CHARACTERISTICS OF REFRACTIVITY AND SEA STATE IN THE MARINE ATMOSPHERIC SURFACE LAYER AND THEIR INFLUENCE ON X-BAND PROPAGATION

Predictions of environmental conditions within the marine atmospheric surface layer (MASL) are important to X-band radar system performance. Anomalous propagation occurs in conditions of non-standard atmospheric refractivity, driven by the virtually permanent presence of evaporation ducts (ED) in marine environments. Evaporation ducts are commonly characterized by the evaporation duct height (EDH), evaporation duct strength, and the gradients below the EDH, known as the evaporation duct curvature. Refractivity, and subsequent features, are estimated in the MASL primarily using four methods: in-situ measurements, numerical weather and surface layer modeling, boundary layer theory, and inversion methods. The existing refractivity estimation techniques often assume steady homogeneous conditions, and discrepancies between measured and simulated propagation predictions exist. These discrepancies could be attributed to the exclusion of turbulent fluctuations of the refractive index, exclusion of spatially heterogeneous refractive environments, and inaccurate characterization of the sea surface in propagation simulations. Due to the associated complexity and modeling challenges, unsteady inhomogeneous refractivity and rough sea surfaces are often omitted from simulations. This dissertation first investigates techniques for steady homogeneous refractivity and characterizes refractivity predictions using EDH and profile curvature, examining their effects on X-band propagation. Observed differences between techniques are explored with respect to prevailing meteorological conditions. Significant characteristics are then utilized in refractivity inversions for mean refractivity based-on point-to-point EM measurements. The inversions are compared to the other previously examined techniques. Differences between refractivity estimation methods are generally observed in relation to EDH, resulting in the largest variations in propagation, where most significant EDH discrepancies occur in stable conditions. Further, discrepancies among the refractivity estimation methods (in-situ, numerical models, theory, and inversion) when conditions are unstable and the mean EDH are similar, could be attributed to the neglect of spatial heterogeneity of EDH and turbulent fluctuations in the refractive index. To address this, a spectral-based turbulent refractive index fluctuation model (TRIF) is applied to emulate refractive index fluctuations. TRIF is verified against in-situ meteorological measurements and integrated with a heterogenous EDH model to estimate a comprehensive propagation environment. Lastly, a global sensitivity analysis is applied to evaluate the leading-order effects and non-linear interactions between the parameters of the comprehensive refractivity model and the sea surface in a parabolic wave equation propagation simulation under different atmospheric stability regimes (stable, neutral, and unstable). In neutral and stable regimes, mean evaporation duct characteristics (EDH and refractive gradients below the EDH) have the greatest impact on propagation, particularly beyond the geometric horizon. In unstable conditions, turbulence also plays a significant role. Regardless of atmospheric stability, forward scattering from the rough sea surface has a substantial effect on propagation predictions, especially within the lowest 10 m of the atmosphere

Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges

With the rapid development of marine activities, there has been an increasing number of maritime mobile terminals, as well as a growing demand for high-speed and ultra-reliable maritime communications to keep them connected. Traditionally, the maritime Internet of Things (IoT) is enabled by maritime satellites. However, satellites are seriously restricted by their high latency and relatively low data rate. As an alternative, shore & island-based base stations (BSs) can be built to extend the coverage of terrestrial networks using fourth-generation (4G), fifth-generation (5G), and beyond 5G services. Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs. Despite of all these approaches, there are still open issues for an efficient maritime communication network (MCN). For example, due to the complicated electromagnetic propagation environment, the limited geometrically available BS sites, and rigorous service demands from mission-critical applications, conventional communication and networking theories and methods should be tailored for maritime scenarios. Towards this end, we provide a survey on the demand for maritime communications, the state-of-the-art MCNs, and key technologies for enhancing transmission efficiency, extending network coverage, and provisioning maritime-specific services. Future challenges in developing an environment-aware, service-driven, and integrated satellite-air-ground MCN to be smart enough to utilize external auxiliary information, e.g., sea state and atmosphere conditions, are also discussed

The response of the ionosphere to the injection of chemically reactive vapors

As a gas released in the ionosphere expands, it is rapidly cooled. When the vapor becomes sufficiently tenuous, it is reheated by collisions with the ambient atmosphere and its flow is then governed by diffusive expansion. As the injected gas becomes well mixed with the plasma, a hole is created by chemical processes. In the case of diatomic hydrogen release, depression of the electron concentrations is governed by the charge exchange reaction between oxygen ions and hydrogen, producing positive hydroxyl ions. Hydroxyl ions rapidly react with the electron gas to produce excited oxygen and hydrogen atoms. Enhanced airglow emissions result from the transition of the excited atoms to lower energy states. The electron temperature in the depleted region rises sharply causing a thermal expansion of the plasma and a further reduction in the local plasma concentration

Propagation modeling for the analysis of radar systems.

