Approved for public release; distribution is unlimited. / Direct-Sequence Spread-Spectrum (DS-SS) is among the preferred modulation techniques for military applications. DS-SS offers three greatly desired characteristics. It allows for the development of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI) systems and has a very good performance in fading channels. This thesis investigates the performance of the "Cross-Product RV (CRV) decomposition" as the basis of blind-equalization algorithms. The CRV is a rank-revealing decomposition alternative to the Eigenvalue Decomposition (EVD) that can provide a recursively updated estimate of the signal and noise subspace at a reduced computational cost. The CRV updating algorithm is implemented in MATLAB and evaluated in a previously proposed communication scheme intended for use in an underwater acoustic network called Seaweb. The underwater channel is modeled with the Monterey-Miami Parabolic Equation Model (MMPE) for various multipath perturbations. The receiver performance is examined using Monte Carlo simulation. Bit-error rates versus signal-to-noise ratio are presented for various, noise assumptions, and receiver synchronization assumptions. / Lieutenant, Hellenic Navy

This research concerns the continuing development of Seaweb underwater networking. In this type of wireless network the radio channel is replaced by an underwater acoustic channel which is strongly dependent on the physical properties of the ocean medium and its boundaries, the link geometry and the ambient noise. Traditional acoustic communications have involved a priori matching of the signaling parameters (e.g., frequency band, source level, modulation type, coding pulse length) to the expected characteristics of the channel. To achieve more robust communications among the nodes of the acoustic network, as well as high quality of service, it is necessary to develop a type of adaptive modulation in the acoustic network. Part of this process involves estimating the channel scattering function in terms of impulse response, the Doppler effects, and the link margin. That is possible with the use of a known probe signal for analyzing the response of the channel. The estimated channel scattering function can indicate the optimum signaling parameters for the link (adaptive modulation). This approach is also effective for time varying channels, including links between mobile nodes, since the channel characteristics can be updated each time we send a probe signal.

The U.S. Navy is developing through-water acoustic communications capability for undersea, distributed systems. These wireless communication links form a wide-area network of fixed nodes consistent with future autonomous sensors on the seafloor. Mobile nodes may operate in the domain of the grid using the fixed nodes as both navigation reference points and communication access points. This thesis evaluates the experimental performance of such networked communications between an undersea vehicle and a ship. Physical-layer considerations include refraction, wind-induced ambient noise, and vehicle aspect angle.

Approved for Public Release; Distribution is Unlimited / Littoral waters when compared to the open ocean create an environment of greater reverberation with acoustic energy scattering from the sea surface, bottom, topographic features, and regions that lack homogeneity within the volume. If the ocean surface is rough on the scale of an acoustic wavelength, considerable scattering can occur that can significantly influence coherent propagation. Because the rough surface is also evolving dynamically, such scattering can introduce Doppler shifting and spreading of the acoustic pulse spectrum. This thesis builds upon prior efforts in ocean acoustic modeling and is focused on examining surface scattering and its affect upon coherent propagation. The dynamics/physics associated with surface scattering are explored in detail and mathematical relationships are developed and employed in revisions to the Monterey Miami Parabolic Equation (MMPE) model. The thesis provides background information associated with the MMPE and highlights earlier work related to surface scattering. It presents a formal analysis of an exact surface scattering approach in the context of a continuous wave (CW) benchmark exercise and the Doppler shifts associated with a dynamic rough surface. It expands on prior rough sea surface work to include modeling based on an empirical fetch-limited ocean wave spectrum and compares modeling results with measured data. Interest in broadband pulse propagation in shallow water is increasing with the need for improved active sonar systems and with the growth of applications such as underwater acoustic communications. / Naval Undersea Warfare Center Division Newport

