signals are scintillating. The smoothing algorithm has been used to determine the carrier amplitude and phase time histories of the scintillating signals along with the distortion of the pseudorandom noise (PRN) code’s autocorrelation function. These quantities provide a characterization of scintillation that can be used to study the physics of scintillations or to provide off-line test cases to evaluate a tracking algorithm’s ability to maintain signal lock during scintillations.Aerospace Engineering and Engineering Mechanic