It is well understood in the defence procurement industry that there is a shortfall in the understanding of military mobile radar system performance in complex meteorological environments. To meet this challenge, the work presented in this thesis has combined advanced radar propagation methods with a novel clutter modelling algorithm to describe system performance at the level needed to meet modern naval requirements. The need for these new methods is demonstrated by sets of data gathered in anomalous propagation (anaprop) environments by the author. A new flexible radar model created during this project has allowed the author to analyse the radar data taken and to explore the benefits of performance modelling of radar systems in complex littoral and anaprop environments. A prototype system that exploits the model to try to estimate the local conditions has also been developed. Tests on this technology demonstrator have indicated that more advanced applications of these techniques could allow future radar systems to sense their local environment to improve tactical awareness and enhance sensor optimisation

Wet steam drying: Microwave-assisted droplet evaporation in open-cell ceramic foams

In many energy and process engineering systems where fluids are processed, droplet-laden gas flows may occur. As droplets are often detrimental to the system’s operation, they are required to be removed. According to the state-of-the-art, industrial droplet removal is achieved through a sequential arrangement of several separators followed by droplet collection and discharge. This results in a high-quality gas stream, yet at the expense of bulky and expensive systems that are difficult to retrofit to existing facilities. In addition, the multiple sequential separators produce high pressure drops, further increasing operating costs. Alternatively, a single droplet separation stage and in situ evaporation would provide compact solutions for facilities. However, compact engineering solutions for the removal of entrained droplets are difficult to achieve with conventional flow control and conduction heat transfer approaches such as Joule heating. Joule heating requires a well-defined and homogeneous electrical resistance to ensure uniform heating, which is technically challenging to apply in fine separators and thus compact removal devices are hence often costly and ineffective. Therefore, it becomes necessary to investigate alternative heating approaches to overcome these challenges, such as volumetric heating using microwaves. The research conducted in this thesis aims to analyze the potential of a compact microwave solution approach for droplet removal. The compactness of the approach relies on a novel fine separator structure enhanced by microwave-heat transfer for efficient in-flow droplet evaporation. The investigation targets at fundamental studies of the combined effect of droplet flow filtering and heat transfer from numerical calculations and experimentation. As novel fine separators, solid open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drops. Using susceptors, such as dielectric materials, for the skeleton and exposing them to microwaves is an efficient way to use them as heating elements. Silicon carbide (SiC) based open-cell foam samples were considered for the study as they are good susceptor materials. First, pore-scale fluid numerical simulations on representative foam models were used to obtain a deeper insight into the effects of pore size and pore density on the droplet retention time within foams. Numerical findings were reported considering the pressure gradient and the residence time distribution of droplets under different superficial flow velocities, droplet sizes, porosities and pore densities. Next, the temperature-dependent permittivity of SiC-based foam materials was determined by the cavity perturbation technique using a waveguide resonator at a microwave frequency of 2.45 GHz up to 200 °C. The permittivity was of particular interest as it is a crucial parameter for predicting and designing systems utilizing microwave heating. Along the permittivity measurements, electromagnetic wave propagation simulations were used to derive novel mixing relations describing the effective permittivity of foams while considering their skeletal morphology. The derived relations facilitate an efficient and reliable estimation of the effective permittivity of open-cell foams, producing good agreement to experimental data. Using the foams dielectric properties and the fluid characteristics of droplet-laden streams, a microwave applicator was designed to concentrate the electric field on the open-cell foams. The applicator was constructed for carrying out experimental studies on droplet evaporation removal under different flow velocities, microwave power and different SiC-based foams. Measurements of droplet size, velocity, number density and flux at the inlet and outlet streams of the applicator were performed using a 2D-phase Doppler interferometer. Eventually, it was found from the experimental data analysis that the application of open-cell ceramic foams as a filter medium reduced 99.9 % of the volumetric flow of droplets, while additional microwave exposure increased the reduction to 99.99 %. In addition, microwave-heated foams prevent droplet re-entrainment and structure-borne liquid accumulation within foams, thus avoiding water clogging and flooding. Hence, open-cell foams can be used as fine droplet separators as long as microwave heating may effectively evaporate accumulations of liquid. An important factor in designing future devices based on this microwave heating approach is the temperature, as it changes the arcing breakdown voltage of the gas, thus limiting the microwave input power and droplet flow velocity. Although more investigations are needed to develop an applicable and optimal product, the results presented in this thesis provide a first insight into the viability of using microwave heating and fine filtering as a compact solution for droplet removal

COMBAT SYSTEMS Volume 1. Sensor Elements Part I. Sensor Functional Characteristics