The overall objective of this work is to evaluate the ability of homing and docking an unmanned underwater vehicle (Hydroid REMUS 100 UUV) to a moving unmanned surface vehicle (Wave-Adaptive Modular Surface Vehicle USV) using a Hydroid Digital Ultra-Short Baseline (DUSBL) acoustic positioning system (APS), as a primary navigation source. An understanding of how the UUV can rendezvous with a stationary USV first is presented, then followed by a moving USV. Inherently, the DUSBL-APS is susceptible to error due to the physical phenomena of the underwater acoustic channel (e.g. ambient noise, attenuation and ray refraction). The development of an APS model has allowed the authors to forecast the UUV’s position and the estimated track line of the USV as determined by the DUSBL acoustic sensor. In this model, focus is placed on three main elements: 1) the acoustic channel and sound ray refraction when propagating in an in-homogeneous medium; 2) the detection component of an ideal DUSBL-APS using the Neyman-Pearson criterion; 3) the signal-to-noise ratio (SNR) and receiver directivity impact on position estimation. The simulation tool is compared against actual open water homing results in terms of the estimated source position between the simulated and the actual USBL range and bearing information. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Lateral habitats provide a multitude of benefits to riverine fishes, including invasive Silver Carp (Hypophthalmicthys molitrix) and Bighead Carp (H. nobilis), hereafter bigheaded carp. Harvesters have focused removal efforts in lateral habitats (e.g., backwaters and side channels); however, little research has examined the lateral habitat use of bighead carps. The Starved Rock Pool (SRP) is the downstream most pool in the upper Illinois River where contracted commercial fishermen target bigheaded carp to reduce dispersal pressure towards the Laurentian Great Lakes. To examine bigheaded carps’ movement between the main channel and lateral habitats in SRP, fish were implanted with transmitters and tracked using acoustic telemetry. The ranges and detection probabilities of acoustic telemetry receivers have typically been modelled and examined in with linear distance tools. To derive more realistic receiver ranges and detection probabilities, this study used minimum bounding geometry on detected transmissions obtained from boat-mounted transmitters. Receiver detection ranges estimated using minimum bounding geometry were smaller than those estimated using the linear distance method, but estimated detection probabilities within receiver ranges were higher using the minimum bounding method compared to the linear distance method. Detection histories of bigheaded carp implanted with transmitters were examined to assess fish habitat use from June 2016 to April 2018. During 2017, multiple environmental variables (temperature, river discharge, chlorophyll a, dissolved oxygen, total dissolved solids, and turbidity) were measured weekly and zooplankton samples were collected during June and August to assess potential associations between environmental variables and bigheaded carp habitat use that might be useful for informing locations and times for focusing contracted harvest of bigheaded carps. Habitat selection was also examined using a resource selection index (W) and a mark-recapture multistate model in program MARK. Across all seasons, bigheaded carp used lateral habitats more frequently than main channel habitats. Habitat use was strongly influenced by temperature and marginally by main channel discharge. No strong associations between zooplankton and bigheaded carp habitat use were observed during this study; however, there were some differences in zooplankton community structure and abundance among lateral habitats related to rotifers that may have potentially been related to use of specific lateral habitats by bigheaded carp. While having high return percentages to all lateral habitats, bigheaded carp disproportionately selected for a few individual habitats, possibly due to those habitats being locations where tagging was conducted. Harvest efforts in lateral habitats, especially prior to spawning (spring staging), during lower temperature periods (overwintering), and during higher discharges should be most effective because of bigheaded carps’ particularly high use of lateral habitats during these times. Recurring removal efforts in lateral habitats within SRP may facilitate targeting of individuals that frequently return to these lateral habitats and may also reduce bigheaded carp abundance in nearby locations.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Geoffrey Xie, John Gibson. Includes bibliographical references (p. 65-66). Also available online.

Underwater communication is necessary for a variety of applications, including transmission of diver speech, communication between manned and/or unmanned underwater vehicles, and data harvesting for environmental monitoring, to name a few. Examples of communication between underwater vehicles include unmanned or autonomous underwater vehicles (UUV or AUV) for deep water construction, military UUVs such as submarine drones, repair vehicles for deep water oil wells, scientific or resource exploration, etc. Examples of underwater communication between fixed submerged devices are sensor networks deployed on the ocean floor for seismic monitoring and tsunami prediction, pollution monitoring, tactical surveillance, analysis of resource deposits, oceanographic studies, etc. The underwater communication environment is a challenging one. Radio signals experience drastic attenuation, while optical signals suffer from dispersion. Because of these issues, acoustic (sound) signals are usually used for underwater communication. Unfortunately, acoustics has its own problems, including limited bandwidth, slow propagation, and signal distortion. Some of these limitations can be overcome with advanced modulation and coding, but to do so requires better understanding of the underwater acoustic propagation environment, which is significantly different than air- or space-based radio propagation. The underwater environment must be studied and characterized to exploit these advanced modulation and coding techniques. This thesis addresses some of these concerns by proposing a derivation of the envelope level crossing rate of the underwater channel, as well as a simulation model for the channel, both of which agree well with the measured results. A velocity estimator is also proposed, but suffers from a high degree of root mean square error

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 39-43).

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 40-44).