This document includes: CHAPTER 1. SIGNATURES, OBSERVABLES, & PROPAGATORS. CHAPTER 2. PROPAGATION OF ELECTROMAGNETIC RADIATION. I. – FUNDAMENTAL EFFECTS. CHAPTER 3. PROPAGATION OF ELECTROMAGNETIC RADIATION. II. – WEATHER EFFECTS. CHAPTER 4. PROPAGATION OF ELECTROMAGNETIC RADIATION. III. – REFRACTIVE EFFECTS. CHAPTER 5. PROPAGATION OF ELECTROMAGNETIC RADIATION IV. – OTHER ATMOSPHERIC AND UNDERWATER EFFECTS. CHAPTER 6. PROPAGATION OF ACOUSTIC RADIATION. CHAPTER 7. NUCLEAR RADIATION: ITS ORIGIN AND PROPAGATION. CHAPTER 8. RADIOMETRY, PHOTOMETRY, & RADIOMETRIC ANALYSIS. CHAPTER 9. SENSOR FUNCTIONS. CHAPTER 10. SEARCH. CHAPTER 11. DETECTION. CHAPTER 12. ESTIMATION. CHAPTER 13. MODULATION AND DEMODULATION. CHAPTER 14. IMAGING AND IMAGE-BASED PERCEPTION. CHAPTER 15. TRACKING. APPENDIX A. UNITS, PHYSICAL CONSTANTS, AND USEFUL CONVERSION FACTORS. APPENDIX B. FINITE DIFFERENCE AND FINITE ELEMENT TECHNIQUES. APPENDIX C. PROBABILITY AND STATISTICS. INDEX TO VOLUME 1. Note by author: Note: Boldface entries in the table of contents are not yet completed

Development of Computer Modelling Techniques for Microwave Thermography

Microwave thermography obtains information about the temperature of internal body tissues by a spectral measurement of the intensity of the natural thermally generated radiation emitted by the body tissues. At the lower microwave frequencies radiation can penetrate through tissue for distances useful for a range of medical applications. Radiation from inside the body may be detected and measured non-invasively at the skin surface by a microwave thermography system consisting of a suitable antenna to detect the radiation and a radiometer receiver to measure its intensity. In the microwave region the radiative power emitted per unit bandwidth is proportional to the temperature of the emitting tissue and the total radiative power received from the body tissues, P, is a weighted volume average of temperature P = kB ∫w(r) T(r) dV where k is Boltzmann's constant, B is the bandwidth, T(r) is the temperature at the position r and w(r) is the weighting function. The weighting function depends on the structure and dielectric properties of the tissues being viewed, the measurement frequency and the characteristics of the antenna. The Glasgow developed microwave thermography system operates at a central frequency of 3.2 GHz, chosen to give the optimum compromise between the depth from which radiation may be received, which decreases with increasing frequency, and the lateral spatial resolution which increases with increasing frequency. A Dicke configuration radiometer receiver and a cylindrical low-impedance waveguide antenna, which operates in contact with the skin surface, are used. The output from the radiometer is calibrated to degrees Celsius to give a "microwave temperature" of the tissues being viewed. The tissue temperature distribution, T(r), reflects the vascular and metabolic state of the tissue. Diseases which affect these physiological functions will result in changes in the tissue temperature and hence in the measured microwave temperature. It is not possible, however, to solve the indirect problem of retrieval of the temperature distribution in the tissue from a single frequency measurement of microwave temperature. It is therefore necessary to model the temperature distribution in the tissue and, from this, solve the direct problem of calculation of the microwave temperature. Measured microwave temperatures may then be compared with those modelled to indicate the physiological state of the tissue. Pennes (1948) The temperature distribution in the tissue may be determined by solution of the steady-state heat transfer equation KV2T +Wbcb(Ta -T) + Q = 0 where K is the thermal conductivity of the tissue, Wb is the perfusion rate of blood through the tissue, cb is the specific heat capacity of the blood, Ta is the arterial blood temperature and Q is the rate of metabolic heat generation in the tissue. The boundary condition of heat loss at the skin surface is governed by the equation K dT/dn= h(T-Te ) where Te is the ambient temperature and h is the heat transfer coefficient due to the combined effects of heat loss by radiation, convection and evaporation. The microwave temperature may be calculated from the modelled temperature distribution and use of plane wave theory to determine the weighting function, with an increased power attenuation constant to account for the response of the antenna. The modelling of the tissue is simplified by the fact that both the tissue thermal conductivity and the microwave dielectric properties of the tissue depend primarily on the water content of the tissue. This thermal and electromagnetic modelling has been carried out to determine the expected microwave temperature profiles across the female breast. Microwave and infra-red temperature measurements were made on a group of young, normal women and a group of older, post-menopausal women with breast disease. In general the younger women will have higher water content breast tissue than that of the older women due to the higher proportion of glandular and connective tissue and the smaller proportion of low water content fat tissue